Is Partial Discharge (PD) an issue?

By H du Preez, Consultant


Published in:

Electricity+Control, July 2014 (pages 16-19)



Read the full article  - Is Partial Discharge an issue? - in PDF format.


We know that Partial Discharges (PDs) take place in all medium and high voltage machines and equipment, but Low Voltage (LV) motors, operating with electronic adjustable speed systems, may also be subjected to partial discharge conditions.

Partial Discharge (PD) is a localised electrical discharge in an insulation system that does not completely bridge the electrodes. It is a phenomenon that occurs only at higher ac voltages (above 2 000 Vac rms (root mean square) line voltages). Partial Discharge (PD) was originally believed to be a problem only above 4 000 V.

The higher the voltage, the more destructive the activity; the higher the altitude, the lower the voltage for the onset of destructive Partial Discharge (PD). Partial Discharge (PD) is a leading cause, and indicator, of insulation breakdown.

Partial Discharge (PD) arises in a motor winding when electrical stresses in the air rise above withstand levels. It is usually caused as a result of low energy discharge pulses that occur continuously during operation which cause the insulation to slowly break down and eventually fail. Partial Discharge (PD) PD causes premature failure of the insulation – shortening the life of the machine.


Take note

  • Partial Discharge (PD) activity can lead to insulation failure.
  • Regular assessment of motor insulation must be done.
  • Partial Discharge (PD) measurements can be made on line.