A novel stator earth fault protection for large generator based on fault current

A stator earth fault protection scheme based on fault current is presented in this paper. It trips out the faulted generator only if the fault current following the breakdown channel exceeds the tolerance capacity of the generator. Otherwise, it will just emit alarm signals. This protection scheme can avoid unnecessary trip-out of large generator, which influences the safe operation of power system, while ensuring the generator security. To achieve the scheme, methods of calculating fault current in real time are provided for three common generator neutral earthing methods basing on the zero-sequence equivalent circuits. An implementation scheme is given on the basis of the sub-harmonic injection protection device. The protection algorithm flow and protection criterion are discussed as well. Simulation results show the accuracy of the fault current calculation method and the validity of the protection scheme.