The Precise Location of Partial Discharge Sites Using Modulated X-Rays

Although techniques for detecting partial discharge activity in high voltage insulation systems are well developed, there exists at present no unified approach to the problem of locating discharge sites. It has been known for at least 20 years that irradiation of a partial discharge by ionising radiation may modify both discharge magnitude and repetition rate, but the effect is subtle, and its effect on the display of a conventional discharge detector may be completely masked by discharge signals from other sites. A new method is proposed and has been experimentally verified wherein partial discharge sites are found by scanning an insulation system with a modulated X-ray beam, and subsequently recovering a signal at the modulation frequency from the output of a conventional PD detector, using correlation and/or spectral analysis techniques. As a test object is scanned by the X-ray beam, knowledge of PD sites is obtained when a signal at the modulating frequency is recovered. The technique is applicable to a wide range of practical insulation systems and offers high spatial resolution and noise immunity. The results of successful searches for multiple PD sites are presented.