PARTIAL DISCHARGE MEASUREMENTS

 PARTIAL DISCHARGE PHENOMENON: TERMINOLOGY USED

1. Electrical Discharge: The movement of electrical charges through an insulating (dielectric) medium, initiated by electron avalanches.

2. Partial Discharge: An electrical discharge that partially bridges the dielectric or

insulating medium between two conductors. Examples are: internal discharges, surface discharges and corona discharges.

➢ Internal discharges are discharges in cavities or voids which lie inside the volume of the dielectric or at the edges of conducting inclusions in a solid or liquid insulating media.

➢ Surface discharges are discharges from the conductor into a gas or a liquid medium and form on the surface of the solid insulation not covered by the conductor.

➢ Corona is a discharge in a gas or a liquid insulation around the conductors that are away or remote from the solid insulation.

3. Discharge Inception (Applied) Voltage: It is the lowest voltage at which discharges of specified magnitude will recur when an increasing ac voltage is applied.

4. Discharge Extinction (Applied) Voltage: It is the lowest voltage at which discharges of specified magnitude will appear when an applied ac voltage, which is more than the inception voltage, is reduced.

5. Discharge Magnitude: It is the quantity of charge, as measured at the terminals of a sample due to a single discharge.

6. Discharge Energy: It is the energy dissipated by a single discharge.

7. Average Current: It is the average value of the discharge current during a cycle due to a single or multiple discharges. Ia, the average current over an interval T can be expressed as

when, q is the apparent charge in rth discharge.

8. Quadratic Rate: It is the average value of the square of the discharge magnitudes. D, the quadratic rate is given as

9. Discharge Detector: It is a device or an instrument used for either detecting and/or measuring the discharges.

10. Sensitivity: It is the magnitude of the smallest individual discharge that can be measured under particular test conditions.

11. Resolution: It is the minimum interval between two discharges which can be measured without the magnitude of one discharge affecting the other.