PD testing remains the best early warning indicator of insulation degradation. Unlike other insulation testing techniques, PD measurement uniquely enables the detection, localisation, and characterisation of specific insulation defects, making it a critical diagnostic tool in HV asset management. Rotating machines are particularly susceptible to PD activity due to high electrical and mechanical stresses - at no point on the HV network is the HV closer to the ground point.

Offline PD testing is conducted accordingly to the IEC 60034-27 and/or IEEE 1434 standard(s) at working frequency, using a resonant test set and High Voltage Coupling Capacitor (HVCC) PD sensor. HV is applied in a stepped approach, phase to ground (with the remaining phases grounded) and unlike on-line PD testing elevated voltages allow tolerances to be understood without overstressing/damage the machines insulation, whilst isolating the assets from cross-coupling from other assets and associated noise. PD Inception Voltage (PDIV), PD Extinction (PDEV) and maximum PD charge (in pC & mV) are recorded and can be trended against previous and future test results.

To find out more about Offline PD testing, contact us via our online form.