PARTIAL DISCHARGE REPRESENTATION:

                          The weak points in an insulation like voids, cracks, and other imperfections lead to internal or discharges in the insulation and as they are small, were not revealed in capacitance measurements but revealed as power loss components, contributing for an increase in the dissipation factor

                                ‘PARTIAL DISCHARGES’ in a course of time reduces the strength of insulation leading to a total or partial failure or breakdown of the insulation

Consider           Ca as capacitor with a void inside the insulation.

Capacitance of the void is represented by a capacitor in series with the rest of the insulation capacitance (Cb).

The remaining void-free material is represented by the capacitance Cc

When the voltage across the capacitor is raised, a critical value is reached across the capacitor Ca and a discharge occurs through it i.e. it becomes short circuited. This is represented by the closure of the switch.

Generally Ca << Cb << Cc.

A charge Δqa present in the capacitor Ca flows through Cb and Cc giving rise to a voltage pulse across the capacitor Cc. A measure of the voltage pulse across the capacitor gives the amount of discharge quality