BHARAT COKING COAL LIMITED

(A subsidiary of Coal India Limited)

Summer Training Project Report On

Receiving and Distribution of Power

In Lodna Area (BCCL), Dhanbad

Under the guidance of :

Mr.N.Ansari, Chief Manager (E&M), Lodna Area

Mr.Joydev Khan,Elec. Supervisor,DG Station Jealgora

Submitted By:

Aditya Ranjan, B.Tech EEE, NIT Calicut

Manu Raj, B.Tech EEE, NIT Calicut

Vikash Kumar, B.Tech EEE, NIT Calicut

AcknowledgementThe satisfaction, which accompanies the successful completion of the training, is incomplete

without the mention of a few names. We take this opportunity to acknowledge the efforts of the

many individuals who helped us undergo this training successfully. First and foremost, we would

like to express our heartfelt appreciation and gratitude to our Industry Guide and Mentor Mr

Joydev Khan (Electrical Supervisor). His vision and execution aimed at imparting practical

knowledge of the industry and fostered the ideal environment for us to learn. This training report

is a result of his teaching, encouragement and inputs in the numerous meetings he had with us,

despite his busy schedule. He has provided the scope and directed our studies in a manner to

make them most beneficial to us.

We extend our sincere thanks to Mr N.Ansari, Chief Manager (E&M) Lodna Area for his

splendid support and cooperation throughout the project and his valuable talks despite his busy

schedule

Finally, we would like to thank my Institute National Institute of Technology Calicut, Kerala

for providing us an opportunity to undergo this summer training program and

Mr.R.N.Vishwakarma, Sr.Mgr (HRD Department) for providing us the necessary

arrangements and permissions to undergo industrial training in Bharat Coking Coal Limited.

Dhanbad which is a subsidiary of a MAHARATNA Company COAL INDIA LIMITED.

Aditya Ranjan,S-6,EEE,NIT Calicut

Manu Raj,S-6,EEE,NIT Calicut

Vikash Kumar,S-6,EEE,NIT Calicut

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Sl. No. Topic Page No.

1. Introduction of the Organization 5

2. BCCL 6

3. Lodna Area 7

4. 33/11 kV Sub-station at Jealgora 8

5. Diesel Generating Sets at Jealgora 53

6. Surface sub-station at Bagdigi Colliery 55

7. Safety and Precautions 59

8. Key Learning 60

9. Bibliography 61

Index

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Introduction of the Organization

COAL INDIA LIMITED:Coal India Limited (CIL) is an Indian state-controlled coal mining company headquartered in Kolkata,

West Bengal, India and the world's largest coal miner with revenue exceeding  624.15 billion (FY

2012). It was formerly owned entirely by the Union Government of India, under the administrative control

of the Ministry of Coal. It is involved in coal mining and production industry. In April 2011, CIL was

conferred the Maharatna status by the Union Government of India  and ranked as one of India's most

valuable company by market value.

Coal India Limited was formed in 1973 as Coal Mines Authority Limited. In 1975 it was changed to Coal

India Limited as a holding company with five subsidiaries:

Bharat Coking Coal Limited (BCCL)(Dhanbad, Jharkhand)

Central Coalfields Limited (CCL)(Ranchi, Jharkhand)

Western Coalfields Limited (WCL)(Nagpur region)

Eastern Coalfields Limited (ECL)(Sanctoria, Asansol, West Bengal)

Central Mine Planning and Design Institute Limited (CMPDIL)(Ranchi, Jharkhand)

BHARAT COKING COAL LIMITED

Bharat Coking Coal Limited (BCCL) is a subsidiary of Coal India Limited with its headquarters

in Dhanbad, India. It was incorporated in January, 1972 to operate coking coal mines (214 in number)

operating in the Jharia and Raniganj Coalfields, taken over by the government of India on 16th Oct, 1971.

Mining areas in Jharia and Raniganj Coalfields within the leasehold of Bharat Coking Coal

Limited and Eastern Coalfields Limited are faced with problems of fire and subsidence due to

the centuries old history of mining. In the past, coal seams of good quality occurring at shallow

depth were mined unscientifically, leaving small stooks (coal pillars) in the underground

workings. The operators extracted as much coal as possible without supporting or stowing the

mined out workings. The mines were operated in small leaseholds and later closed due to

economic and other reasons. Some of these workings either caught fire or became

unstable/subsidence prone later. The magnitude of the problems compounded manifold with the

growth of habitation over these areas and is now a matter of serious concern

History of fire in Jharia Coalfield (JCF) dates back to 1916. Since then a number of other fires

were reported. According to the investigation made after Nationalization, 70 fires were known to

exist in BCCL covering an area of 17.32 SQ KM. It was estimated that about 37 million tonne of

good quality prime coking coal was destroyed and about 1864 million tonne coal has been

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blocked due to these fires. Subsequently 7 more fires were also identified. These 77 fires were

spread over in 41 collieries of BCCL. Efforts were made to address the issue and 10 fires were

successfully liquidated and others were controlled.

ADMINISTRATIVE AREAS:

There are 13 areas in BCCL:

Administrative area Name

Area No 1 Barora Area

Area No 2 Block II Area

Area No 3 Govindpur Area

Area No 4 Katras Area

Area No 5 Sijua Area

Area No 6 Kusunda Area

Area No 7 Putki Balihari Area

Area No 8 Kustore (abolished)

Area No 9 Bastacolla Area

Area No 10 Lodna Area

Area No 11 Eastern Jharia Area

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Area No 12 Chanch Victoria Area

Area No 13 Western Jharia

We underwent our training at the DG Station and 33/11 kV sub-station, Jealgora in Lodna Area (Area No10). The duration of our training was 3 weeks dating from 19-6-12 to 10-7-12 .

Power required for industrial purpose and for residential consumers in Lodna Area is supplied by Damodar Valley Corporation (DVC). The sub-station at Jealgora receives 2 incoming feeders of 33kv from DVC Patherdih and 2 more feeders from DVC via Sudamdih and Digwadih. It steps down to 11 kV and then distributes it to different collieries and localities in Lodna Area.

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BHARAT COKING COAL LIMITED

(A subsidiary of Coal India Limited)

DG Station , Jealgora Lodna Area

A) 33/11 kV Sub-Station , receiving from DVC , Patherdih

1. Source of Supply : Grid Sub Station , DVC , Patherdiha) Voltage of Receiving and Electrical Supply 33 kV , 3 Phase , 50Hzb) Contract Demand = 22 MVAc) No. of Feeders :

i) Direct from DVC , Patherdih = 2 No.ii) Jealgora via Sudamdih = 1 No.iii) Jealgora via Digwadih = 1 No.

2. Substation Capacity- Max. 40 MVA 4x7.5/10 MVA Transformers.

33 V / 11 kV3. Power Supplied at 11 kV to :

i) E.J Area – Bhowra Power House - one feederii) Patherdih Coal Washery - two feederiii) Lodna Area

a) Bararee Colliery - Two Feedersb) Jealgora Colliery - Two Feedersc) Lodna Power House - Three Feeders

(Lodna Colliery, Bagdigi Colliery, Joyrampur Colliery)

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Layout of the Sub-station at Jealgora.

8

Substation Yard :

i) Substation Yard :

A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Electric power may flow through several substations between generating plant and consumer, and its voltage may change in several steps.Substations may be owned and operated by a transmission or generation electrical utility, or may be owned by a large industrial or commercial customer. Generally substations are controlled and monitored by use of SCADA .A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages.

ii) Elements of Substation :

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Substations generally have switching, protection and control equipment, and transformers. In a large substation, circuit breakers are used to interrupt any short circuits or overload currents that may occur on the network. Smaller distribution stations may use circuit breakers or fuses for protection of distribution circuits. At some sub-stations auto reclosers are also used. Substations themselves do not usually have generators, although a power plant may have a substation nearby. Other devices such as capacitors and voltage regulators may also be located at a substation.

a) Isolators:In electrical engineering, an isolator switch is used to make sure that an electrical

circuit can be completely de-energized for service or maintenance. Such

switches are often found in electrical distribution and industrial applications

where machinery must have its source of driving power removed for adjustment

or repair. High-voltage isolation switches are used in electrical substations to

allow isolation of apparatus such as circuit breakers and transformers, and

transmission lines, for maintenance. It is operated at OFF load.

In the substation following type of isolator is used for the protection:

Horizontal break center rotating double break isolator:

This type of construction has three insulator stacks per pole. The two one each

side is fixed and one at the center is rotating type. The central insulator stack can

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swing about its vertical axis through about 900C. The fixed contacts are provided

on the top of each of the insulator stacks on the side. The contact bar is fixed

horizontally on the central insulator stack. In closed position, the contact shaft

connects the two fixed contacts. While opening, the central stack rotates through

900, and the contact shaft swings horizontally giving a double break.

The isolators are mounted on a galvanized rolled steel frame. The three poles

are interlocked by means of steel shaft. A common operating mechanism is

provided for all the three poles. One pole of a triple pole isolator is closed

position.

b) Circuit breaker:

A circuit breaker is an automatically-operated electrical switch designed to protect an

electrical circuit from damage caused by overload or short circuit. Its basic function is to

detect a fault condition and, by interrupting continuity, to immediately discontinue

electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit

breaker can be reset (either manually or automatically) to resume normal operation.

Circuit breakers are made in various sizes in standard ratings, from small devices that

protect an individual household appliance up to large switchgear designed to protect

high voltage circuits feeding an entire city. Once a fault is detected, contacts within the

circuit breaker must open to interrupt the circuit; some mechanically-stored energy

(using something such as springs or compressed air) contained within the breaker is

used to make the contacts instantly.

The circuit breaker contacts must carry the load current without excessive heating and

mechanical stress produced when interrupting the circuit. Contacts are made of copper

or copper alloys, silver alloys, and other materials. When a current is interrupted, an arc

is generated. This arc must be contained, cooled, and extinguished in a controlled way,

so that the gap between the contacts can again withstand the voltage in the circuit.

Different circuit breakers use vacuum, air, insulating gas or oil as the medium in which

the arc forms and quenched. Different techniques are used to extinguish the arc

including:

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Lengthening of the arc

Intensive cooling (in jet chambers)

Division into partial arcs

Zero point quenching (Contacts open at the zero current time crossing of the AC

waveform, effectively breaking no load current at the time of opening. The zero

crossing occurs at twice the line frequency i.e. 100 times per second for 50Hz ac

and 120 times per second for 60Hz ac )

Connecting capacitors in parallel with contacts in DC circuits

Finally, once the fault condition has been cleared, the contacts must again be closed to

restore power to the interrupted circuit. Circuit breakers are important to minimize

damage at the point of fault, to maintain the power quality and to leave the healthy

circuit least affected. For selective operation of circuit breakers on fault, in a circuit,

relays are properly co-ordinated.

Types of circuit breaker:

Many different classifications of circuit breakers can be made, based on their features such as

voltage class, construction type, interrupting type, and structural features.

Electrical power transmission networks are protected and controlled by high-voltage

breakers. The definition of high voltage varies but in power transmission work is usually

thought to be 72.5 kV or higher, according to a recent definition by the International

Electro technical Commission (IEC). High-voltage breakers are nearly always spring

charged or compressed air, with current sensing protective relays operated through

current transformers. In substations the protection relay scheme can be complex,

protecting equipment and buses from various types of overload or ground/earth fault.

High-voltage breakers are broadly classified by the medium used to extinguish the arc.

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Bulk oil

Minimum oil

Air blast

Vacuum

SF 6

In Jealgora substation mostly SF6 circuit breaker is used with 2 MOCB and 1 VCB also.

The breaker uses SF6 (Sulfur Hexafluoride) gas for arc extinction purpose. This gas has

excellent current interrupting and insulating properties, chemically, it is one of the most

stable compound in the pure state and under normal condition it is physically inert, non-

flammable, nontoxic and odorless and there is no danger to personnel and fire hazard.

It's density is about. 5 times that of air insulating strength is about 2-3 times that of air

and exceeds that of oil at 3 Kg/Cm sq.pressure.

Nowadays, upto 66 kV VCBs are mostly used. For above 66 kV SF6 Circuit Breakers are used.

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SF6 breaker called as maintenance free breaker, has simple construction with few moving

parts: The fission products created during breaking and not fully recombined are, either

precipitated as metallic fluoride or absorbed by a static filter which also absorbs the residual

moisture.

Since no gas is exhausted from the breaker and very little compressed air is required for

operation, noise during the operation is also very Jess.

Since SF6 gas is inert and stable at normal temperature, contacts do not settler from oxidization

or other chemical reactions, whereas in air or oil type breakers oxidation of contacts would

cause high temperature rise. SF6 gas circuit breakers, designed to conform to the same

standards as air or oil breakers, but in operation it is possible to get better service even at

higher fault levels.

Sulfur hexafluoride gas is prepared by burning coarsely crushed roll sulfur in the fluorine gas, in

a steel box, provided with staggered horizontal shelves, each bearing about 4 kg of sulfur. The

steel box is made gas tight. The gas thus obtained contains other fluorides such as S2F10, SF4

and must be purified further SF6 gas generally supplier by chemical firms. The cost of gas is low

if manufactured in large scale.

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During the arcing period SF6 gas is blown axially along the arc. The gas removes the heat from the arc by axial convection and radial dissipation. As a result, the arc diameter reduces during the decreasing mode of the current wave. The diameter becomes small during the current zero and the arc is extinguished. Due to its electro negativity, and low arc time constant, the SF6 gas regains its dielectric strength rapidly after the current zero, the rate of rise of dielectric strength is very high and the time constant is very small.

15

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Another type of Circuit Breaker which was used earlier but is very rare in use nowadays is the Minimum Oil Circuit Breaker (MOCB).

In this type of circuit breaker we have primary and secondary on an insulated bus-bar with one fixed contact and another moving contact. The contacts are immersed in oil to normalize the arc-chute while making contact. It also has separators to separate the three phases. For closing and tripping system we have electromagnetic coils. Other important elements of an MOCB are:-

a) P.T-Potential transformb) C.T-Current Transformc) Ammeterd) Voltmetere) Protective Relaysf) Ammeter Selector Switchg) Voltmeter Selector Switchh) kWh meteri) power factor meter

INNER VIEW OF MOCB

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Rating of the MOCB:

Type-HKK12/1240 Form-KM

Voltage-12kV Close/Open Coil voltage-220 V DC

Insulation Level-75/35kV Motor Voltage-220 V DC

Frequency-50Hz Mass-(incl. oil)-200 kg

Normal Current-1250 A oil-8 kg

Breaking Current-Symmetrical/Asymmetrical

(40/44 kA)

One more type of Circuit Breaker which is used is the VCB(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.

Construction: Fig shows the parts of a typical vacuum circuit breaker. It consists of fixed contact, moving contact and arc shield mounted inside a vacuum chamber. The movable member is connected to the control mechanism by stainless steel bellows .This enables the permanent sealing of the vacuum chamber so as to eliminate the possibility of leak .A glass vessel or ceramic vessel is used as the outer insulating body. The arc shield prevents the deterioration of the internal dielectric strength by preventing metallic vapours

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falling on the inside surface of the outer insulating cover.

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

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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.

Ratings and specifications of the VCB at Jealgora Sub-station:-

a) VCB Bottle:

Mfg. by: Bharat Electronics VS-1204,Made in India in collaboration With SIEMENS, AC, Germany.12 kV , 2000 A , 26.3 kA

b) Circuit Breaker:

Mfg. by: Andrew Yule Co. Ltd. Calcutta.Sys volt 11KVPhase – 3Cycles – 50 HzINSL – 28/75KVRated Current – 800ABreaking Current – 18.4 KAMaking Current – 46.9KAShort time current – 18.4 KA for 3 secondsTrip Coil – 110V DCClosing Coil – 110V DC

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Lightning arrester:

High Voltage Power System experiences over voltages that arise due to natural lightning or the

inevitable switching operations. Under these overvoltage conditions, the insulation of the power

system equipment are subjected to electrical stress which may lead to catastrophic failure.

Broadly, three types of over voltages occur in power systems: (i) temporary over-voltages,(ii)

switching over voltages and(iii) lightning over voltages. 

The duration of these over voltages vary in the ranges of microseconds to sec depending upon

the type and nature of over voltages. Hence, the power system calls for overvoltage protective

devices to ensure the reliability.

 

Conventionally, the overvoltage protection

is obtained by the use of lightning / surge

arresters. Under normal operating

voltages, the impedance of lightning

arrester, placed in parallel to the

equipment to be protected, is very high

and allow the equipment to perform its

respective function. Whenever the

overvoltage appears across the terminals,

the impedance of the arrester collapses in

such a way that the power system

equipment would not experience the overvoltage. As soon as the overvoltage disappears, the

arrester recovers its impedance back. Thus the arrester protects the equipment from over

voltages.

 

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The technology of lightning arresters has undergone major transitions during this century. In the

early part of the century, spark gaps were used to suppress these over voltages. The silicon

carbide gapped arresters replaced the spark gaps in 1930 and reigned supreme till 1970.

During the mid-1970s, zinc oxide (ZnO) gapless arresters, possessing superior protection

characteristics, replaced the silicon carbide gapped arresters. Usage of ZnO arresters have

increased the reliability of power systems many fold.

Rating of the Lightening Arrestor used in the Sub-station:

For 33 kV line-33x1.1=36 kV

For 11 kV line-11x.80=9 kV

TRANSFORMERS:

A transformer is a device that transfers electrical energy from one circuit to another through inductively

coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a

varying magnetic flux in the transformer's core and thus a varying magnetic field through

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thesecondary winding. This varying magnetic field induces a varying electromotive force (EMF), or

"voltage", in the secondary winding. This effect is calledinductive coupling.

If a load is connected to the secondary, current will flow in the secondary winding, and electrical energy

will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the

induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp) and is given by

the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows:

By appropriate selection of the ratio of turns, a transformer thus enables an alternating current (AC)

voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less

than Np. The windings are coils wound around a ferromagnetic core, air-core transformers being a

notable exception.

Transformers range in size from a thumbnail-sized coupling transformer hidden inside a

stage microphone to huge units weighing hundreds of tons used to interconnect portions of power

grids. All operate on the same basic principles, although the range of designs is wide. While new

technologies have eliminated the need for transformers in some electronic circuits, transformers are

still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are

essential for high-voltage electric power transmission, which makes long-distance transmission

economically practical.

In Jealgora sub-station there are 4 transformers, each of 7.5/10 MVA 33/11-6.6 kV.

Specifications of Transformer-2 at Jealgora sub-station:

kVA : 7500 / 10000 Diagram no. 21810178Volts at no load : HV 33000 LV 8800/11000Amperes : HV 131.25 LV 656.2/393.7Phases : HV Three Delta LV Three Star

Type of cooling : ONAN / ONAFFrequency : 50 Hz

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Year of Manufacture : 1978Oil (Volume) : 7800 litresTotal Weight : 27,880 KgCore Winding : 12,800 KgOil (weight) : 6670 Kg

Tap Changing Diagram:

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HV ON LOAD TAP CHANGER

LV LINK LV LINK

Position Connection

0-4 3-5 & 2-4

36300 1 17-16 11000 660035829 2 17-15 11000 660035357 3 17-14 11000 660034886 4 17-13 11000 660034414 5 17-12 11000 660033983 6 17-11 11000 660033471 7 17-10 11000 660033000 8 17-9 11000 660032523 9 17-8 11000 660032057 10 17-7 11000 660031586 11 17-6 11000 660031114 12 17-5 11000 660030643 13 17-4 11000 660030171 14 17-3 11000 660029700 15 17-2 11000 6600

ELECTRICAL PROTECTION :

The following electrical protection have been provided on the transformers :-

(i) Differential Protection

(ii) Restricted Earth Fault

(iii) Winding temp relay

(iv) Oil temp relay

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(v) Pressure relief valve, vent pipe.

(vi) Buchholz relay

(vii) Over current relay

(viii) Local Breaker Back up protection

(ix) Surge arrestors on HV, MV & LV sides.(In addition, Spark gap rods )

The main Tank - The transformer is transported on trailer to substation site and as far

as possible directly unloaded on the plinth. Transformer tanks up to 25 MVA capacity

are generally oil filled, and those of higher capacity are transported with N2 gas filled in

them +ve pressure of N2 is maintained in transformer tank to avoid the ingress of

moisture. This pressure should be maintained during storage; if necessary by filling N2

Bushings - generally transported in wooden cases in horizontal position and should be

stored in that position. These being more of fragile material, care should be taken while

handling them. In service these should kept clean.

Radiators – These should be stored with ends duly blanked with gaskets and end

plates to avoid in gross of moisture, dust, and any foreign materials inside. The care

should be taken to protect the fins of radiators while unloading and storage to avoid

further oil leakages. The radiators should be stored on raised ground keeping the fins

intact.

Oil Piping -. The Oil piping should also be blanked at the ends with gasket and blanking

plates to avoid in gross of moisture, dust, and foreign

All other accessories like temperature meters, oil flow indicators, PRVs,

buchholz relay; oil surge relays; gasket ‘ O ‘ rings etc. should be properly packed

and stored indoor in store shed. Oil is received in sealed oil barrels. The oil

barrels should be stored in horizontal position with the lids on either side in

horizontal position to maintain oil pressure on them from inside and subsequently

avoiding moisture and water ingress into oil. The transformers are received on

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site with loose accessories hence the materials should be checked as per bills of

materials.

Transformer Oil:

Transformer oil or insulating oil is usually a highly-refined mineral oil that is

stable at high temperatures and has excellent electrical insulating properties. It is

used in oil-filled transformers, some types of high voltage capacitors,

fluorescent lamp ballasts, and some types of high voltage switches and circuit

breakers. Its functions are to insulate, suppress corona and arcing, and to serve

as a coolant.

The oil helps cool the transformer. Because it also provides part of the electrical

insulation between internal live parts, transformer oil must remain stable at high

temperatures for an extended period. To improve cooling of large power

transformers, the oil-filled tank may have external radiators through which the oil

circulates by natural convection. Very large or high-power transformers (with

capacities of thousands of kVA) may also have cooling fans, oil pumps, and even

oil-to-water heat exchangers. .

Large, high voltage transformers undergo prolonged drying processes, using

electrical self-heating, the application of a vacuum, or both to ensure that the

transformer is completely free of water vapor before the cooling oil is introduced.

This helps prevent corona formation and subsequent electrical breakdown under

load.

Oil filled transformers with a conservator (an oil tank above the transformer) may

have a gas detector relay (Buchholz relay). These safety devices detect the build

up of gas inside the transformer due to corona discharge, overheating, or an

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internal electric arc. On a slow accumulation of gas, or rapid pressure rise, these

devices can trip a protective circuit breaker to remove power from the

transformer. Transformers without conservators are usually equipped with

sudden pressure relays, which perform a similar function as the Buchholz relay.

The flash point (min) and pour point (max) are 140 °C and −6 °C respectively.

The dielectric strength of new untreated oil is 12 MV/m (RMS) and after

treatment it should be >24 MV/m (RMS).

Large transformers for indoor use must either be of the dry type, that is,

containing no liquid, or use a less-flammable liquid.

Testing and oil quality

Transformer oils are subject to electrical and mechanical stresses while a

transformer is in operation. In addition there is contamination caused by chemical

interactions with windings and other solid insulation, catalyzed by high operating

temperature. As a result the original chemical properties of transformer oil

changes gradually, rendering it ineffective for its intended purpose after many

years. Hence this oil has to be periodically tested to ascertain its basic electrical

properties, make sure it is suitable for further use, and ascertain the need for

maintenance activities like filtration/regeneration. These tests can be divided into:

1. Dissolved gas analysis

2. Furan analysis

3. PCB analysis

4. General electrical & physical tests:

Color & Appearance

Breakdown Voltage

Water Content

Acidity (Neutralization Value)

Dielectric Dissipation Factor

Resistivity

Sediments & Sludge

Interfacial Tension

Flash Point

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Pour Point

Density

Kinematic Viscosity

Current Transformer and Potential Transformer:

a) Current Transformer: In electrical engineering, a current transformer (CT) is

used for measurement of electric currents. Current transformers, together

with voltage transformers (VT) (potential transformers (PT)), are known

as instrument transformers. When current in a circuit is too high to directly

apply to measuring instruments, a current transformer produces a reduced

current accurately proportional to the current in the circuit, which can be

conveniently connected to measuring and recording instruments. A current

transformer also isolates the measuring instruments from what may be very high

voltage in the monitored circuit. Current transformers are commonly used in

metering and protective relays in the industry. Like any other transformer, a

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current transformer has a primary winding, a magnetic core, and a secondary

winding. The alternating current flowing in the primary produces a magnetic field

in the core, which then induces a current in the secondary winding circuit. A

primary objective of current transformer design is to ensure that the primary and

secondary circuits are efficiently coupled, so that the secondary current bears an

accurate relationship to the primary current. Current transformers are used

extensively for measuring current and monitoring the operation of the power grid.

Along with voltage leads, revenue-grade CTs drive the electrical utility's watt-hour

meter on virtually every building with three-phase service and single-phase

services greater than 200 amps. The CT is typically described by its current ratio

from primary to secondary. Often, multiple CTs are installed as a "stack" for

various uses. For example, protection devices and revenue metering may use

separate CTs to provide isolation between metering and protection circuits, and

allows current transformers with different characteristics (accuracy, overload

performance) to be used for the devices.

Rating: 11 kV, 50 Hz.

Turns Ratio of the CT used at Jealgora: 300/5-5

Most often we use CBCT i.e. Core Balance Current Transformer.

b) Potential transformer: Potential transformers are instrument transformers. They

have a large number of primary turns and a few number of secondary turns. It is

used to control the large value of voltage. These may be of 3 limb or of 5 limb. 

WORKING:

The potential transformer works along the same principle of other transformers. It

converts voltages from high to low. It will take the thousands of volts behind

power transmission systems and step the voltage down to something that meters

can handle. These transformers work for single and three phase systems, and

are attached at a point where it is convenient to measure the voltage.

Rating:

33/√3 kV/ 110/√3 V

Primary winding: 33/√3 kV

Secondary winding: 110/√3 V.

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Type: Earthed

Protective relays:

In electrical engineering, a protective relay is an electromechanical apparatus, often with more

than one coil, designed to calculate operating conditions on an electrical circuit and trip circuit

breakers when a fault is detected. Unlike switching type relays with fixed and usually ill-defined

operating voltage thresholds and operating times, protective relays have well-established,

selectable, time/current (or other operating parameter) operating characteristics. Protection

relays may use arrays of induction disks, shaded-pole magnets, operating and restraint coils,

solenoid-type operators, telephone-relay contacts, and phase-shifting networks. Protection

relays respond to such conditions as over-current, over-voltage, reverse power flow, over- and

under- frequency. Distance relays trip for faults up to a certain distance away from a substation

but not beyond that point.

The relays are compact and self-contained devices which can sense abnormal conditions.

Whenever abnormal condition occurs, the relays contacts get closed. This in turn closes the trip

circuit of a circuit breaker.

For switchyard protections following type relays are used:

1. Overcurrent relay

2. Earth fault relay

3. REF relay

4. Differential relay

5. Directional relay

6. Over flux relay

7. Buchholz relay

8. IDMT relay and Instantaneous Relay.

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Restricted earth fault protection relay:

The REF protection method is a type of "unit protection" applied to transformers or generators

and is more sensitive than the method known as differential protection.

An REF relay works by measuring the actual current flowing to earth from the frame of the unit.

If that current exceeds a certain preset maximum value of milliamps (mA) then the relay will trip

to cut off the power supply to the unit.

Differential protection can also be used to protect the windings of a transformer by comparing

the current in the power supply's neutral wire with the current in the phase wire. If the currents

are equal then the differential protection relay will not operate. If there is a current imbalance

then the differential protection relay operates.

REF protection is applied on transformers in order to detect ground faults on a given winding

more sensitively than differential protection.

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Directional relay:

Directionalized relays are relays that use a polarizing circuit to determine which "direction" (in

the zone of protection, or out of the zone protection) a fault is. There are many different types

and different polarizing methods - ground polarizing, voltage polarizing, zero sequence voltage

polarizing, negative sequence polarizing, etc.

The basic operation of this relay is just like any non-directional relay, but with an added torque

control - the directionalizing element. This element allows the relay to operate when it is

satisfied that the fault is within the zone of protection (ie not behind where the relay is looking).

Directional relays have protection zones that include all of the power system situated in only one

direction from the relay location. (This is in contrast to magnitude relays which are not

directional, i.e., they trip based simply on the magnitude of the relay.

Consider the one-line diagram in Fig. 1.

Fig. 1

If the relays R1 and R2 in Fig. 1 are directional relays, then

- R1 “looks” to the left but not to the right, and

- R2 “looks” to the right but not to the left.

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OVER CURRENT AND EARTH FAULT PROTECTION:

The over current protection is needed to protect the transformer from sustained overloads and

short circuits. Induction type over current relays are used which in addition to providing overload

protection acts as back up relays for protection of transformer winding fault. Fig 10 shows the

combined over current and earth fault protection. The earth fault protection is used to provide

protection against any earth fault in the windings of the transformer. It works on the principle

that when the transformer winding is sound the currents in all the three phases will balance and

no current will spill into the earth fault relay. The arrangement is such that the relay does not

respond to any out of balance current between windings caused by tap changing arrangement

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Fig 10 illustrates the use of earth fault and over current relays for both star and delta

connections of the transformer. Instantaneous type of earth relay is used. When the winding is

delta connected the earth relay is operated by the residual current from three C.T.s connected

as shown in left hand side of the fig. If the transformer winding has an earthed neutral then the

residual current from the three line current transformers is balanced against the current of the

current transformers provided in the neutral as on the right hand side.

When the system works normal, the sum of three currents in the C.T.s is zero and no current

flows through the operating winding of the instantaneous earth fault relay and through the

neutral of the transformer. However if fault is outside the protection area current flows in the

neutral and lines as well, but the sum of currents in the lines is balanced by the current in

neutral and hence earth relay is not operated. Now if earth fault occur within the protected zone

say in the winding itself current will flow only in the neutral of the main transformer and thus

there will be no balancing current in the relay circuit so, the relay is energized and the circuit

breaker is opened. The trip contacts of the over current relay and earth fault relay are in parallel

so, with the energisation of either over current relay or earth fault relay the circuit breaker of the

concerned side will be tripped.

Differential Relay:

"A differential relay responds to vector difference between two or more similar electrical

quantities”

From the definition the following aspects are known; -

1- The differential relay has at least two actuating quantities say I1, I2

2- The two or more quantities should be similar i.e. current/current.

3- The relay responds to the vector difference between the two i.e. to I1-I2, which includes

magnitude and/or phase angle difference.

       Differential protection is generally unit protection. The protected zone is exactly determined

by location of CT's and VT's. The vector difference is achieved by suitable connections of

current transformer or voltage transformer secondaries. Most differential relays are current

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differential relays in which vector difference between the current entering the winding and

current leaving the winding is used for sensing and relay operation.

      Differential protection principle is used in the following applications.

       - Protection of generator, protection of generator transformer unit.

       - Protection of transformer 

       - Protection of feeder (transmission line) by pilot wire differential protection.

       - Protection of transmission line by phase comparison carrier current protection.

       - Protection of large motor.

       - Bus-zone protection.

During the normal conditions the three secondary currents of CT's are balanced and current

flows through the relay coil. During fault in the protected zone, the balance is distributed and

differential current flows through the relay operating coil. The differential current is above the

pick-up value, the relay operates and the Secondary of CT is never left on open circuit.

   

Biased or per cent differential relay

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       The reason for using this modification is circulating current differential relay is to overcome

the trouble arising out of differences in CT ratios for high values of external short circuit

currents.

       (Refer the previous paragraph). The percentage differential relay has an additional

restraining coil connected in the pilot wire as shown in Fig. (3).

       In this relay the operating coil is connected to the mid-point of the restraining coil   becomes

the sum of ampere turns in its tow halves, i.e (I1N/2) + (I2N/2) which gives the average

restraining current of (I1 + I2)/2 in N turns. For external faults both I1 and I2 increase and thereby

the restraining torque increases which prevents the mal-operation.

       The operating characteristic of such a relay is given in Fig. (4).

       the ratio of differential operating current to average restraining current is Fixed percentage.

        Hence the relay is called 'percentage differential relay'.

      The relay is so called 'Biased differential relay' because the restraining coil is also called a

biased coil as it provides additional flux.

  The percentage of biased differential relay has a rising single pick up characteristic. As the

magnitude of through current increases, the restraining current decreases.

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Buchholz relay:

In the field of electric power distribution and transmission, a Buchholz relay, also called a gas relay or a sudden pressure relay, is a safety device mounted on some oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is used as a protective device sensitive to the effects of dielectric failure inside the equipment.

The relay has two different detection modes. On a slow accumulation of gas, due perhaps to slight overload, gas produced by decomposition of insulating oil accumulates in the top of the relay and forces the oil level down. A float switch in the relay is used to initiate an alarm signal that also serves to detect slow oil leaks.

If an arc forms, gas accumulation is rapid, and oil flows rapidly into the conservator. This flow of oil operates a switch attached to a vane located in the path of the moving oil. This switch normally will operate a circuit breaker to isolate the apparatus before the fault causes additional damage. Buchholz relays have a test port to allow the accumulated gas to be withdrawn for testing.

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IDMT relay (Inverse Definite Minimum Time Lag Relay):

The IDMT relay work on the induction principle, where an aluminum or copper disc rotates

between the poles of electromagnet and damping magnet. The fluxes induce eddy current in the

disc which interact and produce rotational torque. The disc rotates to a point where it operates a

pair of contact that breaks the circuit and removes the fault condition. In IDMT relay its

operating is inversely proportional to fault current and also a characteristic of minimum time

after which this relay definitely operates.

Associated Electrical Industries power-board overload used for 11kV 3-phase circuit protection

on HV switchboards.

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Fitted with an auxiliary attracted armature relay and drop-flag indicator. Plug-setting is 100% (5A

in this case) which corresponds to a primary current of 50 Amperes. Time-setting multiplier is

set to 0.05 of a second..

Earthing of Transformer:

1. All non-current carrying metal parts of the 11 KV structure shall be provided with

duplicate earth connection using conductors of adequate rating. The main earth bus for

the structure shall be a minimum of 25 x 3 mm Cu or equivalent GI for soil resistivity

greater than or equal to 100 ohm-m.

2. Lightning arrester shall be provided with separate earth pit connected through No.6

SWG Cu or equivalent G.I. The L.A. earth pit shall be interconnected with other earth

electrodes.

3. Body of the transformer shall be provided with duplicate earth connections from opposite

points.

4. The Breaker controlled switching center shall be earthed using conductors of same size

as that of the neutral.

5. All earthing conductors shall be Copper, Aluminum or GI of adequate size. In areas

where resistivity is less than 100 ohm-m, Copper conductors are to be used and above

100 ohm-m GI conductors may be used.

6. The distance between earth pipes shall be 5 m and that between plates shall be 8 m.

7. Depth of an earth pit should not be less than 2.5 m.

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NOTE: Transformer Body Earth Pits and Neutral Earth Pits are separate.

Cables:

A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power. Power cables may be installed as permanent wiring within buildings, buried in the ground, run overhead, or exposed. Modern power cables come in a variety of sizes, materials, and types, each particularly adapted to its uses.[4] Large single insulated conductors are also sometimes called power cables in the industry.[5]

Cables consist of three major components: conductors, insulation, and protective jacket. The makeup of individual cables varies according to application. The construction and material are determined by three main factors:

Working voltage, determining the thickness of the insulation; Current-carrying capacity, determining the cross-sectional size of the conductor(s); Environmental conditions such as temperature, water, chemical or sunlight exposure,

and mechanical impact, determining the form and composition of the outer cable jacket.Cables for direct burial or for exposed installations may also include metal armor in the form of wires spiraled around the cable, or a corrugated tape wrapped around it. The armor may be made of steel or aluminum, and although connected to earth ground is not intended to carry current during normal operation.Power cables use stranded copper or aluminum conductors, although small power cables may use solid conductors (For a detailed discussion on copper cables, see: Copper wire and cable.).The cable may include non-insulated conductors used for the circuit neutral or for ground (earth) connection.The overall assembly may be round or flat. Non-conducting filler strands may be added to the assembly to maintain its shape. Special purpose power cables for

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overhead or vertical use may have additional elements such as steel or Kevlar structural supports.Some power cables for outdoor overhead use may have no overall sheath. Other cables may have a plastic or metal sheath enclosing all the conductors. The materials for the sheath will be selected for resistance to water, oil, sunlight, underground conditions, chemical vapors, impact, or high temperatures. In nuclear industry applications the cable may have special requirements for ionizing radiation resistance. Cable materials may be specified not to produce large amounts of smoke if burned. Cables intended for underground use or direct burial in earth will have heavy plastic or metal, most often lead sheaths, or may require special direct-buried construction. When cables must run where exposed to mechanical impact damage, they may protected with flexible steel tape or wire armor, which may also be covered by a water resistant jacket.

Cable termination quality is very important and should be very good while original installation for longer durability.

UPTO NOW WE HAVE SEEN THE KEY COMPONENTS PRESENT IN A SUB-STATION YARD, NOW WE WOULD KNOW ABOUT THE CONTROL PANEL AND DIFFERENT ROUTINE TESTS CONDUCTED ON TRANSFORMER OIL, CIRCUIT BREAKERS, AND RELAYS ETC. AT THE SUB-STATION.

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Supervisory Control Panel for 11 kV breakers:

The control panel consists of the protective relays and alarms. We also have a smart demand controller to monitor the Voltage, Current, kVA, kW, kVAR, kVAh, kWh, power factor etc.

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Operations at the sub-station consist of several routine tests of which relay testing is an important one.

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Front View of the Relay Control Panel.

For testing the relay necessary connections are made using the Over Current test set which has two units:

1. Unit A: Current control unit.2. Unit B: Injection transformer unit.

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UNIT A- Current Control

UNIT-B Injection Transformer

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After making the connections, twice the value of normal plug-setting is applied to the relay and time is checked using a tongue-tester for which the relay withstands. Set TMS at 1 on the relay to be tested. If the relay unit trips in 10 s, when current applied is double the plug setting then the tested relay is O.K.

PRE COMMISSIONING TESTS ON EQUIPMENT AT

33/11 KV SUB STATIONS (Jealgora)

TESTS ON TRANSFORMERS

1. IR (Insulation Resistance)Values

a) For 33/11 KV Power Transformer 2500 V Megger is to be need.

b) Power Transformer neutral Earthing is to be disconnected.

c) Line terminal of the megger is to be connected to one of the HV Bushings of

Power transformer and Earth terminal of megger is to be connected to Power Transformer Body Earth Point.

IR Values are to be read on the megger by meggering the Power transformeri) The above Value is to be noted as HV to Bodyii) Then IR Value between LV terminal and body of Power transformer is to bemeasured & noted.ii) IR Values between HV & LV terminals are to be measured & noted.iv) The temperature of transformer oil at which the IR Values are measured isalso to be noted.v) Particulars of megger is also to be noted.The maximum value shall be 60MΩ at 600C temperature for transformer whichare in service. For new transformer the value obtained shall be tallied withmanufactures test results.

2. D.C. Resistance or Winding ResistanceThe Resistance of HV winding LV winding between their terminals are to bemeasured with precision milli ohm meter/ micro ohm meter.HV side RY= YB= BR=LV side ry = yb = br =rn = yn= bn =

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The values shall be compared with original test results.

3. Turns Ratio TestWith turns Ratio meter, turns Ratio between HV & LV windings at various taps to bemeasured & recorded.At normal tap for 33/11 KV Delta/Star transformer the turns turns ratio is 5.196. Atother taps values will be as per the percentage raise or lower at the respective tappositions.

4.Voltage Ratio TestWhen “Turns Ratio meter” is not available, Voltage Ratio Test is done at Various tapposition by applying 3 phase LT(415V) supply on 33 KV side of Power transformer.At Various taps applied voltage and Resultant voltages LV side between variousPhases and phases& neutral measured with precision voltmeter & noted.

5. Short Circuit TestThe four terminals on LV side of Power transformer are shorted with 50 sq. mm.copper cable. Three phase LT supply is applied on HV side of power transformer atnormal tap and currents measured in all the phases on HV side and phases & neutralon LV side values noted.The Resultant HV & LV currents areas follows:-HV side current LT Voltage applied on 33 KV side of PTR X Rated HVcurrentin all Phases = 33000 X Impedance Volts / 100 of PTRLV side phase LT Voltage applied on 33 KV side of PTR X Rated LVcurrentCurrent in all phases = 33000 X Impedance Volts / 100 of PTRLV side neutral current shall be zero or less than 1.0 amp.

6. BDV Test of OilOil samples from top oil & bottom oil of Power transformer main tank as well as

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OLTC tank are to be collected and tested. Across 2.5 mm gap test Kit. Test result is obtained by taking the average of 6 readings. Test Result- The oil shallstand for 60 kV for a gap of 2.5 mm to qualify for successful testing.

The main function of transformer oil is insulating and cooling of the transformer. It should have the following properties:

High dielectric strength Low viscosity Freedom from inorganic acids, alkali, and corrosive sulfur Resistant to emulsification Freedom from sludging under normal operation Rapid settling of arc products Low pour point High flash point

Enemies of insulating oil are: Oxidation Oxidation is the most common cause of oil deterioration.

Careful and routine vacuum dehydration to remove air and water is essential to maintaining good oil.

Contamination Moisture is the main source of contamination. It tends to lower the dielectric strength of the oil and promote acid formation when combined with air and sulfur.

Excessive Temperature Excessive heat breaks down the oil and will increase the rate of oxidation. Avoid overloading the transformer.

Corona Discharges Sparking and local overheating can also break down the oil and produce gases and water.

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PRE COMMISSIONING CHECKS ON POWERTRANSFORMERS

Check that

1) Top & Bottom valves of radiators are in open position

2) All drain valves are in closed position with dummy plates in position duly

fitted

with bolts & nuts

3) All filler valves in closed position with dummy plates in position duly fitted

with

bolts & nuts

4) No oil leakages from radiators, valves, dummies, top cover, inspection

covers, oil

level gauges etc.

5) Silica gel breather is in position with silica gel filled & oil in oil cup

6) The air path of silica gel breather is free without any seals to holes of the

oil cup

7) Equalizing valve of the interconnecting pipe of vent pipe to conservator

tank is in

open position.

8) Top oil filling point of conservator tank is in closed position with cover duly

bolted.

9) The valves on either side of Buchholz relay are in open position.

10) Thermometer pockets on main tank top cover are having oil inside &

Thermometer sensing bulbs are in position duly nuts fixed properly.

11) The double earthing of neutral of Power transformer is done as per

standards.

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12) The double earthing of body of Power transformer is done as per

standards.

13) The oil levels in conservator tank, OLTC Conservator tank.

14) The operation of main Buchholz relay & OLTC Buchholz relay ( Trips

&alarms to

be checked)

15) Operation of Transformer alarms.

16) The vent pipe diaphragm is intact.

17) The lock pieces are provided, duly welded to base channels, for the

support

wheels of transformers (If wheels are provided)

Tests on Breakers

A) I) Status of Breaker “Open”Measure IR values between “IN” & “Out” terminals Each limb of breakershall be more than 1000 MΩII) Status of Breaker “Close”Measure resistant of each limb by connecting “IN” & “Out” terminals to aprecision Micro ohm meter.The values shall tally with manufacturer’s test report.- 4 -III) Status of Breaker “Close”Measure IR values between phase & Body ground terminal of breaker for alllimbs the values shall be more than 1000 MΩB) Opening time & closing time tests to be done on all limbs. The values shall tallywith test results of the Manufacturer.C) As follows:a) IR values of current Transformers are to be measured.b) Polarity check on current transformers is to be made.c) Primary injection test on current transformer is to be done to check operation ofrelays functioning of meters.d) Secondary Injection test on relays is to be done.e) DC tests on breakers panel are to be done.f) Calibration of meters is to be done.

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g) D.C. interlock are to be tested.h) Check that all Jumpers, clamps etc. are in to CTi) Clean all the bushings.j) Ensure no leakages from the CTs.

Tests on Potential TransformersA) IR value are to be checked with megger.B) Ratio test is to be done.C) Polarity check is to be done.D) Check that there are no oil leakagesE) Clamps & Jumpers properly tightened.

Tests on Lightening Arrestorsa) IR value are to be checked.b) Jumper connection to be checked

Other tests in a Sub Stationa) Battery charger & Battery to be checked for proper operationb) Earth Resistance is to be measured & noted.c) Meggering of Bus Bars is to be done.d) Check the entire earthing system in the Sub Station is as per standards.

Safety Instruments required while testing:

1. Hand Gloves2. Helmet3. Apron4. Mining Shoes5. Fire Alarm6. Discharge Rod7. Fire Extinguisher-Foam, CO2, Gas, Sand etc.

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B) Diesel Generating Plant

A diesel generator is the combination of a diesel engine with an electrical generator (often an alternator) to generate electrical energy. Diesel generating sets are used in places without connection to the power grid, as emergency power-supply if the grid fails, as well as for more complex applications such as peak-lopping, grid support and export to the power grid. Sizing of diesel generators is critical to avoid low-load or a shortage of power and is complicated by modern electronics, specifically non-linear loads.

Diesel generator set

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Diesel generator on an oil tankerThe 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.Set sizes range from 8 to 30 kW (also 8 to 30 kVA single phase) for homes, small shops & offices with the larger industrial generators from 8 kW (11 kVA) up to 2,000 kW (2500 kVA three phase) used for large office complexes, factories. A 2,000 kW set can be housed in a 40 ft ISO container with fuel tank, controls, power distribution equipment and all other equipment needed to operate as a standalone power station or as a standby backup to grid power. These units, referred to as power modules are gensets on large triple axle trailers weighing 85,000 pounds (38,555 kg) or more. A combination of these modules are used for small power stations and these may use from one to 20 units per power section and these sections can be combined to involve hundreds of power modules. In these larger sizes the power module (engine and generator) are brought to site on trailers separately and are connected together with large cables and a control cable to form a complete synchronized power plant.Diesel generators, sometimes as small as 200 kW (250 kVA) are widely used not only for emergency power, but also many have a secondary function of feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators.Ships often also employ diesel generators, sometimes not only to provide auxiliary power for lights, fans, and winches, etc. but also indirectly for main propulsion. With electric propulsion the generators can be placed in a convenient position, to allow more cargo to be carried. Electric drives for ships were developed prior to WW I. Electric drives were specified in many warships built during WW II because manufacturing capacity for large reduction gears was in short supply, compared to capacity for manufacture of electrical equipment. Such a diesel-electric arrangement is also used in some very large land vehicles such as rail-road locomotives.

There are three diesel generating sets at the DG Station. These are synchronous generators which are required to operate at times of power failure in the grid or some emergency situations in the mines. The specifications of the diesel generators are as follows:

1. DG set No-1 - 1.1MVA , 11 kV Made in GermanyDiesel Engine - 1328 HP, 428 rpm

2. DG set No-2 - 4.4 MVA , 11 kV , Made in USSRDiesel Engine - 5050 HP, 800 rpm

3. DG set No-3 - 4.4 MVA , 11 kV , Made in USSRDiesel Engine - 5050 HP, 800 rpm

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Each Diesel Engine has 32 pistons, 16 cylinders and 4 crankshafts which are connected to a main shaft which serves as the prime- mover of the synchronous generators. There are 2 air compressors situated 10 ft. below having an air capacity of 30 kg.

To start such a bulky engine compressor blows in air which passes through filter and goes to the combustion chamber.

Cooling is done using water both externally and internally. Coolers are present at the outer and inner surface of the engine.

The diesel engine consumes approximately 800 liters of diesel per hour and produces a lot of noise which is quite disadvantageous for economic generation of power.

There are separate control panels for all the three generating sets which are used for control and monitoring purposes.

The full load current rating of the exciter of the generating panel is 200 A. The generator has a 6-pole rotor which takes mechanical input from the main

shaft of the diesel engine. For protection all types of relays are there such as:

i. Reverse power relayii. Over Current and Earth fault Relayiii. Under Voltage Relay.iv. Under frequency Relay.

BAGDIGI COLLIERY (LODNA AREA)

Layout of the surface sub-station at Bagdigi Colliery:

55

At the sub-station, it has 3 incoming feeders of 11 kV from Jealgora. There are three indoor transformers with the following ratings:

b. T-1: Primary Control 1000kVA, 11kV/3.3 kV.c. T-2: Primary Control 1000kVA, 11kV/550 V.d. T-3: Primary Control 2000kVA, 11kV/3.3 kV.

There are 3 neutral earth pits and three body earth pits for the transformers.

56

There are three 3.3 kV cables going underground in the mine and three over-head 11 kV lines incoming from Jealgora.

From the substation, power is distributed to run the winding engine, colliery offices, lamp charging station and the underground substation which then further distributes power to the H.T. pumps and other high voltage equipments.

There are two winding engines:

1. Steam-run Winding Engine which is used for transportation in No. 9 pit.

2. Electrical Winding Engine which is used for transportation in No.12 Pit.

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Specification of the Electrical Winding Engine:

Mfg. by: Poland Date of Installation: 15.06.1982Motor Manufacturing: Yaska, Japan.Type: Slip-ring 3-phase induction Motor.Rating: 150 kW, 3.3 kVGear ratio- 19.5:1Drum Diameter: 3 m

At the site, we went down through No.12 Pit, depth-224.5 m and diameter of the shaft-5.2 m and landed on seam 8.

We visited the Underground sub-station near pit bottom 8th seam and again went to the 7th seam retaining wall/sump to see the H.T. Pumps and its electrical Layout. We were accompanied by Mr. Dwarika Paswan, (Elec. Supervisor) Bagdigi Colliery.We had to use safety lamp, belt, boots and safety helmet while going underground.

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The Safety Lamps are charged at the charging station where they are charged for 16 hours so as to be used for 8 hours.

SAFETY AND PRECAUTIONS:ELECTRICITY :

E : Earthing must be done properly and effectively.

L : Loose connection must be avoided.

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E : Efficient workmanship desirable.

C : Cleanliness and clearance is must.

T : Tightness of all connection and joint is must.

R : Regular and reliable checking is must.

I : Inspection of insulation at regular interval is must.

C : Continuous trouble free services.

I : Isolate correctly , Ignorance may cause danger.

T : Think twice before handling / energizing electrical apparatus.

Y : You may kill your-self or other.

CAUTION :

C : Confident and careful while handling the electrical apparatus

A : Always on the alert , accident can avert .

U : Un-authorized prohibited.

T : Treat always the apparatus as live.

I : Incorrect operation is dangerous.

O : Open Electrical apparatus only when it is dead and earthed.

N : Never be alone while handling the electrical apparatus & donot ignore safety

instructions.

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DANGER :

D : Discharge before touching electrical apparatus.

A : Acquaint yourself before handling electrical apparatus.

N : Never negotiate with the safety rules.

G : Great care is must.

E : Earth the metallic parts.

R : Reliance on others must be avoided.

Key Learning

• Understanding of Sub-station Layout and all its key components and the

control panel.

• Working of the Diesel generating Sets.

• Working of Distribution sub-station at the Bagdigi Colliery.

BIBLIOGRAPHY:

1. Theory and Performance of Alternating Current Machines, M.G.Say.

2. Power Systems Engineering, I.J.Nagrath and D.P.Kothari.

3. Electrical Machine Design, A.K.Sawhney.

4. Power System Protection and Switchgear, Badri Ram, D N Vishwakarma.

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5. Websites: ksebgrid.blogspot.in

yourelectrichome.blogspot.in

www.electrical-res.com

www.en.wikipedia.org

www.circuitmaniac.com

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