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While there is a great deal of good information on PD on the internet and in technical papers, there is also a great deal of hype, misrepresentation and sales propaganda out there. Consequently, it is important to get information on this diagnostic from the proper standards.
Partial Discharge (PD) is a very fast, small electrical spark or discharge that does not completely collapse the applied voltage. HV Diagnostics supplies a diagnostic tool that can identify the presence and location of Partial Discharge in your insulation, terminations and splices.
The locations where PD occurs are hit repeatedly and constantly and will cause cable failure if given the time to breakdown. This test is important for any new cable installation where workmanship defects and cable manufacturer defects can be examined and corrected before energization. It is also a useful tool in maintenance testing as cable that originally has these voids can be severely degraded over time. It is best to catch the defects in a controlled testing environment instead of having a catastrophic failure during operation.
PD is normally no more than a few mV in amplitude and when considering that the applied voltage is normally several kilovolts, with good modern test instruments, you are literally detecting a needle in haystack, when you detect and measure PD. The PD series of partial discharge detectors, primarily geared at cables, allows the operator to detect and locate PD. The systems have been designed to work with the HVA Series of VLF high voltage test generators. The powerful software that comes with the PD systems has been engineered to be user friendly and flexible allowing the operator to detect and interpret PD activity coming from the device under test (DUT).
As in any diagnostic field, be it medical or engineering, providing a true and accurate diagnosis of the health of a person or device, often requires the combination of more than one diagnostic test. It is very seldom that simply one diagnostic is sufficient to provide enough information to make a complete and accurate assessment. With electrical apparatus such as cables, performing a couple of tests is always better than simply pinning your hopes on just one. The PD/TD series of test instruments provide a combo package of Partial Discharge and Tan Delta in one integrated system allowing the testing engineer to perform a multitude of diagnostic tests, thereby gaining a better understanding as to the condition of that device.
For example, there are many case studies from the field, where a cable has had no PD present, had good TD results, but then went on to fail the 30 minutes withstand (hipot) test. In other cases, a cable that passed the withstand test, had no PD present and failed the TD diagnostic test – moisture in a splice was one example. In other cases, we have had cables that passed both the TD and withstand test but had PD activity present in a termination. There are obviously also those cases where a cable can fail all 3 types of tests and one could argue that even the relatively simple but effective withstand test would have been sufficient. The bottom line is that there is no one tool will work every time to effectively diagnose the condition of an electrical device such as a cable.
All the combo systems are shipped in a rugged injection molded transport case(s) that house the instrument and all its accessories. The PD/TD combo systems combine with the HVA series of VLF AC sources. HVA Systems are sold separately. All the customer needs to provide is a Windows compatible laptop/PC and true desire to accurately assess their cable systems.
