DISCUSSION OF AN ELECTROMAGNETIC PROBE FOR DETECTING AND LOCATING DISCHARGES IN LARGE ROTATING-MACHINE STATORS

The detection and location of discharges in rotating-machine high-voltage windings is useful in directing attention to abnormalities in the insulation structure which can lead to premature failure of the winding. In order to achieve a practically useful test it is necessary to distinguish between conditions involving many small size voids which are not severely limiting and relatively few large voids. For this purpose, probe tests are more effective then tests involving measurements on a complete winding. An electromagnetic probe used in combination with a suitable detector and amplifier has been found to overcome objectionable features of previously used capacitive probes. Studies on complete windings have indicated the suitability of the test for the detection and location of large internal voids and surface discharging. The optimum tuned frequency to provide a good compromise between sensitivity and selectivity was found to be approximately 5 MHz for the windings studied. Tests on generator windings with this probe also reveal the extent of propagation of high-frequency pulses through windings. Further studies are planned to explore more precisely the types of winding defects for which this test method may be expected to yield meaningful results. Copyright © 1969 by The Institute of Electrical and Electronics Engineers, Inc.