Processes Contributing to Low DC Tracking Failure

This paper describes the correlation between tracking phenomena and the behavior of dissolved and deposited metals from copper or brass electrodes at the interface between an electrolyte and paper phenolic laminate. The test method resembles the IEC tracking test, but with the application of a low dc voltage. The paper also describes the results of an analysis of the dissolved and deposited metals obtained by electron microscopy and X-ray diffraction. It was found that the dissolved metallic compounds from positive copper or brass electrodes were Cu(OH)Cl and Cu2OH)3C1, or Cu(OH·Cl)2·2H2O and Cu2(OH)3C1, respectively. On the other hand, the deposited metals originating from the negative copper or brass electrodes were Cu or Cu and Zn, respectively. When the deposited metals bridged the electrodes, the test solution was evaporatedby joule heating caused by leakage current in the deposited metals on the insulation surface, after which scintillation appeared at the edge of the positive copper or brass electrodes. Theseprocesses were repeated until tracking took place.