Online Partial Discharge Testing
At Megavar we have seen firsthand the damage that partial discharge (PD) can cause to HV assets. We know that the best front line defence against PD, is regular online surveys to identify and localise causes of PD, so that maintenance can be performed before insulation fails with catastrophic results. Our engineers are trained in the use of the Doble PDS100 and the HVPD PDSurveyor™ to perform efficient regular inspections of all asset classes.
Partial Discharge (PD), as its name would suggest, is an electrical discharge that occurs across a portion of the insulation between two conducting electrodes, without completely bridging the gap. After initiation, the PD can propagate and develop into electrical trees until the insulation is so weakened that it fails completely with breakdown to earth or between the phases of a 3-phase system.
Failure of High Voltage insulation is the No. 1 cause of HV system failures with IEEE statistics indicating that electrical insulation deterioration causes up to 90% of electrical failures of certain high voltage equipment. On-line PD testing of MV and HV plant gives advance warning of pending insulation failure thus allowing the plant owner to take remedial action during planned outages.
Unlike off-line testing, on-line PD testing and monitoring gives an accurate picture of the plants health and performance under service conditions.
The Benefits of On-Line Partial Discharge Field Measurements
- It is truly a predictive test, indicating insulation degradation in advance of the failure.
- It is a nonintrusive test, requiring no interruption of service and is performed under normal operating voltage and load.
- It is a nondestructive test; it does not test to failure or adversely affect the equipment under test.
- It need not use any overvoltage, thereby not exposing the tested equipment to higher voltage stresses than those encountered under normal operating conditions.
- Trending can be accomplished by storing results to allow comparison with future tests.
- In many instances the site of the partial discharge occurrence can be located within the test object, so the localised problem can be repaired.
- The cost to perform a PD survey is relatively inexpensive compared with off-line testing, allowing annual surveys to be performed economically at most facilities.
Megavar performs surveying of all asset classes using the HVPD and Doble Instruments to identify sources of high PD and determine their cause and risk levels.
HVPD PD Surveyor
The unique combination of the TEV, Acoustic and HFCT measurement circuits provide an instant, real-time indication of any PD activity in both MV plant and cables, with measurements made in decibels (dB's) for switchgear PD measurements and picoCoulombs (pC's) for the cable PD measurements, as per on-line PD testing convention and practice.
The PDSurveyor™ has been designed by HVPD to meet the specific requirements of both utility and industrial MV plant owner customers further to their requests for a simple, portable and easy-to-use PD test device which can be used by all operational staff in MV substations. The PDSurveyor™ is the only handheld PD scanning device in the marketplace which contains three built-in PD sensors to enable the unit to be used to test both PD in MV switchgear / plant and also the PD activity MV cables.
Doble PDS100 Partial Discharge Surveyor
The PDS100 provides complete substation PD survey capabilities. By simply walking around HV apparatus, sources of PD and external interference can be detected and identified. Routine RFI surveying will assist in locating PD activity while the apparatus is still in service.
The PDS 100 is an RFI surveying tool that is designed for use in a live substation without the need for outages or special connections, the unit can detect partial discharge (PD) in just a few seconds, thus making it perfect for condition based maintenance programs. Whole substations can be surveyed and analysed.
