What is partial discharge?

• Partial discharge (PD) is a local electric discharge, which is the result of defects or inhomogeneous 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 coloumb [C] (1C corresponds to 1As). Common values of partial discharges are between 1 and 10 000 pC.
• Normally it is assumed that a partial discharge of less than 10 pC doesn’t lead to any harm in the insulation material.
• Teh 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 separate between corona discharges, which are outside of the test object and internal partial discharges, which are inside of the test object.

During the production of an electric insulation small imperfections or inhomogeneous 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 electric field might occur at these flaws. This overwork can lead to a locally limited electric discharge. Broadly spoken a partial discharge appears whenever a discharge bridges the distance between two electrodes partially, a partial disruptive discharge of the insulation. Partial discharge tests are possible in small and medium series.

Measurements conform to VDE 0532 Abs. 12 are possible

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