project in wbpdcl at stps

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INDEX

Topics Page no.

Acknowledgement …………………………… 2

Introduction …………………………………. 3

Overview ……………………………………… 4

Department …………………………………… 5

Industrial Safety………………………………. 6

Mechanical Operation………………………… 8

Coal Handling Plant …………………………. 17

Cost Control &Fuel Efficiency ………………. 24

Inside Power House ………………………….. 27

Outside Power House ………………………… 31

Control &Instrumentation …………………… 36

Relay & Instrumentation ……………………. 49

Conclusion …………………………………… 58

Submitted by Sourav Nandi

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Acknowledgement

During our vocation training, we are extremely helped by the employees of STPS Sushanta Dutta(AM),IPH Vivekananda Karmakar(AM),IPH Abhijeet Gorai(AM),IPH Subhrananda Roy(AM),T&A Mahesh Kr Barnwal(AM),C&I Prasanta Singh(HOD),OPH Suresh Singh(AM),OPH S Shyamal(OPH),AM Pradip Pramanik(AM),ECR JoydebBhattacharya(HOD),R&I A Chattopadhyay(AM),R&I Sujoy Pal(AM),MO Sk Riyadullah(AM),MO A Maji(AM),CHP A Masanda(AM),CHP SS Patra(Manager),CHP S Mondal(AM),CC&FE Tathagata Guha Roy(SOA),Water Treatment Raju Karmakar(Operator),CHP S Bhattacharya(Manager),HR&A Tathagata Roy(AM),HR&A

We are also thankful to Documentation cell and many other staff whose names are not mentioned here we also Apologize personally for this. We are feel sorry if any kind of unknowing done odds during our Vocational Training. At last we thank the entire management of STPS for excellent co operation with us.

Introduction


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In general a thermal power station means that a place where mechanical energy of steam is converted to electrical energy via turbine, alternator and other elements that supports the system. In a thermal power plant in which the prime mover is steam driven. Water is heated,

turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because such facilities convert forms of heat energy into electricity. Some thermal power plants also deliver heat energy for industrial purposes, for district heating, or for desalination of water as well as delivering electrical power. A large part of human CO2 emissions comes from fossil fueled thermal power plants; efforts to reduce these outputs are various and widespread. The energy efficiency of a conventional thermal

power station, considered as salable energy as a percent of the heating value of the fuel consumed, is typically 33% to 48%. This efficiency is limited as all heat engines are governed by the laws of thermodynamics. The rest of the energy must leave the plant in the form of heat. This waste heat can go through a condenser and be disposed of with cooling water or in cooling towers. If the waste heat is instead utilized for district heating, it is called co-generation. An important class of thermal power station is associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas and in these plants, freshwater production and electricity are equally important co-products. Now, for successful completion of the process, a good numbers of process parameters (like steam pressure & temperature, drum level, feed water flow, etc) need continuous monitoring, which demands instruments.

Therefore a power plant is a industry where its needed to have every kind of engineering section to give its attention.

Santaldih Thermal Power Station


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Overview

Santaldih power station is situated in Purulia Dist. Of West Bengal State in India, and it is one of the most important thermal power stations under West Bengal Power Development Corporation limited. In this plant there is actually six plants four of them are of 120MW (old plants 1-4) and two of them are of 250MW (new plants 5-6). Actually the two new plants are in running condition. As the old plants have stopped working as in this plants there was some turbine humming that reduced the efficiency of the production. The total area of acquired land for STPS: For Township: 350 Acre, For Plant: 800 Acre, For Ash Pond: 100 Acre. Unit : 1 Commissioned on : 01.01.1974, Unit : 2 Commissioned on : 16.07.1975, Unit : 3 Commissioned on : 06.12.1978, Unit : 4 Commissioned on : 30.03.1981,Unit : 5 commissioned on 07.11.2007, Unit : 6 Commissioned on 16.09.2011,

For Unit 1,2,3,4,5,6 – Cooling Towers were supplied/erected by M/s Paharpur Cooling Towers Ltd.. STPS draws water from river Damodar, 8 KM from Power Station.

For Unit : 5 & 6 Main Plant Package : M/s BHEL Railway Network Pac : M/s RITES Water System Package from Panchet Dam Reservoir to STPS : M/s SPML CHP Package : M/s Mchnally Bharat Engg. Co. Ltd.

M/s BHEL was awarded the main plant on turnkey basis. While Mcnally Bharat had completed the Coal Handling Plant and SPML had done the Raw water make-up System. This plant operates in a very highly efficient way and at the month of May when the west Bengal have high demand of power, Santaldih has given 101% of its generating ability and was duly congratulated by the authority. All the workers here work in a united and efficient mannerism and thus they have a smooth progress with a fully automated process control. Santaldih thermal power station is about 10-15km from the Santaldih railway station. They have their own bus facility to communicate from the railway station

Capacity: The Current capacity of STPS has been expanded in capacity by 2 x 250 MW(Unit 5 &6)

Awards: This power station has received 5 times Meritorious Award from CEA since 1990 on account of Low Specific Oil Consumption and Performance

Division of Departments


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In STPS the management is divided in few groups to make the work progress in proper way. Following it’s given an overview of that distribution.

INDUSTRIAL SAFETY


STPS Technical Dipartments

Safety Mechanical Operations

Maintenance

Mechanical Maintenance

Electical Maintenace

Turbine & auxiliary

Boiler & Auxiliary

Control and Instrumentation

Relay & Instrumentation

Inside Power House

Outside Power House

Coal & Fuel Handling

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NO JOB IS SO URGENT OR NO SERVICE IS SO IMPORTANT THAT IT PREVENTS US FROM TAKING THE TIME TO DO SAFELY

NEEDS FOR SAFETY AND ITS OBJECTIVE:-

Industrial Safety is a science of accident prevention directed to the study of the causes that contribute to industrial accidents and also to find out the remedies for these causes. Industrial safety includes safe working conditions, effective use of safety equipment, safety education, accident prevention, safety survey and audit etc.

Need For Safety:

To increase the production and thus to contribute to the economical growth of the nation; To reduce the cost of the product by avoiding the unnecessary overhead To eliminate the waste of labour resources so as to conserve and make the best use of

skilled labour available; Humanitarian motives - the desire to be safe and escape from needless suffering and

avoid human wastage.

Safety in Electrical Works:-

Because of special nature of electrical work, employees working on electrical equipment must be cautious and alert at all times, recognizing the seriousness of consequences which might result from a mishap. There are many unanticipated and unusual happenings that can lead to trouble in electrical work. Regard all electrical equipment as potentially dangerous.

All voltages should be handled properly and safely. It must be realized that relatively low voltage such as 240V and 120V can cause injury. Very special care should be exercised when working at Height.

Avoid working on live equipment in so far practicable. Trouble shooting and making connections to energized 440 volts circuits or higher must be done under the supervision of authorized Electrical supervisor.

When it is necessary to work on or near live circuits, it is important to work on only one wire at a time and to insulate all conductors which may come in contact with the body.

Adequate protective equipment must be used when working on live circuit. Special attention should be given to rubber gloves to be sure these are in good condition.

Only non-conductive ladders should be used by electrical workers. Insulation of electrical wire cannot always be a depended upon to give protection from

shock. Familiarize yourself with the conditions at hand. Treat all electrical equipment designed for 440 volts and above as though it were live,

even though it is known or believed to be dead or de-energized. Keep the area around electrical equipment dry to minimize possibility of shock. Obtain

dry boards to stand on if necessary. In so far as practicable, work shall not be performed on electrical equipment having

moving parts while it is in operation. As an additional precaution, fuses must also be pulled out where provided. Finger rings, braclets and metal wrist watch hands should not be worn by persons

working with electrical equipment.


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Electrical switches must be tagged properly by authorized person when electrical motor driven equipment is to be worked on.

Never close a switch without first having full knowledge concerning the circuit and the reason why the switch was tagged open previously.

Do not operate any oil immersed switch with the oil pan in the lowered position. On 2400 volts and above, make sure the disconnect switch on the line is open and tagged

out before opening the enclosure or dropping the oil tank of a circuit breaker, starter, or other electrical device.

In opening disconnects, shield the eyes from a possible flash. In opening disconnects of any kind, wear rubber gloves. Use a disconnecting pole on high voltage.

Be sure the circuit breaker is open before attempting to remove draw out type circuit breaker from their enclosures.

Replace cover plates on lights and power cabinets or other electrical enclosures after repairs.

Safety belts shall be a part of a line men's equipment and,shall be used whenever the linemen is supported with climbing hooks at an elevation. Lineman should check their safety belts before each use.

Ground and short circuit any line as close to the work as possible. Grounds should be clamped to pole ground wires or an overhead ground wire.

Handle telephone or signal wires with core since these may come in contact with high voltage wires, thus, becoming dangerously charged.

In working hot lines 440 volts over, two men should always work on the pole together except when changing fuses. One man must keep himself in the clear and in a position to aid his pole mate if necessary.

Suitable barricades must be installed around exposed temporary high voltage electrical equipment such as field transformers.

Barricades or markers must be provided for unattended open ground conduct or manways, watch carefully for flammable materials seepage into manholes and take necessary precautions to prevent being overcome by vapours or igniting the materials.

Inspect all electrical extensions before placing in service. Avoid wrapping cord around any part of the body.

Mechanical Operation


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Mechanical operation is the department where the actual job of maintaining and control of the entire production is done. This department actually controllers the entire plant starting from pump to coal bunkers the mechanical operation deals with everything. So there’s nothing special to distinguish between other department and this one.

In STPS they are having the built in DCS system to control the process parameters from remote. They are using Maximo software to use the DCS interface. The feedback system in DCS is also programmed and every Bit of the total process could be monitored and automatically controlled. In the mechanical Operation section there are some electrical parameters also to be monitored. Such as synchronization of the flow to put it on the grid and likewise the other process parameters are maintained. To keep the entire system alive the operation department needs some maintenance job also. Following is a brief description of the part that mechanical operation and maintenance deals with.

Boiler and auxiliaries

zA Boiler or steam generator essentially is a container into which water can be fed and steam can be taken out at desired pressure, temperature and flow. This calls for application of heat on the container. For that the boiler should have a facility to burn a fuel and release the heat. The boiler used here is pie(π) type , one side of the pie has furnace & in the other side has the structure for flue gas circulation to use efficiently the total heat of the boiler. The Boiler is Water Tube type. The steam produces here is natural circulation type. The average temperature of the boiler is 11000C to 12000C. Average steam temperature in the boiler is 4500C to 5000C. Safety valve is used in top of the boiler to release the excess pressure of

steam. The functions of a boiler thus can be stated as:-

a) To convert chemical energy of the fuel into heat energy

b) To transfer this heat energy to water for evaporation as well to steam for superheating.

c) The basic components of Boiler are: -d) Furnace and Burnerse) Steam and Superheating

a. Low temperature superheaterb. Platen superheaterc. Final superheater.

Economiser


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It is located below the LPSH in the boiler and above air pre-heater. It is there to improve the efficiency of boiler by extracting heat from flue gases to heat water and send it to boiler drum.

Advantages of Economiser include

1) Fuel economy: – used to save fuel and increase overall efficiency of boiler plant.2) Reducing size of boiler: – as the feed water is preheated in the economiser and enter

boiler tube at elevated temperature. The heat transfer area required for evaporation reduced considerably.

Air Preheater

The heat carried out with the flue gases coming out of economiser are further utilized for preheating the air before supplying to the combustion chamber. It is a necessary equipment for supply of hot air for drying the coal in pulverized fuel systems to facilitate grinding and satisfactory combustion of fuel in the furnace. Air Preheater used here is Rotary type. The air goes to furnace through mill is 800C. The air goes to furnace by PA Fan and the air is mixture of hot air(1800C) & cold air(300C). Air needed for generation is 1000 TON/HR.

Reheater

Power plant furnaces have a reheater section containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the reheater tubes to pickup more energy to go drive intermediate pressure turbines.

Deareator

Water coming in Deareator from LP-3 Heater. In Deareator water send through nozzles and break into drops. In this process the dissolved gasses are separated from water. Hot steam is send in deareator to rise the temperature of the water. The inlet temperature of the water is 1200 C and the outlet temperatue is 160 0 C. From Deareator the water goes to BFP

Steam turbines

Steam turbines have been used predominantly as prime mover in all thermal power stations. The steam turbines are mainly divided into two groups: -

Impulse turbine

Impulse-reaction turbine

The turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft. There is a high pressure turbine at one end, followed by an


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intermediate pressure turbine, two low pressure turbines, and the generator. The steam at high temperature (536 ‘c to 540 ‘c) and pressure (140 to 170 kg/cm2) is expanded in the turbine.

Condenser

The condenser condenses the steam from the exhaust of the LP-turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases. The functions of a condenser are:-

1) To provide lowest economic heat rejection temperature for steam.

2) To convert exhaust steam to water for reserve thus saving on feed water requirement.

3) To introduce make up water.

We normally use surface condenser although there is one direct contact condenser as well. In direct contact type exhaust steam is mixed with directly with D.M cooling water.

Low Pressure Heater

There are three LP Heater–LP 1,LP 2,LP 3 . In LP1 the hot steam is tapping from 6 th stage of LP Turbine, the inlet temperature of water is 300C and outlet is 700C. From the 5th stage of LP Turbine the hot steam goes to LP 2 for rise the temperature of water, the inlet temperature of water is 700C and outlet temperature is 900C. In LP3 the steam tapping from 3rd stage of LP Turbine, the temperature of inlet water is 900C and outlet is 1200C. After that the water goes to derator.

Boiler feed pump

Boiler feed pump is a multi stage pump provided for pumping feed water to economiser. BFP is the biggest auxiliary equipment after Boiler and Turbine. It consumes about 4 to 5 % of total electricity generation. BFP pressurizes the water coming from Deareator at 180kg/cm 2. The number BFP is three. After that the water goes to HP Heater.


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Cooling tower

The cooling tower is a semi-enclosed device for evaporative cooling of water by contact with air. The hot water coming out from the condenser is fed to the tower on the top and allowed to tickle in form of thin sheets or drops. The air flows from bottom of the tower or perpendicular to the direction of water flow and then exhausts to the atmosphere after

effective cooling.


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Steam Cycle


Condencer(Hot Wall) CEP LPH1

LPH2LPH3Derator

Boiler Feed Pump HPH5 HPH6

BFP Discharger

Economiser

Boiler Drum

6 Down comer

Bottom Ring Header

Boiler Water Wall

Super Heater Header

Primary super Heater

Platen Super Heater

Final Super Heater

Main Steam Line Turbine

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Turbine & Auxiliary

Turbine:

The operation of a steam turbine is based upon the principle that the steam issuing from a small opening attains a high velocity. This velocity attained during the expansion of the steam depends on the initial and final heat content of the steam. The difference of the two heat energy is converted into kinetic energy.

There are 3types of turbine in the shame shaft. Shown in the figure.

HP Turbine :

It has 18 stages. Fixed blades are connected with static part of the turbine & and moving blades are connected with rotor of the turbine. Pressure drops are take place at fixed blade & in moving blade temperature drops are take place.

Steam Pressure inlet in HP Turbine is 155 Kg/cm2 at 5400C, and steam pressure outlet is 40 Kg/cm2 with some temperature drop. That means 115 kg/cm2 pressure is dropped in 18 stages.

IP Turbine: In IP Turbine the pressure and temperature fall again. The Turbine inlet

pressure and temperature is 38Kg/cm2 and 5400C.LP Turbine:

The inlet pressure and temperature of LP Turbine are 6kg/cm2 & 1300C. LP turbine has 16 stages. As the pressure is very low that’s why the blade arrangement of this turbine is bigger than HPT & IPT.

After this stage the steam is goes to condenser.


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General Description:

250MW capacity turbine at Santaldih Thermal Power Station which has been supplied by BHEL is of KWU (Kraft Work Union-Germany) design. The turbine is a machine of:

Condensing (means turbine exhaust steam going into the condenser)

Tandem (means one shaft will follow the other shaft)

Compounded (means it has both impulse and reaction staging)

Horizontal (means all the shafts are rotating horizontally)

Reheat type (means high pressure turbine exhaust is going to boiler for reheating and entering into the intermediate pressure turbine for further expansion). It has got separate high pressure, intermediate and low-pressure sections. The HP and IP sections are of single flow cylinder and LP section is of double flow cylinder. The turbine rotors are rigidly coupled with each other and with generator rotor.The entire turbine except first stage of HPT is provided with reaction blading. The first stage of HP turbine is provided with impulse blading

TURBINE SPECIFICATIONS :

Type: Three cylinders reheat condensing turbine having:

i) Single flow HP turbine with 1(one) impulse and 24 reaction stages.

ii) Single flow IP turbine with 16 reaction stages.

iii) Double flow LP turbines with 8 reaction stages per flow.

Rated Parameters

Nominal rating : 250 MW

Peak loading (without HP heaters) : 250 MW

Maximum Load under valve wide open(VWO)condition:-262.5MW

Rated speed. : 3000 RPM

Main steam flow at full load (With HP heaters in service) : 738.3 tons/hr.

Main steam flow at full load (Without HP heaters in service) : 674.3 tons/hr.

Main steam pressure / temperature at full load : 147.10 kg/cm2 / 5370C.

Condenser pressure. : 50 mm Hg with CW inlet temperature 330C.


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Water Handling Plant


DM Plant

Clarified Water Storage Rank

Clarifloculator (Mud separator)

Raw Water Pond (3 pump)

New Intake pump House (6 pump)

Water Used For Cooling Of Bearings Of BFP, ID fan, FD fan, PA fan, CEP

DM Transfer Pump

DM Storage Tank

DMCW Feed Water

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Ash handling system

The disposal of ash from a large capacity power station is of same importance as ash is produced in large quantities. Ash handling is a major problem.

i) Manual handling: While barrows are used for this. The ash is collected directly through the ash outlet door from the boiler into the container from manually.

ii) Mechanical handling: Mechanical equipment is used for ash disposal, mainly bucket elevator, belt conveyer. Ash generated is 20% in the form of bottom ash and next 80% through flue gases, so called Fly ash and collected in ESP.

iii) Electrostatic precipitator: From air preheater this flue gases (mixed with ash) goes to ESP. The precipitator has plate banks (A-F) which are insulated from each other between which the flue gases are made to pass. The dust particles are ionized and attracted by charged electrodes. The electrodes are maintained at 60KV.Hammering is done to the plates so that fly ash comes down and collect at the bottom. The fly ash is dry form is used in cement manufacture.


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Coal Handling Plant(CHP)

As we know the main thing or u can say the heart of a thermal power plant is the fuel that is used to vaporize the water to steam and draw the mechanical force. Actually it is the conversion of chemical energy that is within the coal into the mechanical energy of steam.

The job of CHP is mainly to keep the coal supply line live always and not to create any problem in generation that is caused by coal. Actually CHP department deals with the jobs that to fill up the coal bunker at the right time, to stack the extra coal as per requirement and looking over the efficient usage of coal.

The entire CHP department is fragmented in three parts i.e. electrical, civil, mechanical maintenance. The electrical department deals with the motor conveyer etc. and the mechanical department checks the mechanical arrangements like hoper, crusher etc. in coal handling plant the flow of the material is as follows:

SYSTEM DESCRIPTION: The coal handling Plant is envisaged for unloading of coal received in wagons and Conveying the unloaded coal to bunkers through crushers, alternatively stacking the crushed coal, reclaiming and supplying it to the coal bunkers. The Reclaiming process included the system of Stacker-cum-reclaimer. The choice of selecting the above systems for feeding coal to bunkers and unloading it from wagons depends on the plant conditions and the Engineer-in-Charge has to take most judicious decision so that the bunker position remains always healthy (and hence no interruption of generation due to coal feeding) and to unload maximum number of wagons to have enough stock of coal in the yard and also to minimize the demurrage charges.

Daily coal consumption

at 68.5%PLF & 3657.9 Ton

at 80% PLF & 4272 Ton

at 100%PLF 5340 Ton

Annual Coal requirement

at 68.5%PLF 1.335 MT at 80% PLF 1.602 MT at 100%PLF 1.871MT

Flow of system: Coal received in Bottom Open Bottom Release type wagons (BOBR). BOBR wagons are unloaded by compressed air system while in stationary condition on the track hopper.

Coal from Track Hopper is scooped by either of two (2) paddle feeders for each stream and is fed to either conveyor 31A or Conveyor 31B. Conveyor 31A in turn discharges to


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conveyor 32A, similarly Conveyor 31B to Conveyor 32B in underground Transfer point TP-31.

Conveyor 32A/32B takes uncrushed coal to TP-32 wherein, Conveyor 32A/32B can feed two reversible belt feeders. The reversible belt feeders, depending upon the direction of the belt speed, shall feed to either of Conveyors 33A/33B or conveyor 34A/34B.

Conveyor 33A/33B taking feed from either of Conveyor 32A or 32B via reversible belt feeders feed on either of existing Conveyor 3A or 3B at the location of the existing pent house. Separate junction house is built for this purpose which will house the drive arrangement etc. of conveyor 33A/33B. Existing Conveyor 3A/3B shall be properly fed by means of bifurcating chute along with flap gates. From this point coal is carried up to Bunker by the

existing conveying system.Coal of lump size(-)300mm is received by either of the conveyor34A/34B from either of the reversible belt feeder RBF-1A/B at transfer house TP-32 through two way discharge chutes fitted with Flap Gates FG-31 or FG-32.

In normal operation, uncrushed coal is taken from TP-32 to the Crusher House -2 through the Conveyor No.34A/B. Coal from Conveyor 34A/B is fed to the Roller Screens through the Reversible Belt Feeders. These Roller Screens screen out (-) 20mm size coal and feed the oversized (+) 20mm size coal to the crushers. Crushers reduce the coal size to (-)20mm.

In Crusher House-2. Conveyor 34A feeds reversible Belt Feeder.(RBF-2A through one chute while Conveyor 34B feed the other Reversible Belt Feeder (RBF-2B) by means of a separate chute. There are 3X100% Roller Screens/Crushers combinations in the Crusher house. While RBF-2A can feed either of Crushers CR-2A or CR-2B; RBF-2B can feed either of Crushers CR-2B or CR-2C. Crushed coal from crusher and undersize coal from Roller screens is fed to any of 3X100% Belt feeders BF-1, BF-2 or BF-3. Discharge from Belt Feeder is received by any of the Conveyors 35A/B depending on position of Flap Gates FG-35, FG-36 or FG-37 in the chutes.

Conveyor 35A discharges to either Conveyor 36A or Conveyor 36B through two way discharge chute fitted with Flap Gate FG-39 in TP-34. Similarly Conveyor 35B can feed to either Conveyor 36A or Conveyor 36B through another two way discharge chute fitted with Flap Gate F-38 in the same TP-34.


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Conveyor 36A can discharge to either Conveyor 38A for stockpiling or bypass Conveyor-37A through a two way discharge chute fitted with Flap Gate FG-41, in TP-35. Similarly Conveyor 36B can feed to either Conveyor 38A for stockpilingOr bypass the same TP-35. There is a provision in Stacker-cum reclaimer machine for self feeding of Conveyor 38A by passing Boom Conveyor.

In the crushed coal stockpile coal is stacked by Stacker cum Reclaimer (S/R- 3).Again when coal is needed from stockpile to Boiler Bunkers, Stcker-cum-Reclaimer reclaim coal from crushed coal stockpile and discharges into trunk conveyor.38A.

By-pass Conveyor 37A can discharge to either Conveyor 38B or Conveyor 41 through a two way chute fitted with a Flap Gate FG-42 in TP-38 and Conveyor 38B can discharge to Conveyor 39A or 39B through Flap Gate 44 in TP-39.

Trunk conveyor 38A can discharge to Conveyor 37B through discharge chute in TP-36. Conveyor 37B can discharge to either conveyor 39A/B through two way discharge chute fitted with flap gate FG-45 in TP-39.

Conveyor39A can discharge to either Boiler bunker Conveyor 40A/B through a two way chute fitted with flap gate FG-47 in TP-37.Similarly Conveyor 39B can discharge to either Boiler Bunker Conveyor 40A/B through an another two way chute fitted with Flap Gate FG-48 in the same TP-37.Conveyors 40A/B feed boiler Bunker of U#5 through Traveling Trippers -1&2 and Bunker of U#6 through Traveling Trippers -3&4.

There is provision for feeding existing Stockpile, Conveyors 6B or 6A through a Fixed Tripper FT-31 in TP-40 on Conveyor 41 with a two way chute fitted with Flap Gate FG-43 or a discharge chute at head end of Conveyor 41 in TP-41.

There is facility of Cross Feeding existing Trunk Conveyor 6B by another Reclaim Conveyor 42 which receives feed from Reclaim Hopper RH-32 through Rod Gates RG-2F/G, Rack & Pinion Gate RPG-2F/G and Vibrating Feeders VF-2F/G.

Auxiliary equipment is provided as per normal engineering practice. Belt Weighers are provided as shown in Flow Diagrams on different Conveyors and another one on stacker Reclaimer’s Boom Conveyor. In line Magnetic Separators are provided over discharge pulleys of Conveyors as shown in Flow diagram. Metal Detectors MD-1 & MD-2 are provided on Conveyor nos.40A/B. Bunker level indicators are provided for Boiler Bunkers. Coal Sampling system is provided in TP-37. Electric and Manual Hoists of desired capacities are provided for maintenance of different equipment. Electric Hoists have been provided for all Hoists of capacity 5 Te and above or lift 15 meters and above. Sump pumps with 100% standby have been provided in all underground areas. Hydraulic press type Belt Vulcaniser provided for CHP.

Dust Extraction, Dust suppression and Ventilation Systems have been provided for the entire Coal Handling Plant. Also service water, service air and drinking water facilities for CHP area have been done. The design/rated capacity of each of the two streams is 800TPH.


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CONVEYOR DRIVES

Conv.

No.

Numberof driveEquipment

Motor

Rating

KW

Motor rpm (Synchronus)

Consumed

KW (at

shaft)

Nominal

Reduction

Type ofGearB ox

HoldBack

Brake

drum on

input

Type ofCoupling

L.S. H.S.

31A/B 2 55 1500 33.947 15.4 Helica NO YES Gear Fluid32A/B 2 132 1500 100.457 15.4 Helica YES NO Gear Fluid3 3AB 2 90 1500 63.792 15.4 Helica YES NO Gear Fluid34A/B 2 132 1500 91.483 15.4 Helica YES NO Gear Fluid35AB 2 55 1500 41.404 15.4 Helica YES NO Gear Fluid36A/B 2 55 1500 45.536 15.4 Helica YES NO Gear Fluid37A 1 90 1500 61.963 15.4 Helica YES NO Gear Fluid37B 1 90 1500 64.525 15.4 Helica YES NO Gear Fluid38A 1 132 1500 93.461 15.4 Helica YES NO. Gear Fluid39A/B 1 90 1500 47.906 15.4 Helica

lYES YES Gear Fluid

39AB 2 200 1500 157.505 18.9 Bevel YES NO Gear Fluid

40A/B 2 75 1500 54.723 15.4 Bevel YES NO Gear Fluid

41 1 90 1500 67.887 15.4 Helica YES NO Gear Fluid42 1 90 1500 74.882 15.4 Helica YES NO Gear FluidBF-1,2,3 3 22 1500 14.608 47.1 Helica

lNO NO Gear Pin-

BushF-1AB (reversible)

2 22 1500 17.125 47.1 Helical

NO NO Gear Pin-Bush

RBF-2A/B (reversible)

2 22 1500 17.125 47.1 Helical

NO NO Gear Pin-Bush

OPERATION FOR STACKER CUM RECLAIMER

This machine can do the combined function of making the stockpile on either side of the rail track and also reclaim them for feeding to the coal bunker. Stacking operation is done by chevron method and reclaiming operation is done by block-cutting method.

The entire control & operation of the Stacker/re claimer machine will be from operator's cabin on the machine itself through PLC system.

Control & Operation of the machine will be possible in the following modes:a) Stacking (Manual /Auto mode)b) Reclaiming (Manual /Auto mode)

STACKING OPERATION :For stacking material into a stockpile of trapezoidal cross section, the boom

is slewed so that material will be discharged at the required point of the stockpile.The stacking boom is brought to the bottom most (lowest luff limit) the

beginning of the stockpile or at the required level at the beginning of a previously


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abandoned semi stacked stockpile. Warning signal should be given to warn personnel's on or near the machine or the yard conveyor. The boom conveyor and the yard conveyor shall be started in remote/auto sequential manner. The boom conveyor and yard conveyor should start stacking direction. Interlocking should be such that Yard conveyor should not start unless boom conveyor is running in stacking mode (with CHP in stacking mode). The actuator operated back plate on boom conveyor at bucket wheel side is set in forward direction (i.e. open position) and the machine moves at operational/Idle speed and commences forming the first layer of the stockpile. At both the ends of the travel the machine travel direction is reversed automatically and the machine travels to and fro at operational/idle speed between two end limits. After a no. of such cycles, the top of the stacked coal shall gain height and when it comes close to boom structure, the operator receives a signal by means of suitable sensing probe and the boom luffs up automatically. The extent of luffing at the end of each layer is preset. Stacking cycles shall be repeated until the maximum height oft stockpile is reached.

To make trapezoidal stockpile, the stacking boom is slewed by a small predetermined angle and stacking operation is continued to complete the stockpile.

For stacking on other side of the track rails on which the machine travels, the boom is luffed above the yard conveyor level to clear the yard conveyor (to avoid collision) and then slewed to required position. Then the machine is moved suitably to the beginning of the pile and the same operations described above are repeated to make the stockpile.

RECLAIMING OPERATION :

The machine is positioned at the beginning of stockpile. The boom is adjusted to top layer and bucket wheel boom is slewed to the beginning of the first cut. Flow rate set point is properly adjusted. The machine should be set for reclaiming mode. Warning signal should be given to the personnel on or near the machine and yard conveyor. The yard conveyor and boom conveyor is started in reclaiming direction. The Boom conveyor and bucket wheel are started in sequence in auto mode and necessary interlocks should be provided. The boom conveyor has to be interlocked such that it can not start in reclaiming mode unless main line conveyor is running. The actuator operated at boom pivot end back plate is adjusted for reclaiming position. The bucket wheel starts to take first bite when the slewing drive is started. Then operation is set to auto mode. The boom is slewed in the required direction until the bucket wheel completes the bite and comes out of the stockpile. Further slewing of the boom is stopped and the travel drive is started. The machine is moved forward at operational/idle travel speed by a bite step which is predetermined. The travel motion is then stopped and slew gear is reversed to once again bite into the pile. The coordinated slew left /right and the travel bite step motions are continued until the end of the selected zone.

After completion of reclaiming the first layer , the machine is brought back to starting point at operational/idle travel 'speed . To take into account for the pile geometry after the top most layer is reclaimed, the m a c h i n e is moved back so as to position the boom in suitable position for second layer bite.


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The boom is now lowered by a predetermined distance so as to position the Bucketwheel for second layer reclamation. The machine is moved forward and the coordinated slew left/right and travel bite motions are continued in auto mode until all the layers of the stockpile are reclaimed. The belt weigher mounted on boom conveyor will indicate the reclaiming rate.To maintain a preset flow rate from their reclaimer, the weight measurement obtained from the belt weigher is compared with the flow rate required andthe necessary corrective action is taken by varying the slewing speed.

The depth of cut in travel direction should be controlled and coordinatedwith the slewing speed so as to get the

. required reclaiming r a t e

Coal Handling plant Protection Systems:

There are various kind of protection and screening systems used in coal handling plant to protect and safely operate the entire process and utmost to increase the production efficiency. Now the following is the description of the few instruments that’s used in coal handling plant to provide better operation:

Belt Protection:

MAGNETIC SEPERATOR

Over band magnetic separator are ideal for the continuous separation of ferrous items from

large volumes of material carried by conveyor belts or vibratory feeders. Typical applications

include removing tramp iron from processed coal. They are used to protect the crushers

/Pulverizes by removing potentially damaging tramp iron. Magnetic separators are mounted

over a conveyor either in line with it or transversely across it. Ferrous items are lifted

magnetically from the feed conveyor.

METAL DETECTOR: Metal Detectors are used to detect tramp metal pieces in the material to prevent damage to the processing crushers, grinders, pulverizes in Bulk Material Handing Plants. They are also used to avoid metallic contamination in food products, pharmaceutical products, explosives, etc. They can also be used to vent pilferage of costly metals and for security purpose. High frequency electromagnetic field is set up in the aperture of the search coil by oscillator or exciter coil. The receiver part of the coil is penetrated by this field and in normal condition when no tramp metal piece is present, the voltage induced in this coil is negligible. When a ferrous metal piece is passing through this field, it provides low impedance path to the flux lines. Thus while the tramp metal piece enters in coil aperture, it creates disturbance in the flux which produces e,m.f. in the receiver. In case of non-ferrous metals, eddy currents are induced in the metal piece and they set up their own field reacting with main field thus disturbing original field distribution and causing e.m.f. to be generated in receiver coil. This voltage is then processed its unity and magnitude to alarm presence of metal piece unallowable size.


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Motor Protections

Zero Speak Switch (ZSS ): Zero speak switch is a switch a switch that makes the motor trip when the belt or the motor is running below 80% of its rated speed. This switch is attached with the tell end of the motor and when the motor rotates it senses the induced generated current created between motor and pulley and when the rated speed Is not above 80% it makes the motor to trip.

Pool chord switch: this one is basically used in safety purpose of the working personal on the belt. In this mechanism of tripping the belt the switch is tied with a chord. And if someone pulls the chord it senses and ends up tripping the circuit.

Belt Sway Switch: this one is the protection system that helps keeping the belt position fixed on the rotor path. This sensor is attached with the belt and if the belt shifts sidewise from its actual position the movement is sensed by it.

Spam501c: in case of motor protection there is one kind of relay protection that gives protection under the ground fault, overload, under voltage and other motor fault conditions. This relay is also used in CHP to electrically protect the motor.


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Cost Control & Fuel Efficiency

This is the department which deals with the actual controlling of the cost of the generating industry. This department looks after the every efficiency related matter that is used to maintain the quality and cost of the power plant. The entire job of this department is to calculate the entire thing as required..

The following is a brief discussion of the jobs that C& FE used to do:

The main supplier of coal in Santaldih Thermal power Station is Coal India Ltd. As they are having branches like BCCL, ECL and MCL thus the total supply is divided in parts. Among them BCCL supplies 80% of the required coal whereas ECL supplies 17% and MCL supplies the rest 7% which is imported coal.

The main ports that are used are basically paradeep and Haldia port to import coal from Indonesia and few other countries.

The price of the coal basically depends on the Grade of the coal and the gradation of the coal is made by the gross calorific value of the coal. There are 7 kind of coal as mentioned below:

Grade A Calorific value more than 6200kcal/kg

Grade B Calorific value more than 5600kcal/kg but less than 6200kcal/kg

Grade C Calorific value more than 4940kcal/kg but less than 5600kcal/kg

Grade D Calorific value more than 4200kcal/kg but less than 4940kcal/kg

Grade E Calorific value more than 3360kcal/kg but less than 4200kcal/kg

Grade F Calorific value more than 2400kcal/kg but less than 3360kcal/kg

Grade G Calorific value more than 1300kcal/kg but less than 2400kcal/kg

After the coal reaches the Coal handling plant of STPS the samples are taken to test its grades and other quality and efficiency related matters.

Mainly two tests are performed to have the knowledge about the quality of the coal

A) Ultimate Analysis: This analysis is done to determine the percentage of

carbon(C), Oxygen(O2), Nitrogen(N2), Hydrogen(H2), Sulpher(S2) present in per kg coal. This presence of the mentioned thing determines the fuel efficiency of the coal.


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B) Proximate Analysis: This test determines the percentage of Fixed

Carbon(FC), Volatile Matter(VM), Inherent Moisture(IM), Ash and Total Moisture(TM) in per Kg of fuel.

Thus by performing these tests the coal is first judged that if its perfectly suitable for the furnace. In STPS the usual coal that’s used is lignite with an average gross calorific value of 3900Kcal/Kg. The used coal has fixed carbon percentage of 40% volatile matter 40 and above and grindabality index greater than 48.

The Useful heat value of the coal can be calculated by using the formulae

UHV=8900-138*(A+M)A : Ash percentageM : Moisture percentage

There is another option of having Indonesian cola as an imported fuel which is generally taken when the Indian coal supply can’t match up to the demand level. As in the government rule only 20% of used coal can be exported from the outside of the country thus this is mandatory to have the maximum quantity of coal from the inside of country and coal India is the monopoly supplier of it.

Furnace Oil: In furnace the initial ignition is made via oil. The oil is sprayed

inside and the set to fire then coal is injected, the oil that’s used are named as Low Viscous furnace oil.

Cost control : The most important thing of an is to control its expenditure to

maximize the percentage of income. Thus the most important economic part of the process industry is seen by this department.

To make the handling of fuel and generation of transformer economically efficient the following parameters are what the C&FE department used to maintain.

Damarage Control : Damarage cost is the cost that the Indian rail used to take

from the STPS corporation when the wrecks that they used to send to STPS are not made empty or not unloaded within time. If this cost can be reduced by being a bit careful and quick then the economic efficiency of the coal increases sharply.

Grade Slippage: Grade slippage is one more reason that reduces the cost

affectivity. Grade slippage means that when the coal that STPS receives from coalindia is below in grade than the coal desired from them. Thus if this could be maintain and the coal would be as desired then this makes the economy of the power plant a healthy one and as well as increases the efficiency.

Grindable Index Maintain: if the grindable in the coal mills are maintained

then it will make the losses of coal in coal mills to reduce and will increase the furnace efficiency.


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Stone Percenatage: its usual that when coal comes from the mine there are

stone that’s come with the coal. So if this stone percentage can be maintained by continuously checking it out and a the economic efficiency can be maintained.

In some cases there are some business deal between the supplier and STPS authority

that helps STPS to be more efficient economically.

Fuel Efficiency: The Efficiency of the Thermal Power Plant are dependent upon

various parameter of fuel as well as in operation. And ultimate energy efficiency in Santaldih Thermal Power Station is around 36%


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Elctrical Maintainance

Inside Power House Department (IPH)

This department deals with the things that are established inside the station. That is the electrical maintenances of Motor, Turbine, Alternator etc.This is a segmentation of the maintenance department of STPS.The following are the brief descriptions of the elements that IPH deals with:

Permanent Magnet Generator (PMG) : This is the part of the total

generating system that generates the initial excitation field for the exciter. This is a permanent magnet generator that is coupled with the turbine. When the turbine is made to rotate by the steam that is produced by the boiler the coupling with this PMG makes the PMG rotate and it generates a EMF that is fed to the main exciter to produce the adequate excitation DC voltage. The PMG is rated as follows:

KW: 35KW Voltage: 220V

AMP: 105A Phase: 3

Power Factor:1 Frequency: 400Hz.

RPM: 3000 Insulation Type: F

Serial No. 10250A13101 SPEC: 1EC34

Exciter : This one is one of the most important parts of the generating job. This instrument,

dealt by the IPH section is used to give the alternator the DC excitation. The developed EMF from PMG is fed to this instrument and the rotor of this instrument generates the excitation voltage. A rotating rectifier diode circuit is attached with the rotor of the exciter. Thus the created emf is rectified to DC and fed to the alternator rotor circuit.

The following is the rating of the exciter:


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Excitation Voltage: 106v DC

Speed: 3000rpm

Excitation amp: 36.5amp

KW: 1350kW

Voltage Dc: 420V

Amp Dc: 3200amp

Insulation Type: F

Alternator : This is the heart of the generating station. This is the part where the

power is actually generated. As per the alternator principle the stator field of the alternator is excited by a DC excitation current and the rotor of the alternator is made to rotate via the mechanical force of the steam. When the magnetic field around a conductor changes, a current is induced in the conductor. Typically, a rotating magnet, called the rotor turns within a stationary set of conductors wound in coils on an iron core, called the stator. The field cuts across the conductors, generating an induced EMF (electromotive force), as the mechanical input causes the rotor to turn. The rotating magnetic field induces an AC voltage in the stator windings. There are three sets of stator windings, physically offset so that the rotating magnetic field produces a three phase current, displaced by one-third of a period with respect to each other. The rotor's magnetic field may be produced by induction (as in a "brushless" alternator), by permanent magnets (as in very small machines), or by a rotor winding energized with direct current through slip rings and brushes.

Brushless Alternator : The kind of alternator that is used in STPS is brushless alternator that reduces the periodic maintenance cost and also reduces the brush contact losses. A brushless alternator is composed of two alternators built end-to-end on one shaft. Smaller brushless alternators may look like one unit but the two parts are readily identifiable on the large versions. The larger of the two sections is the main alternator and the smaller one is the exciter. The exciter has stationary field coils and a rotating armature (power coils). The main alternator uses the opposite configuration with a rotating field and stationary armature. A bridge rectifier, called the rotating rectifier assembly, is mounted on a plate attached to the rotor. Neither brushes nor slip rings are used, which reduces the number of wearing parts. The main alternator has a rotating field as described above and a stationary armature (power generation windings).Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and hence alternator output. The result of all this is that a small DC exciter current indirectly controls the output of the main alternator.


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The following is the specification of the alternator used:

KW: 250000kW Power Factor: 0.85

KVA: 294100 kVA Stator Voltage: 16500V

Current: 1029Amp R.P.M: 3000rpm

Frequency: 50Hz Connection: YY

Insulation Class: F Coolant: H2

AVR(Automatic Voltage Regulator): AVR is very useful instrument in Power Plant.It used when synchronizing is takes place from Grid to Power Station we adjust the frequency through synchroscope.and when frequency is differ then speed will also differ then the AVR is used.AVR control the speed of Alternator.

6.6kV Switchgear System: In an electric power system, switchgear is the combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is important because it is directly linked to the reliability of the electricity supply. High voltage switchgear was invented at the end of the 19th century for operating motors and other electric machines.[1] The technology has been improved over time and can be used with voltages up to 1,100 kV.The department IPH takes care of only the 6.6kv switch gear system and in that case only vacuum circuit breakers are used.

Vacuum Circuit Breaker(VCB): Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched to a very small amount (<2–3 mm). At or near current zero the arc is not hot enough to maintain a plasma, and current ceases; the gap can then withstand the rise of voltage. Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 35,000 volts. Unlike the other types, they are inherently unsuitable for interrupting DC faults. Vacuum circuit breakers tend to have longer life expectancies between overhaul than do air circuit breakers.

The breakers that’s used :

Rating of BHEL make V.C.B:

Model No. VM12 Rating: 1250Amp, 2500Amp

Voltage: 6.6kV System Voltage: 7.2kV

Rating of L&T makes V.C.B:

Model No. CNCS-1000C, CNCS-1250C, CNCS-4000H :

Ratings: 1000/1250A/4000Aamp Voltrage-415V


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Other Related Motor and Drives: motors and drives are the thing that one industry uses whenever it needs any control over the process that’s running to produce the outcome. The departments IPH deals with all that kind of motors and drives that are basically used in control of the process and few of them are to run the process smoothly. Following are the brief description of few of them:

Boiler Feed Pump: The motor that is used in the boiler feed pump is a huge motor that carries the water pressure from 15bar to 150bar.The rating of that motor is as follows:

Forced Draft(FD) and Induced Draft(ID) Fans: The FD and ID fans are one of the most important part of the boiler fans. The FD fan supplies the combustion air into the boiler and ID fan drives the exhaust gas through the stack. This fans are driven by some motors that are maintained by the department

Ratings of the HT Motors

DrivesNo of

MotorsRatings (KW)

RPMFull Load

(Amp)

No Load

(Amp)

PF(FL)

Makers

FD FAN 2 800 1487 88.5 29 0.83 BHEL

ID FAN 2 1925 746 208 70 0.84 BHEL

BFP 3 4600 1493 466 110 0.89 BHEL

PA FAN 2 1575 1488 165 34.5 0.87 BHEL

DMCW PUMP (TURBINE)

2 161 1482 18.5 6.5 0.82 BHEL

BOWL MILL 6 425 985 51.5 25 0.77 BHEL

CEP 3 325 1482 35.5 10 0.86 BHELMAIN AIR

COMPRESSOR

4 180 2955 21 0.89FUJI

ELECTRIC

Outside Power House


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This department deals with the maintenance of all the departments that’s outside the power house or one can say all the equipments that’s set out or away from the generating house are maintained by OPH. Say it’s the switch yard or the transformers they are all under this department. Following is a brief description of few of the parts of OPH’s caring,

Generating Transformer: Generating transformer is said to be the

main transformer that’s used to step up the generated voltage from the alternator. The generated voltage in STPS is 16.5kV which is too low a voltage to be transmitted. Thus this voltage is stepped up to the voltage 220kV to be convenient in transmission. The transformers which are used as generating transformer are oil cooled type and these transformers have aircell type oil conservator. This transformer has another special feature that this one has a thermo siphon type oil filtration system. Activated alumina is used in the tank to filter the oil in it. The breathing system for the conservator tank aircell is featured with silica gel breather that helps dry out the breathing air. The rating of the transformer is as follows:

MVA Rating (ONAN/OFAF/ONAF): 189 /252 /315 MVA (60%/80%/100%)

High Voltage: 235kVA Current: 774.81 A,

LV side: 16.5 KV, Current: 11035.21 A

Vector Group: YNd1, Z: 14.5%,

Make: BHEL

Station Transformer: Station transformer is the transformer that’s used to

give supply to the 6.6kV switch gear system and into the internal requirement of Power Station.

For station transformer 1& 2

MVA(ONAN/ONAF): 12.5/16,

VOLT(HV/LV): 132 KV/6.6 KV,

AMPERES(HV/LV): 70A/1400 A,

Vector Group: Yd1,

Z: 10.1%

For station transformer 3 and 4


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HV/LV1/LV2: 40/25/15

MVAHV Side: 220KV, 104.973A,

LV1 Side: 6.9KV, 2091.85A,

LV2 Side: 6.9KV, 1255.11A

Z(at 40 MVA Base) = 12.99%(HV-LV1), 12.81%(HV-LV2), 24.806%(LV1-LV2)

Vector Group:YNyn0d1,

NGR = 9.950 Ohm,

CTR: 2500:1,

Make: BHEL

Station transformer: 5

ONAF/ONAN: 40/24 MVA,

HV: 220 KV, 104.97 A,

LV: 6.9 KV, 3346.95 A,

Z= 15.97%,

Vector Group: YNyn0,

CTR: 2500:1,

Make: BHEL

Unit Transformer: There is another kind of transformer in STPS that is unit

transformer. This one is used to feed the self units of STPS like the township, these steps down the 1605kv to 6.9kv and used in ESP and other small auxiliaries. The ratings are as follows:

ONAN/ONAF: 16/20 MVA, Voltage: 16.5/6.9 KV,

HV: 699.81A, LV: 1673.479A,

Vector Group: Dyn11, CTR: 2000:1

Z = 10%, NGR = 9.950 Ohm,

OLTC on HV side, Make: BHEL

Switch Yard: Switch yard is the heart of the power plant which makes the main

distribution system of a power plant. In STPS the entire switchyard system is divided


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into two parts; one side of 132kV and another side of 220kV. In this switch yard the entire power is distributed through feeders to the grid. STPS can also receive power from that grid while running in dark condition. The following are the brief description of the components of the switchyard:

Feeder: The STPS generating station have 11 feeders that’s feeding power to 11

different substations. They have,

220Kv feeders for Asansol, Durgapur, Bishnupur1 & 2, Chandil

132Kv feeders for Purulia1 & 2

33Kv feeder for Bhojudih 1& 2

11Kv feeder for Colony 1& 2

Busbar Arrangements:

Main and Transfer bus arrangement:

in this case the bus bars are arranged in such a way that when any equipment of the main bus gets faulty it could be by-passed or isolated through the transfer bus. This arrange ment is known as main bus transfer bus arrange ment.

Three Bus Scheme:

The three bus scheme is that in this arrangement there are two main bus and one transfer bus system. It gives greater degree of shut down flexibility.

Tie Transformer: Tie transformers are those kind of transformers that are used

to tie up between two different bus voltage levels. This are basically auto transformers that matchup between the two bus arrangements. The ratings are as follows:

130 MVA Tie(Auto) TransformerMVA (HV/IV/LV):130/130/43.33

KILO VOLT (HV/IV/LV): 220/132/34.5

AMPERES (HV/IV/LV): 341.2/568.6/Loaded

Connection Symbol: YNa0d11

Make: CGL100 MVA Tie (Auto) Transformer

MVA (HV/LV/TERT): 100/100/33.33HV: 220 KV, 262.4 A,


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LV: 132 KV, 437.4 A TERT: 33 KV, 583.1 AHV/LV: Yy0, HV/T: Yd11, LV/T: Yd11HV/LV: 8.10%, HV/T: 31.10%, LV/T: 19.55%Make: CG

Current Transformer and Potential Transformer:

Current Transformer and potential transformers are basically used for measurement purpose. This transformers are mainly used for the purpose of measurement. These transformers are mainly of having single bar primary, several protection cores and one metering core of respective accuracy classes and secondary.

Current Transformer(CT): 245 KV, 2000 A, 31.5 KA for 3 Sec., 5 Core, 1 Phase, Outdoor Oil Filled Type Current Transformer, Make: BHEL, Jhansi

In case of potential transformer, Electromagnetic Voltage transformer(EMVT) is common up to 220KV and its insulation is economically designed by cascaded connections of several VTs in which their primaries are in series coupling windings alongside the primary winding equalize the voltage.

Circuit Breaker: Circuit breakers are basically used as the protection system. Previously air blast circuit breakers were used as the protection but now-a-days sulpher hexa fluoride(SF6) is used. As this circuit breaker has the following advantages over the general circuit breakers:

Simplicity of the interrupting chamber which does not need an auxiliary breaking chamber;

Autonomy provided by the puffer technique The possibility to obtain the highest performance, up to 63 kA, with a reduced number

of interrupting chambers Short break time of 2 to 2.5 cycles High electrical endurance, allowing at least 25 years of operation without

reconditioning; Possible compact solutions when used for gas insulated switchgear or hybrid

switchgear Integrated closing resistors or synchronized operations to reduce switching over-

voltages Reliability and availability Low noise levels

Rating of SF6 Circuit Breaker

245 KV, 2000 A,


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31.5 KA for 3 Sec,

SF6, 3 Phase,

Outdoor Type Spring Charged Circuit Breaker,

Make: AREVA

Isolator: Isolators are kind of conducting switches that makes two circuits to get isolated or connected with each other. There in a isolator there are some male and female part of connector which conducts when they touch each other and as a result the circuit is connected.

The specifications are as follows:

245 KV, 2000 A,

31.5 KA for 3 Sec,

Mechanically Ganged,

AC Motor Operated,

Two Column HCB Isolator,

Make: GR Power

CONTROL & INSTRUMENTATIONThis department deals with the entire maintenance of quality and controlling the

system mechanism. The various control mechanisms they use to maintain the constant and uninterrupted generation. In this department the mainly used elements are various kinds of temperature and pressure sensors, few optical sensors and also there is some valve mechanisms to be dealt with. Actually the entire department deals with the production


P a g e | 36

consistency and its maintenance and observation. Following are a brief introduction and description of the things that the department deals with.

INTRODUCTION In a Thermal Power Station, Chemical Energy of fuel, which is either Coal or Oil, is converted to Electrical Energy. Actually, this energy conversion takes place in different stages.Firstly, in Boiler, the chemical energy in fuel (Coal /Oil) is converted into heat energy. During process of combustion, the carbon, Sulphur etc available in the fuel reacts with air and liberates heat & flue gases. This heat is absorbed by the water of water-walls of the furnace and generates steam (heat energy).Secondly, in Turbine, this heat energy, in the form of steam, is converted into mechanical energy.And finally, in Generator, which is directly coupled with the turbine, this mechanical energy is converted into electrical energy or electricity.Therefore, a Thermal Power Plant/Station can be regarded as a Process Industry. Now, for successful completion of the process, a good numbers of process parameters (like steam pressure & temperature, drum level, feed water flow, etc) need continuous monitoring, which demands instruments. In a modern boiler of a Thermal Power Station, combustion process is very fast due to high steaming rate with increased unit capacity. Moreover, to reduce cost, the present boilers are operated at maximum permissible temperature limit of its metal.Further, due to small capacity Drum and high steam output to water storage ratio, the modern boiler demands continuous water feeding and constant drum water level. This is essential to prevent starvation of the boiler. To prevent boiler explosions and flame failure, the furnace draft (pressure) is to be maintained constant.From the viewpoint of metallurgical aspects, steam temperature is to be maintained constant at turbine end.All the above things indicate that the steam pressure & temperature, drum water level, furnace draft etc is to be maintained constant. In older and low capacity boiler, most of the above parameters are maintained manually. But in modern boilers, due to high process reaction rate, the control of various reactions mentioned above is beyond the purview of human and hence necessitates automatic control, which intern demands instrumentation.At present, from the technical aspect of view, we are going through that Era when technology reaches to the State of Art. In this State of Art era, a remarkable revolution has takes place in the field of Instrumentation. Digital Control System (DCS) has replaces the conventional instrumentation system. Adaptation of DCS has created a new era of instrumentation.

Measurement part deals with the measurement of different parameters of the process by deploying different sensor which is mainly known as primary instrument and brings it (measured value) in the notice of operating personnel by displaying it on indicator or recording it on recorder or storing it in Data Acquisition System (DAS) or in some cases, by generating audiovisual alarm signal & protective signal. Indicator, Recorder & DAS are mainly known as secondary instrument.

Sometimes, primary instrument i.e. primary sensing device is termed as Transmitter or Transducer. Transduction means the conversion of energy. So Transducer is the device, which converts energy from one form to another form.

Control part takes care for automatic/manual control of different parameters of the process. Setter, error generator, controller (Mainly PI controller. In some cases it may be PID


P a g e | 37

controller), auto/manual station, amplifier, electrical to pneumatic converter, positioner, actuator, etc. are the main component of control part.

Pressure Measurement: Pressure & Vacuum are the most common & important process parameter of a thermal power plant. Pressure & Vacuum are measured at so many points / parts of the process. Still Drum Pressure, Steam Pressure at Turbine end, Deaerator Pressure, Furnace Pressure, Lube Oil Pressure, Furnace Oil Pressure, Feed Water Pressure, Condenser Vacuum are the most important process parameter. Bourdon Tube Pressure Gauge, Diaphragm Pressure Gauge, Capsule Pressure Gauge, Bellow Pressure Gauge, Electronics Pressure Transmitter (Bourdon Tube, Bellow, Diaphragm or Capsule type) & Kenotometer (For back pressure measurement. Here for Condenser Vacuum measurement) are mainly used for measurement of Pressure & Vacuum. Depending upon the importance of the parameter, which is to be measured, either Pressure Gauge or Electronics Transmitter is used for measurement of that particular parameter.The Electronics Pressure Transmitters, which are normally used in thermal power station, are mainly either (i) Reluctance Type or (ii) Capacitance Type. Now a day, Capacitance type transmitters are widely used.Reluctance type transmitters, which are mainly used in thermal power plant, operate either on the basis of LVDT (Linear Variable Differential Transformer) principle or Force Balance principle. All Russian type & George Kent, U. K, type electronic transmitter are reluctance type. Russian transmitters are based on LVDT principle. The output of these transmitters is 1-0-1 Volts AC. Delta – pi transmitters of George Kent, U. K, are based on Force Balance principle. The output of these transmitters is 4 - 20 mA DC.Capacitance type Fuji and Rosemount make transmitters are mainly Capacitance type. The output of these transmitters is 4 - 20 mA D.C.All the above pressure transmitters are used in process plant where conventional instrumentation is adopted.

Now a day DCS has replaces the conventional instrumentation system, microprocessor based capacitance transmitters are widely used. These transmitters are normally known as ‘Smart Transmitter’. As per requirement of the user, the out put of these transmitter may be conventional 4 - 20 mA D.C or conventional 4 - 20 mA D.C signal in Digital Form or both conventional signal and conventional signal in digital form. Piezoelectric pressure transmitter :When certain asymmetrical crystals are elastically deformed along specified axes , an electric potential produced within the crystal causing a flow of electric charge in external circuit, called piezoelectric effect .Quartz / tourmalin ( natural crystals ) . Recently JFET / MOSFET etc are replacing conventional circuits .Smart transmitter :ICP are integrated circuit piezoelectric sensors with built in microelectronics ( amplifier and signal conditioner ) which operate over a simple two wire cable is called smart sensors .When microprocessors and miniature electronics are used with the transmitter for storing important parameters like range , scale , calibration , self diagnostic trouble shooting etc with a remote capability for sending data to and receiving data from a measurimg unit located at field .Advantages – Drift free Calibration remote & easy Can be directly connected to modern DCS system

Temperature Measurement:


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Temperature may be defined as Degree of Heat, where as heat is usually taken to mean Quantity of Heat. Thermometer is used to measure temperature. A thermometer measures the temperature of a body. But the quantity of heat, which the body contains, depends upon not only ‘its temperature’ but also ‘its mass’ and ‘nature of its materials. steam temperature, Drum temperature, SH & RH metal temperature, T/G Lube Oil & Bearing Babbitt temperature, Generator Gas temperature, HPT exhaust temperature etc has great importance in thermal power plant. Expansion thermometer or Change of state thermometer or Radiation and Optical Pyrometer or Electrical method of temperature are normally used in thermal power plant. And for measurement of temperature at those points / parts of the process, which are remote & critical from location point of view and / or which demands accuracy, precision and remote transmission, are normally measured by deploying Electrical method of temperature detection system. Normally, K – type Thermocouple (TC), Copper Resistance thermometers (CRT) and Platinum Resistance thermometers (PRT) are widely used in a thermal power plant.

Thermocouple (TC): When two dissimilar metals are welded together at one end and then heated, a voltage, which can be measured and the measured value can be calibrated in terms of temperature, is developed on the free end. This phenomenon is known as the principle of thermoelectricity. TC generates on the order of 20 – 50 mV through the range of their operating temperature. TC can be of the different types of material and construction. It may be a single/ simplex TC or duplex, Chromel / Alumel, Copper / Constantan; beaded, mineral insulated etc. Depending upon measuring range, Chromel – Alumel, Chromel – Copel and Platinum Rhodium – Platinum thermocouple are widely used in a thermal power plant. J Resistance Temperature Detector (RTD): The resistance of pure metallic conductors

increases with temperature and this change can be detected electrically. RTD operates on the basis of this principle. It is a highly accurate method of temperature measurement and particularly useful for measurement of lower temperature scales down to – 400 OF and can be used up to 1300 OF.

In practice, Copper, Nickel and Platinum wire are used for RTD because they can be manufactured to a high degree of purity and they have high temperature co-efficient and are able to resist corrosion and oxidation. Normally, CRT is used for lower temperature scales. Nickel is a cheap substitute of Platinum up to 600 OF and Platinum can be used up to 1300 OF

Disadvantages of RTD are – Not suitable for very high temp . Lead resistance introduces error . Circuit to be made low voltage driven , otherwise self heating will make the result

erroneous . At vibration prone area thermocouples are preferable than RTD .

Thermistors: Non metallic semi-conductor of ceramic materials having –ve temperature co-efficient of resistance are used for this purpose . This temp coefficient at room temp is about ten times higher than that of copper or platinum .So thermistors are more sensitive as well as smaller in size .Used only upto 100 degC . In thermal power plants thermistors are used for HT DRIVE bearing temp measurement .Thermistors are made by sintering mixtures of metallic oxides such as manganese ,nickel ,cobalt ,copper , iron and uranium. Important points about thermistors are –

Identical elements cannot be manufactured so individual elements to be calibrated separately .

Self heating will induce error . Lead resistance will not be a problem as thermistor has very high resistance .


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Mainly used for switching purpose.

Measurement of Level: In thermal power plant, measurement of level is essential for the purpose of safe and efficient operation of the plant. For the purpose of co-ordination and control, level measurement is also required. In thermal power station, measurement of level is carried out for liquid and solid. The coal level in the pulverize coal bunkers are measured, which are the example of measurement of level of solid. Measurement of Boiler drum water level, Deaerator water level, Condenser Hot well level, etc is the example of measurement of level of liquid.In thermal power plant, liquid level is also measured to generate audiovisual alarm signal as well as protective signal when the measured level falls below or raises above a preset value (level). Normally, float & switch type level sensor, which works on buoyancy method, is used for this type of level measurement. Condenser hot well level High / Low -- alarm, HPH / LPH level High / Low -- alarm, Deaerator level High / Low -- alarm, etc are generated by the float & switch type level sensor.In some cases, level is measured for remote indication and for control. For this type of level measurement differential pressure transmitters (dp transmitter) are normally used. The dp transmitter may be of LVDT type, Reluctance type or Capacitance type.Now a day, resistance method of liquid or water level measurement is widely used for measurement water level of pressurised vessel i.e. for measurement of boiler drum water level, Deaerator water level, HPH’s shell water level, etc. Hydra-state and Level state are most familiar level measuring device of this category. These are an electronic replacement of Gauge glass providing a significant improvement in accuracy, visibility, reliability & safety, enabling transmission of the water level condition to a remote display and the application of alarm and control functions. The discrimination between water and steam is based on the significant difference in resistivity between the two states over the saturation range. The dimensions of the Probe of device are selected to provide a resistance typically less than 105 ohms when the Probe is immersed in water which results in a resistance greater than 5X106 ohms for the steam condition.

Measurement of Flow:

Like pressure, temperature and level, flow is also most important process parameter, which is monitored continuously for purpose of Control, Co-ordination and Safe Operation of the process.

In a thermal power plant, flow of liquid as well as flow of solid is also measured for periodic as well as for on line efficiency calculation, which plays an important role in the modern concept of power plant operation, of the process.

Normally, rate flow instruments are widely used for measurement of flow of Steam, Feed Water, Spray Water, Fuel Oil, Air, D. M. Water etc and integrators are used for measurement of flow of Coal. Coal flow integrators are basically required to know the coal consumption, coal stock and to assess the performance of the unit and to deal with supplier.

Normally, for remote indication and control, differential pressure transmitters (dp transmitter) are widely used for measurement fluid flow. But, when local indication of fluid flow are required for guidance of operating personnel then ‘Rote-meter’ or / and ‘Turbine flow meter’ are used for measurements of fluid flow.

We know that if a restriction is introduced in the flow path of fluid then a differential pressure (dp) is developed across the restriction. Now, this DP has a relationship the


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quantity of fluid flowing in the path. This relationship can be mathematically expressed as: -

Where, Q is the quantity of fluid flowing in the path, dp is the differential pressure developed across the restriction and k is a constant which depends upon the cross sectional area of the flow path and density of the flowing fluid.This relationship can be derived from Bernoulli’s equation, which states that sum of the Pressure Head, the Velocity Heat and the Elevation Head at one point is equal to their sum at another point in the direction of flow from the first point plus the loss due to friction between the two points. Normally, in a Thermal Power Plant, Orifice Plate, Flow Nozzle, Piezomatric Ring etc are used as restriction. Flow Nozzle is used for Steam Flow (M.S. Flow) and Feed Water Flow measurement. Orifice Plate is used for measurement of Condensate Flow, BFP & CEP re-circulation Flow, SH & RH attemparation Flow etc. Piezomatric Ring is used for measurement of Air Flow. Orifice plates – It consists of a thin metal plate with a central hole .Upstream side has sharp edge of the hole . The pressure taps must be one at upstream and one at down stream .Applicable to everywhere since head loss is not considerable here , but not much durable in high pressure application .Nozzle – Restriction part of the nozzle consists of a convergent portion of rounded profile and a cylindrical throat .Corner pressure taps should only be used .Nozzles should be used where head loss is not very important .Durable but cost is high .Ventury tubes- Head loss is minimum here . Available in two forms .Nozzle entrance type consists of a cylindrical entrance followed by a followed by a nozzle entrance throat followed by a conical divergent section .Pressure taps are taken at the face of the nozzle section and in the throat of the nozzle .Turbine flowmeter :Basically a rotor fitted with number of blades mounted in the center of a pipeline with its axis parallel to the flow .The blades rotate when the fluid impinges on them .Angular velocity is proportional to the linear velocity of the fluid which in tern is proportional to the flow rate ..An electrical pick-up coil detects the angular velocity , which is electronically conditioned to give the flow rate .Advantages – Accurate Repeatability good Can operate under high pressure and temperature condition Fast response Easy to install

Disadvantages – Unsuitable for high viscous fluid Moving parts subject to wear and damage Unsuitable for dirty liquid

Analytical Instruments or Analyser: Unlike the aforesaid instruments, where measurement is done by displacement and mechanical means – based on physical properties, some instruments are used to analyze the sample – based on chemical heating or paramagnetic effects. Such instruments are normally termed as ‘Analytical Instruments or Analyzer.In a modern thermal power plant, analytical instruments are essential to measure ‘Oxygen in

Flue Gas’, ‘Dissolved Oxygen in Feed Water’, ‘Conductivity of Feed Water’ at different points of the process or circuit, ‘PH of Feed Water’ at different points of the


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process or circuit, ‘Silica content of Feed Water’ and ‘Purity of Hydrogen’ in generator casing.

Oxygen in Flue Gas: The percentage of O2 in flue gas is an indication of percentage of excess air. Too much excess air leads to inefficiency and low excess air leads to improper and incomplete combustion. So, measurement of O2 in Flue Gas provides good information to the operating personnel for safe and efficient operation.

Dissolved Oxygen in Feed Water: At high temperature and pressure, O2 in the Feed Water reacts with metal parts of Boiler and Turbine and results into corrosion. Dissolved O2 is removed effectively by deaeration and further traces of Dissolved O2, if any, is taken care by proper dozing of Hydra gene. So, measurement of O2 in Feed Water provides good information to the operating personnel for safe operation.

Conductivity of Feed Water: The conductivity of boiler make-up water and condensate water in an indication of dissolved salts in the water, which is fed to the Boiler Drum. Increase of conductivity will cause silica deposition on last stages of the turbine and causes damage to the thrust bearing and it may damage the turbine if no corrective action is taken. So, measurement of Feed Water Conductivity is essential for safe operation of the unit.

pH of Feed Water : The PH value of liquid gives an indication that whether the liquid is acidic or alkaline or neutral. The liquid is called acidic if the pH value is in between 1 and 6 and alkaline if the pH value is in between 8 and 14 and neutral if the pH value is 7. To prevent corrosion of the pressurised parts of the boiler, the pH value of Feed Water must be higher than 7.

Silica content of Feed Water: Silica in steam causes fine silica deposition on the turbine blades particularly on the last stages. Again silica deposition on turbine may cause the damage of the turbine. So for safe operation, measurement of silica in Feed Water is very much essential.

Hydrogen Purity: In thermal power plant, H2 is used for cooling of the core and winding of both the Stator and the Rotor of Generator or Alternator. The decrease of H2 purity in generator casing will cause increase of the core and winding temperature of both the Stator and the Rotor of Generator. Again the increase of the core and winding temperature of both the Stator and the Rotor of Generator will lead to the reduction of load of the generator i.e. the load of the unit. So, measurement of generator casing H2

purity is most important for economic operation of the unit. Stator Cooling Water Resistivity : In some thermal power station, where generator stator

winding is cooled by D. M. water, the resistivity of stator cooling water is measured. If the said resistivity falls below a pre-set value then the generator trips automatically because electrical current conduction may take place from generator stator winding to earth through stator cooling water due to its low resistance or low resistivity. So, stator cooling water resistivity is most important parameter for safe operation of the generator.

Special Supervisory Instruments for Turbine:Some instruments, which are called as Turbine Supervisory Instruments, are required to

monitor the characteristics of turbine under different load condition. These instruments play an important role during start-up and shutdown of the turbine as well as during sudden load disturbances.

Turbine supervisory Instrumentation System monitors the following main parameters of the turbine. Axial Shift, Differential Expansion, Shaft Eccentricity, Over all Thermal Expansion of HPT & IPT, Turbine Speed, TG Bearing Vibration & TG Bearing Babbitt Temperature.

In the past, Pneumatic Instruments were used for measurement of Axial Shift, Differential Expansion, and Eccentricity & Speed. After that, with advancement of technology,


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Variable Reluctance type pickup and Taco Generator were used for measurement of these parameters. Now a day, with further advancement of technology, Eddy Current Pick-up are widely used for supervision of turbine parameters.

Oxygen Analyser The oxygen analyser probe is designed to measure the net concentration of oxygen remaining after all fuels have been oxidised. The probe is permanently positioned within the exhaust duct and performs the system without any sampling system.

Hydrogen Purity meter. (analyser)The measurement principle used in the on-line hydrogen purity meter is the thermal conductivity of gases. Gases have thermal conductivities, which are different for different gases. The thermal conductivity of a gas mixture is a function of individual conductivities and gas concentrations.

Dust and Opacity monitorWhen a beam of light crosses a medium containing smokes or dust particles, some of the light is transmitted and some is lost due to scattering. The fraction, which is transmitted, is called the transmittance and the fraction, which is lost, is the opacity.SOx and NOx analyserNon-dispersive absorption type IR spectroscopic technique is used to measure SOx and NOx. A non-dispersive type uses narrow frequency band source.Equal intensity chopped infrared beams are passed through a measuring cell (MC) and a reference cell (RC) simultaneously. The reference cell is filled with a standard non-absorbing gas while the measuring cell contains the process gas.SWAS SWAS is the commercial name adopted for the steam and water analytical system. The instruments available under this system have a separate sampling handling system and henceforth are not in-citu type. In the main power plant these package is provided by ABB and for the DM plant lab. these are mostly of YBL make.

pH measurementpH is the measure of degree of acidity or alkalinity in a fluid. The scale value is defined as the negative logarithm of the hydrogen ion concentration, orpH = -log10[H+]In a solution both H+ and (OH)- are present. The dissociation constant is defined as the product of the number of H+ ions (OH)- ions and this is 14 always.The principle of pH measurement is based on the property of H+ ions, which react with a special glass membrane/electrode and produce a potential difference between the solution and the electrode. A suitable measuring circuit measures this potential difference. For a potential difference to exist a salt bridge needs to be developed; linking the two cells that has conductivity but does not alter the emf conditions in the two cells

Positioner : The positioner is a high gain proportional controller & the primary function

of a positioner is to ensure that the control valve plug position is always directly proportional to the controller output pressure 0.2 to 1.0kg/cm2, regardless of gland fiction, actuator hysteresis, off balance of forces on the valve plug etc.. The controller output signal does not directly actuate the valves stem but is fed to a bellows or diaphragm unit, which is connected to the flapper- nozzle or spool valve system. Assume that the system is in equilibrium and then the controller output increases slightly. The flapper is moved towards the nozzle and the


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variable output pressure begins to increase. This output pressure continues to increase until the valves spindle moves, mechanical feedback (cam arrangement) then restores the equilibrium. Thus the force applied to move the valves spindle is sufficient to overcome the effect of all forces. So, the positioner is a servo- amplifier used with the valve actuator to assure that the control v/v stem accurately takes the position that the input signal commands.

Positioners are not normally required for ON-OFF service. Most positioners are used where air as the operating fluid and as source of power.

TURBINE SUPERVISORY INSTRUMENTATION

Specification of a Turbine Supervisory Instrumentation (TSI) system can be an exhausting process when the individual parameters must be specified.

When an existing TSI system is being retrofitted, the immediate indication is that a one-for-one replacement of each original parameter is sufficient. This approach may be adequate if the original system was complete. However, recent experience with retrofitting TSI systems has brought to light that many of the existing systems can be greatly enhanced with additional parameters. Also, certain parameters should be considered for complete replacement including a different type of sensor.TSI systems not only measure bearing vibration levels, but can include:

Shell expansion Differential expansion Eccentricity Valve position Turbine speed and acceleration Thrust position Shaft Relative Vibration Case Vibration Phase angle Bearing temperature

FURNACE SAFEGUARD SUPERVISORY SYSTEM (FSSS )

A. Introduction :

The Furnace Safeguard Supervisory System (FSSS) is designed to assure the execution of a safe, orderly operating sequence in the start up and shut down of fuel firing equipment and to prevent errors of omission and commission in following such a safe operating procedure. The system provides protection, should there be a malfunction of fuel firing equipment and associated air systems. The safety features of the system are designed for protection in most common emergency situations. However the system cannot supplement the intelligence and the reasonable judgment of the operator in all the situations.

B. Basic Functions of FSSS :


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a. Prevent any fuel firing unless a satisfactory furnace purge sequence has first been completed.

b. Prevent start-up of individual fuel firing equipment unless certain permissive interlocks have first been satisfied.

c. Monitor and control the proper component sequence (manual or automatic) during start-up and shutdown of fuel firing equipment.

d. Make continued operation of fuel firing equipment subject to certain safety interlocks remaining satisfied.

e. Provide components status feedback to the operator.f. Provide flame supervision when fuel-firing equipment is in service and initiate fuel

trip upon certain adverse operating conditions.g. Provide master fuel trip when certain adverse operating conditions exists.

C. Boiler Trip Conditions :

1. Both ID fans OFF.2. Both FD fans OFF.3. 3.TotalAir flow (secondary + primary) less than 30% of MCR (252 tph).4. Furnace pressure very high (+150mmwc).5. Furnace pressure very low (-175mmwc).6. Drum level very high (+225mm) 10secs delay.7. Drum level very low (-225mm) 5 secs delay.8. Loss of all fuel trip. *9. Loss of reheat protection 10 secs delay. **10. 10.Loss of 220V dc > 2secs.11. 11.Loss of unit critical supply (24V dc).12. 12.Loss of 110V AC > 2secs & loss of fireball. ***13. 13.Generator class-A trip.14. 14.Flame failure trip. ****15. 15.Both emergency push buttons pressed.

*Loss of fuel trip generates when all coal feeders OFF and (all LONV closed or LOTV closed) and (all HONV closed or HOTV closed). Logic is armed from any oil nozzle valve not open.

**Loss of Reheat protection generates when any coal feeder proven and Generator Circuit Breaker open and (any HPBP or LPBP valve < 2%). When turbine is in service either of the HPCV or HPBP and either of the IPCV or LPBP both valves should be open > 2% and any feeder proven.

***Loss of 110vAC & loss of fireball happens when all feeders OFF and 110vAC fails in an oil elevation in service or in a coal elevation with mill ON condition.

****Flame failure logic exists in coal firing condition only. Coal elevation not in service votes for flame failure. If running coal elevation monitoring fireball scanner not showing 2/4 flame and is not supported by ¾ oil guns then it will also vote. If any feeder running and all coal elevation vote for flame failure then flame failure logic acts and boiler trips on flame failure.

UPS (Uninterruptable Power Supply), 230V AC :- this is considered the second stable source. The main functions of UPS are


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To provide power in uninterrupted manner to the load. The power should be pure. Output Power should be stable irrespective of input voltage or frequency variations.

The standard block diagram of any UPS is as shown in figure 1 ;-

The normal 415v or 230v ac source is the incoming source to UPS. A transformer is used to transform 415v to 230v ac if the supply is 415v. Then this input is filtered & fed into a controlled rectifier ckt for rectification. The controlled rectifier is used to vary the value of output DC voltage. This voltage is fed to inverter & also to battery for charging. The inverter transforms the dc input voltage into a stable ac output voltage. This output voltage is the final UPS output voltage, which is used to feed the critical loads.

In case if there is no input power to UPS then the output of rectifier is nil. The battery then comes into the picture. The dc voltage stored in the battery drive the inverter to produce the required AC output power. Thus in case of any sudden power failure, no interruption to the critical loads would occur.

If there is any problem in the inverter ckt or in battery, the output is automatically switched over to the bypass system, consisting of SVR (static voltage regulator). This regulator has a regulatory ckt to supply regulated (constant) voltage output.

Now, to switch over from inverter output to SVR output & vice versa one critical component is needed, i.e. transfer switch. Normally one switch is kept ON & the other is automatically OFF. The function of transfer switch is that the load should not experience any change in the supply change over. Normally within 1.5 cycles of 50 Hz sine wave (30 mSec) this changeover should be completed.

The transfer switch transfer the load automatically to SVR (bypass) in case of

battery dc voltage low Inverter failure. Excessive inverter overload/short ckt on load

The load re-transfer, back to the inverter, is completed automatically with the very small interruption in the output waveform when the inverter has returned to normal & maintained a stable output.

Here the UPS output is 230v ac, single phase. This power is fed to critical panels like control desk, all the computerised operating console, important panels like Turbine protection, turbine control, turbine supervisory, generator seal system etc.

In normal running condition two static switches1,2 are on catering 50% of load each. In case any one develops fault, that switch changes to OFF state keeping the healthier one to cater 100% load. The faulty inverter would break automatically from the load bus before it can affect the operation of healthy inverter(within one half cycle).

If both failed then the load is transferred to transfer sw 3. All the transfer switches used here consisting of IGBTs for fast transfer.

There is one maintenance bypass sw which can be made on manually during any major shutdown of UPS system.

24V DC: - The principal duty of this system is to provide secure DC for the following loads

Process control panels


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Annunciation panels Display of vital parameters Providing power to some vital remote panels which require 24V power, like LP bypass,

AVR etcFor better supply all the panels are wired from 2 sources with diode coupling.

DISTRIBUTED CONTROL SYSTEMS

DCS (Distributed Control System) is a computerized control system used to control the production line in the industry. Distributed control system (DCS) is the most modern control platform. It stands as the infrastructure not only for all advanced control strategies but also for the lowliest control system. While a product (Food, medicine, Oil..etc) passing through many stages in the factory before it reaches it's final so the product can be sold out, during those stages it requires a kind of control in order to adjust the quality of it. However, to adjust the quality it is required to control many physical quantities such as pressure, Temperature..etc. Further more, in some dangerous applications such as petrochemical factories and nuclear reactors the control will much critical, However, losing the control may lead to an explosion of the plant

WORKING PRINCIPLE


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Conceptually, the DCS is similar to the simple PC network. However, there are

some differences. First, the hardware and software of the DCS is made more flexible, i.e. easy to modify and configure, and to be able to handle a large number of loops. Secondly, the modern DCS are equipped with optimization, high-performance model-building and control software as options. The data highway is the backbone for the DCS system. It provides information to the multi-displays on various operator control panels sends new data and retrieve historical data from archival storage, and serves as a data link between the main control computer and other network.

On the top of the hierarchy, a supervisory (host) computer is set. The host computer is responsible for performing many higher level functions. These could include optimization of the process operation over varying time horizons (days, weeks, or months), carrying out special control procedure such as plant start up or product grade transition, and providing feedback on economic performance.

ELEMENTS OF DCS

The typical DCS system shown in figure consists of of the following elements:

Local Control Unit (LCU)- This is denoted as local computer in Figure 3. This unit can handle 8 to 16 individual PID loops, with 16 to 32 analog input lines, 8 to 16 analog output signals and some a limited number of digital inputs and outputs. Data Acquisition Unit-This unit may contain 2 to 16 times as many analog input/output channels as the LCU. Digital (discrete) and analog I/O can be handled. Typically, no control functions are available.


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Batch Sequencing Unit-Typically, this unit contains a number of external events, timing counters, arbitrary function generators, and internal logic. Local Display- This device usually provides analog display stations, analog trend recorder, and sometime video display for readout.

Bulk Memory Unit-This unit is used to store and recall process data. Usually mass storage disks or magnetic tape are used.

General Purpose Computer- This unit is programmed by a customer or third party to perform sophisticated functions such as optimization, advance control, expert system, etc. Central Operator Display.-This unit typically will contain one or more consoles for operator communication with the system, and multiple video color graphics display units.

Data Highway- A serial digital data transmission link connecting all other components in the system may consist of coaxial cable. Most commercial DCS allow for redundant data highway to reduce the risk of data loss. Local area Network (LAN)-Many manufacturers supply a port device to allow connection to remote devices through a standard local area network.

ADVANTAGES OF DCSOne of the main goals of using DCS system is allowing the implementation of digital control algorithms. The benefit of digital control application can include:

1.Digital systems are more precise. 2.Digital systems are more flexible. This means that control algorithms can be changed and control configuration can be modified without having rewiring the system. 3.Digital system cost less to install and maintain.

4.Digital data in electronic files are easier to deal with. Operating results can be printed out, displayed on color terminals, stored in highly compressed form. In santaldih thermal power station units 5 & Unit 6 the DCS is the main thing that helps controlling the parameters of the entire generation process. From the Mechanical operation or control room the entire computerized control and feedback system is designed via the DCS.

DCS basically is a software controlled system where the total parameters are maintained by programming in the system. The software used here is IBM developed Maximo.

Relay & Instrumentation


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A protective relay is device that detects the fault and initiates the operation of the circuit breaker to isolate the defective element from the rest of the system.

The relay circuit connection divided into three parts viz

First part of the primary winding of a current transformer (C.T) which is connected in series with the line to be protected.

Second part consists of secondary winding of C.T and the relay operating coil

Third of the tripping circuit which may be either a.c. or d.c. It consists of a source of supply, the tripping coil of the circuit breaker and the relay stationary contacts.

When a short circuit occurs at a point on the transmission line, the current flowing in the line increases to an enormous value. This results in a heavy current flow through the relay coil, causing the relay to operate by closing its contacts. This is turn closes the trip circuit of the breaker, making the circuit breaker open and isolating the faulty section from the rest of the system. In this way, the relay ensures the safety of the circuit equipment from damage and normal working of the healthy portion of the system

GENERATOR PROTECTION:

Over current: it is occurs mainly due to partial breakdown of winding insulation or due to overload on the supply system. Over current protection for alternators is considered unnecessary because of the following reason:

The modern tendency is to design alternators with very high values of internal impedance so that they will stand a complete short-circuit at their terminal for sufficient time without serious overheating. On the occurrence of an overload, the alternators can be disconnected manually.

The disadvantage of using overload protection for alternators is that such a protection might disconnect the alternators from the power plant bus on account of some momentary troubles outside the plant and, therefore, interfere with the continuity of electric service

Over speed: The chief cause of over speed is the sudden loss of all or the major part of load on the alternator. Modern alternators are usually provided with mechanical centrifugal device mounted on their driving shaft to trip the main valve of the prime-mover when a dangerous over speed occurs

Over voltage: The field excitation system of the alternators is so designed that over-voltage conditions at normal running speeds cannot occur. However, over voltage is an alternator occurs when speed of the prime-mover increases due to sudden loss of alternator load.

Unbalanced loading: Unbalanced loading means there are different phase currents in the alternator. Unbalanced loading arises from faults to earth or faults between phases on the circuit External to the alternator. The unbalanced current, if allowed to persist, may either severely burn the mechanical fixing of the rotor core or damage the field winding.


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Stator Faults: The stator faults means the faults associated with the three phase armature windings at the generator. These faults are mainly due to the insulation failure of the armature windings. The main types of stator faults are –

Phase to earth faults. Phase to phase faults. Inter turn faults involving turns of same phase winding.

The most important and common fault is phase to earth fault the other two or not very common while inter turn fault is very difficult to detect.

Phase to earth fault: This fault mainly occurs in the armature slots. The faults are dangerous and can cause severe damage to the expensive machine. The fault current is less than 20 ampere because negligible burning of core if machine is tripped quickly but if the fault current is high severe burning of stator core can take place. This may lead to the requirement of replacing the lamination which is very costly and time consuming. So to avoid the damage due to phase to earth faults a separate sensitive earth fault protection is necessary. For the generator along with the earthling resistance.

Phase to phase fault The phase to phase fault means short circuit between two phase winding such fault are uncommon because the insulation used between the coils of different phases in a slot is large. But once phase to earth fault occurs due to the overheating phase to phase fault also may occur. This fault is likely to occur at end connections of the armature windings which are over heating parts. Outside the slots such a fault causes severe arching with very high temperature. This may lead to melting of copper and fire if the insulation is not fire resistant.

Stator inter turn faults: The coil used in the attenuator are generally multi turned coils. So short circuit between the turns of one coil may occur which is called and inter turn fault. This fault occurs due to current surges with high voltage of (L di/dt) voltage across the turns. But if the coils used are single turn then the fault cannot occur. Hence for the large machines of the order of 50 MVA and more. It is a normal practice to use single turn coils but in some countries multi turn coil is very commonly used where protection against inter turn fault is must .

Rotor Faults : The rotor of an alternator is generally a field winding as most of the alternators are of rotating field type. The field winding is made up of number of turns so the conductors to earth faults are short circuit between the turns of the field winding, are the commonly occurring faults with respect to a rotor. These faults are caused due to severe mechanical and thermal stresses, acting on the field winding insulation.

The field winding is generally not grounded and hence single line to ground fault does not give any fault current. A second fault to earth will short circuit the part of the field winding and may thereby produce an unsymmetrical field system. Such an unsymmetrical system give rise to the unbalanced force of the rotor and result in excess pressure on the bearings and the shaft distortion, if such a fault not cleared very early. So it is very much necessary to know


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the existence of the first occurrence of the earth fault so that corrective measure can be taken before second fault occurs.

The unbalanced loading on the generator is responsible to produce the negative sequence current. These current produces a rotating magnetic field which rotates in opposite direction to that of rotor magnetic field. Due to this field there is induced e.m.f in the rotor winding. These causes over heating of the rotor. Rotor earth fault protection and rotor temperature indicators are the essential and are provided to large rating generators.

MOTOR PROTECTION

STATOR FAULTS :The stator faults means the faults associated with the three phase armature windings at the generator. These faults are mainly due to the insulation failure of the armature windings. The main types of stator faults are –

1. Phase to earth faults.2. Phase to phase faults.3. Inter turn faults involving turns of same phase winding.

The most important and common fault is phase to earth fault the other two or not very common while inter turn fault is very difficult to detect.

Phase to earth fault: This fault mainly occurs in the armature slots. The faults are dangerous and can cause severe damage to the expensive machine. The fault current is less than 20 ampere because negligible burning of core if machine is tripped quickly but if the fault current is high severe burning of stator core can take place. This may lead to the requirement of replacing the lamination which is very costly and time consuming. So to avoid the damage due to phase to earth faults a separate sensitive earth fault protection is necessary. For the generator along with the earthling resistance.

Phase to phase fault : The phase to phase fault means short circuit between two phase winding such fault are uncommon because the insulation used between the coils of different phases in a slot is large. But once phase to earth fault occurs due to the overheating phase to phase fault also may occur. This fault is likely to occur at end connections of the armature windings which are over heating parts. Outside the slots such a fault causes severe arching with very high temperature. This may lead to melting of copper and fire if the insulation is not fire resistant

Stator inter turn faults: The coil used in the attenuator are generally multi turned coils. So short circuit between the turns of one coil may occur which is called and inter turn fault. This fault occurs due to current surges with high voltage of (L di/dt) voltage across the turns. But if the coils used are single turn then the fault cannot occur. Hence for the large machines of the order of 50 MVA and more. It is a normal practice to use single turn coils but in some countries multi turn coil is very commonly used where protection against inter turn fault is must.

ROTOR FAULT : The rotor of an alternator is generally a field winding as most of the alternators are of rotating field type. The field winding is made up of number of


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turns so the conductors to earth faults are short circuit between the turns of the field winding, are the commonly occurring faults with respect to a rotor. These faults are caused due to severe mechanical and thermal stresses, acting on the field winding insulation.

The field winding is generally not grounded and hence single line to ground fault does not give any fault current. A second fault to earth will short circuit the part of the field winding and may thereby produce an unsymmetrical field system. Such an unsymmetrical system give rise to the unbalanced force of the rotor and result in excess pressure on the bearings and the shaft distortion, if such a fault not cleared very early. So it is very much necessary to know the existence of the first occurrence of the earth fault so that corrective measure can be taken before second fault occurs.

The unbalanced loading on the generator is responsible to produce the negative sequence current. These current produces a rotating magnetic field which rotates in opposite direction to that of rotor magnetic field. Due to this field there is induced e.m.f in the rotor winding. These causes over heating of the rotor. Rotor earth fault protection and rotor temperature indicators are the essential and are provided to large rating generators.

Ground fault: The ground fault protection is achieved using Earth Leakage Circuit Breaker (ELCB). When the fault current or leakage current flows through earth return path then it forms the earth fault. These faults are relatively frequently and hence protection is required against these which is provided with the help of Earth Leakage Circuit Breaker (ELCB).

The schematic diagram Earth Leakage Circuit Breaker (ELCB)as shown in figure 6.3

Under normal operating conditions, the current in line and neutral conductor is same so the net current (IL-IN) flowing through the core is zero. Eventually there will be not be any production of flux in the core and no induced e.m.f.. So the breaker does not trip.

If there is a fault due to leakage from live wire to earth or a person by mistake touching to the live terminal then the net current through the core will zero but equal to


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(IL-IN) or If which will set up flux and e.m.f. in C.T, As per the present value the unbalanced in the current is detected by C.T and relay coil is energized which will give tripping signal for the circuit breaker. As C.T operates with low value of current, the core must be very permeable at low flux densities.

In core of three-phase circuits, single ring shaped core of magnetic material, encircle the conductor of three phases as shown in figure. A secondary is connected to relay circuit. Under normal condition, the components of fluxes due to fields of three conductors are balanced and secondary carries negligible current.

During faulty condition, the balance is distributed and current is induced in the secondary to the trip the circuit breaker through relay.

PHASE FAULT: This protection is also called short-circuit protection. At the time of such a fault, the current increases by 8 to 10 times the full load current of the motor. Attracted armature type relay unit is connected in each phase with a current setting of 4 to 5 times the full load current. This is because starting current can be 4 to 5 times of full load current.

Hence to operate the relay only under fault condition such a setting is necessary. Such a protection as shown in figure


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The phase fault can cause burn out of coils and stampings and hence motor should be disconnected as quick as possible when fault occurs. Fast over current relays also are used to provide phase fault protection.

PHASE REVERSAL PROTECTION: The direction of induction motor depends on the direction of rotating magnetic field produced by stator windings. For a particular phase-sequence RYB the motor rotates in a particular direction of rotating magnetic field. But if any two lines are interchanged after repairs the phase sequence reverses such as YRB. Then the direction of rotating magnetic field also reverses and the induction motor starts rotating in opposite direction. Such a change of direction is dangerous if the induction motor is used to cranes, hoists, lifts or in threading mills etc,

Thus to disconnect induction motor from supply if there is phase reversal, phase reversal protection is provided

This protection is provided using motor driven disc working on electromagnetic principle. The secondary of two current transformers connected in two lines drive the motor to operate the disc. The arrangement is such that for a normal direction of motor, disc rotate in particular direction which keeps the auxiliary contacts closed. But if there is a phase-reversal then the torque produced reverses to rotate the disc in the opposite direction. Due to this auxiliary contact get opened. This inturn either operates the circuit breaker or de-energizes starter coil to disconnect the motor from the supply. Thus phase reversal protection for the induction motor is achieved. Now a day’s solid state phase reversal relay sensing the phase reversal is used.

Transformer protection:

Buchhloz Relay: The operation of buchhloz relay is as follows:1. In case of incipient faults within the transformer, the heat due to the fault

causes the decomposition of some transformer oil in the main tank. The products of decomposition contain more than 70% of hydrogen gas. The hydrogen gas being light tries to go into the conservator and the process gets entrapped in the upper part of relay chamber. When a predetermined amount of gas gets accumulated, it exerts sufficient pressure on the float to cause it to tilt and close the contacts of mercury switch attached to it. This completes the alarm circuit to sound an alarm.

2. If a serious fault occurs in the transformer, an enormous amount of gas is generated in the main tank, the oil in the main tank rushes towards the conservator via the Buchhloz relay and in doing so tilits the flap to close the contacts of mercury switch. This completes the trip circuit to open the circuit breaker controlling the transformer.


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COMBINED LEAKAGE AND OVERLOAD PROTECTION : In this system of protection, two overload relays and one leakage or earth relay are connected. The overload relays are sufficient to protect against phase-to-phase faults. The trip contacts of overload relays and earth fault relay are connected in parallel. Therefore with the energizing of either overload relay or earth relay, the circuit breaker will be tripped.

CIRCULATING –CURRENT SCHEME : During normal operating conditions, the secondaries of CTs carry identical currents. Therefore, the entering and leaving the pilot wires at both ends are the same and no currents flows through the relays. If ground or phase-to-phase fault occurs, the currents in the secondary of CTs will no longer be the same and the differential current flowing through the relay circuit will clear the breaker on both sides of the transformer, the protected zone is limited to the region between CTs on the high voltage side and the CTs on the low voltage side of the power transformer.

It is worthwhile to note that this scheme also provides protection for short-circuits between turns on the same phase winding. When a short-circuit occurs between the turns, the turn-ratio of the power transformer is altered and causes unbalance between current transformer pairs. If turn-ratio of power transformer is altered sufficiently, enough differential current may flow through the relay to cause its operation. However, such short-circuits are better taken care of by Buchhloz relays.

EARTH FAULT : The three leads of the primary winding of power transformer are taken through the core of a current transformer which carries a single secondary winding. The operating coil of a relay is connected to this relay. Under normal operating conditions (i.e. no fault to earth), the vector sum of three phase currents is zero and there is no resultant flux in the core of the current transformer no matter how much the load is out of balance. Consequently, no current flows through the relay and it remains inoperative. However, on the occurrence of an earth fault, the vector sum of three phase currents is no longer zero. The resultant current sets up flux in the core of


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the C.T. which induces e.m.f in the secondary winding. This energizes the relay to trip the relay to trip the circuit breaker and disconnect the faulty transformer from the system.

Overheating : The overheating of the transformer is basically of sustained overloads and short circuits. The permissible overload and the corresponding duration is dependent on the type of transformer and class of insulation used for transformer. Higher load is permissible for very short duration of time. The longer time is a dangerous as it causes overheating of transformer. Similarly the failure of the cooling system, through rare, is another possible cause of overheating.

Generally the thermal overload relays and temperature relays, sounding the alarm are used to provide protection against overheating. Similarly temperature indicators are also provide on the transformers, when temperature exceeds the permissible limits, the alarm sounds and the fans are started. The thermocouples or resistance temperature indicators are also provide near the winding. These are connected in a bridge circuit. When temperature exceeds the limiting safe value, the bridge balance gets disturbed and alarm is sounded. If the corrective action is not taken within certain period of time then the circuit breaker trips.

Winding fault: The winding faults are called internal faults. These faults are

Phase to phase fault Earth fault In turn fault

The overheating or mechanical shocks cause to deteriorate the winding insulation. If the winding insulation is weak, there is a possibility of short circuit between the phases or ground. Also the possibility of short circuit between the adjacent turns of the same phase winding is also possible.

When such internal fault occurs, the transformer must be quickly disconnected from the system. If such a fault persists for longer time, there is possibility of oil fire. The differential protection is very commonly used to provide protection against such faults. But this protection is not economical for transformers below 5 MVA for which an over current protection is used. For the high capacity of transformer in addition to main differential protection is also providing as a backup protection. For earth fault protection, the restricted earth fault protection system, neutral current relays or leakage to frame protection system is used.

Open circuit: The open circuit is one of the three-phases as if causes the undesirable heating of the transformer. A separate relay protection is not provide for the open circuits are much harmless compared to other faults. In case of such faults, the transformer can be manually disconnected from the system.

Except from the above relay there are many relays are used for Transformer protection. These are given below:


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Differential relay Restricted earth fault relay Neutral displacement relay Oil temperature high relay Oil temperature low relay Winding temperature high relay Winding temperature low relay

Conclusion

Santaldih Thermal Power Station (STPS) is one of the eminent power station in West Bengal. The current capacity of this power station is 500MW (2x250).This Power Plant is running under WBPDCL. Between Power Plant and Township The Communication system is good . Canteen of The Power Plant is very good quality of the food is good and price is very cheaper than other. Guest House of The Power Plant is moderate.

During Our Vocational Training we learnt a lot of things in various departments. This experience will be very helpful for our future. The valuable carier guidance of Many


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Employees will also help us. During our session unit 6 is stopped due to breaking of ID fan and vibration in Turbine. So we have opportunity to seen the Unit 6.In this training we use the opportunity to learnt practical knowledge on various arrangement of Transformer, Bus bar, Alternator, Motor, Circuit Breaker, Relay etc.

RECOMANDATION

After spending our session in STPS and depend upon our small experience we request you to decorate the Power plant organize way. If there is CC TV then it will be better for security purpose. The power plant should be smoke free zone. During Industrial Training Well Arrangement should be maintained .Library should contains many useful book.


project in wbpdcl at stps

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