The document provides information about the power distribution system at Sealdah Power House in Kolkata, India. It describes the key components of the power house including transformers, switchgear, bus bars, isolators, circuit breakers, and protective relays. The power house receives 6KV high voltage from CESC which is stepped down to 415V by transformers before being distributed to Sealdah railway station for lighting, equipment, and facilities. There is also a backup diesel generator at one of the substations in case of outages.

1. 15th
June to 18th
June 2015
Power House

2. 4 PowerHouse
Introduction: A substation is a part of an electrical generation, transmission and
distribution system. Substations transform voltage from high to low
or reverse or 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.
A substation has a step up transformer which increase the voltage while decreasing
the current while a step down transformer decrease the voltage while increasing the
current for domestic and commercial distribution .The word substation comes from
the days before the distribution system became a grid. The first substation were
connected to only one power station, where the generators were housed and were
subsidiaries of that power station.
6 KV. Distribution System in Sealdah Area
Sealdah Power House LT Distribution system

3. 5 PowerHouse
In SEALDAH POWERHOUSEthe control is divided into two sections.
i. The Low Tension section
ii. The High Tension section
 The main components of the Power House :
 Switch Gear
 Transformers (300KVA. & 500 KVA.)
 Isolator
 Bus Bar
 Bus Coupler
 Circuit breakers (Air circuit breakers on L.T. side & vacuumcircuit breakers on
H.T. side)
 Relays (Earth Fault Relay & Over CurrentRelay)
 Hooter / Alarm
The components are described in brief fromthe power housebellow.
 Switch Gear: It is a
combination of electrical
disconnect switches, fuses
and circuit breakers used to
control, protect and isolate
electrical equipment.
This switchgear is
connected to the incoming
supply from CESC. There
are two connections
available (one kept for
emergency). Incoming Switch Gear
The connections are coupled together by a Bus coupler and then sent to the
Transformers for further step down of voltage, as required. If any fault occurs
upstream (i.e., in supply side), this switchgear immediately disconnects from

4. 6 PowerHouse
the supply thereby preventing further spreading of fault and hence keeping
alive the essential railway operations.
 Step down transformer: A transformer is a device that transfers electric
energy from one circuit to another circuit through
inductively coupled conductors---the transformers coil---a varying current in
the first or primary winding creates a varying magnetic flux in the transformer
core and thus a varying magnetic field through the secondary winding. This
varying magnetic field induces a varying electromotive force (EMF) or voltage
in the secondary winding. This effect is called mutual induction.
If a load is connected to the secondary, an electric current will flow in the
secondary winding and electrical energy will be transferred from the primary
circuit through the transformer to the load. In an ideal transformer ,the
induced voltage (Vs) in the secondary winding is proportion to primary voltage
(Vp) and is given by the ratio of the number of turns in the secondary(Ns) to
the number of turns in primary(Np) as follows,
Vs/ Vp = Ns/ Np
By appropriate selection of the ratio of turns, a transformer thus allows an
alternating current voltage to be “stepped up” by making Ns greater than Np
or “stepped down” by making Ns less than Np.
In the vast majority of transformers, the winding are coils wound around a
ferromagnetic core, air-core transformers being a notable exception.
In SEALDAH POWER HOUSE two transformers are used, two 300 KVA and
another 500 KVA.
Two 300 KVA transformers are connected in parallel.
A spare 500 KVA transformer is kept for backup.

5. 7 PowerHouse
300 KVA. Transformer in Sealdah Power House
500 KVA. Transformer in Sealdah Power House

6. 8 PowerHouse
 500 KVA. Transformer ratings :
 Isolator: In electrical engineering, an isolator switch is used to make sure that
an electrical circuit can be completely de-energised for serviceor 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 transformer
and transmission lines for maintenance.
C Serial No. 1581/D7-08
Maker AUTOMATIC ELECTRIC GROUP
KVA. 500 KVA.
Voltage At No Load H.V: 6000 V. ; L.V: 415 V.
Amperes H.V: 48.11 A. ; L.V: 695.62 A.
Phases H.V: 3 ; L.V: 3
Type of cooling Oil Natural Cooling
Frequency 50 C/S
Impedance voltage 4.37 %
Vector Group Ref. Dy11
Core and Wedge 1140 kg.
Weight of oil 451 kg.
Total weight 2105 kg.
Oil amount 530 liters
Maximum temperature rise in oil 45 degree

7. 9 PowerHouse
 Bus Bar: In electrical power distribution, a bus
bar is a metallic strip (or bus) that conducts
electricity within a distribution board or
substation.
Its main purpose is to conduct a substancial
current of electricity and not to function as a
structural member. It is a wide and thick strip of
metal generally copper wich carry high voltage
power. The bus bars are used instead oc wire to
reduce the transmission losses.
Bus Bar in the Control Panel
 Bus coupler: Bus coupler provides electrical
isolation bus by employing coupling
transformers and fault isolation resistors. The
Bus couplers contain two isolation resistors (one
per wire) and an isolation transformer (with a
ratio one to the square root of two). The
purpose of bus coupler is to prevent a short on a
single stub from shorting the main data bus. The
buses of two different voltage levels cannot be
connected in series. So, bus coupler is used to
join the buses of different voltage level.
Bus Coupler
 Protective Relays: A relay is fault sensing device. Many relay use an
electromagnet to operate a switching mechanism mechanically, but other
operating principles are also used. Relays are used where it is necessary to
control a circuit by a low-power signal (with complete electrical isolation
between control and controlled circuit) or where several circuits must be
controlled by one.

8. 10 PowerHouse
The first relays were used in long distance telegraph circuits, repeating the
signal coming from one circuit and re-transmitting it to another. Relays were
extensively used in telephone exchanges and early computers to perform
logical operations.
A type of relay that can handle the high
power required to directly control an
electric motor is called a conductor. Solid-
state relays control power circuits with no
moving parts, instead using a
semiconductor device to perform
switching. Relays with calibrated operating
characteristics and sometimes multiple
operating coils are used to protect
electrical circuits fromoverload or faults; in
modern electric power systems these
functions are performed by digital
instruments still called ‘Protective Relays’.
Protective Relay
The Relays used in Sealdah Power Houseare of mainly two types,
 Over CurrentRelay
 Earth Fault Relay
 The Relay specification (Based on one sample on HT. panel):
Over Current Relay Earth Fault Relay
Model No. CDG31EG001SBCH Model No. CDG31EG001SBCH
Serial no. - 130954160621011 Serial no. - 130954160621011
C.T. SEC : 5 AMPS;2.5-10 Amps. C.T. SEC : 5 AMPS;1-4 Amps.
Frequency : 50 Hz. Frequency : 50 Hz.

9. 11 PowerHouse
 Oil Circuit Breaker (O.C.B.): The oil in OCB’s serves two purposes. It
insulates between the phases and the ground, and it provides the medium for
the extinguishing of arc. When electric arc is drawn under oil, the arc vaporises
the oil and creates a large bubble that surrounds the arc. The gas inside the
bubble is around 80%hydrogen, which impairs ionisation. The decomposition
of oil into gas requires energy that comes from the heat generated by the arc.
The oil surrounding the bubble conducts the heat away from the arc and thus
also contributes to deionisation of the arc.
Oil Circuit Breaker
 The Oil Circuit Breaker specification (Based on one sample on the LT.
panel of 1 no. PF. Substation):
Sl. No. 2K2132
Type HN2T
Normal current 400 A.
Service voltage 415 V.
Design frequency 50 Hz.
Breaking capacity 25 MVA.
Trip coil rating 5 A.
Calibration 100/200 %

10. 12 PowerHouse
C.T. ratio 800/5
 Air Circuit Breaker (A.C.B.): The working principle of this breaker is rather
different from those in any other types of circuit breakers. The main aim of all
kind of circuit breaker is to prevent the reestablishment of arcing after current
zero by creating a situation where in the contact gap will withstand the system
recovery voltage. The air circuit breaker does the same but in different
manner. For interrupting arc it creates an arc voltage in excess of the supply
voltage. Arc voltage is defined as the minimum voltage required maintaining
the arc. This circuit breaker increases the arc voltage by mainly three different
ways,
i. It may increase the arc
voltage by cooling the arc
plasma. As the
temperature of arc plasma
is decreased, the mobility
of the particle in arc
plasma is reduced, hence
more voltage gradient is
required to maintain the
arc.
ii. It may increase the arc
voltage by lengthening the
arc path. As the length of
arc path is increased, the
resistance of the path is
increased, and hence to
maintain the same arc
current more voltage is
required to be applied
across the arc path. That
means arc voltage is
increased.
iii. Splitting up the arc into a
number of series arcs also
increases the arc voltage. Various internal parts of an Air Circuit Breaker

11. 13 PowerHouse
 The Air Circuit Breaker specification (Based on one sample on LT.
panel):
 Rated Characteristics:
 Substation of PF. No. 1: The 6 KV. high voltage is transmitted to the 1 no.
platform of Sealdah rail station from the power house and stepped down to
415 v. (Phase to phase) by a 300 KVA. transformer situated in the substation.
The 415 V. supply is then distributed to the entire Sealdah station, all the
platforms, the offices, ticket counters, train boards, digital clock,
announcement speakers and all of the lights and fans of Sealdah Main and
South both sections are run by this supply.
 The Diesel Engine-Alternator arrangement situated at substation of PF.
No. 1:
There is a diesel engine coupled with a alternator in the 1 no. platform
substation for delivering power when main power is not available means at the
Maker PULSER
Frame LH800 DM1T3P
Sl. No. Y606183
IEC-947-2 IS:13947 (PART-2)
Utilization category 8
In 400A.
ITH @40 degree C. 800A.
ICS & ICU 50 Ka.
ICW 50 Ka., 1sec.
Power Factor 0.25
Ui=1000VUe=415V Frequency : 50/60HZ
U/V 40 AC

12. 14 PowerHouse
time of load shading. This alternator produce 3 phase 415 V and make run the
essential systems of Sealdah Station at the time of load shading.
The Diesel Engine and Alternator arrangement at PF. No. 1 Substation

13. 15 PowerHouse