Partial discharge PC value standard

The PC value of partial discharge (PD) (usually referring to the amount of partial discharge charge, measured in pC, picocoulombs) is an important parameter for evaluating the insulation performance of power equipment. The standards vary depending on the type of equipment, voltage level, application scenario, and international/national standards. The following are common standards and reference values:
1, General standard (IEC 60270)
The International Electrotechnical Commission standard IEC 60270 specifies the measurement methods and limits for partial discharge:
Allowable discharge capacity (typical scenario):
High voltage equipment (such as transformers, GIS): At rated voltage, the partial discharge capacity is usually required to be ≤ 10-500 pC, depending on the equipment type and voltage level.
Cable system (such as medium voltage cable): The local discharge capacity in the handover test is generally required to be ≤ 5-20 pC.
Test conditions:
When the test voltage is 1.5 times the rated voltage (Um), the partial discharge must meet the limit requirements.
2, Equipment classification standards
1. Power Transformers (IEC 60076-3)
Transformers with rated voltage ≥ 72.5 kV:
Under a test voltage of 1.5 × Um/√ 3, the local discharge capacity is ≤ 500 pC;
Under the operating voltage of 1.1 × Um/√ 3, the local discharge capacity is ≤ 100 pC.
2. Gas insulated switchgear (GIS, IEC 62271-203)
At a voltage of 1.1 × Um, the local discharge capacity is ≤ 5-10 pC (specific limit according to the design protocol).
3. Power cables (IEC 60840/IEC 62067)
Medium voltage cable (10~35 kV): Local discharge during handover test ≤ 10 pC;
High voltage cables (≥ 110 kV): Partial discharge capacity is usually required to be ≤ 5 pC.
4. Electric motors and generators (IEC 60034-27)
The partial discharge capacity of high-voltage motors is generally required to be ≤ 1000 pC at 1.2 × rated voltage.
3, Chinese National Standard (GB/T)
GB/T 7354 "Partial Discharge Measurement":
The testing method for partial discharge has been specified, and the limit values should refer to specific equipment standards.
GB 50150 "Standard for Hand over Test of Electrical Equipment in Electrical Equipment Installation Engineering":
For example, in partial discharge tests, transformers of 110 kV and above have a discharge capacity of ≤ 100 pC.
4, Precautions in practical applications
Background noise: During measurement, it is necessary to ensure that the environmental noise is less than 50% of the allowable value (for example, if the standard limit is 10 pC, the noise should be less than 5 pC).
Equipment status: The limit value of new equipment (factory/handover test) is stricter than that of equipment in operation.
Trend analysis: If the partial discharge of operating equipment continues to increase, even if it does not exceed the standard, a warning should be issued.
5, Typical Limit Reference Table
Equipment type test conditions PC value limit (pC)
High voltage transformer 1.5 × Um/√ 3 ≤ 500
GIS 1.1×Um ≤10
High voltage cable (110kV) 1.5U0, 30 minutes ≤ 5
Medium voltage switchgear 1.1 x rated voltage ≤ 20