TRANSFORMER PROTECTION RELAYING


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                       TRANSFORMER PROTECTION RELAYING

Transformers are one of the major equipment in a power system and due to this we need to make sure it is protected because it has a very high chance of fault occurrence and it will take more time and money to repair it so in order to prevent it we should take better protective measures

MAJOR FAULTS OCCURRING IN TRANSFORMERS

  • Open circuit faults
  • Earth Faults
  • Phase to phase faults
  • Intern-turn faults
  • Overheating

TRANSFORMER RELAYING

BUCHHOLZ RELAY PROTECTION

Buchholz relay is also known as gas accumulated relay this is commonly used on all oil immersed transformer provided with conservator

It has mainly two elements the upper elements consists of float which is attached to a hinge in a way that it can move up and down and the movement will be depended on the oil level and the lower element consists of mercury switch and baffle plate, the baffle plate alignment will change when oil enters to the relay from the inlet in high pressure

If any faults occur inside the transformer the oil will be overheated and gases will be generated, due to the heat generated by the current the oil will be decomposed and gas is generated and by that we can detect the winding faults this relay function is basically a mechanical phenomenon, the gas produced due to the decomposition of the oil will cause the oil level to drop down and by that position of the float will be lowered and thus the mercury switch will be tilted, the mercury switch contacts will be closed and energizes an alarm circuit

CORE BALANCE LEAKAGE PROTECTION

It provides the protection for faults on high voltage windings.when the earth fault occurs the sum of the three current will not be zero and a current is induced in the secondary of the current transformer and it causes the trip relay to operate and thus the transformer will be isolated from the bus bar

COMBINED LEAKAGE AND OVERLOAD PROTECTION

The core balance protection method can’t handle overload protection, so we need to use the combined leakage method for the overload protection, overload relays have high current settings and can be operated for faults between phases

The overload relay and the earth relay are connected together so If any of them are energized the circuit breaker will be tripped