Partial discharge test

What is partial discharge?

• Partial discharge (PD) is a local electrical discharge, which results of defects or inhomogenous insulation material. Current impulses of the partial discharge will be measured at the terminals of the test object.
• The scale unit of partial discharge is Coulomb [C] (1 C corresponds to 1As). Common values of partial discharges are between 1 pC and 10000 pC.
• Normally it is assumed, that a partial discharge of less than 10 pC doesn’t lead to any harm to the insulation material.
• The partial discharge test is a so called “non-destructive” test. This means, if there aren’t any high PD-levels, the test item won’t get harmed. Furthermore the partial discharge test provides a measurement of the test item’s quality.

Appearance of partial discharges in simple insulating arrangements

A - PD in solid insulating material (Treeing channels)
B - Corona discharges at sharp edges
C - Surface- or sliding discharge
D - Discharge in layer insulating material
E - Cavity discharge in gas filled cavities

We differ between corona discharges, which are outside of the test object and internal partial discharges, which are inside of the test object.

Fully automatic partial discharge test place to measure partial discharges down to 2,5 pC and up to 70 kV AC

During the production of an electrical insulation, small imperfections or inhomogenous areas can occur in the insulation material. If there is an insulating material located between the electrode system, which is tapped to the voltage, a local overwork due to the electrical field might occur at these
flaws. This overwork can lead to a locally limited electrical discharge. Broadly spoken, a partial discharge appears, whenever a discharge bridges the distance between to electrodes partially, a partial disruptive discharge of the insulation. Partial discharge tests are possible in small and medium series.