Technogeeeki

a brief overview of
132kv sub-
station/grid-
station
3 years ago
technogeeeki

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a short overview of a
typical grid station is
given, i hope it will help,
and will build an idea
how these substations
work .

Grid Station
Substation is an
assembly of apparatus,
which transform the
characteristics of
electrical energy from
one form to another, say
from one voltage level to
another level, hence a
substation is an
Intermediate link
between the Generating
station and consumers.
The most important part
of electric power system
is the Grid Station. A
132kv Grid Station is that
part of power system
where high voltage of
132kv is received, stepped
down to 11kv and then
given to di erent feeders
that feed distribution
lines. This whole process
is carried out by di erent
parts and equipment.

Parts of Grid
Station:
The main parts of the
grid station are the switch
yard, 11kv control room,
132kv control room,
battery room. All of them
are discussed below one
by one along with their
respective switching,
protection and control
equipment.
1. Switch yard
Switch yard is divided
into three parts i.e. line
bay, bus bar and
transformer bay.

Line bay:

Line bay consists of

Wave trap:    it traps the

waves associated with
132kv line, which are
used for communication
purposes.
Isolator:    an isolator is
installed which isolates
the grid from the line.
Isolators are “no load”
switches and are
operated under no-load
conditions. Its operating
under load condition is
very dangerous as
disconnecting high
voltages will create a
large ash.
Earth switch:    an earth
switch is also installed
with the isolator, with
the help of which we
ground any static charges
before
working/maintenance.
 Line Circuit breaker:    a
high rating SF6 C/B is

installed which operates

automatically under
abnormal conditions and
disconnect the grid from
the line to avoid any
damages. It can also be
operated manually and
unlike isolators the can
be operated under load
conditions as they have
quenching media in
them.
Line CT:    after circuit
breaker a current
transformer is installed
which calculates current
and give indication to the
C/B when over current
fault occurs hence acts as
a protective device as
well as measuring device.
Its CT ratio is generally
600/5A.
Isolator:    again an
isolator is installed.

Bus bar:

After line bay it comes

132kv bus bar. It acts as a
node point between line
bay and transformer bay.
Bus bar helps in getting
connections to several
units (transformers)
from a single 132kv line.
It can be used for
incoming connections as
well as outgoing ones.

PT:    A potential
transformer is also
connected in parallel to
132kv bus bar through an
isolator, which measures
voltage as well as give
indication to over voltage
relay under over voltage
conditions.
Transformer bay:

Transformer bay consists

of

Transformer Isolator:  
after bus bar another
isolator is used which
isolates transformer
from the line. Operating
it in ON load condition is
very dangerous as high
voltages produce arc
while
connecting/disconnectin
g and they don’t have any
quenching media.
CT:    again a current
transformer is installed
which calculates current
and give indication to the
transformer C/B when
over current fault occurs
hence acts as a protective
device as well as
measuring device. Its CT
ratio is generally 200/5A.
Transformer Circuit
breaker:    again an SF6

circuit breaker is
installed which operates
automatically under
abnormal conditions and
disconnect transformer
from the bus bar to avoid
any damages. It can also
be operated manually
and unlike isolators the
can be operated under
load conditions as they
have quenching media in
them.
Lightning arrester
(132kv):    lightning
arresters are devices
which arrests and ground
any thunder storms
falling on the power
transformer and secure it
from any harm. They are
installed on each phase at
a relatively more height.
They are grounded and
have a non-linear
resistor which act as
insulator for132kv
voltage and as a
conductor for higher
voltages like that of
thunder storms and
lightning bolts. In this
way they ground these
high voltages and
provide safety to the
transformer and whole
system.
Power transformer:    then
the power transformer is
installed which steps
down 132kv to 11kv.
(power transformer is
discussed in detail in the
next section)
Lightning arresters
(11kv):    again on the LT
side of power
transformer small
lightning arresters are
used. And the purpose is
again the safety of
transformer from
thunder lightning.
Cables (11kv):    these
cables give the
transformer output to
the 11kv incoming panel
 of the respective
transformer.

Power transformer

These are the step down

transformers with Delta
circuit con guration on
input side (HT) and Star
circuit con guration on
output side (LT). This
transformer steps down
132Kv to 11Kv. An input of
132kv is given to the
transformer primary coil
through three input
wires i.e. Red(R),
Yellow(Y) and Blue (B)
and then 11kv is taken
from secondary coil. The
transformers use the
magnetic induction
process to step down the
132Kv to 11Kv due to
speci c turn ratio in
coils.

The main parts of a power

transformer are its
windings and bushes.
Some other parts, also
known as accessories are:
Conservator oil:    also
called mineral oil. It
helps in insulation of
windings as well as in
cooling.
Conservator tank:    it is
xed at an upper position
and is lled about 70% to
80% of mineral oil.
Radiator tubes:    the
circulation of
transformer mineral oil
takes place through these
tubes, as heated oil goes
up and cooled oil goes
down, hence continue the
oil circulation for better
cooling.
Cooling fans:    these fans
also help in transformer
cooling. They are tted
below or at the side of
radiator tubes and
provide cool air.
Bucchloz relay:    this relay
is tted near conservator
tank and is also called
oat relay and gas
detecting relay. This
relay detects the gases
that are produced in the
transformer under
abnormal conditions and
operates to trip the
transformer, hence avoid
further damages.
Diaphragm:    diaphragm
is a cap shaped object and
xed on the top of power
transformer, it acts as
emergency exit for
transformer inner oil and
gases.
Wheels: transformer has
small wheels upon which
it can be rolled from one
place to another. As they
hold the transformer at a
height from the ground
or foundation so air ow
is possible beneath
transformer.
Oil temperature indicator:
   this indicator detects
the temperature of
transformer oil. If the
transformer oil get
heated to such a
temperature that can
harm transformer, the oil
temperature indicator
operates. It has two

settings, 1st is alarm and

the other is tripping.
Winding temperature
indicator:    this indicator
supervise winding
temperature. Like oil
 temperature indicator it
also have two settings,
one is alarm and the
other is tripping the
transformer.
Tap changer:    this is an
instrument connected
with the power
transformer that is used
to vary the transformer
output. It actually
changes the number of
turns in the secondary
coil of transformer.
Dehydrating Breather:    it
is a tube on the side of
transformer connected to
conservator tank. It
extracts un-moisture air
from the outside to ll
the vacuum in the tank.
To extract water particles
from the air, silica gel is
used which is lled in the
breather tube. Note that
vacuum is created when
some gases are expelled
through the same tube.

Transformer cooling

When the transformers

operate continuously, as
a result the core, coils,
main tank and the
transformer oil heats up
to a high temperature
which can a ect the
operation, maintenance,
and output voltage of the
transformer. In grid
stations transformers are
kept cool through three
di erent processes. That
are:

1. ONAN:    It stands for oil

natural air natural. In this
method fans are OFF and
the transformer is cooled
by natural air, same is
the case of oil which
circulates by
spontaneous motion of
hot and cold oil.
2. ONAF:    It stands for oil
natural air forced. This
method is applied under
a bit higher temperature.
Oil circulation takes place
by itself while the air is
provided by radiator fans.
3. OFAF:    It stands for oil
forced air forced. This
method is applied under
highest temperatures.
Fans are ON that provide
more air and the
circulation of oil is also
 speedup by oil circulation
pump.

2. 11Kv Room
The outputs of each
power transformer is
than brought into 11Kv
Room through power
cables. The 11Kv room
has incoming panels for
each transformer,
di erent outgoing panels
for each incoming panel
and a bus coupler. All of
them are explained
below.

11kv Incoming Panels:

These panels are tted in

the 11Kv room, receiving
11Kv from each
transformer as each
transformer has its own
incoming panel. The
incoming have a number
of parts like 11Kv C/B, bus
bar, relays and power
meter etc. that are
included in each of the
incoming panel.

11kv Outgoing panels:

The output of incoming
panel is given to several
outgoing panels through
a rigid bus bar. They also
have di erent parts like
current transformer,
vacuum circuit breaker,
relays and di erent
meters and indicators.

Bus bar coupler:

As the name “bus bar

coupler” indicates that it
couples the bus bars of
two incomings. It also
known as bus coupler. It
couples one 11kv bus bar
to another when one of
the transformer is faulty
so that the supply
towards the consumers is
not disturbed. The
advantage is the uniform
(un-interrupted) supply.
It is installed between the
two incoming panels in
the 11kv control room.

It is possible that a
transformer gets
damaged and is out of
work, so to transfer the
load of one transformer
to other in grid station
the bus coupler connects
the incoming of damaged
transformer to the
incoming of the other
working transformer.

3. 132kv control
room
As the name control
room indicates that it is
the room from where the
whole grid is controlled.
Each and every circuit
breaker, current
transformer, potential
transformer, power
transformer and its
accessories, yard
lightning and other
equipment are controlled
from the control room of
the grid station. This
room also has a number
of panels like control
panels, relay panel,
transformer auxiliary
panel, AC DC panel and
recti er/battery charger.
Each of them is discussed
below.
132kv line protection
panel:

This panel is especially

for 132kv line. It consists
of distance relay, over
current and earth fault
relay and DC supervision
relay.

Distance relay:    this relay

shows the zone where
the fault occur as well as
the phase in which occur
i.e. A, B & C.
Over current and earth
fault relay:    this relay
does tripping as well as
shows whether the fault
(over current) was due to
phase to phase short
circuit or phase to
ground one.
DC supervision relay:    DC
supervision relay shows
whether the system
(panel and relays) is
healthy or not.
132kv line control panel:   
This control panel
controls the line bay i.e.
the system from the
tower to the bus bar.

Transformer control
panel:   This panel
 controls the system
inside bus bar.
Transformer CT, PT,
circuit breaker etc comes
under the umbrella of
this panel. It gives
indications of di erent
faults and problems.

Transformer auxiliary
control panel:    This panel
controls various
operations related to the
working and protection
of the power
transformer.In 132kv
control room it is
installed one for each
power transformer. It has

              Two meters: one

shows the tap position
and the other shows
temperature of
transformer in .
             Two selector type
switches: one for cooling
fans ON OFF and other
for tap changer.

It also gives di erent

indications like

Cooling fans automatic

ON OFF
 Cooling fans manual ON
OFF
Fans supply fault
Winding temperature alarm
Fan motor circuit breaker
trip

It also have an
Emergency stop press
button which is used in
emergency.

Also an automatic
voltage regulator is
installed in the
transformer auxiliary
control panel.

AC DC panel:

This is another
important panel in the
132kv control room. It
controls AC and DC
supply of the whole grid.
It has two parts one for
AC and other for DC.

AC panel:    AC panel
consists of three meters
for R, Y & B phases, a
voltmeter and a KWH
meter. It controls AC
supply of
Switch yard lights
Tap changer
 132kv breaker motor
Battery charger
Transformer cooling fans
Control panels.

It also controls AC supply

(220 v) of the 11kv
incoming and outgoing
panels.

DC panel:    It also have a

DC ammeter and a DC
voltmeter to show
current and voltage. It
controls DC supply of
control room building
lights (DC)
switch yard DC lights
11kv & 132kv breaker
motors
11kv switch-gear
protection
DC emergency bus
Control and relay panels.

It also have battery alarm

and under/over voltage
relay.

Recti er:

A recti er is an
instrument/circuit that
changes AC into DC. In
the grid station it is used
for several purposes i.e.
 It charges batteries
Provide DC supply to the
load
Shares load with battery
during overload
condition.

The recti er used in grid

has a voltmeter and an
ammeter for incoming
AC and another voltmeter
and ammeter for
outgoing DC.

It also have control

switches like

ON/OFF
Auto/manual
Boost/ oat (for boost 
and normal charging of
battery)
Load/battery.

Relay panel:

This panel controls

di erent relays like
overcurrent relay,
distance relay,
di erential relay, oil
temperature and winding
temperature relay and
many more that are
discussed as under.
 Over current relay:

As the name indicates

these relays keeps the
transformer safe from
over current which may
cause serious problem to
the transformer. As we
know that some time the
consuming of electric
power increase to a
dangerous level that
causes a huge current due
to over loading. The relay
trips and gives indication
of the type and area of
tripping.

Di erential relay:

These relays operate on

the fault between
transformer input and
output. The fault may be
due to low voltage, high
voltage or may be due to
earth fault.

Oil temperature relay:

These relays as the name

indicates supervise the
oil temperature. As we
have discussed earlier
that as the transformer
operates continuously,
the temperature of oil
increases, this
temperature may
sometime increase to a
dangerous situation as a
result this relay operates.

Winding temperature
relay:

These relays as the name

indicates supervise the
winding temperature. As
we have discussed earlier
that as the transformer
operates continuously,
the transformer winding
heats up. This
temperature may
sometime increase to a
dangerous situation
which cause this relay to
operates.

T/F buchholz Relay:

This relay operates as the

buckle action occurs.
Buckle reaction is
discussed before. As we
know that buckle action
occur when dangerous
gasses produce in main
tank so this situation is
also an alarming
situation and it must also
be noticed as well so this
job is done through this
relay.

4. Battery room
Battery bank is the
conserved source of 110v
dc voltage.

It gives supply to the

protection system of the
grid when supply from
the recti er stops.

In the grid station’s

battery room/bank, there
are generally 55 cells of
2v dc each. These cells
are connected in series to
get 110v. The batteries are
charged by the recti er.

These are lead acid

batteries having speci c
gravity of 1.220 and are of
150 A.H capacity.

A battery have the

following components:

Container/jar: it is
generally made of plastic
and gives support to the
electrolyte and plates.
Electrolyte: a solution of
35% sulphuric acid
 (H2SO4) and 65% water

(H2O) is lled in the

container.
Plates: two dis-similar
plates are dipped in the
electrolyte, one made of
“lead oxide” act as
cathode and other made
of “lead” act as anode.
Connection leads: the
electrodes are connected
with the connection
leads.
Vent cap: Every battery
have a vent cap that is
used to evolve any gas
bubbles produced during
conduction in electrolyte.

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