ABSTRACT
Most of the fault detection techniques used in real time fault detection in power systems is time-domain based. The over current, over voltage, earth fault, impedance relays, and so forth are mostly time-domain based. The fault frequencies to be detected can be simply derived by replacing the fundamental frequency with Low-order harmonics in the equations describing these frequencies. Stator faults usually progress from incipient to a very advanced stage in a matter of seconds. Like stator faults, rotor faults also have been reported to be detectable using odd harmonics in the motor terminal voltage at motor switch-off. Eccentricity faults are related to deformation of air-gaps of an electric machine. Low-order harmonic components that appear in the line voltage of inverters supplying induction motors can provide additional information on the fault of induction machines. Voltage unbalance and machine asymmetries that also change the negative sequence current and impedance can cause misdiagnosis when faults involve only a few turns.
