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April 20, 2012

What are the advantages of static relay over electromagnetic relay?

Advantages of static relay over electromagnetic relay:

  1. Low power consumption as low as 1mW.
  2. No moving contacts; hence associated problems of arcing, contact bounce, erosion, replacement of contacts.
  3. No gravity effect on operation of static relays. Hence can be used in vessels, i.e., ships, aircrafts etc.
  4. A single relay can perform several functions like over current, under voltage, single phasing protection by incorporating respective functional blocks. This is not possible in electromagnetic relays.
  5. Static relay is compact.
  6. Superior operating characteristics and accuracy.
  7. Static relay can think, programmable operation is possible with static relay.
  8. Effect of vibration is nil, hence can be used in earthquake-prone areas.
  9. Simplified testing and servicing. Can convert even non-electrical quantities to electrical in conjunction with transducers.

Why busbar protection is needed?

 (a) Fault level at busbar is high

(b) The stability of the system is affected by the faults in the bus zone.

(c) A fault in the bus bar causes interruption of supply to a large portion of the system network.

What are the main safety devices available with transformer?

Oil level guage, sudden pressure delay, oil temperature indicator, winding temperature indicator .

What are the limitations of Buchholz relay?

  1. Only fault below the oil level are detected.
  2. Mercury switch setting should be very accurate, otherwise even for vibration, there can be a false operation.
  3. The relay is of slow operating type, which is unsatisfactory.

What are faults associated with an alternator?

(a) External fault or through fault

(b) Internal fault
1, Short circuit in transformer winding and connection
2, Incipient or slow developing faults

What are the various faults that would affect an alternator?

(a) Stator faults
1, Phase to phase faults
2, Phase to earth faults
3, Inter turn faults

April 6, 2012

What are the uses of Buchholz’s relay?

Bucholz relay is used to give an alarm in case of incipient( slow-developing) faults in the transformer and to connect the transformer from the supply in the event of severe internal faults. It is usually used in oil immersion transformers with a rating over 750KVA.

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