Hello!

I have a problem to quantifying the contribution of an hydro electric alternator in a arcing fault after that his field breaker has been open. The remanent magnetization of the alternator can force it to contribute for a certain time (in term of second). I believe that this cannot be neglected.

In this particular case, the fault clearing time and the bolted fault current cannot give good result since there is still energy in the alternator.

Is someone aware of something about this?

How should it be considered?

Thank you,

Generators can be modeled a couple of ways. Without getting too detailed the decremental decay method will give high IE because the generator AVR is compensating for the fault current and voltage drop as a result of the fault. AVR systems are very complex. Using standard arc flash calculations limited to 2 seconds will usually produce lower IE. I use the higher of the two.