The changes in discharge properties during irradiation forms the basis of X-ray induced PD (XIPD) location methods. By using an aperture arrangement to restrict and direct a beam of radiation during PD measurements, selected regions of the insulation can be systematically investigated. Large insulation systems can be tested with progressively restricted radiation sources to identify the regions responsible for the discharge. An example of this procedure is illustrated which relates to an XIPD test performed on a cylindrical insulator, rejected for exhibiting high PD levels. The insulation material in this case is epoxy resin impregnated paper.
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