report wbseb

Vocational Training

A t

WBSEBSonarpur

(33 KV Sub-stat ion)

Report Submitted By:SAIKAT ADAK

Netaji Subhash Engineering College

Order No: DIR/HRD/VAC/100

Training Duration: 19.06.2006 to 15.07.2006

Training at Sonarpur Sub Station (33 KV)Submitted by SAIKAT ADAK

VOCATIONAL TRAINING AT SONARPUR SUB-STATION (33 KV)

If this is the age of computer then electricity is the most important part of this age. To generate electricity we have power generating station. To transmit the energy from generation end to demand end distribution system is developed. Power is needed in various heavy industries and houses that is why power generation and transmission is most important need in this age.In a sub-station various transformers are mounted for stepping up and stepping down purposes. Sub-station plays a most important part in the distribution system. West Bengal State Electricity Board (WBSEB) is a State Government undertaking. WBSEB is the main power transmitter in rural areas. Sonarpur sub-station is part of WBSEB. It is a 132 KV/33KV/25KV sub-station.It was established in1962 primarily to supply eastern railway with 25 KV. Then it had only two transformers (T1, T20 to cater the need of eastern railway. Later with development of nearby areas it was used to supply various areas with 33 KV lines. Now it has total five transformers and supplies power to Behala-Falta, Garia, Mahinagar and Sonarpur areas.

I N T E R C O N N E C T I O N : Interconnection is basically made for backup and efficient transmission. Sonarpur sub-station is connected with three sub-stations – Kasba, Behala-Falta and Lakshmikantapur. Sonarpur sub-station is fed with 132 KV by these sub-station-stations. Lakshmikantapur sub-station is connected to Sonarpur by Behala-Falta double circuit. But the principle

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25 KV 33 KV

Lakshmikantapur Jeerat

Falta Behala Kasba

Sonarpur

Eastern Railway

Sonarpur Garia Mahinagar


feeder of Sonarpur is Kasba through 132 KB. In Sonarpur it is step down to 32 KV and sends to Garia, Sonarpur, Mahinagar. 25 KV single phase power is sent to Easter Railway.

E Q U I P M E N T S : In sub-station-station we came across a number of equipments, which are integral parts and important for distribution of power. A brief analysis is done here about the equipments shown in Sonarpur Sub-station.

I N S T R U M E N T T R A N S F O R M E R S : CT & PT The line in the sub-station operates at high voltages and carry large amount of current. The measuring instrument and protective devices are designed for low voltages. Therefore they will not work satisfactorily if mounted directly on the power lines. The function of instrument transformers is to transfer voltages and currents of power lines to a value which is convenient for operation of measuring and relays.

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C U R R E N T T R A N S F O R M E R (CT ) : It is a step down transfer which steps down the current to a know ratio. The primary of this transformer consists of one or more thick wires connected in series with the line and hence is dependant upon the load connected to the system. The secondary consists of a large number of turns of fine wires and provided for the measuring instruments and relays, a current which is a constant function of the line current. It also does the work of sensing abnormalities in current and sent signal the relays to isolate the defective system.

S p e c i fi c a t i o n o f C T :Voltage class - 11 KV, 50 HzOutgoing - 200/100/1 Amp.Incoming - 200/100/1 Amp.

P O T E N T I A L T R A N S F O R M E R S ( PT ) : It is a step down transformers, which steps down the voltage to known ratio. The primary of this transformer consists of a large number of turns of fine wires connected across the line. The secondary winding consists of a few turns and provided for measuring instruments and relays. PTs are used to operate voltmeters, potential coil of wattmeter and relay from high voltage lines by step down to lower voltage.

S p e c i fi c a t i o n o f P T :Ratio - 33 KV / 100 VPrimary Winding - 33 KVType - EarthedSecondary Winding - 100 V

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T R A N S F O R M E R S : Transformers are the most essential part of a sub-station. In Sonarpur there are three transformers; TR-1, TR-2, TR-3, all of which are 33/11 KV, 6.3 MVA. These transformers supplies power to thelocal factories like Shalimer, Daubor etc., Railway Car-shade and residence of Sonarpur region.Inside the transformer a high voltage windings are wound over low voltage winding on a metallic core. There are three such arrangements each for a phase. These three arrangements are inside the transformer tank, which is filled with transformer oil. Transformer oil does the primary work of cooling the windings and core which tend to release heat during operation.Externally transformers have the appearance of a huge metallic container. We can observe conservator tank, Bucholtz Relay, Breather, Oil and Winding temperature meter etc. It also has large radiator grills to dissipate the heat from transformer oil and cool it down. The bushings are present for taking in and out the power lines from the transformer. Conservator tank helps in maintaining the oil level inside the transformer. The vaporized oil is condensed to liquid form in that tank. Breather serves the purpose of absorbing moisture from air that comes in contact with Transformer Oil. Breather contains silica gel which absorbs moisture. In modern transformers balloon arrangement is used. The balloon membrane is a porous material which allows dry air to pass through and absorbs moisture which degrades the Transformer Oil. Transformer also has a tap changing arrangement which helps in varying the voltage in transformer. Tap changer is based on the H.V. winding because precision is higher than low voltage winding and as H.V. winding is wound outside, bringing the tap pointer is easier and mechanism is easier than tap changer in L.V. winding, which is inside.Tap changers are of two types:

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i) ON Load tap changerii) OFF Load tap changer

During yearly maintenance the important tests are Transformer Oil Test and Insulation Resistance test.In Transformer Oil test:

Limit per ISAcidity (mg of KOH/gm)Neutralization Value

0.5 max

Tan Delta (90°, °C)Dielectric Dissipation Factor

0.2 max

Resistivity (Ω-cm at 90°) 0.1000 X 1012 minDielectric StrengthBreak Down Voltage (BDV)

50 KV min

Moisture content (PPM) 0.25 maxInsulation ResistanceHV-E, LV-E, HV-LV

5000X106 Ω

S p e c i fi c a t i o n o f T r a n s f o r m e r s :Transformer – 1:Type: Three PhaseVolts at no load: HV – 33000

LV - 11000Amps: HV – 110.22

LV – 330.66Frequency: 50 Hz.Cooling Type: ONAMVector group: DYN-11Mass of oil: 2680 Kg.Total mass: 13350 Kg.Volume of oil: 3100 Ltrs.

Transformer – 2 and 3:Type: Power transformerKVA: 6300

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Vector Diagram

2N

2V

2V

2WDYN-11

Vector Diagram

2N 2V

2V

2W

(DYN-11)

1U

1V1W


Volts at no load: HV – 33000LV - 11000

Amps: HV – 110.22LV – 330.66

Frequency: 50 Hz.Cooling Type: ONAMVector group: DYN-11Total amount of TFRS: 13620 Kg.Core and Winding:

7120 Kg.Weight of oil:

2680 Kg.Maxm oil temperature: 50-55°CPhases: HV – 3

LV - 3Test voltage:

HV – 70 KVLV – 28 KV

C O N D U C T O R S : Conductors carry electrical power from sending end to receiving end stations. They are one of the most important as most of capital outlay is invested on them. The distribution of current throughout the cross-section of a conductor is uniform only when D.C is passing through it. When A.C flows through a conductor, the current is non-uniformly distributed over the cross-section in a manner that current density is higher at the surface compared to the centre of the conductor. This effect becomes more pronounced with increase in frequency. This phenomenon is called SKIN EFFECT. This causes large power loss in A.C transmission. To minimize this effect

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stranded conductors are used which have added advantage of flexibility. Aluminium conductor steel reinforced (ACSR) is most commonly used in overhead transmission lines. Aluminium is used because it is cheaper and lighter than copper but with less conductivity and tensile strength. To strengthen the conductor, it is steel reinforced. ACSR conductors have different specifications and are differentiated with names of animals like deer, dog, panther, zebra etc.

In Sonarpur sub-station 132kv lines were ACSR, the main bus was ACSR-moose and transfer bus was ACSR-panther. The 220kv Jeerat –Lakshmikantapur line has ACSR-zebra while 33kv lines have ACSR-dog. The interconnections within the sub-station are done with ACSR-panther. The aluminium bus pipes used in 132kv lines are 2.5 inches in diameter while in 33kv and 25kv lines it is 1.5 inches in diameter.

S p e c i fi c a t i o n s o f C o n d u c t o r s :ACSR-panther: 30 aluminium and 7steel wires.ACSR-zebra : 54 aluminium and 7 steel wires.

I S O L A T O R S : Isolators are used in breaking a circuit. Isolators can be both mechanically or remotely operated. Isolators operate on no-load condition. It does not have specified current breaking or current making capacity. While opening a circuit, the circuit breaker is opened first, and then isolator and lastly earthing isolator is closed. While closing a circuit, earthing isolator is opened first, and then isolator is closed followed by circuit breaker.

C I R C U I T B R E A K E R S (CB) : Circuit breakers are most important protective devices. With the help of C.T, P.T and relays they can be made to trip automatically to disconnect

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any faulty circuit. Circuit breakers consist of fixed contact, moving contact, extinguishing chamber, roller, insulation, breather etc. The moving contact with the help of rollers is responsible for closing and opening of circuit. They are inside the extinguishing chamber and the whole arrangement is kept inside an oil-filled chamber. Transformer oil is responsible for cooling.Circuit breakers are of many types, but in Sonarpur sub-station we come across vacuum circuit breakers and oil circuit breakers.

V A C U U M C I R C U I T B R E A K E R S (VCB) : A vacuum system is one in which the pressure is at a value below the atmospheric pressure and is measured in terms of millimeters of mercury. In a vacuum of the order of 0.00001 torr the mean free path is of the order of few meters and thus, when the electrodes are separated by a few millimeters an electron crosses the gap without any collision. Therefore, in a vacuum the current growth prior to breakdown cannot take place due to electron avalanches.

S p e c i fi c a t i o n s o f V C B :Ratings: Voltage- 36kv, Current- 1250amps, Frequency- 50hz, Poles- 3, Breaking Capacity- 25ka, Making Capacity- 62.5ka, Short Time Current- 25ka, D.C Component- 50%, Shunt Trip- 30vdc, Closing Coil- 30 VDC, Make- Crompton Greaves.

O I L C I R C U I T B R E A K E R S : In these breakers, some insulating oil is used as an arc-quenching medium. The contacts are opened under oil and an arc is struck between them. Mineral oil has better insulating properties than air.

T Y P E S O F O I L C I R C U I T B R E A K E R :

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The oil circuit breakers find extensive use in power systems. They are of following types:-1) Bulk oil circuit breaker:

a) Plain break oil circuit breakers, andb) Arc control oil circuit breakers.

2) Low oil circuit breakers.

S p e c i fi c a t i o n s o f O C B :Type: KAD, Mechanism- spring box (manual), Voltage- 12kv, Current-800 Amps, Phase- 3, Frequency- 50 Hz, Breaking Capacity- 18.4 KA, Making capacity- 46 KAP, I.L. – 28 KV / 75 KVP, Short time rating- 18.4 KA for 3 seconds, Shunt trip- 30 VDC, Make- Alstom.

L I G H T N I N G A R R E S T O R : A lightning arrestor or a surge diverter provides protection against lightning and traveling waves. They are protective devices that conduct the high voltage surges on the power system to the ground.

Types of lightning arrestors:1) Rod gap arrestor,2) Horn gap arrestor,3) Multi-gap arrestor,4) Thyrite lightning arrestor.

Lightning arrestors are composed of insulators with air gaps and non-linear resistances in between them. Neal gapless arrestors have zinc sulfide which does the work of both line gaps and non-linear resistance.

D.C . S Y S T E M : Protection scheme of transformers and circuit breakers are D.C based. It is such that because this system is completely independent in operation

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from A.C supply except charging of battery which are D.C sources. Moreover this system is free from any voltage fluctuations which might affect the protection system adversely and even cause failure.The D.C system consists of power stack VRLA (Valve Regulated Lead Acid) batteries and battery charger.Power-stack batteries – These are maintenance free type and work on oxygen recombination principle. The oxygen gas generated at the positive plate is transported in gaseous state through porous and highly absorbent mat separator to negative plate where it gets reduced thus effectively reducing hydrogen evolution. Battery charger – Battery charger is charging the battery in various modes and at the same time to supply load requirements. The system consists of two battery chargers- 1) Float charger, 2) Float cum boost charger (FCBC) with contactor interlocking circuit and alarm indication circuit. They work on 415vac, 3-phase, and 50 Hz supply.

S p e c i fi c a t i o n s o f B a t t e r y C h a r g e r :Type - Auto/Manual 30vdc, 16 amps. Float cum boost charger.Ratings- I/p- 230(+/-) 20% VAC Phase- 1, Frequency-50(+/-) 2 hz Output D.C- Float- 32.5vdc Boost-27.4vdc Output Current- Load-0.6amps Battery-10ampsMake- Hillton Electronics, Kolkata-700010.

P R O T E C T I N G P O W E R F R O M S T E A L I N G : In the sub-station we saw a meter which is manufactured by Secure Meters Ltd. It can measure everything related to power. This instrument is connected with main controlling center by internet (telephone line). So any time any controller can compare the amount of power left by the sub-

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station and the amount of power for which consumers paid bill. Hence can check the power lost in the way. Now some units are given which a Secure Meter can measure - VA, Wh, VA, V, A, W, PFAC, Hz, Time, VAHr

S Y S T E M L A Y O U T : Power is led to Sonarpur Transmission sub-station through two lines- one from Kasba sub-station, another from Behala-Falta sub-station. The supply is of 132 KV magnitudes which is step down by two 132/25 KV transformer and 132/33 KV transformer. 25KV is supplied to eastern Railways and 32 KV is supplied to Garia, Mahinagar and Sonarpur regions.

The 32 KV line is also fed to Sonarpur Distribution sub-station. It has three transformers of which two are in group-1 and other is in group-2. These transformers are step down transformer of rating 33/11 KV. After stepping down to 11 KV the voltage is fed to local consumer factory and Railway Car shade.

All the transformers are protected by current transformers (CT), Circuit Breakers (CB) and lightning arrester (LA). Potential Transformer (PT) and Current Transformers (CT) are both protection as well as measuring device which helps a measuring inflow and outflow of energy.

Transfer Bas is provided in the sub-station so that for any occurrence of fault or maintenance, the main bus is disconnected, power can be transmitted to the various transformers. Power is transferred to the transferred bus with the help of a bus coupler. CT and PT of the bus coupler are for safety purpose.

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SCHEMATIC LAYOUT DIAGRAM OF KALIKAPUR 33 KV SUB-STATION: During our training period, we visited Kalikapur sub-station is as it resembles with Sonarpur sub-station. It is also a 33/11 KV sub-station. It has VCB, CT, PT, transformer (33/11 KV), oil circuit breaker etc. The layout of this sub-station follows:

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COMMUNICATION: Communication is essential in power system for better arrangement. Communications are of following type.

PLCC – Power Line Carrier communication:It is a communication method where signals are already existing power lines rather than optical fibers or radio waves. This equipment operates at frequency below 600 KHz to transmit information.The power line carrier is usually coupled to the power line by means of coupling capacitor, in conjunction with a line trap. Supply to this system is DC. The web trap is a tuned inductor where high frequency gets blocked and power frequency (50 Hz) electric signal passes to electric circuit. Coupling capacitor blocks the low frequency but passes the high frequency. Line Matching Unit (LMU) matches the impedance of the power line with that of co-axial cable for carrier communication. LMDU (Line Matching Dual Unit) is used in one phase while another has LMU. Two phase system is for backing purpose. The signal is then sent to transmitter. After amplification it then sent to handset through the exchange.

VHF – Very High Frequency:There are separate tower in which antenna is fitted for communication of substations. A VHF set is employed for this purpose for frequency in range of 30 MHz to 300 MHz. The VHF is a trans-receiver set. It works on DC and has a battery charger.

Telephone Line:This is very common way of communication and is in every sub-station.

SATCOM:This method of communication is through the satellite with the help of SATCOM and VSAT equipments. Till now it is under process.

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BULK CONSUMERS UNDER SONARPUR 33 KV S/S:

NAME OF CONSUMER TYPE & MAX. DEMAND

1. M/s OMGC L.T –50 KVA2. Divn. Rly. Manager, E/Rly, Sealdah. H.T –150 KVA3. NIC Limited. H.T –240 KVA4. Shalimar Chemicals. H.T –150 KVA5. S.K Paul & Co. H.T –250 KVA6. Dabur India Ltd. H.T –450 KV7. Rupali Udyog. L.T –125 KVA8. Laurel Bakery Pvt. Ltd. L.T –67 KVA9. Senbo Industries. Engineering College, Garia

H.T –500 KVA

10. Arim Icecream Ltd. (Unit I) L.T –63 KVA11. Diach Engineering. L.T –66 KVA12. Ben & Jerry Cake Works Ltd. L.T –50 KVA13. ACC Ltd. H.T –200 KVA14. Future Institute of Engg. and

Management.L.T –80 KVA

15. Divn. Engineer,E/Rly, Sealdah,Sonarpur carshed

H.T –200 KVA

16. Netaji Subhash Engineering College L.T –125 KVA

O P E R A T I O N A N D M A I N T E N A N C E : Sonarpur 33kv /11kv substation has mainly two kinds of work which can be categorized as operation and maintenance.

Operation: the main job in operation is to measure the amount of energy flowing in and out of substation, amount of load being supplied by the substation. According to the load the need of changing of tap in the

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transformer is also the duty of ‘operation’. Reporting and recording about winding and oil temperature, maintaining the daily log chart is also the work of operation. If any anomaly or fault is located it is duty of operation to report it to the maintenance and control room.

Maintenance: Maintenance department is responsible for maintenance and reporting of transformers, C.T, P.T circuit breakers etc. They take readings of different component (transformer, CB etc.) and check the trend of performance. Maintenance department also has the job of taking care of towers under Sonarpur sub-division jurisdiction. They are tower numbers 27 to 43 in Kasba-Sonarpur line, 16 to 56 in Joka-Sonarpur line and 165 to 254 in Jeerat-Lakshmikantapur line. They do the work of line patrolling, clearing brush and prevent plants growing around the towers. They also check whether tower legs and conductors insulation are in good condition.

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