A new method for synchronous generator core quality evaluation

A new technique for detecting the presence and severity of inter-laminar short circuits as well as estimating the status of core compression (or looseness) in laminated magnetic cores of synchronous generators, with a single test equipment is demonstrated in this paper. The core loss measurement obtained from a flux injection probe that injects flux (of varying amplitude, frequency, and wave-shape) into two nominally adjacent teeth over a localized region, is used as an indicator for detecting and distinguishing the two fault conditions. An injection probe system was developed and tested, in the laboratory, using stacks of full size generator laminations with various induced fault conditions. The injection probe was shown to detect the presence of shorted laminations at the bottom of the slot and to gauge the degree of core compression or looseness. In addition, a unique differential probe was developed and tested to demonstrate the capability of detecting as few as five shorted laminations.