bccl-presentation

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 guidanceof :
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

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Acknowledgement
The 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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Index
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

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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 (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 Stationand 33/11 kVsub-station, Jealgora
in Lodna Area(AreaNo10). The durationof our training was 3 weeks dating
from 19-6-12 to10-7-12 .
Power requiredfor industrial purpose andfor residential consumers inLodna
Areais suppliedby Damodar Valley Corporation (DVC). The sub-stationat
Jealgorareceives 2 incoming feeders of 33kv fromDVC Patherdihand 2 more
feeders fromDVC via Sudamdih and Digwadih. It steps downto 11 kV and then
distributesit todifferent collieries andlocalities inLodnaArea.

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(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 , Patherdih
a) Voltage of Receiving and Electrical Supply 33 kV , 3 Phase , 50Hz
b) Contract Demand = 22 MVA
c) 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 kV
3. Power Supplied at 11 kV to :
i) E.J Area – Bhowra Power House - one feeder
ii) Patherdih Coal Washery - two feeder
iii) Lodna Area
a) Bararee Colliery - Two Feeders
b) Jealgora Colliery - Two Feeders
c) Lodna Power House - Three Feeders
(Lodna Colliery, Bagdigi Colliery, Joyrampur Colliery)

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Layout of the Sub-station at Jealgora.

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SubstationYard :
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.

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ii) Elements of Substation :
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

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side is fixed and one at the center is rotating type. The central insulator stack can
swing about its vertical axis through about 900
C. 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

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

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High-voltage breakers are broadly classified by the medium used to extinguish the arc.
 Bulk oil
 Minimum oil
 Air blast
 Vacuum
 SF6
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.

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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.

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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 transform
b) C.T-Current Transform
c) Ammeter
d) Voltmeter
e) Protective Relays
f) Ammeter Selector Switch
g) Voltmeter Selector Switch
h) kWh meter
i) 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
falling on the inside surface of the outer insulating cover.

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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

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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 11KV
Phase – 3
Cycles – 50 Hz
INSL – 28/75KV
Rated Current – 800A
Breaking Current – 18.4 KA
Making Current – 46.9KA
Short time current – 18.4 KA for 3 seconds
Trip Coil – 110V DC
Closing 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.
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.

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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
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

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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. 21810178
Volts at no load : HV 33000
LV 8800/11000
Amperes : HV 131.25
LV 656.2/393.7
Phases : HV Three Delta
LV Three Star
Type of cooling : ONAN / ONAF
Frequency : 50 Hz
Year of Manufacture : 1978
Oil (Volume) : 7800 litres
Total Weight : 27,880 Kg
Core Winding : 12,800 Kg
Oil (weight) : 6670 Kg

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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 6600
35829 2 17-15 11000 6600
35357 3 17-14 11000 6600
34886 4 17-13 11000 6600
34414 5 17-12 11000 6600
33983 6 17-11 11000 6600
33471 7 17-10 11000 6600
33000 8 17-9 11000 6600
32523 9 17-8 11000 6600
32057 10 17-7 11000 6600
31586 11 17-6 11000 6600
31114 12 17-5 11000 6600
30643 13 17-4 11000 6600
30171 14 17-3 11000 6600
29700 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
(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 )

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

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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
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.

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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
 Pour Point
 Density
 Kinematic Viscosity

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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
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

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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.
Type: Earthed

32
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.

33
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.

34
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.
B1 B2
Bus 1
Bus 2 Bus 3
y x
x
L
I23I21
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.

35
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
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

36
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
differential relays in which vector difference between the current entering the winding and
current leaving the winding is used for sensing and relay operation.

37
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
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.

38
(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.

39
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.

40
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.
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..

41
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.
NOTE: Transformer Body Earth Pits and Neutral Earth Pits are
separate.

42
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
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

43
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.

44
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.

45
Operations at the sub-station consist of several routine tests of which
relay testing is an important one.
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.

46
UNIT A- Current Control
UNIT-B Injection Transformer

47
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 transformer
i) The above Value is to be noted as HV to Body
ii) Then IR Value between LV terminal and body of Power transformer is to be
measured & 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 is
also to be noted.
v) Particulars of megger is also to be noted.
The maximum value shall be 60MΩ at 600C temperature for transformer which
are in service. For new transformer the value obtained shall be tallied with
manufactures test results.
2. D.C. Resistance or Winding Resistance
The Resistance of HV winding LV winding between their terminals are to be
measured with precision milli ohm meter/ micro ohm meter.
HV side RY= YB= BR=
LV side ry = yb = br =
rn = yn= bn =
The values shall be compared with original test results.

48
3. Turns Ratio Test
With turns Ratio meter, turns Ratio between HV & LV windings at various taps to be
measured & recorded.
At normal tap for 33/11 KV Delta/Star transformer the turns turns ratio is 5.196. At
other taps values will be as per the percentage raise or lower at the respective tap
positions.
4.Voltage Ratio Test
When “Turns Ratio meter” is not available, Voltage Ratio Test is done at Various tap
position 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 various
Phases and phases& neutral measured with precision voltmeter & noted.
5. Short Circuit Test
The 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 at
normal tap and currents measured in all the phases on HV side and phases & neutral
on 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 HV
current
in all Phases = 33000 X Impedance Volts / 100 of PTR
LV side phase LT Voltage applied on 33 KV side of PTR X Rated LV
current
Current in all phases = 33000 X Impedance Volts / 100 of PTR
LV side neutral current shall be zero or less than 1.0 amp.
6. BDV Test of Oil
Oil samples from top oil & bottom oil of Power transformer main tank as well as
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 shall
stand for 60 kV for a gap of 2.5 mm to qualify for successful testing.

49
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.

50
PRE COMMISSIONING CHECKS ON POWER
TRANSFORMERS
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.
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)

51
Tests on Breakers
A) I) Status of Breaker “Open”
Measure IR values between “IN” & “Out” terminals Each limb of breaker
shall be more than 1000 MΩ
II) Status of Breaker “Close”
Measure resistant of each limb by connecting “IN” & “Out” terminals to a
precision 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 all
limbs the values shall be more than 1000 MΩ
B) Opening time & closing time tests to be done on all limbs. The values shall tally
with 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 of
relays 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.
g) D.C. interlock are to be tested.
h) Check that all Jumpers, clamps etc. are in to CT
i) Clean all the bushings.
j) Ensure no leakages from the CTs.
Tests on Potential Transformers
A) 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 leakages
E) Clamps & Jumpers properly tightened.
Tests on Lightening Arrestors
a) IR value are to be checked.
b) Jumper connection to be checked
Other tests in a Sub Station
a) Battery charger & Battery to be checked for proper operation
b) 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.

52
Safety Instruments required while testing:
1. Hand Gloves
2. Helmet
3. Apron
4. Mining Shoes
5. Fire Alarm
6. Discharge Rod
7. Fire Extinguisher-Foam, CO2, Gas, Sand etc.

53
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
Diesel generator on an oil tanker
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.
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

54
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 Germany
Diesel Engine - 1328 HP, 428 rpm
2. DG set No-2 - 4.4 MVA , 11 kV , Made in USSR
3. DG set No-3 - 4.4 MVA , 11 kV , Made in USSR
 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 relay
ii. Over Current and Earth fault Relay
iii. Under Voltage Relay.
iv. Under frequency Relay.

55
BAGDIGI COLLIERY
(LODNA AREA)
Layout of the surface sub-station at Bagdigi Colliery:

56
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 Control1000kVA, 11kV/3.3 kV.
c. T-2: Primary Control1000kVA, 11kV/550 V.
d. T-3: Primary Control2000kVA, 11kV/3.3 kV.
There are 3 neutral earth pits and three bodyearth pits for the
transformers.
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.

57
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.
Specification of the Electrical Winding Engine:
Mfg. by: Poland Date of Installation: 15.06.1982
Motor Manufacturing: Yaska, Japan.
Type: Slip-ring 3-phase induction Motor.
Rating: 150 kW, 3.3 kV
Gear ratio- 19.5:1
Drum 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.

58
We visited the Underground sub-station near pit bottom8th 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.
The Safety Lamps are charged at the charging station where they are
charged for 16 hours so as to be used for 8 hours.

59
SAFETY AND PRECAUTIONS:
ELECTRICITY :
E : Earthing must be done properly and effectively.
L : Looseconnection must be avoided.
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.

60
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 & donotignore safety
instructions.
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.

61
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.
5. Websites: ksebgrid.blogspot.in
yourelectrichome.blogspot.in
www.electrical-res.com
www.en.wikipedia.org
www.circuitmaniac.com

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