Which relay is used for protection of alternator from loss of excitation?

The Type 40 is an offset mho impedance relay used for loss of excitation protection of a generator operating in parallel with other system generators.

What is loss of excitation protection?

Loss of excitation protection is used to protect the synchronous machine (alternator or generator) acts as induction motor when the excitation fails. Loss excitation protection operates under many circumstances such as diode failure, rotor winding short circuit, AVR failure, etc.

Which relay is used for alternator?

The differential protection is provided in the generator by using longitudinal differential relay. Generally instantaneous attracted armature type relays are used for this purpose because all they have high speed operation and also they are free from being affected by any AC transient of the power circuit.

What are main protection used for alternator?

01. Stator winding fault. It is the most severe fault and considered most important for alternator protection. This vital protection of alternator stator is Differential circulating current scheme or Mertz price differential current protection scheme of alternator is discussed in a separate post.

What causes loss of excitation?

Generator loss of excitation (LoE) can be caused by a short circuit in the field winding, unexpected field breaker opening and by a failure in the excitation system. According to Chinese statistics, generator failure due to LoE accounts for more than 60% of all generator failures [1].

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Which abnormality is possible in alternator?

Alternators need to be protected not only from short circuits but also from abnormal operating conditions such as overexcitation, overvoltage, underexcitation, loss of field, unbalanced currents, loss of prime mover and abnormal frequency conditions.

What are the rotor faults in alternator?


  • There is internal Fault like;
  • On the other hand, there is external fault like;
  • Stator winding fault.
  • 1.1. Differential protection or Merz-Price circulating current protection system of alternator.
  • 1.2. …
  • 1.3. …
  • 1.4. …
  • Alternator Prime Mover failure fault or reverse power fault-

Which is the pilotless protection method for line?

Which is the pilotless protection method for feeder line ? Differential protection.

How do you protect alternator from overload?

Furthermore, such protection on the alternator will take out the alternator for a long time even in case of harmless momentary troubles. Thus leading to blackouts and interruption of electric supply. The rare cases of overload protection involve a thermocouple installed in the stator winding.

Can Relays be used to protect an alternator against one phase open circuit?

The relay then closes its contacts to disconnect the alternator from the system. Merz-price circulating-current system protects against phase-to-ground and phase-to-phase faults. … Advantage may be taken of this necessity to protect inter-turn faults on the same winding.