Sorry DanDel, I wasn't very clear in my above comment. The CB has integral protection set on a definite time setting. Whereas the motor's local protection device is set on an inverse curve (IDMT), as per our protection scheme. Hence, a trip was experienced on the MCC and none on the motor...
Thanks dpc, that sounds like a logical approach. However it alleviates one problem by creating another. The purpose of the stand alone GF relay, or a CB with integrated GF functionality is to introduce more sensitive GF protection. Or at least faster GF protection than the MCC's CB. This solves...
To simply answer your question johl04, it’s because the power companies are supplying inductive loads. A synchronous generator is doubly fed (prime mover and field excitation).
The excitation voltage applied to the generator will determine the phase angle of the generated apparent power (S)...
I am currently having the problem that an earth fault on my motor (LV) is tripping out my MCC rather than isolating the fault to that particular motor, by locally tripping the motor. The obvious cause is that the fault grading is incorrect. However, at this particular sub station we use a CB...
