Non-differential protection of a generator´s stator utilizing fault transients

This paper presents a novel protection scheme for detecting faults on the stator of a generator unit which is directly connected to a distribution system. In the scheme, a multi-channel fault transient detection unit, using the outputs of the current transformers (CTs) at the output of the generator terminal, is employed to extract the fault-generated transient current signals. The detector unit is tuned to extract two bands of fault generated transient signals with different center frequencies. A spectral comparison technique is applied to firstly compute the spectral energies of the two band signals, and then the fault diagnosis determines whether it is an internal and external fault by comparing the ratio of the two signals with a predefined threshold. The scheme offers advantages of immunity to CT saturation, and is capable of detecting both low level and interturn faults. In addition, the protection scheme is also simple in application, and is cost-effective in that it only requires one set of CTs. Simulation studies show that the proposed technique can give correct responses for various fault conditions