Transformer Protection

TRANSFORMER PROTECTION 

CONTENTS  

 Introduction to transformers and relays r elays

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 Need for transformer protection

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Short circuit protection  External faults

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Over current and earth faults

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du/dt protection

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 Frame leakage protection Over flux protection and winding hot spot temp. t emp. protection  In-Phase transformer protection

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Grounding transformers

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Conservator type transformer protection

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conclusion

 I  NTRODUCT  I ON ON TO TRANSFORMER 

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 A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors. Working P  Working  P rinciple rinciple of A of  A T ransformer  ransformer 

 A transformer consists of a primary coil and a secondary coil  wound on a soft iron core. When an alternating current flows in the t he primary coil, a changing  magnetic flux is generated around the primary coil. The changing magnetic flux is transferred to the secondary coil  through the iron core. The changing magnetic flux is cut by the secondary coil, hence induces an e.m.f. in the secondary coil.

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The magnitude of the output voltage can be controlled by the ratio of  the number of primary coil and secondary coil.  A basic transformer is shown below showing its terminals and   primary &secondary &secondary circuits.

Ty pes of  of T  T ransformers ransformers 

 A wide variety of transformer designs are used for different  applications, though they share several common features.

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 Important common transformer types include:

1.

 Power transformers

2.

 Autotransformer 

3.

 Polyphase transformers

4.

 Instrument transformers

 APPL I CAT  CAT  I ONS  ONS   A major application of transformers is to increase voltage before transmitting electrical energy over long distances through wires .

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Transformers are also used extensively in electronic products to  step down the supply voltage to a level suitable for the low voltage circuits they contain. o

The transformer also electrically isolates the end user from contact with the supply voltage.

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 I  NTRODUCT  I ON ON TO RELAYS  

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 A relay is an electrical switch that opens and closes under the control of another electrical circuit.  In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts.  It was invented by Joseph Henry in 1835. Working of a RELAY:  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 make a connection. These contacts can be considered to be a switch. They allow current to flow between 2 points thereby closing the circuit.

TYPES OF RELAYS  

Some of the common relays which we used in the book are as follows.

1.

Overload pr protection re relay

2.

Buchholz relay

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Over current relay

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Distance relay

 APPL I CAT  CAT  I ONS  ONS 

 Relays are used to and for: 

Control a high-voltage circuit with a low-voltage signal, as in in  some types of modems or audio amplifiers,

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Control a high-current high-current circuit with a low-current signal, as in the starter solenoid of an automobile etc«

General Electomagnetic Relay

 NEED FOR TRANSFORMER  PROTECT  I ON  ON  

Transformers are a critical and expensive component of the power   system.

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The comprehensive transformer protection provided by multiple  function protective protective relays is appropriate for critical transformers of all  applications.

TRANSFORMER PROTECT  I ON ON OVER V  I  E W  W   

The type of protection for the transformers varies depending on the application and the importance of the transformer. are protected primarily against faults and Over loads.

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The type of protection used should minimize the time of disconnection

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and reduce the risk of catastrophic failure to simplify eventual repair.

 Short   Sh ort circuit  circuit  protection  protection

C ompleted connections ompleted  connections for   for  percentage  percentage differential rela differential  rela y  ying  ing 

 EXTERNAL-FAULT BACK-UP PROTECT  I ON  ON 

Back-up relaying for transformer Connected to one source.

Back-up relaying with two sources.

Over  Over C  C urrent and  urrent  and E  E art  art h F ault P  ault  P rotection rotection  S cheme

du/dt protection

 Distribution transformer protected with spark gap

F rame rame Leakage P rotection rotection

OVER FLUX PROTECT  I ON  ON  

Transformer over fluxing fluxing can be a result result of  Over voltage voltage  Low system frequency

WI  ND I  NG HOT-SPOT TEMPERATURE PROTECT  PROTECT  I ON  ON 

 Protection based on winding hot-spot temperature can potentially  prevent short circuits and catastrophic transformer failure. 

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The ambient temperature, transformer loading, and transformer  design determine the winding temperature.

 P rotection rotection of  I   I  N-PHASE t   N-PHASE  t  y  y pe  pe transformers

G rounding b rounding  bank  protection  protection

Conservator-Type Transformer protection using   BUCHHOLZ relay

CONCLUS  I ON  ON  

Transformer is used to increase voltage before transmitting electrical  energy over long distances through wires in order to minimize the line losses.

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Transformer being the core equipment in transmission t ransmission and  distribution system and the cost of the equipment is huge it is to be well   protected.

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The type of protection for the transformers transf ormers varies depending on the application and the importance of the transformer.

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So transformers are protected primarily against faults and Over  loads.

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 More over the protection of transformer is essential so as to maintain the continuity of power supply.

Queries?????????????

Thank You