The insulation resistance test is a direct current evaluation test of the insulation and gives a reliable indication of the presence of moisture, contamination, or breakdown in the insulation. This test also establishes a benchmark for future comparative tests.
PD defined is a localized dielectric breakdown within a small portion of an electrical insulation system under stress of high voltage, which does not bridge the space between two conductors. Partial Discharge is not yet a complete failure of the insulation, however, it is an indication of what is to come. PD testing determines the presence, and locates PD activity within a system.
Upon completion of an insulation resistance test, we can determine and clasify the type of insulation fault a cable has. If the insulation resistance measurement falls below 100Ω, this is considered a low ohmic resistance fault that can be located by the use of a Time Domain Reflectometer, however if the fault that exists is beyond 100Ω, the fault must then be converted to a low ohmic resistance fault by process of permanent burning, impluse current, or voltage decay
Cable diagnostics and pre-location can provide invaluable data for directly buried cables. Acoustic pinpointing is possible thru the use of a surge generator and a “ground” microphone pinpointing device to show the exact location of the fault.