TRANSFORMER PROTECTION
CONTENTS
CONTENTS
Introduction to transformers and r Introduction to transformers and relayselays
Need for transformer protection Need for transformer protection
Short circuit protectionShort circuit protection
External faults External faults
Over current and earth faultsOver current and earth faults
du/dt protectiondu/dt protection
Frame leakage protection Frame leakage protection
Over flux protection and winding hot spot tOver flux protection and winding hot spot temp. protectionemp. protection
In-Phase transformer protection In-Phase transformer protection
Grounding transformersGrounding transformers
Conservator type transformer protectionConservator type transformer protection
I
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NTRODUCT
NTRODUCT
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ON TO TRANSFORMER
ON TO TRANSFORMER
A transformer is a A transformer is a device that transfers electrical energy fromdevice that transfers electrical energy from
one circuit to
one circuit to another through inductively coupled conductors.another through inductively coupled conductors.
Working Working P P rinciplerinciple of of A T A T ransformer ransformer
A transformer consists of a primary coil and a A transformer consists of a primary coil and a secondary coil secondary coil
wound on a soft iron core. wound on a soft iron core.
When an alternating current flows in tWhen an alternating current flows in the primary coil, a he primary coil, a changing changing
magnetic flux is generated around the primary
magnetic flux is generated around the primary coil.coil.
The changing magnetic flux is transferred to The changing magnetic flux is transferred to the secondary coil the secondary coil
through the iron core. through the iron core.
The changing magnetic flux is cut by The changing magnetic flux is cut by the secondary coil, hencethe secondary coil, hence
induces an e.m.f. in the secondary coil. induces an e.m.f. in the secondary coil.
The magnitude of the output voltage can be The magnitude of the output voltage can be controlled by the ratio of controlled by the ratio of
the number of primary coil and secondary coil. the number of primary coil and secondary coil.
A basic transformer is shown below showing its terminals and A basic transformer is shown below showing its terminals and
primary &seco
Ty
Ty
pes
pes
of
of
T
T
ransformers
ransformers
A wide variety of transformer designs are used for A wide variety of transformer designs are used for different different applications, though they share several common features. applications, though they share several common features.
Important common transformer types Important common transformer types include:include: 1.
1. Power transformers Power transformers 2.
2. Autotransformer Autotransformer 3.
3. Polyphase transformers Polyphase transformers 4.
APPL
APPL
I
I
CAT
CAT
I
I
ONS
ONS
o
o A major application of transformers is to increase voltage before A major application of transformers is to increase voltage before
transmitting electrical energy over long distances through wires transmitting electrical energy over long distances through wires
..
o
o Transformers are also used extensively in electronic products toTransformers are also used extensively in electronic products to
step down the supply voltage to a level suitable for the low voltage step down the supply voltage to a level suitable for the low voltage
circuits they contain. circuits they contain.
o
o The transformer also electrically isolates the end user fromThe transformer also electrically isolates the end user from
contact with the supply voltage. contact with the supply voltage.
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NTRODUCT
NTRODUCT
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ON TO RELAYS
ON TO RELAYS
A relay is an electrical switch that opens and closes under the A relay is an electrical switch that opens and closes under the
control of another electrical circuit. control of another electrical circuit.
In the original form, the switch is operated by an electromagnet to In the original form, the switch is operated by an electromagnet to
open or close one or many sets
open or close one or many sets of contacts.of contacts.
It was invented by Joseph Henry in 1835. It was invented by Joseph Henry in 1835.
Working of a RELAY:Working of a RELAY:
Apply a voltage to the coil and a magnetic field is generated. This Apply a voltage to the coil and a magnetic field is generated. This
magnetic field sucks the contacts of the relay in, causing them to magnetic field sucks the contacts of the relay in, causing them to make a connection.
make a connection.
These contacts can be considered to be a switch. They allowThese contacts can be considered to be a switch. They allow
current to flow between 2
TYPES OF RELAYS TYPES OF RELAYS
Some of the common relays which we used inSome of the common relays which we used in
the book are as follows. the book are as follows. 1
1.. OOvveerrllooaad pd prrootteeccttiioon rn reellaayy 2
2.. BBuucchhhhoollz z rreellaayy 3
3.. OOvveer r ccuurrrreennt t rreellaayy 4
4.. DDiissttaanncce e rreellaayy
APPL
APPL I I CAT CAT I I ONS ONS
Relays are used to and for: Relays are used to and for:
Control a high-voltage circuit with a low-voltage signal, as iControl a high-voltage circuit with a low-voltage signal, as inn some types of modems or audio amplifiers,
some types of modems or audio amplifiers,
Control a high-currenControl a high-current circuit with a low-current signal, as t circuit with a low-current signal, as inin the starter solenoid of
General Electomagnetic Relay
General Electomagnetic Relay
NEED FOR TRANSFORMER
NEED FOR TRANSFORMER
PROTECT
PROTECT
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ON
ON
Transformers are a critical and expensive component of the power Transformers are a critical and expensive component of the power system.
system.
The comprehensive transformer protection provided by multipleThe comprehensive transformer protection provided by multiple function protec
function protective relays is appropriate for critical transformers of tive relays is appropriate for critical transformers of all all applications.
applications.
TRANSFORMER PROTECT
TRANSFORMER PROTECT I I ON OVER V ON OVER V I I E E W W
The type of protection for the transformers varies depending on theThe type of protection for the transformers varies depending on the application and the importance of the transformer.
application and the importance of the transformer.
are protected primarily against faults and Over loads.are protected primarily against faults and Over loads.
The type of The type of protection used should minimize the time protection used should minimize the time of disconnectionof disconnection
Sh
C
C
ompleted
ompleted
connections
connections
for
for
percentage
percentage
differential
EXTERNAL-FAULT BACK-UP PROTECT
EXTERNAL-FAULT BACK-UP PROTECT I
I ON
ON
Back-up
Back-up relaying relaying for for transformer transformer Back-up Back-up relaying relaying with with two two sources.sources. Connected to one source.
Ov
Over
er C
C urrent
urrent and
and E
E art
art h F
h F ault
ault P
P rotection
rotection
S
du/dt protection
du/dt protection
Distribution transformer protected with spark gap
Distribution transformer protected with spark gap
F
OVER FLUX PROTECT
OVER FLUX PROTECT I I ON ON
Transformer Transformer over fluxover fluxing ing can can be be a rea result of sult of Over vOver voltageoltage
Low system frequency Low system frequency
WI
WI ND ND I I NG NG HOT-SPOT TEMPERATURE PROTEHOT-SPOT TEMPERATURE PROTECT CT I I ON ON
Protection based on winding hot-spot temperature Protection based on winding hot-spot temperature can potentiallycan potentially
prevent short circuits and catastrophic transformer failure. prevent short circuits and catastrophic transformer failure.
The ambient temperature, transformer loading, and transformer The ambient temperature, transformer loading, and transformer
design determine the winding temperature. design determine the winding temperature.
P
G
Conservator-Type Transformer protection using
Conservator-Type Transformer protection using
BUCHHOLZ relay
BUCHHOLZ relay
CONCLUS
CONCLUS
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ON
ON
Transformer is used to increase voltage Transformer is used to increase voltage before transmitting electrical before transmitting electrical energy over long distances through wires in order to minimize the line energy over long distances through wires in order to minimize the line losses.
losses.
Transformer being the core equipment in tTransformer being the core equipment in transmission and ransmission and distribution system and the cost of the equipment is huge
distribution system and the cost of the equipment is huge it is to be it is to be well well protected.
protected.
The type of protection for the transfThe type of protection for the transformers varies depending on theormers varies depending on the application and the importance of the transformer.
application and the importance of the transformer.
So transformers are protected primarily against faults and So transformers are protected primarily against faults and Over Over loads.
loads.
More over the protection of transformer is essential so as to maintain More over the protection of transformer is essential so as to maintain the continuity of power supply.
