A Dry Tracking Resistance Test Method Using a Trigger Discharge

There are many kinds of tracking resistance test methods which may be classified into two groups: wet and dry. In the wet methods, the tracking phenomenon seems inevitably to be affected by the artificial contamination, so the dry method which does not use the artificial contamination may be regarded more suitable than the wet method for the purpose of defining the tracking property. However, the dry methods developed up to this time use relatively high electric voltages, and the form of discharge used in the test is somewhat different from that in actual tracking. So, it is desirable to reduce the testing voltage to get tracking resistance by the dry methods. We have developed a new dry method in which a test voltage less than 1000 volts dc is employed. In our method, the third electrode, the so-called trigger electrode, is inserted between the pair of main electrodes, and the discharge at low voltage between the main electrodes is induced by the small-trigger discharge between the trigger electrode and one of the main electrodes. In our method, it becomes possible to differentiate the tracking resistances of some of those materials whose tracking resistances were not hitherto discriminated by the high voltage test; and some of those materials, which show erosion in the IEC method, show tracking failure by our method. Furthermore, our method provides good reproducibility in results, a rather simple arrangement, and a much shorter time required for testing, than for the IEC method.