Partial Discharge vs. Tan Delta Test

They are two entirely different tests although, in extreme cases with very lossy internal partial discharges, it might be possible to detect a change in C tan delta. Partial discharge tests are primarily used to detect internal discharges in insulating structures. It's a very sensitive test that is most effective for high capacitance devices, such as solid dielectric cables, high pressure pipe type cables and terminations, low pressure oil-filled cables and terminations, transformers, transformer bushings, etc. The difficulty arises in shielding or separating internal ionization from extraneous interference. There are several manufacturers of PD detectors.

Tan delta (or dissipation factor) is most frequently measured with a Schering bridge and represents the tangent of the loss angle between current and voltage (delta being that angular difference).

Power factor is the cosine of the phase angle between current and voltage and for angles ≤ 10° power and dissipation factors are considered equal (sin 10° = 0.1736; tan 10° = 0.1763).

noted and accepted.

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PD Causes and Effects

What's a Partial Discharge?A partial discharge is an electrical discharge or spark that bridges a small portion of the insulation between two conducting electrodes.Partial discharge can occur at any point in the insulation system, where the electric field strength exceeds the breakdown strength of that portion of the insulating material.

Partial discharge can occur in voids within solid insulation, across the surface of insulating material due to contaminants or irregularities, within gas bubbles in liquid insulation or around an electrode in gas (corona activity).

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