A study of electrical signature analysis for two-pole synchronous generators

Abstract

Electrical signature analysis (ESA) has been increasingly used in condition-based maintenance programs of synchronous generators. The fault diagnosis is based on the analysis of failure patterns in the current or voltage signatures, which allow to distinguish possible incipient faults in the machine. The failure patterns are usually dependent on the line frequency, rotor rotation frequency and some structural features of the machine. The rotor rotation frequency pattern, for example, is indicative of rotor mechanical problems and rotor winding inter-turn short-circuit. In the specific case of two-pole synchronous machines, the rotation frequency is equal to the line frequency. Thus, the ESA failure patterns coincide with the network harmonics. Therefore, it is necessary to distinguish the effect of the network harmonics and the machine internal faults in order to get a reliable diagnosis for the machine. This work investigates the behavior of the even harmonics in synchronous generators (SGs) aiming to improve the ESA for fault diagnosis of two-pole SGs. The investigation has been performed through experimental tests accomplished in a scale model laboratory developed to simulate faults in a small SG in a controlled way. A system developed for turbogenerator predictive maintenance based on ESA has been used for this purpose. This system is in operation in a Brazilian 404 MW thermal power station.