This document is a training project report submitted by Arnab Nandi on completion of his vocational training at various substations under the Serampore Division of West Bengal State Electricity Distribution Company Ltd. from July 16-30, 2016. The report provides an overview of the electrical power distribution system in India and West Bengal, describes the key components of substations including transformers, relays, circuit breakers, and more. It also discusses commercial aspects like tariffs, energy meters, and load curves. The training helped Nandi study the working of electrical power distribution systems and the significance of substation equipment.

1. A
Training Project Report
On
Electrical Power Distribution
System
Submitted on completion of Vocational Training
At
WestBengal State ElectricityDistribution Company
Limited
SUBMITTED BY
Arnab Nandi
Electrical Engineering
Academy of Technology
Roll No: 16901613025
Reg. No: 131690110525 of 2013-14
Training Session: 16th July 2016 to 30th July 2016

2. Page | 1
CERTIFICATION
This is to certify that Arnab Nandi, student of Electrical Engineering
of Academy of Technology, affiliated to Maulana Abul Kalam Azad
University of Technology (formerly known as West Bengal University
of Technology, WBUT), has completed his Vocational Training from
Serampore Division of West Bengal State Electricity Distribution
Company Ltd. (WBSEDCL) under the supervision of A. Chanda from
16.07.2016 to 30.07.2016.
A. Chanda
Divisional Manager
Serampore Division (WBSEDCL)

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STUDENT DECLARATION
I undersigned, Arnab Nandi declare that this project report entitled,
“ElectricalPowerDistribution System”, is the result of vocational training
carried out from 16th July 2016 to 30th July 2016 at various sub-stations and
supply offices under Serampore Division of WestBengalState Electricity
Distribution Company Ltd. (WBSEDCL).
This project has not been previously submitted to any other university /
institutions for any other examination and for any other purposeby any other
person. I will not use this project report in future to use as submission to any
other university, institutions or any publisher. I also promise not to allow /
permit any other persons to copy/ publish any part /full material of this report
in any form.
ARNAB NANDI
Electrical Engineering,
Academy of Technology
Roll No: 16901613025
Reg. No: 131690110525 of 2013-14

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PREFACE
This project report has been prepared in fulfillment of Industrial Training
carried out after 6th Semester of B.Tech course. The industrial training was
conducted at various sub-stations and supply offices under Serampore Division
of West Bengal State Electricity Distribution Company Ltd. (WBSEDCL) from
16.07.2016 to 30.07.2016.
The blend of learning and knowledge acquired during my visit to the sub
stations and supply offices is presented in this project report.
The rationale behind the industrial training and preparing this report is to study
the working and steps involved in electrical power distribution system, the
equipments in an electrical sub-station, and the significance of each one of them
in distributing power to consumers.
I have tried my best to cover all the aspects of the electrical power distribution
system and their brief detailing in this project report.

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ACKNOWLEDGEMENT
With profound respect and gratitude, I take this opportunity to convey my
heartfelt gratitude to various individuals involved in making this training a truly
learning and enriching experience. I am extremely grateful to all the technical
staff of Serampore Division, West Bengal State Electricity Distribution
Company Ltd. (WBSEDCL) for their co-operation and guidance that helped me
a lot during this course of training.
I am also thankful to Mr. Pradyot Kr. Pal (Chief Engineer, Commercial,
(WBSEDCL), Prof. Arup Kumar Chattopadhyay (H.O.D, Talent
Transformation Cell) and Department of Electrical Engineering of Academy of
Technology for organizing this training and constant co-operation which has
been a significant factor for the accomplishment of this training.

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TABLE OF CONTENTS
Introduction................................................................................................................................. 6
Power System Components.......................................................................................................... 7
Distribution System...................................................................................................................... 8
Electrical Substation..................................................................................................................... 9
Transmission Substation.......................................................................................................10
Distribution Substation.........................................................................................................10
Substation Equipments ...............................................................................................................11
Transformers.......................................................................................................................11
Relays..................................................................................................................................17
Circuit Breakers....................................................................................................................18
Isolators ..............................................................................................................................20
Bus Bar................................................................................................................................20
Distribution Feeder..............................................................................................................21
Control Panel.......................................................................................................................21
Capacitor Bank.....................................................................................................................22
Lightning Arrestor................................................................................................................22
Batteries..............................................................................................................................22
Secondary Distribution System....................................................................................................23
Overhead Distribution..........................................................................................................25
Underground Distribution.....................................................................................................25
Commercial View........................................................................................................................26
Tariff...................................................................................................................................26
Energy Meter.......................................................................................................................26
Load Curve ..........................................................................................................................27
Conclusion..................................................................................................................................28
Bibliography...............................................................................................................................29

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INTRODUCTION
The electricity sector in India is predominantly controlled by Government of India's public
sector undertakings PSUs). Major PSUs involved in the generation of electricity include
National Thermal Power Corporation Ltd. (NTPC), National Hydroelectric Power
Corporation Ltd. (NHPC) and Nuclear Power Corporation of India (NPCI). Besides PSUs,
several state-level corporations, are also involved in the generation and intra-state distribution
of electricity. The Power Grid Corporation of India is responsible for the inter-state
transmission of electricity and the development of national grid.
India is world's 6th largest energy consumer, accounting for 3.4% of global energy
consumption. Due to India's economic rise, the demand of energy has grown at an average of
3.6% per annum over the past 30 years.
During the year 2014-15, the per capita electricity generation in India was 1,010 kWh with
total electricity consumption (utilities and non-utilities) of 938.823 billion or 746 kWh per
capita electricity consumption. Electric energy consumption in agriculture was recorded
highest (18.45%) in 2014-15 among all countries.
West Bengal State Electricity Distribution Company Ltd.
West Bengal State Electricity Board (WBSEB) was state owned electricity regulation board
which came into being on 01.05.1955 and was operating within the state of West Bengal until
31.03.2O07.It has now been re-structured and split into two companies namely West Bengal
State Electricity Transmission Company Ltd. (WBSETCL) and West Bengal State Electricity
Distribution Company Ltd. (WBSEDCL). The split came into effect on O1.O4.2OO7 under
the provisions of West Bengal Power Reform Scheme, 2007.
WBSETCL is responsible for transmitting power at 66 kV, 132kV, 220kV and 400kV in the
state of West Bengal.
WBSEDCL is responsible for distributing power at 33kV level and below. This state utility
at present has the consumer strength of over 68Lakhs. WBSEDCL provides power to
96% of West Bengal, catering to every sector — from ordinary villages to huge
industrial units. It serves a customer base of more than 1.65 crore across West
Bengal. The service network spans over 5 Zones, 18 Regional Offices, 70
Distribution Divisions and 501 Customer Care Centers.
Meeting 80% of the state’s peak power demand, WBSEDCL has achieved a profit of
Rs. 95.13 crore (PAT) in 2010-11. To mitigate short power supply and being an
environ-friendly corporate, WBSEDCL has set up Purulia Pumped Storage
Project with a capacity of 900MW hydel power.

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POWER SYSTEM COMPONENTS
Electric power is generated at 11-25kV in a power station. To transmit over long distances, it
is then stepped-up to 400kV, 220kV or 132kV as necessary. Power is carried through a
transmission network of high voltage lines. Usually, these lines run into hundreds of
kilometers and deliver the power into a common power pool called the grid. The grid is
connected to load centers (cities) through a sub-transmission network of normally 33kV (or
sometimes 66kV) lines. These lines terminate into a 33kV (or 66kV) substation, where the
voltage is stepped-down to 11kV for power distribution to load points through a distribution
network of lines at 11kV and lower.
The power network, which generally concerns the common man, is the distribution network
of 11kV lines or feeders downstream of the 33kV substation. Each 11kV feeder which
emanates from the 33kV substation branches further into several subsidiary 11kV feeders to
carry power close
to the load points
(localities,
industrial areas,
villages, etc.,). At
these load points,
a transformer
further reduces
the voltage from
11kV to 415V or
220v to provide
the last-mile
connection
through feeders
(also called as
Low Tension LT
feeders) to
individual
customers, either
at 240V (single-Φ
) or at 415V
(three-Φ ).
Figure 1: Electricity Generation, Transmission and Distribution

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DISTRIBUTION SYSTEM
The main function of an electrical power distribution system is to provide power to individual
consumer premises. Distribution of electric power to different consumers is done with much
low voltage level. Distribution of electric power is done by distribution networks.
Distribution networks consist of following main parts:
 Feeder: It is a conductor which connects the substation to the area where power is to be
distributed.
 Distributor: It is a conductor from which tapings are taken from pole mounted
transformer to the customer.
 Service Mains: It is a small cable which connects the distributor to the customer’s meter.
Distribution System can be classified into the following types depending on the modes of
classifications:
 Type of Voltage:
 Primary Distribution System: 11kV, 6.6kV or 3.3kV
 Secondary Distribution System: 415V or 220V.
 Type of Construction:
 Overhead System
 Underground System
 Number of Wires:
 Two wire • Three wire • Four wire
 Scheme of Connection:
 Radial Distribution System
 Ring or Loop Distribution System
 Interconnected Distribution System
Figure 2: Radial Distribution Figure 3: Ring Distribution Figure 4: Interconnected Distribution

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ELECTRICAL SUBSTATION
An electrical substation is a subsidiary station of an electricity generation, transmission and
distribution system where voltage is transformed from high to low or the reverse using
transformers. Electric power may flow through several substations between generating plant
and consumer, and may be changed in voltage in several steps.
A substation that has a step-up transformer increases the voltage while decreasing the current,
while a step-down transformer decreases the voltage while increasing the current for
domestic and commercial distribution.
Figure 5: Electrical Substation
Figure 6: Single Line Diagram of 33kV/11kV Substation

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There are several factors that need to be considered for deciding for a substation. Some
important primary factors in the design of substation are operational flexibility, supply
reliability, security and short circuit withstand capability etc.
One important factor to be considered first is the site selection. Substation design and some
equipment selection depends on site selection. Some factors which are considered during site
selection are:
 The site should be near the load center keeping in view the future load growth.
 Access road to the site for smooth movement of construction machines, equipment
and transformers.
 Interference with communication signals. The construction company have to take
permission from the appropriate authority
 Land should be fairly leveled to minimize development cost
 The substation site should be as near to the town / city but should be clear of
public places, aerodromes, and military or police installations.
 The land should not have water logging problem
 The land should be far away from obstructions, to permit easy and safe approach
or termination of high voltage overhead transmission lines
 TransmissionSubstations:
The three-Φ power leaves the generator and enters a transmission substation at the power
plant. This substation uses large transformers to convert or step up the generator's voltage
(11kV) to extremely high voltages (220kV) for long-distance transmission on the
transmission grid.
 Distribution Substations:
A distribution substation transfers power from the transmission system to the distribution
system of an area. It is uneconomical to directly connect electricity consumers to the main
transmission network, unless they use large amounts of power, so the distribution station
reduces voltage to a level suitable for local distribution. The input for a distribution
substation is typically at least two transmission or sub transmission lines. The output is a
number of feeders. The feeders run along streets overhead (or underground, in some
cases) and power the distribution transformers at or near the customer premises. In
addition to transforming voltage, distribution substations also isolate faults in either the
transmission or distribution systems. Distribution substations are typically the points
of voltage regulation, although on long distribution circuits (of several miles/kilometers),
voltage regulation equipment may also be installed along the line.
SUBSTATION EQUIPMENTS

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Transformers:
A Transformer is a static, alternating electromagnetic device that transfers electrical
power between two or more circuits using electromagnetic induction. It is a constant power
device, constant flux device and a constant frequency device.
Since transformer is a constant power device: Vp Ip = Vs Is
As it is a constant flux device we get: IpNp= IsNs where,
 Vp and Vs are voltage of the primary and secondary sides respectively
 Ip and Is are currents of primary and secondary sides respectively
 Np and Ns are turns in the coils of primary and secondary sides respectively
Equating the above two equations we get:
𝐕𝐩
𝐕𝐬
=
𝐈𝐬
𝐕𝐩
=
𝐍𝐩
𝐍𝐩
Transformers are used to change the voltage level of the supply. While the transformers in
generating stations steps up the voltage to reduce the power losses (increasing voltage
Figure 7: Arrangement of equipments in a substation
Figure 8: Development of Transformer Symbol

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reduces the current, thus reducing the I2R losses), the transformers in transmission and
distribution systems gradually decreases the voltages in steps as required by the loads.
They are usually filled with oil and are cooled either by the surrounding atmosphere by air
blasts obtained from fans trained on them. Some also circulate the oil for additional cooling.
Because of the high voltages imposed on the incoming side, there is an elaborate electrical
connection going through the cover which is called as bushing. The supply circuits connected
to the terminals of the primary winding and the outgoing distribution feeders connected to the
terminals of the secondary winding.
PowerTransformers (PTR):
It is used for the transmission purpose at heavy load, high
voltage greater than 33 kV and 100% efficiency. It is bigger in
size as compare to distribution transformer, it used in
generating station and Transmission substation at high
insulation level. They can be of two types: Single Φ
Transformers and Multi Φ Transformers.
Specifications of 132/33 kV Transformer:
 Rating: 31.5 MVA
 Φ : 3
 Vector group: YNd1
 Voltage Ratio: 132kV/33kV
 Current Ratio: 132A/552A
 % Impedance: 12.04%
 Type of Cooling: ONAN
Specifications of 33/11 kV Transformer:
 Rating: 6.3 MVA
 Φ : 3
 Vector group: Dyn11
 Voltage Ratio: 33kV/11kV
 Current Ratio: 110.22A/330.66A
Figure 9: Parts of a Power Transformer
Figure 10: Power Transformer

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Instrument Transformers:
These transformers are used for the measurement purposes at that points where standard
voltmeters and ammeters cannot be used. They are of two types:
 Current Transformer (CT): A CT is used for
measurement of alternating electric currents. When
current in a circuit is too high to apply directly 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 isolates the measuring instruments from
what may be very high voltage in the monitored circuit.
 Potential Transformer (PT): They are parallel connected type of instrument
transformer, used for metering and protection in high-voltage circuits. They are
designed to present negligible load to the supply being measured and to have an
accurate voltage ratio to enable accurate metering. A potential transformer may have
several secondary windings on the same core as a primary winding, for use in
different metering or protection circuits.
Figure 11: Current Transformer
Figure 12: Potential Transformer

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Distribution Transformers:
A distribution transformer or service transformer is a transformer that provides the
final voltage transformation in the electric power distribution system (415V line), stepping
down the voltage used in the distribution lines to the level used by the customer. If mounted
on a utility pole, they are called pole-mount transformers. If the distribution lines are located
at ground level or underground, distribution transformers are mounted on concrete pads and
locked in steel cases, thus known as pad-mount transformers.
Specifications of 33 kV CT:
 Rated Voltage: 33kV
 Number of Cores: 3
 Rating: 20VA
 Ratio: 400-200A/5A
Specifications of 33 kV PT:
 High Voltage Rating: 33/ √3 kV
 Low Voltage Rating: 110/ √3 V
 Φ : 3
 Vector Group: YNyn
Specifications of 415V Distribution Transformer:
 Rating: 200kVA
 Vector group: Dyn 11
 High Voltage: 11kV
 Low Voltage: 415-240V
 HV Amp: 10.5A
 LV Amp: 278.2A
Figure 13: Circuit diagram showing connection of CT and PT for measuring high voltage and current

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TransformerAccessories:
 Conservator: It consists of an airtight metal drum fixed above the level of the top of
the tank and connected with the tank is completely filled with oil. The conservator is
partially is filled with oil. The function of conservator is to take up construction and
expansion of oil without allowing it to come in contact with outside air. Transformer
oil will expand due to the heat generated because of losses.
 Breather: When the temperature changes, expansion of contacts and there is a
displacement of air. When the transformer cools the oil level goes down air is drawn
in. The oil should not be allowed to come in contact with the atmospheric air as it may
take moisture, which may spoil its insulating properties. The breather consists of a
small vessel, which contains a drying agent like Silica gel crystal.
Figure 16: Transformer Accessories
Figure 14: Pole Mounted Distribution Transformer
Figure 15: Pad Mounted Distribution Transformer

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 Temperature Indicator: There are two temperature indicators on the transformer
tank one for oil temperature measurement and another for core temperature
measurement. In 31.5 MVA Transformers when oil temperature reaches 65oC cooling
fans starts automatically but when the oil temperature rises at 75oC or winding
temperature rises at 85oC the alarm circuit will be closed. Further increase in oil or
winding temp. The circuit will trip automatically. Cooling fans are placed beside the
radiator tube, which are used for oil cooling. Generally the cooling fans start
automatically but when needed it can be started manually.
 Bushing: It is fixed on the transformer tank and these connections is made to the
external circuits. Ordinary porcelain insulators can be used as bushing up to voltage of
33 kV. Above 33 kV oil filled type bushings are used. In filled bushings, the
conductor is passed through the hollow porcelain insulator which is filled with oil.
 Tap Changer: A tap changer is a
connection point selection mechanism along
a power transformer winding that allows a
variable number of turns to be selected in
discrete steps. A transformer with a variable
turns ratio is produced, enabling
stepped voltage regulation of the output. The
tap selection may be made via an automatic
or manual tap changer mechanism. The tap
changer is generally done on H.V side
because current flow is less than lv side.
Which reduces the flashing during the tap
changing. Here tap changed in 132/33kV
transformer.
 Buchholz relay: It is a gas actuated relay installed in oil immersed transformers for
protection against overheating of the transformer windings. Overheating produces
heat and forces the evolution of H2 gas. It mainly consists of two float switches placed
in the connecting pipe between the main tank and conservator.
Figure 17: On-Load Tap Changer
Figure 18: Operating Mechanism of Buchholz Relay

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Relays:
A relay is a sensing element whose purpose is to sense the fault and generate a trip decision if
a fault within the relay’s jurisdiction is detected. The relay detects the abnormal condition in
the electrical circuit by constantly measuring the electrical quantities, which are different
under normal and fault condition. Relay itself is a low powered device. Hence the current and
voltage measured by the relay are stepped down using a CT or PT with a definite turns ratio.
The electrical quantities which may change under fault condition are voltage, current,
frequency and phase angle. Having detect the fault, the relay operate to close the trip circuit
of circuit breaker.
The following types of relays are generally used in electrical distribution system:
Over Current (O/C) Relay:
This type of relay works when current in the circuit
exceeds the predetermined value. The actuating source is
the current in the circuit supplied to the relay from a
current transformer. These relay are used on A.C. circuit
only and can operate for fault flow in the either direction.
This relay operates when short circuit fault occurs.
Earth Fault (E/F) Relay:
This type of relay sense the fault between the lines and
the earth. It checks the vector sum of all the line currents.
If it is not equal to zero, it trips.
Differential Relay:
Differential protection is a unit-type protection for a specified zone or piece of equipment. It
is based on the fact that it is only in the case of faults internal to the zone that the differential
current (difference between input and output currents) will be high. The general idea behind
the Differential Protection is that the CT's on the primary and secondary side must transform
the respective line currents to the same value when there is no fault. During an internal fault
there is a difference in the currents which is sensed by the differential relay. The relay then
trips the circuit breaker and protects the equipment from fault.
Figure 19: Protection Scheme of Transformer using
OC and EF Relays
Figure 20: Circuit Diagram for Differential Protection Figure 21: Digital Differential Relay

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Circuit Breakers:
A circuit breaker is an equipment, which can open or close a circuit under normal as well as
fault condition. These circuit breaker breaks for a fault which can damage other instrument in
the station. A circuit breaker consists of fixed and moving
contacts, which are touching each other under normal
condition i.e. when breaker is closed. Whenever a fault
occurs trip coil gets energized by the relay. The moving
contacts are pulled by some mechanism and therefore the
circuit is opened or circuit breaks. When circuit breaks an
arc is stack between contacts, the production of arc not
only interrupts the current but generates enormous amount
of heat which may cause damage to the system or the
breaker itself. Therefore the main problem in a circuit
breaker is to extinguish the arc within the shortest possible
time so that the heat generated by it may not reach a
dangerous value. The medium used for arc extinction is
usually oil, air, Sulfur Hexafluoride (SF6) or vacuum.
Oil Circuit Breaker:
A high-voltage circuit breaker in which the arc is drawn in oil to dissipate the heat and
extinguish the arc; the intense heat of the arc decomposes the oil, generating a gas whose
high pressure produces a flow of fresh fluid through the arc that furnishes the necessary
insulation to prevent a restrike of the arc. The arc is then extinguished, both because of its
elongation upon parting of contacts and because of intensive cooling by the gases and oil
vapor.
Air Circuit Breaker:
Air Circuit Breakers are usually used in low voltage applications below 450V. Air Circuit
breakers normally have two pairs of contacts. The main pair of contacts carries the current at
normal load and these contacts are made of copper. When circuit breaker is being opened, the
main contacts open first and during opening of main
contacts the arcing contacts are still in touch with
each other. As the current gets a parallel low resistive
path through the arcing contact during opening of
main contacts there will not be any arcing in the main
contact. The arc in chute will become colder,
lengthen and split hence arc voltage becomes much
larger than system voltage at the time of operation of
air circuit breaker, and therefore the arc is quenched
finally during the current zero.
Figure 22: Operating Mechanism of Circuit Breaker
Figure 23: Operating Mechanism of Air Circuit Breaker

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Air BlastCircuit Breaker:
The air blast circuit breakers employs compressed air (at a pressure of 20 k.g/c.m2) for arc
extinction and are finding their best application in systems operating 132 kV and above (up to
400kV)with breaking capacity up to 7,500 MVA (during short circuit fault)and above. These
breakers have the advantages of less burning of contacts because of less arc energy, little
maintenance, facility of high speed re closure, no risk of explosion and fire hazard and
suitability for duties requiring frequent operations. The drawbacks of such breakers are
additional need of compressor plant for supplying compressed air, current chopping,
sensitivity re-striking voltage and air leakage at the pipe line
fittings.
Vacuum Circuit Breaker:
The idea behind the vacuum circuit breakers is to eliminate the
medium between the contacts-vacuum. The dielectric strength of
vacuum is 1000 times more than that of any medium.
These breakers are used for reactor switching, transformer
switching, capacitor bank switching where the voltages are high
and the current to be interrupted is low.
SF6 Circuit Breaker:
SF6 gas has unique properties such as very high dielectric strength, non-reactive to the other
components of circuit breakers, high time constant and fast recombination property after
removal of the source energizing the spark, which proves it superior to the other mediums
(such as oil or air) for use in circuit breakers .SF6 circuit breakers have the advantages of very
much reduced electrical clearances, performance independent of ambient conditions, noise
less operation, reduce moisture problem, minimum current chopping, small arcing time, no
reduction in dielectric strength of SF6, low
maintenance, reduced installation time and increased
safety.
Specifications of 33kV SF6 Circuit Breaker:
 Rated Voltage: 36kV
 Rated Current: 1250A
 Normal Gas Pressure: 5kg/cm2 at 20oC
 Short Circuit breaking current: 25kA
 Current withstand duration: 25kA for 3sec
Figure 24: Vacuum Circuit Breaker
Figure 25: Operating Mechanism of SF6 Circuit Breaker Figure 26: SF6 Circuit Breaker

21. Page | 20
Figure 28: Main and Transfer Bus Arrangement
Isolators:
An isolator is used to ensure that an electrical circuit is completely de-energized for service
or maintenance. Unlike load switches and circuit breakers, isolators lack a mechanism for
suppression of electric arc. The main difference between a circuit breaker and isolator is that
a circuit breaker is on load device and is triggered by electromechanical mechanisms. An
isolator on the other hand is an off load device and is operated manually.
Bus Bar :
Bus bar is the main current carrying conductor in a power system. The bus is a line in which
the incoming feeders come into and get into the instruments for further step up or step down.
It is generally made of aluminum or copper bars.
There are many different electrical bus system schemes available but selection of a particular
scheme depends upon the system voltage, position of substation in electrical power system,
flexibility needed in system and cost to be expensed.
The most frequently used arrangement is Main Bus and Transfer Bus Arrangement. This
arrangement consists of two bus-bars, main bus and transfer bus. Each generator and feeder
can be connected to either bus bar with the help of Bus Coupler. Bus coupler allows change
from one bus to another under load conditions.
Figure 27: Electrical Isolator

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Distribution Feeder:
Distribution feeder circuits are the connections between the output terminals of a distribution
substation and the input terminals of primary circuits.
The distribution feeder circuit conductors leave the
substation from a circuit breaker or circuit reclose via
underground cables, called substation exit cables.
Several distribution feeder circuits can leave a
substation extending in different directions to serve
customers. The underground cables are connected to
the primary circuit via a nearby riser pole.
Distribution feeders emanating from a substation are
generally controlled by a circuit breaker which will
open when a fault is detected.
Control Panel:
Control and Relay panel is most important equipment of the substation as it work as shield
guard for all substation equipments and electrical network. Moreover, these panels are useful
to control the flow of electricity as per the load demand and detect the faults in power
systems. In this panel, varieties of numerical and electromechanical relays are installed to
provide damage protection to equipments. Meters, Control Switches, Indicating lamps, Push
Buttons, Annunciators and Relays are among of major equipments installed as per designing
requirements.
Energy
Meter
Digital
Relay
Metering
Instrument
s
Hooter
Annunciator
Indicators
Feeder Knob Bus
Coupler
Knob
Figure 29: 3Φ Feeder Bay
Figure 30: Section of a Control Panel

23. Page | 22
 Capacitor Bank:
A capacitor bank is a grouping of several identical capacitors inter-connected in parallel or in
series with one another as required.
Since most of the loads are inductive, there is a net absorption of reactive power. The ratio of
active and reactive power is known as Power factor. Hence the power factor of the power
system reduces which is uneconomical. To compensate this reactive power, capacitor banks
are connected. The capacitors deliver the reactive power required by the inductive loads.
Lightning Arrester:
It is a device used in Electrical Power systems
to protect the insulation of the system from the
damaging effect of lightning. The typical
lightning arrestor is also known surge arrestor
has a high voltage terminal and a ground
terminal. When a lightning surge or switching
surge travels down the power system to the
arrestor, the current from the surge is diverted
around the protected insulation in most
cases to earth.
Lightning arrestors with earth switch are used
after the current transformers to protect it
from lightning i.e. from high voltage entering
into it. This lightning arrestor has an earth
switch that can directly earth the lightning.
The arrestor works at 30o to 45o angle of the
lightning making a cone. The earth switch
can be operated manually, by pulling
the switch towards the ground. This also helps
in breaking the line entering the station. By
doing so maintenance repair of any instrument
could be performed.
Batteries:
The operation of automatic control systems, protective relays and emergency lighting circuits
is supplied by station batteries. Lead-acid batteries are most commonly used in substations
because of their high cell voltage and low cost.
Figure 31: Lightning Arrester attached to pole

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SECONDARY DISTRIBUTION SYSTEM
In secondary distribution system, electrical power is delivered to the consumers either at
415V (three Φ) or 220V (single Φ). Three Φ power at 415V is consumed for industrial use
where the machine loads are mostly three Φ induction motors. 220V single Φ power is
supplied to domestic consumers.
 Each 11kV feeder which emanates from the 33kV substation branches further into
several subsidiary 11kV feeders to carry power close to the load points (localities,
industrial areas, villages, etc.,).
 At these load points, a transformer further reduces the voltage from 11kV to 415V to
provide the last-mile connection through 415V feeders (also called as Low Tension
(LT) feeders) to individual customers, either at 240V (as single-Φ supply) or at 415V
(as three-Φ supply).
 A feeder could be either an overhead line or an underground cable. In urban areas,
owing to the density of customers, the length of an 11kV feeder is generally up to 3
km. On the other hand, in rural areas, the feeder length is much larger (up to 20 km).
A 415V feeder should normally be restricted to about 0.5-1.0 km.
Figure 32: Transmission and Distribution systemshowing respective voltages

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A 3 Φ 3 wire distribution system consists of three wires (R, Y, and B) whereas in 3 Φ 4 wire
system, an additional neutral wire is present.
 When a 3 Φ 415V load is needed to be connected, three wires from three Φ s are
tapped in order to provide a 3 Φ supply to the load.
 When a Single Φ 220V load is needed to be connected, we connect the load between
any of the Φ s and the neutral wire.
The wire connecting the single Φ load with any one of the Φ s of the three Φ supply (either R,
Y or B) is called Live wire. The Neutral wire is connected to the neutral of the three Φ
supply. The earth wire is connected to the earthing or gounding system at the consumer end.
This type of A.C distribution system is called Single Φ Three Wire Distribution.
t
Figure 33: Connection of 3Φ and 1Φ Loads in 3Φ 4 Wire System
Figure 34: 1Φ 3 Wire System showing Live, Neutral and Earth Connections

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Overhead Distribution:
Overhead distribution system is much cheaper as compared to underground distribution as
insulator is not present throughout the entire length of the conductor. However it is more
prone to short circuit faults due to falling of tree branches.
Overhead lines are erected over utility poles made of reinforced concrete, steel or wood. The
distribution lines are connected to the poles using ceramic insulators to prevent conduction
with the metallic poles. Distribution transformers are mounted on utility poles which steps
down the voltage level to 415V or 220V.
Underground Distribution:
Underground distribution system is used in populated areas. Electrical power is distributed
using underground cables. This method is costly as insulator is present throughout the length
of conductor. Underground cables are less porn to short circuit faults, but more porn to open
circuit faults as heat dissipating ability is reduced under the
ground.
Figure 35: Utility Pole and components used in Overhead Distribution
Figure 36: Distribution System at
Consumer's End
Figure 37: Underground Distribution System
Figure 38: Cross-section of Single Core Cable

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COMMERCIAL VIEW
The rate at which electrical energy is supplied to a consumer is known as tariff. Like other
commodities, electrical energy is also sold at such a rate so that it not only returns the cost
but also earns reasonable profit. Therefore, a tariff should include the following items:
 Recovery of cost of producing electrical energy at the power station.
 Recovery of cost on the capital investment in transmission and distribution systems.
 Recovery of cost of operation and maintenance of supply of electrical energy e.g.,
metering equipment, billing etc.
Normally the tariff of electricity is mentioned in rate per kilowatt hour of power consumed or
rate per kWh. 1 kWh refers to the amount of electricity consumed when an appliance of one
kilowatt power rating runs for one full hour or sixty minutes. 1 kWh is also known as one
unit of electricity.
Types of Tariff:
 Simple tariff: When there is a fixed rate per unit of energy consumed, it is called
simple tariff or uniform ate tariff. WBSEDCL doesn't provide this type of tariff.
 Block Rate Tariff: When a given block of energy is charged at a specified rate and the
succeeding blocks of energy are changed at a progressively reduced rate.
 Two Part Tariff: When the rate of electrical energy is charged on the basis of
maximum demand of the consumer and the units consumed.
 Flat Rate Tariff: When different types of consumers are charged at different uniform
per unit rates
Energy Meter:
An energy meter or Watt-hour Meter is a device that measures the amount of electric energy
consumed by a residence, a business, or an electrically powered device. Electric utilities use
electric meters installed at customers' premises to measure electric energy delivered to their
customers for billing purposes. They are typically calibrated in billing units, the most
common one being the kilowatt hour (kWh). They are read once each billing period.
These may be single or three Φ meters depending on the supply utilized by domestic or
commercial installations. For small service measurements like domestic customers, these can
be directly connected between line and load. But for larger loads, step down current
transformers must be placed to isolate energy meters from higher currents.
 Calculationof Units Consumed
Let an electric appliance rated at 75W is used for 4hours a day. Then:
Electricity consumed in one day = 75 x 4 = 300 watt hours.
Electricity consumed in one month = 300 x 30 = 9000 watt hours = 9kWh = 9 units.

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Types of EnergyMeters:
 Electromechanical Type: It is the most conventional type of energy meter. It is made
up of a rotating aluminum disc placed between two electromagnets. The Series
electromagnets is powered by the load current and the Shunt electromagnet by a
current proportional to the load voltage .Series magnet produces the flux which is
proportional to the current flowing and shunt magnet produces the flux proportional to
the voltage. These two fluxes lag by 90 degrees due to inductive nature. The
interaction of these two fields produces eddy current in the disk, exerting a torque,
which is proportional to product of instantaneous voltage, current and Φ angle
between them.
 Electronic Type: These are of accurate, high procession and reliable types of
measuring instruments as compared to conventional mechanical meters. It consumes
less power and starts measuring instantaneously when connected to load. These
meters might be analog or digital. In analog meters, power is converted to
proportional frequency or pulse rate and it is integrated by counters placed inside it. In
digital electric meter power is directly measured by high end processor. The power
is integrated by logic circuits to get the energy
and also for testing and calibration purpose.
Load Curve:
A load curves is a chart showing the
amount of electrical energy customers'
use over the course of time. Power
producers use this information to plan
how much electricity they will need to
make available at any given time.
Figure 39: Electromechanical Energy Meter
Figure 40: Constructionalfeatures of Electromechanical
Energy Meter
Figure 41: Daily Load Curve

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CONCLUSION
The vocational training had been conducted in a very efficient way. I have
acquired thorough knowledge about the power distribution system, the
equipment in an electrical sub-station and a proper knowledge about the
working and construction of each one of them.
The Human Resource Development Department of WBSEDCL had assigned
me the opportunity to carry out this training under the well experienced
engineers working at Serampore Division of WBSEDCL. Despite a huge
demand of power throughout the year and a heavy work pressure, the machines
and instruments at the substations are properly functional due to proper
maintenance and skillful handling. I was able to acquire practical knowledge
about some theoretical engineering topics.
This report covers a brief overview of primary distribution system, secondary
distribution system, working and objective of equipments installed in a sub-
station and the process ofmeasuring energy and charging tariff.

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BIBLIOGRAPHY
 List of Websites:
 www.wbsedcl.in
 www.powermin.nic.in
 www.iitk.ac.in
 www.GEMultilin.com
 www.electrical4u.com
 www.wikipedia.org
 List of Books:
 Power System Engineering by Nagrath and Kothari
 A Course in Power System by J.B Gupta
 Electrical Machinery by Dr. P.S. Bimbhra
 Electric Power Substations Engineering by John D. Mc Donald