Generator Excitation


Thread Starter


Dear All,

Good day!

I have confusion on wether i/we can ON/Energize again generator excitation immediately upon sudden loss of excitation? what will be the operator's action if it will occur? For those who have experienced in the above mention scenario i'd love to hear some inputs form you!

Thank you!

Loss of excitation is a serious condition whose cause must be investigated and understood before re-applying excitation and re-synghronizing the generator. (We presume you are talking about a synchonous generator that is synchronized to grid with other generators, not a single generator supplying a small, local load.)

While you can likely re-apply excitation if the prime mover (turbine; reciprocating engine; etc.) is still at rated speed without fear of too much trouble, before re-synchronizing one should be certain that whatever caused the loss of excitation to trip the generator breaker before will not occur again.

One of the main things loss of excitation protection tries to protect against is a phenomenon known as 'slipping a pole' where the generator rotor excitation is incapable of keeping the generator rotor from losing synchronism with the grid and very suddenly accelerating and possibly coming into synchronism again, very suddenly slowing. This condition can cause very serious physical damage to the coupling between the prime mover and the generator rotor, and also to the prime mover. So, it's important for excitation to never drop below a certain level (particular to each machine) in order to prevent slipping a pole and causing serious damage to the generator-set.

Continued operation of a synchronous generator without excitation or with very low excitation will cause very serious heating of the generator rotor which can very seriously damage the generator rotor and rotor windings.

Therefore the cause of a loss of excitation condition is very important to understand before re-applying excitation and re-synchronizing the generator or re-connecting it to a load to prevent causing damage to the generator-set.

Hope this helps!