Partial Discharge Capacity (pC)
Partial discharge capacity (pC) refers to the amount of charge released during partial discharge phenomena in the insulation system of electrical equipment. It is measured in picoCoulombs (pC), representing the small amount of charge transferred in a single discharge event. The following are its core aspects:
1. Definition and Physical Significance
Partial discharge (PD) is a non-penetrating discharge that occurs in localized areas of insulating materials (such as bubbles, cracks, or impurities) under the influence of an electric field. It does not form a complete conductive channel but progressively degrades insulation performance over time.
Unit of Measurement: 1 pC = 10⁻¹² coulombs, reflecting the charge quantity per discharge. For example, 10 pC indicates a charge transfer of 10 × 10⁻¹² coulombs during a discharge event.
2. Influencing Factors and Hazards
Insulation Degradation: Each discharge can cause molecular structure damage (e.g., chemical bond breakage), material carbonization, or the growth of electrical trees. Over time, these effects accumulate, leading to a reduction in insulation strength.
Safety Thresholds: Different equipment types have varying standard requirements. For example:
High-voltage cables typically require partial discharge levels ≤ 10 pC (at 1.73 times rated voltage).
GIS equipment typically requires ≤ 5 pC.
Exceeding these thresholds (e.g., >10 pC) may indicate serious insulation defects and requires further investigation.