TRAINING REPORT FOR VOCATIONAL TRAINING PROGRAMME AT
DEBAGRAM 132/33/11 KV SUB-STATION
West Bengal State Electricity Transmission Company Limited
Department of “Electrical and Electronics Engineering”
Mirmadan Mohanlal Government Polytecnic
Sayan Roy Arup Mondol
Prasanta Sarkar Prasanta Baidya
Animesh Paul Biswajit Saha
Soumik Pramanik Saikat Sarkar
i. OVERVIEW OF SUB-STATION
ii. OVERVIEW OF TRANSMISSION NETWORK
iii. SWITCHING OPERATIONS
iv. EQUIPMENT & TRANSMISSION
v. OPARATING INSTRUCTION AND MAINTENANCE
vi. CONDTION MONTORING AND DIAGONISTIC TESTING
vii. SYSTEM STUDY TECHNIQUES
viii. TROUBLE SHOOTING
ix. ELECTRICAL SEFTY PROCEDURE, ACCIDETENT PREVENTION
x. TRANSMISSION SUB-STATION & LINE MAINTENANCE
In exercise of power conferred under Section 131(4) of the Electricity Act 2003,
the Govt. of West Bengal unbundled West Bengal state Electricity Board into
two Companies viz. West Bengal State Electricity Distribution Company Limited
(WBSEDCL) and West Bengal State Electricity Transmission Company Limited
(WBSETCL). Under the West Bengal Power Sector Reforms Transfer Scheme
2007, activities relating to Transmission and Load Dispatch business of WBSEB
were transferred to West Bengal State Electricity Transmission Company
Limited (WBSETCL). In effect of the Power Sector Reforms Transfer Scheme
2007, West Bengal State Electricity Transmission Company Limited was
incorporated under the provisions of the Companies Act 1956 on 16.02.2007
and other obtained Certificate of Commencement of business on 21st March,
WBSETCL wholly owned by Govt. of West Bengal, is a professionally managed, a
multi-sited Power Transmission Company in Eastern India. The Company has
developed strong in-house expertise in various facets of power transmission
business. As on the end of financial year 2016-17, the Company operates and
maintains a transmission network of 12962 CKM of Extra High Voltage
Transmission lines along with 117 sub-stations (400 KV- 66 KV) having total
transformation capacity of 27752 MVA, spread over the entire stretch of the
State of West Bengal. With focus of improving performance, the transmission
system was consistently maintained at an availability of 99.91% for the year
2016-2017, at par with international standards.
The Company emphasize on evolving and adopting new technologies
continuously to effectively meet the challenges of power transmission in the
State of West Bengal. On operation and maintenance front, continuous efforts
envisage to provide stable and quality power with minimum extent possible
transmission loss. To cater the need of improving transmission system and to
meet the requirement of increasing demand of both industrial and rural load in
the State of West Bengal, various transmission projects are under execution.
i. OVERVIEW OF SUB-STATION
Debagram 132/33/11 KV Substation WBSETCL
Debagram substation is a 132/33/11 KV substation under West Bengal
State Electricity Transmission Company Limited. Debagram 132 KV
substation connected with the grid via 132 KV Debagram-Krishnagar,
Debagram-Katwa and Debagram-Amtala double circuit transmission lines.
The substation feed power to Railway through Debagram-Debagram TSS
132 KV line and Palassey, Akandaberia, Nakashipara, Muragachha and
Tehatta 33/11 KV Substations of WBSEDCL through 33 KV feeders. The
installed transformer capacity of the substation is 2 X 132/33KV, 50MVA +
3 X 33/11KV, 6.3 MVA + 33/11 KV, 5 MVA. Total 7 nos. 11 KV feeders i.e.
Kaligang, Agradweep, Juranpur, Matiary, Panighata, Bagunda and
Debagram Feeders receive power from the substation. Apart from that 2
nos. capacitor bank also installed at the substation. Single line diagram of
the substation given below.
SINGLE LINE DIAGRAM OF DEBOGRAM 132/33/11 KV SUBSTATION
iii. Switching Operation
1. First close the isolators at both side of the bus coupler breaker.
2. Then close the bypass isolator of the feeder which is to be transferred
to transfer bus.
3. Now energized the transfer bus by closing the bus coupler circuit
breaker from remote.
4. After bus coupler breaker is closed, now the power from main bus
flows to the feeder line through its main
5. Breaker as well as bus coupler breaker via transfer bus.
6. Now if main breaker of the feeder is switched off, total power flow will
instantaneously shift to the bus coupler breaker and hence this breaker
will serve the purpose of protection for the feeder.
7. At last the operating personnel open the isolators at both sides of the
main circuit breaker to make it isolated from rest of the live system.
So, it can be concluded that in Main and Transfer Bus System the
maintenance of circuit breaker is possible without any interruption of
power. Because of this advantage the scheme is very popular for 33 KV
and 132 KV system.
iv. EQUIPMENTS & TRANSMISSION
a. Lightning arrester(LA)
c. Bus bars
d. Circuit Breaker(CB)
e. Electrical power transformer(TR)
f. Instrument Transformers(CT & PT)
g. Control and Relay panel
h. Capacitor bank.
k. Under Ground cable
m. Earthling System
n. Transmission Tower
o. Battery System
p. Communication system(PLCC)
a. Lightning Arrestor(LA)
The device which is used for the protection of the equipment at the substations
against travelling waves, such type of device is called lightning arrester or surge
diverter. In other words, lightning arrester diverts the abnormal high voltage to
the ground without affecting the continuity of supply.
The arrester which uses zinc oxide semiconductor as a resistor material, such
type of arrester is known as a metal oxide surge arrester or ZnO Diverter.
In Debagram Substation lightning arrester is using to protect transformer
and others equipments in the substation
Electrical isolators separate a part of the system from rest for safe maintenance
works. So definition of isolator can be rewritten as Isolator is a manually
operated mechanical switch which separates a part of the electrical power.
Isolators are used to open a circuit under no load. There are many type of
isolator used in substation. Like that,
★ Line Side isolator
★ Main bus side isolator
★ Transfer bus isolator
★ Earthing isolator
Main Bus isolator: A bus isolator is an off load switch that connects the line
breaker and the bus. It sits between circuit breaker and bus.
Line Side isolator: line isolator is an off load switch that connects the line
breaker and the line. It sits between circuit breaker and current transformer.
Transfer Side isolator: Transfer bus side isolator which operates when power
feed through transfer bus.
Earthling isolator: Main function of earth switch is to ground the isolated
bus/conductor. It is interlinked with isolator, when
isolator opens the circuit, earth switch is closed & when
isolator closes the circuit, earth switch is opened.
In Debagram Substation, using rotating type isolator,
it may be operated manually or by using remote control
Busbar Is a very important part of a substation which connects incoming circuit
and outgoing circuit and transformer bays etc.
In Debagram substation there is two types of 132KV busbar ----1. 132 KV Main
Bus 2. 132KV Transfer Bus.
Other bus bar is,33 KV mian bus , 11KV main bus
Size description of hollow Aluminum tube/conductor at Bay side.Busbar of
132KV , 33KV , 11 KV are this type of conductor.
d. Circuit Breaker
Electrical circuit breaker , which can be operated automatically or manually
for protecting and controlling of electrical power system. In the modern power
system the design of the circuit breaker has changed depending upon the huge
currents and to prevent from arc while Operating.
There is 2 Types of Circuit Breakers In Debagram Substation
● SF6 Circuit Breaker
●Vaccume Circuit Breaker
Sulphur hexafluoride gas is known as an SF6
gas which is used as insulating medium for the
high tendency of absorbing free electron.
The negative ion is formed when a free electron
collides with the SF6 gas molecule; it is absorbed
by that gas molecule.
Electrical Power Transformer
In Debogram Substation,there are two 50
MVA,132/33 KV, three 6.5 MVA,33/11 KV and
one 5 MVA ,33/11 KV, for voltage step down
and two 100 KVA 33/0.4 KV earthling
transformer and 100KVA 33/0.4 KV station
Bushing ( HV side & LV side) ,Horn gap arrester , Main tank , Transformeroil ,
Winding (primary & secondary), Core , Tap changer(OLTC) , Conservator tank ,
Breather , Explosionvent/pressure release device(PRV/PRD) , Marshalling box,
Ratting Plate , Oil level indicator(MOG) , Temperature indicator(WT & OT) ,
Radiator , Cooling fan , Oil pump
Buchholz Relay, Over Current protection, Differential protection, restricted
Earth fault protection,Backup Earth fault protection, Winding temperature & Oil
■ Oil NaturalAir Natural(ONAN)
■ Oil NaturalAir Forced (ONAF)
■ Oil Forced Air Forced (OFAF)
■ Oil Forced Water Forced (OFWF)
f. Instrument Transformer (CT & PT)
Specially designed transformer which is used to
to measure high alternating Current and Voltage ,
is called instrument transformers
Current Transformers (CT)
The current transformer is used for measure
alternating current & protection in power
Potential transformer is a voltage step-down
transformer which reduces the voltage of a
suitable value (i.e high voltage circuit to a lower
Main purpose of potential transformer is 1. Voltage measurement , 2.
g. CONTROL AND RELAY PANEL
A control & relay panel is designed to provide to control the associated line or
transformer through outdoor switchgear of substations. The control & Relay
panels are complete in themselves with all main and auxiliary relays,
annunciation relay, switches, wiring, labels, terminal blocks, illumination, cable
etc. These panels are used for the control & monitoring of electrical equipments
such as transformers, busbar, and circuit breakers.Control panel for Outdoor
SF6 Circuit Breaker, Master Trip Relay, Trip circuit Supervision Relay, Indications
& meters etc.
A relay is a switching device which is used to switching high voltage line using
low voltage power supply.
Most important use of relay is for protection from fault.and manual on/off of
Different Types of Relays are:
1. Distance Protection Relay
Impedance Relay is protection relay which functions depending upon the
distance of fault in the line. More specifically, the relay operates depending
upon the impedance between the point of fault and the point where relay is
installed. These relays are known as Distance Relay or Impedance Relay.
2. Overcurrent relay
This type of relay works when current in the circuit exceeds the predetermined
value. In an over current relay or o/c relay the actuating quantity is only current.
There is only one current operated element in the relay, no voltage coil etc. are
required to construct this protective relay.
3. Differential Protection Relay
A differential relay is used to identify all kind fault in a transformer.
Voltage Differential Relay
Biased or Percentage Differential Relay
Voltage Balance Differential Relay
4. Buchholz Relay :
Buchholz relay is used for protection of
all kind of internal fault . It is used on all oil
immersed transformers. Such relay can only
be fitted to the transformers equipped with
the conservator tank as it is installed in
between the conservator tank and the main
h. CAPACITOR BANK
Static capacitor is used in parallel to
improve lagging power factor of
A Capacitor Bank is a group of several
capacitors of the same rating that are
connected in series or parallel configaration
with each other to increase active power or
When the inductive load of the line is
increase then the reactive component
increase so the KVAR increase of the line by adding capacitor in parallel
the inductive load reduces. Also increase the power factor and receiving
Conductors which carry electric power from the sending end sub-station to the
receiving end station.
Most of the conductor in Debagram Substation are ACSR (Aluminium conductor
In 132 kv High volt side moose conductor are used in main buss and panther
conductor are used in transfer buss.
Jumper Wire : Jumper used to connect to terminal of busbar or lines.
Dropper : Dropper is the verticle conductor connected with bushing of
Capacitor (Damping) Reactors are designed
to be installed in series with a shunt-
connected capacitor bank to limit inrush
currents in the capacitor bank due to
switching operations, to limit outrush
currents due to close-in faults and to
control the resonant frequency of the
system due to the addition of the capacitor
k. Underground Cable:
Underground cable essentially constitutes of one or more conductors covered
with suitable insulation and surrounded by a protective cover.
UG cable is divided by two part 1.Power cable and 2.Control cable
underground Cable are used for connection from AC distribution box & DC
distribution box as a power cable
control & relay panel to different equipment such as CB, CT, PT, LA,
transformers accessory as a control cable.
The overhead line conductor should be supported on the towers in such a
way that current from the conductors do not flow the earth to the support. So
the insulators provide necessary insulations between the line conductors and
Types of insulator used as overhead line :
1. Pin Insulator 2. Suspension Insulator 3. Strain Insulator 4. Shackle type
Pin Insulator: The pin insulator is used in
power distribution for the voltage up to 33KV.
It is placed on the cross arm of the supporting
tower. The pin insulator has grooves on the
upper end for keeping the conductor.
Suspension Insulator: In higher voltage,
beyond 33KV, it becomes uneconomical to use
pin insulator because size, weight of the
insulator become more.Each insulator of a
suspension string is called disc insulator
because of their disc like shape.Each disk is
permitted for 11 KV line to earth voltage.
Strain Insulator: When suspension
string is used to sustain extraordinary
tensile load of conductor it is referred
as string insulator. When there is a dead
end or there is a sharp corner in
transmission line, the line has to sustain
a great tensile load of conductor or
strain. A strain insulator must have
considerable mechanical strength as
well as the necessary electrical insulating properties.
m. Earthing System
Earthing or grounding is required to immediate discharge of electricity
directly to the earth or ground during lightning and switching surge
The benefits of earthing or groundingin an electrical system
Safety of operational and maintenance stuff .
Discharge of electrical charge to ground .
Grounding of overhead shield wire.
Common Types of Earthing Used at sub-station :
Earthing mat: a number of rods when joined together through copper
conductors constitute an earthing mat.
It reduces overall grounding resistance .such a mess of conductor laid near
the ground surface ,in limiting the potential gradient . in hard soil or in soils
having low conductivity , driving of rods quite deep may prove expensive.
Earth pit: earth pit are the preferred method of earthing especially for
electrical network. Electricity always flows the path of least resistence and
to diavert the maximum current away from a circuit, earthing pits are
designed to reduce ground resistance.
The main supporting unit of
overhead transmission line is
transmission tower. Transmission
towers have to carry the heavy
transmission conductor at a
sufficient safe height from
Based on numbers of circuits
carried by a transmission tower,
it can be classisfied as-
Single circuit tower
Double circuit tower
Multi circuit tower.
o. Battery System
DC supply is required for
closing and tripping of circuit
breaker control board
indication control and
annunciation system etc.
Battery are also used to
provide illumination in
certain and sensitivity area
for otherwise work with
The battery charger converts AC to DC voltage and also charged the battery
by float (trickle charging) and boost (quick charging) charging method
p. Communication System(PLCC)
The PLCC is used to communicate with sub-station to substation for send &
receive information, data etc.
But Debagram substation this method is not using. Now they are using optical
fibre cable for communication purpose.
V. OPERATING INSTUCTION AND MAINTENANCE
An Operating Agreement (OA) is an agreement between two Operating
Authorities. It is used to confirm that an electrical apparatus operational state
will be held in an agreed state until the OA is cancelled. An OA is used when one
party needs to work on an item of plant or electrical apparatus which requires
isolation and/or earthing from an adjacent Operating Authority. The Operating
Agreement recipient shall verify the isolations and earthing points stated on the
Agreement, and may apply additional locks and tags. An OA is not a work
permit. It does not authorise work to be undertaken. A work permit must be
issued to allow work to take place. The conditions stated on the work permit
must reference the OA. An OA is issued by a switching operator. For standard
outages, the outage requestor will write the associated switching program,
unless otherwise agreed. For the commissioning of other Operating Authority
apparatus, Horizon Power will usually write the switching program. The issue
and relinquishment of Operating Agreement must be recorded as steps in the
Monitoring systems provides all the technical information required to maintain
utmost availability and at the same time maximize performance, including
loading and lifetime benefits. This advanced monitoring solution surveys every
link in the energy supply chain. Accurate monitoring of all primary components
of a substation makes possible optimized loading and performance, and it helps
increase the lifetime of the line.
Electrical Preventive Maintenance
Electrical preventative maintenance isn’t just an important way to avoid
preventable electrical repairs and maintain your system. It’s also a great way to
save money! Using electricity produces heat. Over time, that heat causes
expanding and contracting of an electrical system.
1) Visual inspection of electrical equipment inside substation
2) Thermo-vision scan of the different electrical equipment and transmission
lines before and after preventive maintenance
Electrical Breakdown Maintenance:
Breakdown maintenance is maintenance performed on equipment that has
broken down and is unusable. It is based on a breakdown maintenance trigger.
It may be either planned or unplanned.
VI. CONDITION MONITORING AND DIAGNOSTICS TESTING
To ensure the power system operates safely and reliably, it is essential to
monitor and evaluate the health condition of power equipment on-line or
off-line. This study reviews the research status in condition monitoring and
diagnosis of power equipment, including transformer, gas insulated
switchgear, cable, external insulation, generator, and power capacitor in
recent years. Although much progress has been made in technologies of
condition monitoring and fault diagnosis such as test accuracy, fast and
accurate fault localisation and recognition of fault types, there are still many
deficiencies which needs further research work, including the reliability of
signal collection from sensors, the accuracy of data treatment and analysis,
antiinterference performance of test equipment, appropriate models used
for condition evaluation. The prospective of condition monitoring and
diagnosis technologies of power equipment are also presented in this study.
It is proposed that the application of big data, internet of things and cloud
computing should be expected and given special attention in the near future.
vii. System Study Techniques
System study is a major part of monitoring of the system for every substation.
Generally shift engineers takes voltage, current, megawatt, MVAR, temperature
(OTI & WTI) reading of the each transformer and feeder, charging current and
voltage of battery bank etc. in every hours. The condition of silica gel, oil
leakage, Sf6 gas pressure etc checked in every shift. The system study of the
different equipment of the substation is very much required to take preventive
action in case of any abnormality of the system.
viii. Trouble Shooting
Electrical transmission and distribution equipment; Experience in operating,
maintaining and troubleshooting of Switchyard and substation equipment
The term “troubleshooting” mainly attributes to sort out different problems
such as non-closure of “closing coil” or “tripping coil” of circuit breaker, non-
functioning of remote operating isolators, relays etc.
The interconnectivity of the particular circuit including the various interlocking
limit switches and relay contacts.
Check for simultaneous open & close of slow open & close of main contacts, of
circuit breakers and isolators.
ix. Electrical Safety Procedures, Accident Prevention
What is safety:
"Safety" denotes "Existence" of safe situation", meaning "not dangerous" or
"not risky". To achieve Safety in a job, or at work site, or in the process of
work, two attempts are made-
a. To shield a danger
b. To guard people against the risk of a danger.
Electrical Safety is about attempts an efforts to ensure preventing physical
loss or damage of people caused by Electrical shock i.e. passage of electric
current through one's body.
Safety Precautions in substation:
1. Get the substation
inspected by the local fire
service officer if required.
2. In case of fire, call fire
station & give them guidance.
3. Provide Co2/DCP/Foam as
extinguishing medium at
4. Earthing of Transformer,
breaker etc should be done
5. Provide high temperature trip to Transformer.
6. Attend loose contact or red hotspot in time detected through thermo-
7. Avoid joint in cables.
8. Avoid loose fuse links.
9. Use Safety equipment (PPE) like safety rope, safety belt, insulating rubber
mat, discharge cum earthing rod, safety shoe, hand gloves, high voltage
detector, safety ladder, helmet etc. of proper rating at the time of work.
10. Provide adequate water supplies for firefighting.
11. Ensure availability of First aid box with requisite drugs & other
In any Electrical substation safety is a very important part. We already know
alphabetic letter ABC i.e. " always be careful" So If we do any job related to
Electrical mechanical or other work It should be "Always be careful" &
maintain proper safety because safety 1st Safety must.
X. TRANSMISSION SUB-STATION & LINE MAINTENANCE
Substation maintenance plays a very important role to ensure trouble free
operation of any substation. Maintenance of different equipment done
periodically on different interval as per standard maintenance prcedure of
1. Maintenance of Battery banks carried out monthly by taking specific gravity
and voltage of each lead acid type cells and cleaning of the battery etc.
2. Thermo-vision scanning of different equipment of the substation done
periodically for detection of Hot spots in the connectors.
3. Winter and pre-puja maintenance of the Bus, Transformer, Circuit Breakers,
Isolators, Current transformers, Lightening Arrestors etc. of all the Bays carried
out by tightening of connectors, cleaning of insulators, checking of I.R. value of
the equipment etc.
4. The condition monitoring of the equipment also carried out for evaluation of
health of the particular equipment. In case of any abnormality noticed during
the tests, corrective action taken to avoid failure of that equipment which may
cause breakdown and even accident.
5. Checking the operation of relays and other protective equipments to ensure
safety of the system.
Line maintenance plays a very important role in power transmitting system. For
uninterrupted power supply it is essential to maintain the transmission lines
remains healthy both during normal and hazardous condition. For preventive
and predictive maintenance of transmission lines following methods are
1. Regular line patrolling of the transmission line towers and line components
carried out for detection of loss / damage of any tower member, damage of
conductor, approaching of any earth object like trees near the line, dislocation
of Vibration damper, damage of disc insulator string, sagging of line etc.
2. Thermo-graphic scanning of jumpers for detecting Hot spots.
3. Punctured insulator detection by electric field measurement / voltage
4. Tower footing earth resistance measurement.