5 power house
TRANSCRIPT
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INTRODUCTION
A substation is a part of an electrical generation,
transmission and distribution system. Substation transforms
voltage from high to low or reverse or any of 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 increases the
voltage while decreasing the current, while a step down
transformer decreases the voltage while increases the current
for domestic and commercial distribution. The word substation
comes from the day before the distribution system became a
grid. The first substations where connected to only one power
station, where the generations were house and were
substations of the power station.
In ‘SEALDAH POWER HOUSE’, the control is divided into
two sections. They are –
The Low Transmissions Sections
The High Transmissions Sections
The main components of Power House are-
Transformers (300KVA & 500KVA)
Circuit Breaker (ACB, VCB & OCB) o ACB- Air Circuit Breaker (Used in low Transmission Section
o VCB- Vacuum Circuit Breaker (Used in High Transmission
Section)
o OCB- Oil Circuit Breaker
Relays (EFR & OCR) o EFR- Earth Fault Relay
o OCR- Over Current Relay
Bus Coupler
Hooter / Alarm
Isolators (P.F= 1 Substation)
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The components are describe in brief from the Power House
Below-
TRANSFORMER-
A transformer is a device that transfers electrical energy from
one circuit to another circuit through inductively coupled
conductors. The transformer coli is 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 proportional 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 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
windings are coils would
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around a ferromagnetic core, air-core transformers being a
notable exception.
In SEALDAH POWER HOUSE two transformers are used, one
300KVA and another one is 500KVA transformer is kept for
backup.
THE 500 KVA TRANSFORMER SPECIFICATION-
1 C Serial No. 1581/D7-D8
2 Makers Name Automatic Electro Group
3 KVA 500 KVA
4 Voltage at No Load H.V- 600 V & L.V- 115 V
5 Amperes H.V- 18.11 A & L.V- 695.62 A
6 Phases H.V-3 & L.V- 3
7 Type of Cooling Oil Natural Cooling
8 Frequency 50 C/S
9 Impedance Voltage 4.37%
10 Vector group REF DY11
11 Core & Wedges 1140 KG
12 Weight of Oil 451 KG
13 Total Weight 2015 Kg
14 Oil Amount 530 liters
15 Maximum Temperature of Oil 450
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CIRCUIT BREAKER-
A circuit breaker is an automatically operated electrical switch
designed to protect an electrical circuit from damage caused
by overload short circuit. Its basic function is to detect a fault
condition and interrupt current flow. Unlike a fuse, which
operates once and then must be replaced, a circuit breaker
can be reset (either manually or automatically) to resume
normal operation. Circuit breakers are made in varying sizes,
from small devices that protect an individual household
appliance up to large switchgear designed to protect high
voltage circuits feeding an entire city or Substation or
Powerhouse.
CLASSIFICATION OF CIRCUIT BREAKERS-
There are quite a few ways to classify the circuit breakers.
However, the most general ay of classification is based on
medium used for the arc extinction. Other bases for the
classification of circuit breakers are summarized in the
flow-
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1. BASED ON VOLTAGE-
Based on the voltage levels for which they are used,
the circuit breakers are classified as listed in table
(with corresponding voltage ranges of use)
Category Range of Voltage
Low Voltage Less than 1KV
Medium Voltage 1KV to 52 KV
High/ Extra High Voltage 66 KV to 765 KV
Ultra High Voltage Above 765 KV
2. BASED ON LOCATION -
Circuit breakers are based upon where they are
located, classified as, indoor and outdoor types.
Medium and low voltage breakers are categorized as
Indoor breakers, whereas the circuit breakers, which
have, air as external insulating medium are classified
as outdoor circuit breakers.
3. BASED ON EXYERNAL DESIGNED-
Outdoor circuit breakers can be identified as either
dead tank or live tank type circuit breakers, from the
point of view of their physical structural design. In the
dead tank circuit breakers, the switching device is
located with suitable insulator supports, inside a
metallic vessel at ground potential and filled with
insulating medium. In dead tank circuit breakers, the
incoming and outgoing conductors are taken out
through suitable insulator bushing, and low voltage
type current transformers are located at lower end of
both insulator bushing, i.e. at the line side and the load
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side. In live tank circuit breakers, the interrupter is
located in an insulator bushing, at potential above
ground potential. The live tank circuit breakers are
cheaper (with no current transformer), and require less
mounting space.
4. BASED ON INTERRUPTING MEDIA-
The interrupting media has been a vital factor in the
evolution of circuit breakers. It dedicates the overall
design parameters of the breaker. The choice of air
and oil, as the interrupting media, was predominant till
late 70s. However, today, vacuum and SF6 are the
only dominant interrupting technologies, for medium
and high voltage segments of circuit breaker design
respectively. The medium used for the arc extinction
can be-
Oil.
Air.
Vacuum.
Sulphur Hexafluoride (SF6).
Accordingly, the circuit breakers may be classified into
following categories (which will be treated in detail in
the present report):
Oil Circuit Breakers.
Air-Blast Circuit Breakers.
Sulphur Hexafluoride (SF6) Circuit Breakers.
Vacuum Circuit Breakers.
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In this Powerhouse, they are used three types of
Circuit Breakers. They are-
a) ACB- Air Circuit Breaker
b) VCB- Vacuum Circuit Breaker
c) OCB- Oil Circuit Breaker
ACB (AIR CIRCUIT BREAKER)-
These circuit breakers employ a high-pressure air-blast as
an arc-quenching medium. The contacts are opened in a flow
of air-blast established by the opening of the blast valve. The
air-blast sweeps away the arcing products of the
atmosphere. Consequently, the arc is extinguished and flow
of current is interrupted. Whenever current at high voltages
needs to be interrupted, more breaking units are used, in
series. Dry and clean air supply is one of the most essential
requirements forth operation of the Air Circuit Breakers.
In addition, other gases such as nitrogen, carbon dioxide,
and Hydrogen can also be used. However, air is preferred
because of the fact that the carbon dioxide tends to freeze,
and the hydrogen gas is very explosive. This type of circuit
breaker has been used earlier for open terminal 11KV
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applications, for voltages of
245KV and 400Kv up to 765
KV, especially where faster
breaker operation was
required. This type of breaker
has been used for special
applications where several
super thermal power stations
located in close vicinity to
each other have been inter-
connected. These one-cycle
breakers from the inter-
connecting link which, in the
event of a fault level for the feeder breaker.
The interrupting capability of air circuit breaker is increased
by increasing the normal pressure range. Normally, the
pressure level is around 30 to 35 bars. In order to maintain
the insulation level and reliability of operation, it is also
necessary for the condition of the air to be very dry. Currently,
however, SF6 circuit breakers have practically eliminated the
use of this technology.
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ADVANTAGES-
1. The risk of fire is eliminated in these circuit breakers.
2. The arcing products are completely removed by the blast
whereas the oil deteriorates with successive operations.
So the expenditure of oil replacement is avoided in air-
blast circuit breakers.
3. The size of these breakers is reduced, as the dielectric
strength grows so rapidly that final contact gap for the arc
extinction is very small.
4. Due to the rapid growth of the dielectric strength, the
arcing time is also very small. It causes less burning of
oil. The arc energy is also very small fraction of that in oil
circuit breakers.
5. The arc extinction is facilitate by the high-pressure air and
is independent of the fault current to be interrupted.
DISADVANTAGES-
1. These circuit breakers are very sensitive to variations in
the rate of rise of restriction voltage.
2. The compressor plant that needs considerable
maintenance supplies the air-blast.
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THE AIR CIRCUIT BREAKER SPECIFICATION
(Specification based on one sample on Low
Transmission Panel)-
Makers Name Pulsar
Frame LH800 DMIT3P
SL. No. Y606183
IIEC-947.2 IS: 3947 (Part 2)
Utilization Category 8
Rated Characteristics
IN 400A
ITH @ 400 C 800A
ICS & ICU 50k
ICW 50KA, 1 Sec
Power Factor 0.25
UI=1000v UE=4.15v Frequency = 50/60HZ
U/V 40VCA
VCB (VACUUM CIRCUIT BREAKER)-
In such circuit breakers,
the vacuum is used as
the arc-quenching
medium. The vacuum
circuit breaker takes the
advantage of non-
sustainability of electric
arc in vacuum, and
employs the principle of
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contact separation under
vacuum where there is no
ionization due to medium.
The initial arc caused by
field and thermionic
emission during the contacts
ionization because of
vacuum. The degree of
vacuum in these circuit
breakers is in the range from
10-7 to 10-5 torr. Since
vacuum offers the highest
insulating strength, it has far
superior arc –quenching
properties than any other
medium. When the contacts
in the vacuum circuit breakers are opened in vacuum, an arc
is produced between the contacts by the ionization of metal
vapors of contact. However, the arc is quickly extinguished
because the metallic vapors, electrons and ions produced
during arc rapidly condense on the surface of the circuit
breaker contacts.
CONSTRUCTION-
The vacuum circuit breaker
consists of fixed contact, moving
contact and arc shied mounted
inside the vacuum chamber. The
movable member is connected to
the control mechanism by
stainless steel bellows. This
enables the permanent sealing of
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the vacuum chamber to eliminate the possibility of leak. A
glass vessel or ceramic Bessel is used as the outer insulating
body. The arc shield prevents the deterioration of the internal
dielectric strength by preventing metallic vapors falling on the
inside surface of the outer insulating cover.
APPLICATONS-
For a country, where distances are quite long and
accessibility to remote areas is difficult, the installation of
such outdoor, maintenance-free circuit breakers should
prove definite advantage. Vacuum circuit breakers are being
employed for outdoor applications ranging from 22kv to 66kv.
This technology has been found to be most suitable for
medium voltage application though the experimental
interrupters for the 72.5kv and 145kv have been developed,
they were not found to be commercially viable.
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ADVANTAGES-
1. Vacuum circuit breakers are compact in size and have
longer lives.
2. Operating energy requirements are low, because the
mechanism must move only relatively small masses at
moderate speed, over very short distances.
3. Because of the very low voltage across the metal vapor
arc, energy is very low. (arc voltage is between 50v to
100 v)
4. Due to the very low arc energy, the rapid movement of
the arc root over the contact and to the fact that most of
the metal vapor re-condenses on the contact, contact
erosion is extremely small.
5. There is no generation of gases during and after the
circuit breaker operation.
6. The outstanding feature of these breakers is that it can
break any heavy fault current perfectly just before the
contacts reach a definite open position.
7. They can withstand lighting surges.
8. It is now possible to produce cost-effective VI (Vacuum
Interrupter) designs with electrical lives that exceed the
required mechanical life of the circuit breakers, and that
will even be able to satisfy a recent requirement of
extended short-circuit operating life.
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THE VACUUM CIRCUIT BREAKER SPECIFICATION-
TYPE VBBA
SL. NO. VBBA-4742
Year of Manufacture 2006
Specification IS> 1881
Rated Voltage 7.2 KV
I/L 20/60 KV
Rated Current 800 AMPS
Frequency 50 HZ
Making Capacity 62.5 AMPS
STC 25 KA
OCB (OIL CIRCUIT BREAKER)-
In such circuit breakers, some insulating
oil (i.e. transformer oil) is used as an
arc-quenching medium. The contacts
are opened under oil and an arc is
struck between them. The heat of the
arc evaporates the surrounding oil and
dissociates it into a substantial volume
of hydrogen gas at a high pressure. This
large volume of the hydrogen gas
pushes the oil away from the arc. In an
oil circuit breaker, the arc quenching
process is entirely dependent on arc
energy generated. The arc drawn
across the contacts is contained inside
the interrupting pot, and this the
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hydrogen gas formed by the vaporized oil (gas) is also
contained inside the chamber. As the contacts continue to
move and the moving contact rod separates itself from the
orifice of the chamber, an exit similar to a nozzle allows
escape of the hydrogen gas trapped inside the interrupting
chamber. The escaping high-pressure hydrogen gas, having
a high thermal conductivity, takes away the heat, thus making
the contact gap cool and free from ionization, immediately
after current zero. However, the oil breakers have prolonged
arcing times, due to insufficient vapor pressure generated at
lower interrupting currents. Periodic monitoring of the oil
dielectric conduction and its maintenance is important for the
effective operation of medium oil circuit breaker. However,
maintenance required for oil circuit breakers is of low
technology.
Mainly two processes facilitate the arc extinction:
1. Firstly, the hydrogen gas has high heat conductivity and
cools the arc, thus aiding the de-ionization of the medium
between the contacts.
2. Secondly, the gas sets up turbulence in the oil and forces
it into the space between contacts, thus eliminating the
arcing products from the arc path. This results in
extinguishing the arc and as a result, the circuit current is
interrupted.
ADVANTAGES-
As an arc-extinguishing medium oil has the following
advantages-
1. Oil absorbs the arc energy to produces hydrogen gas
during arcing. The hydrogen has excellent cooling
properties and helps extinguish the arc. (In addition to
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hydrogen gas, a small proportion of methane, ethylene,
and acetylene arc also generated in oil decomposition.)
2. The oil provides insulation for the live exposed contacts
from the earthed portions of the container.
3. Oil provides insulation between the contacts after the arc
have been extinguished.
4. The oil close to the arc region provides cooling surface.
DIS ADVANTAGE-
1. Oil is inflammable and may cause fire hazards. When a
defective circuit breaker fails under pressure, it may
cause an explosion.
2. The hydrogen generated during arcing, when combined
with air, may form an explosive mixture. During arcing, oil
decomposes and becomes polluted by carbon particles,
which reduces strength. Hence, it requires periodic
maintenance and replacement.
TYPES OF OIL CIRCUIT BREAKERS:
The oil circuit breakers find extensive use in the power
system. They can be classified with the reverence to the
quantity of oil used. The types are:
a. Bulk Oil Circuit Breakers
b. Minimum Oil Circuit Breakers
a. BULK OIL CIRCUIT BREAKERS-
These circuit breakers use a large quantity of oil. The oil has
to serve two purposes:
1. It extinguishes the arc during opening of contacts.
2. It insulates the current conducting parts from one another
and from the earthed tank.
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In the bulk oil circuit breakers, the interrupting unit is placed in
a tank of oil at earth potential and the incoming and outgoing
conductors are connected through insulator bushings.
b. MINIMUM OIL CIRCUIT BREAKERS-
These circuit breakers use a small quantity of oil. In such circuit
breakers, oil is used only for arc extinction; the current
conducting parts insulated by air or porcelain or organic
insulating material. In these circuit breakers, the oil requirement
can be minimized by placing the interrupting units, in insulating
chambers at live potential, on an insulator column.
THE OIL CIRCUIT BREAKER SPECIFICATION
(BASED ON ONE SAMPLE ON L.T. PANEL ON 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 %
C.T. Ratio 800/5
RELAY-
A relay is an electromagnetic switch. In other words, it is
activated when a current is applied to it. Normally a relay is
used in a circuit as a type of switch. There are different types
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of relays and they operate at different voltages. When we build
our circuit we must be need to consider the voltage that will
trigger it.
In SEALDAH POWER HOUSE, they are used two types of
relay. They are:
a) Over Current Relay.
b) Earth Fault Relay.
a) OVER CURRENT RELAY-
The name ‘over current relay’ implies that this is a special type
of protection, which is used to protect the costly apparatus from
the effect of huge current flow. Over current relays are those
relays, which operate during the excess current flow through
the network, and trips the circuit of circuit breaker, which
isolates the faulty part of the network from the healthy part.
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Now depending upon the time of operating time, over current
relays are divided in-
1. INSTANTANEOUS OVER CURRENT RELAY-
As the name suggests this relay takes no intentional time to act
or close the contacts of circuit breaker. The operating time of
such relay is approximately 0.1 sec.
2. INVERSE TIME CURRENT RELAY-
This type of relay operating time reduces as the actuating
quantity i.e. the amount of current flow increases. It means
that, for severe fault the operating time of the relay will be less
and for minor fault the operating time will be more.
3. INVERSE DEFINITE MINIMUM TIME OVER CURRENT
RELAY (IDMT)-
In this type of relay, the operation and operating time is similar
to inverse time over current relay near the pickup value but it
becomes almost constantly increases.
4. VERY INVERSE RELAYS-
As the name suggests, in this type of relay, the saturation of
the core occurs at a later stage and it has inverse
characteristics.
5. EXTREMELY INVERSE RELAY-
The slope of time current graph is more than in very inverse
over current relay and for this, the saturation of the core occurs
at later stage.
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OVER CURRENT RELAY SPECIFICATION -
Model No. CDG31EG001SBCH
Serial No. 130954160621011
C.T. Sec 5amps; 2.5-10 Amps
Frequency 50 HZ
b) EARTH FAULT RELAY-
Backup protection of electrical transformer is simple Over
Current and Earth Fault
protection applied against
external short circuit and
excessive over loads. These
over current and earth Fault
relays may be of Inverse
Definite Minimum Time (IDMT)
or Definite Time type relays.
Generally, IDMT relays are
connected to the in-feed side of the transformer.
The over current relays cannot distinguish between external
short circuit, over load and internal faults of the transformer. For
any of the above fault, backup protection i.e. over current and
earth fault protection connected to in-feed side of the
transformer will operate. Backup protection is although
generally installed at in feed side of the transformer, but it
should trip both the primary and secondary circuit breakers of
the transformer.
Over Current and Earth Fault protection relays may be provided
in load side of the transformer too, but it should not inter trip the
primary side Circuit Breaker like the case of backup protection
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at in feed side. Primarily current and time setting and the
characteristic curve of the relay govern the operation. To permit
use of over load capacity of the transformer and co-ordination
with other similar relays at about 125 to 150% of full load current
of the transformer but below the minimum short circuit current.
Backup protection of transformer has four elements; three over
current relays connected each in each phase and one earth
fault relay connected to the common point of three over current
relays as shown in the figure. The normal ranges of current
settings available on IDMT over current relays are 50% to 200%
and on earth fault relay 20 to 80%.
Another range of setting on earth fault relay is also available
and may be selected where the earth fault current is restricted
due to insertion of impedance in the neutral grounding. In the
case of transformer, winding with neutral earthed, unrestricted
earth fault protection is obtained by connecting an ordinary
earth fault relay across a neutral current transformer.
The unrestricted over current and earth fault relays should have
proper time lag to co-ordinate with the protective relays of other
circuit to avoid indiscriminate tripping.
EARTH FAULT RELAY SPECIFICATION-
Model No. CDG31EG001SBCH
Serial No. 130954160621011
C.T. Sec 5 Amp ; 1-4 Amps
Frequency 50 Hz
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BUS COUPLER-
Bus coupler is a device, which is used to couple one bus to
the other without any interruption in power supply and without
creating hazardous arcs. Bus coupler is a breaker used to
couple two bus bar in order to perform maintenance on other
circuit breaker associated with those bus bars.
It is achieved with the help of circuit breaker and isolators.
HOOTER/ALARM-
The alarm is employed to the system to indicate the faulty
condition. If any fault occurs in the system components, the
alarm sounds to notify.
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ISOLATOR-
An isolator is a two-port device that
transmits microwave or radio frequency
power in one direction only. It is used to
shield equipment on its input side, from the
effects of conditions on its output side. For
example, to prevent a microwave source
being detuned by a mismatched load.