Summer Training presentation on 132/33 KV sub-station Minto park, Allahabad
Summer Training from UPPTCL
132/33 KV Sub-Station
Minto Park, Allahabad
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India has been divided into five regions for power system planning
and operation. These regions are the Northern region, Western region,
Eastern region and North-eastern region.
Present almost 70% of the population is enjoying the fruits of
The present day electricity power system is AC i.e. electric power is
generated, transmitted and distributed in the form of alternating current.
The electric power is produced at the power station, which are
located at favourable place, generally quite away from the consumers
A transformer is an electrical device that transfers energy
between two or more circuits through electromagnetic induction.
1.2Types Of Transformer:
Step Up Transformer
Step Down Transformer
Its primary and secondary winding resistances are negligible .
Its leakage flux and leakage inductance are zero .
There are no losses due to resistance, hysteresis and eddy currents.
The efficiency is 100 percent.
In case of ideal transformer Np*Ip = Ns*Is
Ideal transformer as a circuit element :
2.PROTECTION AND COOLING EQUIPMENT:
As the temperature of oil increases or decreases during operation there is
corresponding rise or fall in volume. To account for this an expansion vessel is
connected to the transformer tank.
The conservator has got a capacity between minimum and maximum oil
level equal to 10% of the total oil in transformer.
The conservator is provided with magnetic oil level gauge on one of the end
covers which has a low oil level alarm. The ideal indicates empty 1/4, 30.c, ¾
and full oil level.
Owing the transport limitation and considering possible transient
damages. Large transformer are provided with detachable radiators with
At the time of dispatch these radiators are detach and sent separately
keeping the valve in position on tank flange. The valve blanking plate is
to removed only when the radiators is ready for mounting on flanges. On
removal of blanking plate a small quantity of oil which may have
collected between valve and blanking plate will seep out.
The radiator section is made of 1mm thick cold rolled carbon steel
sheets. The distance between each section is 50mm. The number of
section per radiators and the number of radiators per transformer will
depend upon cooling requirement of that transformer
2.3 BUCHHOLZ RELAY:
The transformer is fitted with double float buchholz relay.
It is fitted in the feed pipe from conservator to tank and it is provided with two
sets of mercury contacts.
The device comprises with the cast iron housing containing the hinged floats,
one in upper part and other in lower part . Each float is fitted with mercury
switches, leads of which are connected to terminal box for external connection.
An arrow in cast on the housing to indicate the direction of conservator. The
operation of buchholz relay should be tested before installing by injecting air at
the lowest cock.
It is connected to the protection circuit to give an early alarm in case of gas
collection and to disconnection of transformer from supply in case the sever fault
inside the transformer.
2.4 SILICA GEL BREATHER:
When transformer is loaded or unloaded the oil temperature inside the
transformer is rise or falls. Accordingly the volume of air is changes by either by
sucking in or pushing out . This transformer phenomena is called BREATHING
The air which I being sucked in container may have foreign impurities and
humidity which changes dielectric stray of transformer oil . Hence it is necessary
that the air entering into the transformer is free room moisture and foreign
impurities. The breather is connected to an outlet pipe of conservator vessel and
the air which is sucked by the transformer is made to pass through silica gel
breather to dehumidify the air and remove the foreign impurities . The air which
is pass through the gel is pass first to oil compartment of the breather. The oil
removes all foreign impurities which enter into the gel compartment. Silica gel
breather keeps all the properties of oil constant so transformer has a long life.
2.5 MARSHALLING BOX:
It has two indicators which indicate the temperature of oil and winding of main
tank, known as OTI and WTI. If the temperature of oil or winding exceeds the
specified value , relay operates to sounds an alarm. If there is further increase in
temperature then relay completes the trip circuit open the circuit breaker
controlling the transformer.
When a transformer is in operation the heat is generated due to iron loss in winding
and core loss. The process of minimise this heat is called cooling.
2.6.1 AIR NATURAL COOLING
In a dry type self-cooled transformer, the natural circulation of surrounding air is
used for cooling. This process of cooling is satisfactory for low voltage small
transformer up to few KVA.
2.6.2 AIR BLAST COOLING
It is similar to natural cooling with an addition that continuous blast of filtered
cooled air is forced through the core and winding for better cooling. A fan
produces the blast.
2.6.3 Forced Oil with Circulating Water Cooling:
In this type of system heat exchanger is used for cooling the
This system is used for large rating of power transformer.
3. EQUIPMENT OF SUB-STATION:
3.1 LIGHTING ARRESTER:
Lighting arresters are protective device
for limiting surge voltages due to lighting
strikes or equipment faults or other events,
to prevent damage to equipment and
disruption of service. This type of
equipment also called surge arresters.
Lighting arresters are installed on many
different pieces of equipment such as
power poles and towers, power
transformer, circuit breaker, bus structure,
and steel superstructure in substation.
3.2 WAVE TRAP:
Wave trap unit is inserted between bus bar and connection of coupling
capacitor to the line. It is parrel tuned circuit comprising L and C. It has low
impedance to 50 Hz and high impedance to carrier frequencies.
Thus coupling capacitor allows carrier frequencies signals to enter the
carrier equipment, but does not allows 50Hz power frequency current to
enter the carrier equipment. This unit prevents the high frequencies signal
from entering the neighbouring line, and the carrier current to flow only in
the protected line for communication between different substations.
3.3 CURRENT TRANSFORMER:
They are commonly used in metering and protective relaying in the electrical
power industry where they facilitate the safe measurement of large currents,
often in the presence of high voltages.
The current transformer safely isolates measurement and control circuitry from
high voltage typically present on the circuit being measured. The CT acts as
constant current series device with an apparent power burden a fraction of that of
high voltage primary circuit.
Common secondary's are 1 or 5 amperes . For example; a 400:1 CT would
provide an output current of 1 ampere when the primary was passing 400
3.4 POTENTIAL TRANSFORMER:
Potential transformer is designed for monitoring single - phase and three –
phase line voltages in power metering application. The primary terminals can
be connected either in line – to –line or in line – to – neutral configuration.
A potential Transformer is a special type of transformer that allows meters
to take reading from electrical service connections with higher voltage than
the meter is normally capable of handling without at potential transformer .
Potential transformer has an accuracy of +_ 5% from 0 to 130% of their
Mainly the isolator is connected after the circuit breaker .The circuit breaker is
trip due to the fault, or when suddenly a heavy current is flows , it means that
the current will not flow after the breaker ,but small amount of current is flows
For making this current total zero the isolator is open and isolator is connected
to ground so all inner current will grounded. This is the main work of isolator
and other equipments are saved.
The insulator serve two purpose . They support the conductor (bus bar ) and
confine the current to the conductor . The most commonly used material for the
manufacturer of insulator is porcelain .
But the most wild use of insulator is to insulate the support or tower from the
electric current .These are several type of insulators (e.g. pin type ,suspension
type , post insulator ,shackle insulator etc.) and their use in the substation will
depend upon the service requirement .For example post insulator is used for bus
bars can directly bolted to the cap.
3.7 CIRCUIT BREAKER:
Circuit breaker is mechanical device which is so designed by which circuit
normal current fault position will be on and off .They are used for high capacity.
A circuit breaker can make or break a circuit either manually or automatically
under all condition viz. no load and short circuit condition .
Types of circuit breaker is :
1. Low voltage air circuit breaker
2. oil circuit breaker
3. Sulphur Hexa Fluoride circuit breaker
4. Air blast circuit breaker
5. vacuum circuit breaker
3.8 CAPACITOR BANK:
The load on the power is varying, being high during morning and evening and
low at other times. During low load period, supply voltage is increased which
increases the magnetization current, this result in the decreased power factor. The
low power factor is mainly due to the fact that most of the load power factor is
highly undesirable as it causes an increases in current, resulting in additional
It is important to have power factor is closed as close to unity as possible. In
order to improve the power factor some device taking leading power factor
should be connected parallel with the load. One of such device can be a capacitor
bank. The capacitor draws a leading current and partly or completely neutralizes
the lagging reactive component of load current.
Practically the voltage inside the capacitor bank in the 132KV substation is of
33KV.When the voltage inside the capacitor bank is bellow from 33.5KV the
capacitor bank operated and increased the voltage unto the desired level. If the
voltage is greater than 36.1KV the capacitor bank is of.
Capacitor bank accomplishes following operation
I. To supply reactive power
II. Increase terminal voltage
III. Improve power factor
3.9 CONTROL PANEL:
This is the main part of the substation. We plant it outside the switchyard. All the
equipment which is install inside the switchyard is connected to the control panel
by a underground cable. These cable are connected to the measuring devices like
as voltmeter and ammeter of high rating.
This control panel also consists a different type of relays like as differential,
earth fault, auxiliary etc. control panel gives all the correct reading for example
when a line is come in switch yard is connected to CVT. This CVT gives an
exact value of incoming voltage on the control panel, If any fault is occurs, the
relay is trip and we can see it on control panel and except it control panel gives
the rating of all feeders and temperature of oil and winding in the transformer.
3.10 BATTERY ROOM :
This is the room, which consist DC batteries. There are 55 DC cell of 2
Volt each. These cells are connected in series, so it will give total of 110V.
This 110V DC Supply is used for operating the control panel, when the AC
supply is off. This 110V DC voltage is also supplied to circuit breakers for
operating; this supply is used when AC is off. We use this supply as a
secondary supply. It means that this DC voltage is used when the AC is
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