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HEAVY EQUIPMENT REPAIR PLANT

Bharat Heavy Electricals Limited Varanasi

An ISO 9001-2000, ISO-14001 & OHSAS-18001 certified company

Industrial Training

HERP, Varanasi.

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ACKNOWLEDGEMENT I am extremely thankful & indebted to the numerous Bharat Heavy Electrical Limited Heavy Equipment Repairing Plant(HERP) Engineers, who provided vital information about the functioning of their respective departments thus helping me to gain an overall idea about the working of organization. I am highly thankful for the support & guidance of each of them.

I am highly indebted to my project guide, Mr Shadab sir, and Mr. Rajiv sir for giving me his valuable time and helping me to grasp the various concepts of power distribution equipments and their control and use.

Last but not the least, I would like to thank my parents & all my fellow trainees who have been a constant source of encouragement & inspiration during my studies & have always provided me support in every walk of life.

SAURABH MISHRA

B.TECH FINAL YEAR

ELECTRICAL ENGINEERING

K.N.I.T. (SULTANPUR)

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INDEX

CONTENT PAGE NO.

Acknowledgement……………………………………………………………………………..2

About HERP…………………………………………………………………………………...4

Existing Electrical Scheme……………………………………………………………………5-6

Rating and Specification of Equipments……………………………………………………...7-8

General description of Equipments…………………………………………………………. .9-27

Transformer………………………………………………………………………….9-13 Metering unit……………………………………………………………………….13-13 Circuit-breaker……………………………………………………………………..14-16 Air Break circuit-breaker………………………………………................................16-18 Minimum Oil Circuit-breaker……………………………………………………...18-21 Vacuum Circuit-breaker…………………………………………………………....21-23 Capacitor bank……………………………………………………………………...23-24

LT Circuit breaker…………………………………………………………………..24-25DG set………………...................................................................................................25-26

Proposed Electrical Scheme…………………………………………………………………..27

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ABOUT HERPIn line with BHEL's objective of providing consistent service at doorstep, HERP was established in the vicinity of power stations at Varanasi. The foundation stone of HERP sprawling in 29.8 acres area at Varanasi was laid on 26th September 1984. Within a short span of 21 months, production activities were started in the plant from 1st April'1986. Having achieved break-even point in the second year of its existence itself, HERP progressed by leaps & bounds. Starting as a manufacturer of O&M spares for boiler auxiliaries, repair activities took off on firm footing in 1990 when rebabbitting of TG set bearings was taken up. Since then, rebabbiting of different kinds of bearings including import substitution (NCL Bearings) as well as bearings of unconventional synchronous condenser have been carried out to the entire satisfaction of the customers. HERP Varanasi has taken up various critical jobs from near by power plants viz: NTPC Tanda, Unchahar, UPRVUNL Obra, Anpara, Parichha and helped them to achieve maximum availability of their units.

Now apart from conventional spares of Bowl Mills & boiler auxiliaries, HERP is manufacturing and supplying turbine fasteners for different power plants, turbine tools and tackles (required for erection and commissioning/ major overhaul of turbines) for various power projects. This year, we will be manufacturing steam turbine strainer assembly, sealing rings & small governing assembly also,

HISTORICAL BACKGROUND

Foundation Day : 26.09.1984Production Commencement : 01.04.1986

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Area : 29.80 Acres

Break-Even Year : 1987-88

Manpower Executives : 45

Supervisors : 29

Workers :79

Total :153

Accredition To : ISO-9001-2000 During

ISO Certification ISO-14001 2003

OHSAS-1800

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EXISTING SCHEME FOR ELECTRICAL POWER DISTRIBUTION IN BHEL VARANASI

The Existing Electrical power distribution scheme at BHEL VARANASI is shown above. From the substation of 132/33 KV, 33 KV supply is taken. After taking 33 KV supply from the substation it is taken to Metering unit for the measuring of power consumption and then to a 33 KV VCB (vacuum circuit breaker). This VCB separates the whole system from the main system of the production plant. Then after it is divided into two parts, in both circuits it is first taken to 33 KV VCB1 and VCB2. And then to 1MVA TRANSFORMER’s, one transformer is air cooled and other is oil cooled, after transformer it is taken to air circuit breakers which are mechanically interlocked with a key.

The interlocking is done for the protection purpose, then it is connected to the LT main circuit breaker and then fed to the capacitor bank for the power factor improvement. After capacitor bank it is send to the LT distribution panel and electrical power is fed to the different loads of the machine shop, administration building pump house e.t.c.

For the uninterrupted power supply in the production plant a 500 KVA Dg set is installed after connecting through a 3 pole air circuit breaker. 3 pole air circuit breaker isolates the DG set circuit from the distribution panel .

For an effective production plant it is necessary that plant should have an effective distribution plant. In the existing plant oil cooled transformer is difficult to manage, there are various points that should be check continuously in oil cooled transformer, oil level leakage level e.t.c. As the production plant is growing the need of power is growing up and the system should be improved.

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RATING AND SPECIFICATION OF THE EQUIPMENTS

EQUIPMENTS RATING AND SPECIFICATIONMETERING UNIT Specification-15/A/33 KV/110 V

Line CTR/PTRAccuracy class CT-0.5sAccuracy class PT-0.5s

TRANSFORMERS Oil cooled TransformerType of cooling- O.N.A.N

Freq- 50 HZ.Core and winding-1800 Kg.

Total weight-4800 Kg.Oil-1400 Litres.

Year-1986Rating- 1MVA

Air cooled TransformerType of cooling-A.N.

Standard- IS 11171-1985Weight-6000 Kg.

Year-1997Sr No.-2011314Rating- 1MVA

VACUUM CIRCUIT-

BREAKERS

Oil circuit-breakerBP-9085794

Standard- IS 13118/IEC 62271-200Rating- 33 KV

Air circuit-breakerBP-9085795

Standard-IS 13118/IEC 62271-200Rating- 33 KV

CIRCUIT-BREAKERS

Mechanical INTERLOCKINGOil and Air circuit-breaker

ICW 65 KA/IS CAT. BIEC-60947-2,IEC-60947-3

Rating-2 MVAMAIN LT BREAKER DIFFERENT LOADS

DB2,DB3,DB4,DB5,DB7,DB10-500V,500ABABBIT MELTING FURNACE-500V,500A

VERTICAL BORING-500V,500ASBCNC 55,SBCNC 60-500V,500A

10 M LATHE-500V,500ACOMPRESSOR(khosla)-500V,500A

PUMPHOUSE-500V,400ABUS DUCT-500V,400A

SAS,ADMINSTRATION BUILDING-500V,500A

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DG SET BREAKER-L&T CN-CS 100CIS13497-2 IEC-947-2

CIRCUIT-BREAKER

Type-36Voltage-33 KV, Freq-50 HZ

SR. NO.-BP 9085792Specification-ISI 3118 IEC-62271-200

Division-BHOPALYear-2009

DG SET JAKSON ENGINEERS LIMITED4PI-CF-4,SAE,15W-40

VALVOLINE CUMMINS ENGINE OILSR. NO.-SL4491

Product SR. NO.-CJS-06033305Product Model-JSP-500

Year-2006Rating-500KVA

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TransformerTransformer is an apparatus for converting electrical power in an ac system at one voltage or current into electrical power at some other voltage or current without the use of rotating parts.Constant voltage transformerIt consists essentially of three parts: the primary coil which carries the alternating current from the supply lines, the core of magnetic material in which is produced an alternating magnetic flux, and the secondary coil in which is generated an emf by the change of magnetism in the core which it surrounds. Sometimes the transformer may have only one winding, which will serve the dual purpose of primary and secondary coils. The high-tension winding is composed of many turns of relatively fine copper wire, well insulated to withstand the voltage impressed on it. The low-tension winding is composed of relatively few turns of heavy copper wire capable of carrying considerable current at a low voltage.Transformer terminology. The primary winding is the winding of the transformer which is connected to the source of power. It may be either the high- or the low voltage winding, depending upon the application of the transformer. The secondary winding is the winding of the transformer which delivers power to the load. It may be either the high- or the low-voltage winding, depending upon the application of the transformer. The core is the magnetic circuit upon which the windings are wound. The high-tension winding is the one which is rated for the higher voltage. The low-tension winding is the one which is rated for the lower voltage. A step-up transformer is a constant-voltage transformer so connected that the deliveredvoltage is greater than the supplied voltage. A step-down transformer is one so connected that the delivered voltage is less than that supplied; the actual transformer may be the same in one case as in the other, the terms step-up and step-down relating merely to the application of the apparatus.Working of TransformerWhen current in the primary coil changes being alternating in nature, a changing magnetic field is produced. This changing magnetic field gets associated with the secondary through the soft iron core

Hence, magnetic flux linked with the secondary coil changes. This induces e.m.f. in the secondary. If Np is the number of turns of the primary coil and Ns is the number of turns of the secondary coil. Let the rate of change of magnetic flux is dØ/dt. Then e.m.f. of primary coil is

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Ep=Np ×dØdt

Similarly e.m.f. of Secondary coil is

Es=Ns×dØdt

Then ratio of e.m.f.s of primary and secondary coils is

EpEs

=Np ×

dØdt

Ns ×d∅dt

=NpNs

Hence e.m.f.s are directly proportional to their respective no. of turns. For an ideal transformer input power and output powers are equal, henceEp.Ip = Es.Is

EpEs

= IsIp

=NpNs

Transformer Cooling

Losses in the transformer are of the order of 1% of its full load kW rating. These losses get converted in the heat thereby the temperature of the windings, core, oil and the tank rises. The heat is dissipated from the transformer tank and the radiator in to the atmosphere. Transformer cooling helps in maintaining the temperature rise of various parts within permissible limits. In case of Transformer, Cooling is provided by the circulation of the oil. Transformer Oil acts as both insulating material and also cooling medium in the transformer. For small rating transformers heat is removed from the transformer by natural thermal convection. For large rating transformers this type of cooling is not sufficient, for such applications forced cooling is used. As size and rating of the transformer increases, the losses increase at a faster rate. So oil is circulated in the transformer by means of oil pumps. Within the tank the oil is made to flow through the space between the coils of the windings. Several different combination of natural, forced, air, oil transformer cooling methods are available. The choice of picking the right type of transformer cooling method for particular appilcatiion depends on the factors such as rating, size, and location.

Transformer Cooling Methods

Different Transformer Cooling methods are:

Air Cooling For Dry Type Transformers

Air natural Type (A.N.) Air Forced type (A.F.)

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Cooling For Oil Immersed Transformers

Oil Natural Air Natural Type (O.N.A.N.) Oil Natural Air Forced Type (O.N.A.F.) Oil Forced Air Natural Type (O.F.A.N.) Oil Forced Air Forced Type (O.F.A.F.)

Oil immersed Water Cooling:

Oil Natural Water Forced (O.N.W.F.) Oil Forced Water Forced (O.F.W.F.)

Air Natural Transformer Cooling:

This type of Transformer Cooling method applies to dry type transformer of small rating. The surrounding air in the vicinity of the transformer is used for cooling. Small transformers below 25kVA can be readily cooled by air natural cooling. However air natural cooling is also used for large dry type transformers. Cooling takes place by convection air currents.

Air Forced Transformer Cooling:

This type of cooling is provided for dry type transformers. The air is forced on to the tank surface to increase the rate of heat dissipation. The fans are switched on when the temperature of the winding increases above permissible level.

Oil Natural Air Natural Transformer Cooling

This type of Transformer cooling is widely used for oil filled transformers up to about 30MVA. In Natural cooling, the oil in the tans gets heated due to the heat generated in the core and windings. The hot Oil flows upward and the cold Oil comes down according to the principle of convection. The oil flows in the transformer tank by the principle of natural convection hence this type of cooling is called Oil Natural Cooling. Heat is transferred from core and transformer windings to the oil and the heated oil is cooled by the natural air. Cooling area is increased by providing the cooling tubes.

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Oil natural Air Forced Transformer Cooling:

In this method, air fans are mounted near the Transformer and the forced air is directed on to the cooling tubes to increase the rate of cooling. The fans are provided with automatic starting. When the temperature of the oil and windings increases above a permissible value the thermostats switch on cooling fans. This happens during heavy load condition and during higher ambient temperatures. In higher rating transformers where the heat dissipation is difficult this type of cooling is used. Fans are used to forced and air blast on radiators. Forced air cooling increases the heat dissipation rate. In this type of cooling oil circulates by natural convection and the blast of air is directed towards the better heat dissipation rate.

Oil Forced Air Forced Transformer Cooling:

Transformers above 60 MVA employ a combination of Forced Oil and Forced Air Cooling. Oil Natural Air Forced type of cooling is not adequate to remove the heat caused by the losses which is approximately equal to 1% of the transformer rating (0.6MW). In case of Forced Oil and Forced, air cooling system a separate cooler is mounted away from the transformer tank. This

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cooler is connected to the transformer with pipes at the bottom and the top. The oil is circulated from the transformer to the cooler through the pump. The cooler is provided with the fans which blast air on the cooling tubes. This type of cooling is provided for the higher rating transformers available at the Substations and Power Stations.

Oil Forced Water Forced Transformer Cooling:

This type of cooling system needs a heat exchanger in which the heat of the transformer oil is given to the cooling water. The cooling water is taken away and cooled in separate coolers. The oil is forced through the heat exchanger. The oil pump pumps the oil from transformer to the het exchanger though the top pipes. Oil from the heat exchanger is pumped back to the transformer through the bottom pipe.

This type of cooling is provided for very large transformers which have ratings of some hundreds of MVA (Generating Transformer will have very high rating and rating equal to the rating of the generator). This type of transformers is used in large substations and power plants.

ELCTRICAL METERING UNIT

Electrical Metering units are always installed in the production plants. The Metering units are installed to keep an eye on the power consumption in the plant. By knowing the consumption of power, efficiently and effectively power can be managed. Metering units also helps in easy billing for the consumption of power. Plants have to pay for only that power they have consumed, so proper data is available from these meters. The rating of metering units in production plant is 33kv, 110kv e.t.c. A Metering cubicle is shown below

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CIRCUIT-BREAKERS

The circuit-breakers are automatic switches which can interrupt faults current. In some applications like single phase traction system, single pole circuit-breakers are used. The part of the circuit-breakers connected in one phase is called the pole .A circuit-breaker for three phase system is called “triple-pole circuit-breakers”.

Each pole of the circuit-breaker comprises one or more interrupters or arc-extinguishing chambers. Interrupters are mounted on support insulators. The interrupter encloses a set of fixed and moving contact. The moving contacts can be drawn apart by means of operating links of the operating mechanism. The operating mechanism of the circuit-breaker gives the necessary energy for opening and closing of contacts of the circuit-breakers. The arc produced by the separation of current carrying contacts is interrupted by a suitable medium and by adopting suitable techniques for arc extinction.

Types of circuit-breakers

The type of circuit-breaker is usually identified according to the medium of arc extinction. The classification of circuit-breakers on the medium of arc extinction is as follows:

1) Air break circuit-breaker.2) Oil Circuit-breaker (tank type of bulk oil).3) Minimum oil circuit-breaker.4) Air blast circuit-breaker.5) Sulphur hexafluoride circuit-breaker.6) Vacuum circuit-breaker.

The mode of arc extinction is either ‘High resistance interruption ’ or ‘Zero-point interruption ’.

High Resistance interruption: In this process the resistance of the arc is increased by lengthening and cooling it to such and extent that the system voltage is no longer able to maintain the arc and the arc gets extinguished. The technique is employed in air break circuit-breakers and d.c. circuit-breakers.

Zero point interruption: In this process, the arc gets extinguished at natural current zero of the alternating current wave and is prevented from restriking again by the rapid build up of dielectric strength of the contact space. This process is employed in almost all a.c. circuit-breakers. HVDC circuit-breakers employ ‘artificial current zero method’.

1)Air break circuit-breaker- Utilize air at atmospheric pressure for arc extinction.

2) Oil circuit –breaker (tank type of bulk oil)-Utilize dielectric oil (Transformer oil) for arc extinction. In bulk oil circuit-breakers, the contacts are separated inside a steel tank filled with dielectric oil.

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3) Minimum oil circuit-breaker- In minimum oil circuit-breakers the contacts are separated in an insulating housing (interrupter) filled with dielectric oil.

4) Air blast circuit-breaker- Utilize high pressure compressed air for arc extinction. They need compressed air plant.

5) Sulphur hexafluoride circuit-breaker- Sulfur hexafluoride is used for arc extinction.

6) Vacuum circuit-breaker- The fixed and moving contacts are housed inside a permanently sealed vacuum interrupter. The arc is quenched as the contacts are separated in high vacuum.

Comparison of circuit-breakers

Types Medium Voltage-breaking capacity

Design Features Remarks

Air break circuit-breaker

Air at atmospheric pressure

430-600V,5-15-35 MVA recently 3.6-12kV, 500MVA

Incorporates: Arc runners arc splitters magnetic coil.

Used for medium low voltages AC. DC Industrial circuit-breakers. Have current limiting features

Miniature circuit-breaker

Air at atmospheric pressure

430-600MVA Small size, current limiting feature

Used for low and medium voltages

Bulk oil circuit-breaker

Dielectric oil 12kV,3.6kV One tank upto 36 kV,3 tanks above 36 kV fitted with arc control devices

Getting obsolete used upto 12 kV, 500 MVA

Minimum oil circuit-breaker

Dielectric oil Preferred for 3.6kV to 145kV

The circuit breaking chamber is separate from supporting chamber. Small size, Arc control device used.

Used for metal enclosed switchgear upto 36 kV, Outdoors type between 36 and 245 kV.

Air blast circuit-breaker.

Compressed air 245kv,35000 MVA upto 1100 kv,50000 MVA

Unit type construction several units per pole, auxillary compressed air

Suitable for all EHV applications, fast opening closing. Also for Arc

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system required. furnaces Duty. SF6 circuit-breaker

SF6 gas 145kV,7500 MVA 245kV,10000 MVA 12kV,1000MVA 36kV,2000MVA 420kV,40MVA

One interrupter pole upto 245 kV.

Suitable for SF6 switchgear and Medium voltage switchgear.EHV Circuit-breaker. Maintenance free.

Vacuum circuit-breaker

Vacuum Preferred for indoor switchgear rated upto 36kV,750 MVA

Variety designs, long life modest maintenance.

Suitable for variety of applications from 3.6 kV to 36 kV.

H.V.D.C circuit-breaker.

Oil or Air-blast 33 kV,2kA Artificial current zero by switching in capacitors.

Used for metallic Return Transfer Breaker.

AIR BREAK CIRCUIT-BREAKER

The air at atmosphere pressure is used as an arc extinguishing medium in Air-Break circuit-breakers. These circuit-breakers employ high resistance interruption principle. The arc is rapidly lengthened by means of the arc runners and arc chutes and the resistance of the arc is increased by cooling lengthening and splitting the arc.

Air break circuit-breakers are used in d.c. circuits and a.c. circuits upto 12 kV.

The air-break circuit-breakers are generally indoor type and installed on vertical panels or indoor draw-out type switchgear.

Construction of Air circuit-breaker

In the air break circuit-breaker the contact separation and arc extinction takes place in air at atmospheric pressure. Fig (a) shows the closed current carrying contacts. As the contacts are opened arc is drawn between them. The arc core is a conducting path of plasma. The surrounding medium contains ionized air. By cooling the arc, the diameter of arc core is reduced. The arc is extinguished by lengthening the arc, cooling the arc and splitting the arc.

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Fig.(b) illustrates the normal arrangement of an air break circuit-breaker. This type of breaker is used for Medium and low voltages.

There are two sets of contacts: Main contacts and Arcing contacts. Main contacts conduct the current in closed position of the breaker. They have low contact resistance and are silver plated. The arcing contacts (2) are hard ,heat resistant and are usually of copper alloy. While opening the contact, the main contact dislodge first. The current is shifted to the arcing contacts. The arcing contacts dislodge later and arc is drawn between them (3). This arc is forced upwards by the electromagnetic forces and thermal action. The arc ends travel along the Arc Runner (Arcing horns.) The arc moves upwards and is split by arc splitter plates (5) as shown by the arrow (4).the arc is extinguished. by lengthening, cooling splitting etc. In some breakers the arc is drawn in the direction of the splitter by magnetic field.

Arc extinction in AC Air break circuit-breaker

The rapid increase in the arc resistance causes the reduction in the fault current and the fault current does not reach the prospective high value. The arc extinction process is assisted by the current zero in the ac wave. The voltage drop across the arc goes on increasing with the increase in the arc resistance and at a current zero, when the recovery voltage across the contacts is less than the arc voltage, the arc gets extinguished. The energy in the system inductance at a current zero is zero. Hence the arc interruption is easier.

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Arc runners:- As soon as the arc leaves the vicinity to the contacts it commutes to a pair of run out horns. In doing so the outer blow out system is switched ON. These blow out coils provide a magnetic field such that the arc footing is subjected to a strong magnetic field. We know from the electromagnetic theory that force is experienced by current carrying element of length dl meters, carrying current I amperes and placed in magnetic field B Weber/metre2 is given by the cross product.

dF=I(dl×B)By the virtue of this force, the arc travels upward and its length increases. The tips of the arc run along the arc runners and come to extremity. At a particular length the system voltage is unable to maintain the arc and the arc is extinguished. For systems having low inductance the energy 1/2×LI2 joules is small and arc gets extinguished before reaching the extremity of runners. For high inductance circuits special techniques such as magnetic blow-out, additional larger arcing horns e.t.c are used.

Operating mechanism of Air circuit-breaker

The operating mechanisms of Air circuit-breakers are generally with operating spring. the closing spring. The closing force is obtained from one of the following means:

-solenoid

-spring charged manually or by motor

-pneumatic

The solenoid mechanisms drive power from battery supply or rectifiers. The solenoid energized by the direct current gives the necessary force for closing the circuit-breaker. The springs used for closing operation can be charged manually or by motor driven gears. At the time of closing operation the energy stored in the spring is released by unlatching of the spring and is utilized in closing of the circuit-breaker.

MINIMUM OIL CIRCUIT-BREAKER

This type is also known as poor oil or small oil circuit-breaker. In minimum oil circuit-breakers the current interruption takes place inside ‘interrupter’. The enclosure of the interrupter is made of insulating material like porcelain. Hence the clearance between the live parts and the enclosure can be reduced and lesser quantity of oil require for internal insulation. Minimum oil Circuit-breaker of two types one pole and three pole.

Construction

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There are two chambers in a minimum oil Circuit-breaker, the oil in each chamber is separated from each other. The main advantage of this is that minimum oil is required and oil in second chamber won’t get polluted. Upper chamber is called the Circuit-breaker chamber and lower one is called the supporting chamber. Circuit breaking chamber consists of moving contact and fixed contact. Moving contact is connected with a piston its just for the movement of the contact and no pressure build due to its motion. There are two vents on fixed contact they are axial vent for small current produced in oil due to heating of arc and radial vents for large currents. The whole device is covered using Bakelite paper and porcelain for protection. Vents are placed in a turbulator. Various parts of minimum oil Circuit-breaker

1. Gas vent valve2. Oil baffle3. Terminal4. Turbulator5. Bakelised paper Enclosure6. Lower fixed contact7. Oil seal8. Oil injection piston9. Drain valve10. Operating links11. Drain valve12. Top chamber13. Moving contact14. Circuit breaking compartment15. Terminal16. Supporting compartments

Operation

Under normal operating conditions, the moving contacts remain engaged with the upper fixed contact. When a fault occurs, the moving contact is pulled down by the tripping springs and an arc is struck. The arc vaporizes oil and produces gases under high pressure. This action constrains the oil to pass through a central hole in the moving contact and results in forcing series of oil through the respective passages of the turbulator.The process of turbulation is orderly one, in which the sections of arc are successively quenched by the effect of separate streams of oil, moving across each section in turn and bearing away its gases.

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Advantages

A low oil Circuit-breaker has following advantages compared to bulk oil Circuit-breaker

1. It requires lesser quantity of oil2. It requires smaller space

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3. There is reduced risk of fire4. Maintenance problems are reduced

Disadvantages

A low oil Circuit-breaker has following disadvantages compared to bulk oil Circuit-breaker

1. Due to smaller quantity of oil, the degree of carbonization is increased2. There is a difficulty of removing the gases from the contact space in time

The dielectric strength of oil deteriorates rapidly due to high degree of carbonization.

INTERLOCKING

Interlocking devices are those which make operation of the switching device dependent upon the position operation of the equipment. Interlocks are provided as a safety measure against erroneous operation of a switching device. The interlocks are of the following forms: Electrical Interlocks, Mechanical Interlocks.

Electrical Interlock can be used between remote equipment, Mechanical Interlocks can be provided for the operating mechanisms of the two adjacent equipment. The Electrical Interlock comprises coil and bolt. When the coil is energized, the bolt is drawn by magnetic attraction and the interlocking is achieved.

VACUUM CIRCUIT-BREAKER

In this breaker, vacuum is being used as the arc-quenching medium. Vacuum offers highest insulating strength; it has far superior arc quenching properties than any other medium. When contacts of a breaker are opened in vacuum, the interruption occurs at first current zero with dielectric strength between the contacts building up at a rate thousands of times, that obtained with other Circuit-breakers.

Principle

When the contacts of the breaker are opened in vacuum (10 -7 to 10 -5 torr), an arc is produced between the contacts by the ionization of metal vapours of contacts. The arc is quickly extinguished because the metallic vapours, electrons, and ions produced during arc condense quickly on the surfaces of the Circuit-breaker contacts, resulting in quick recovery of dielectric strength. As soon as the arc is produced in vacuum, it is quickly extinguished due to the fast rate of recovery of dielectric strength in vacuum.

Working

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When the breaker operates the moving contacts separates from the fixed contacts and an arc is struck between the contacts. The production of arc is due to the ionization of metal ions and depends very much upon the material of contacts. The arc is quickly extinguished because the metallic vapours, electrons and ions produced during arc are diffused in short time and seized by the surfaces of moving and fixed members and shields. Since vacuum has very fast rate of recovery of dielectric strength, the arc extinction in a vacuum breaker occurs with a short contact separation.

Cross sectional view of Vacuum interrupter

Original Vacuum interrupter.

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Working

When the breaker operates the moving contacts separates from the fixed contacts and an arc is struck between the contacts. The production of arc is due to the ionization of metal ions and depends very much upon the material of contacts. The arc is quickly extinguished because the metallic vapours, electrons and ions produced during arc are diffused in short time and seized by the surfaces of moving and fixed members and shields. Since vacuum has very fast rate of recovery of dielectric strength, the arc extinction in a vacuum breaker occurs with a short contact separation.

Advantages:

1. They are compact, reliable and have longer life2. There are no fire hazards3. There is no generation of gas during and after operation4. They can interrupt any fault current. The outstanding feature of a VCB is that it can

break any heavy fault current perfectly just before the contacts reach the definite open position

5. They require little maintenance and are quiet in operation6. Can withstand lightning surges7. Low arc energy8. Low inertia and hence require smaller power for control mechanism.

CAPACITOR BANK

Capacitor banks are used for the power factor correction in the circuit. A capacitor bank is a grouping of several identical capacitors interconnected in parallel or in series with one another. These groups of capacitors are typically used to correct or counteract undesirable characteristics, such as power factor lag or phase shifts inherent in alternating current (AC) electrical power supplies. Capacitor banks may also be used in direct current (DC) power supplies to increase stored energy and improve the ripple current capacity of the power supply.

Single capacitors are electrical or electronic components, which store electrical energy. Capacitors consist of two conductors that are separated by an insulating material or dielectric. When an electrical current is passed through the conductor pair, a static electric field develops in the dielectric, which represents the stored energy. Unlike batteries, this stored energy is not maintained indefinitely, as the dielectric allows for a certain amount of current leakage, which results in the gradual dissipation of the stored energy.

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The use of a capacitor bank to correct AC power supply anomalies is typically found in heavy industrial environments that feature working loads made up of electric motors and transformers. This type of working load is problematic from a power supply perspective as electric motors and transformers represent inductive loads, which cause a phenomenon known as phase shift or power factor lag in the power supply. The presence of this undesirable phenomenon can cause serious losses in terms of overall system efficiency with an associated increase in the cost of supplying the power.

The use of a capacitor bank in the power supply system effectively cancels out or counteracts these phase shift issues, making the power supply far more efficient and cost effective. The installation of a capacitor bank is also one of the cheapest methods of correcting power lag problems and maintaining a power factor capacitor bank is simple and cost effective. One thing that should always be kept in mind when working with any capacitor or capacitor bank is the fact that the stored energy, if incorrectly discharged, can cause serious burns or electric shocks. The incorrect handling or disposal of capacitors may also lead to explosions, so care should always be exercised when dealing with capacitors of any sort.

LT Circuit-breaker

LT Circuit-breaker is an essential part of the distribution system for its protection. LT Circuit-breaker is collection of Circuit-breaker. These Circuit-breakers are connected with different loads. If any fault occurs at any load, the Circuit-breaker removes the faulty part from the healthy part.

LT Circuit-breaker are easy to install in the offices and industrial purposes. And very economic and effective in the protection of the system.

Here shown below the diagram of the LT Circuit-breaker used in BHEL.

DB-7 BABBIT MELTING

FURNANCE

VERTICAL BORING(Russia)

DB-4

SBCNC-60 SBCNC-55 DB-10 DB-5CRANES

(Machine Shop)COMPRESSOR

(Khosla)10M LATHE PUMP HOUSE

BUS DUCT SAS ADMIN. BUILDING

500 KV DG SET

DB-2 406 sq mm Cable MILLING MACHINE

DB-3

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Here above shown the different load in the BHEL-HERP and different parts of the Circuit-breaker that are connected with that loads. Different ratings are for different loads for e.g the rating of pump house is lower than the Lathe machine.

DIESEL GENERATOR SET

A diesel generator is the combination of a diesel engine with an electrical generator (often an alternator) to generate electrical energy. The packaged combination of a diesel engine, a generator and various ancillary devices (such as base, canopy, sound attenuation, control systems, circuit breakers, jacket water heaters and starting system) is referred to as a "generating set" or a "genset" for short.

The DG set provides emergency power supply at the time of power failures. And power cut in the plants. The DG set is connected with the LT circuit-breaker, and provide supply power.

Rating

Generators must provide the anticipated power required reliably and without damage. A standby generator may only need to operate for a few hours per year, but an online generator must operate continuously. When running, a standby generator might be operated with an overload that can be tolerated for the expected short running time. Consequently, a standby generator may be smaller. In contrast, a continuously operating generator cannot exploit an an overload.

To meet the above criteria manufactures give each set a rating based on internationally agreed definitions.

These standard rating definitions are designed to allow correct machine selection and valid comparisons between manufacturers to prevent them from misstating the performance of their machines, and to guide designers. A 500 KVA DG SET is shown below.

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Generator Rating Definitions

Standby Rating based on Applicable for supplying emergency power for the duration of normal power interruption. No sustained overload capability is available for this rating.

Typical application - emergency power plant in hospitals, offices, factories etc. Not connected to grid.

Prime (Unlimited Running Time) Rating: Should not be used for Construction Power applications. Output available with varying load for an unlimited time. Typical peak demand 100% of prime-rated kW with 10% of overload capability for emergency use for a maximum of 1 hour.

Typical application - where the generator is the sole source of power for say a remote mining or construction site, fairground, festival etc.

Base Load (Continuous) Rating based on: Applicable for supplying power continuously to a constant load up to the full output rating for unlimited hours. No sustained overload capability is available for this rating.

Typical application - a generator running a continuous unvarying load, or paralleled with the mains and continuously feeding power at the maximum permissible level 8760 hours per year. This also applies to sets used for peak shaving /grid support even though this may only occur for say 200 hour per year.

Sizing

Typically however it is the size of the maximum load that has to be connected and the acceptable maximum voltage drop which determines the set size, not the ratings themselves. If the set is required to start motors, then the set will have to be at least 3 times the largest motor, which is normally started first. This means it will be unlikely to operate at anywhere near the ratings of the chosen set.

Many gen-set manufacturers have software programs that enable the correct choice of set for any given load combination. Sizing is based on site conditions and the type of appliances, equipment, and devices that will be powered by the generator set.

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PROPOSED ELECTRICAL SCHEME FOR POWER DISTRIBUTION AT BHEL HERP

Above shown figure, is the proposed plan of BHEL HERP. In the future plan of Bharat Heavy Electrical Limited , they are extending their production plant and the extension of plant lead to the more need of power. In the proposed plan some changes are planned. These changes will be as follows-

1. Change the oil cooled transformer with the air cooled transformer.2. Transformers will be replaced with rating 2MVA.3. Power distribution panel is increased 4. A new DG set will be installed of 750 KVA for the increased load.

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5. DG set and the two transformers circuit will be interlocked automatically.

These are the required changes for the proposed plan, oil cooled transformer should be replaced from the air cooled because oil cooled transformer needs a great care and maintenance , wash the oil, check the oil level , check oil leakage and replacing and putting oil is a tough job. And the different equipments will be replaced by greater reading..