What is partial discharge


What is partial discharge?

  • Partial discharge (PD) is a local electrical discharge that occurs in defects or inhomogeneities. The current pulse of the PD is measured at the test object connections.
  • The unit of measurement for partial discharge is Coloumb [C] (1C corresponds to 1As). Usual measured values ​​for partial discharge are between 1 and 10,000 pC.
  • As a rule, it is assumed that partial discharges of less than 10 pC will not damage the insulating material.
  • The partial discharge measurement is a so-called “non-destructive test”, i.e. if no high PD levels occur, the test item will not be damaged. In addition, the partial discharge measurement provides a measured value about the quality of the test item.

Forms of PD on simple insulation arrangements

A - TE in the solid insulating material (treeing channels)
B - Corona discharge on tips or edges
C - surface or sliding discharge
D - discharge in a layer material
E - cavity discharge in gas-filled cavities

A distinction is made between “outer TE” outside and “inner TE” inside the test object.


Fully automatic partial discharge test station for measuring partial discharges up to a minimum of 2.5 pC and a maximum of 70 kVAC


When producing electrical insulation, small imperfections or inhomogeneities can occur in the insulating material. If there is an insulating material between an electrode system to which a voltage is applied, local overstress from the electric field occurs at such weak points. This can then lead to a locally limited electrical charge, i.e. to a partial electrical discharge. In general, one speaks of TE when a discharge process only partially bridges the distance between two electrodes, i.e. in the event of a partial breakdown of the insulating path. Partial discharge tests are possible with us in small and medium-sized series.

Measurements according to VDE 0532 Section 12 are possible