The typical power frequency withstand voltage for a 35kV busbar is around 117kV for 5 minutes, with a partial discharge level below 45kV.

Power Frequency Withstand Voltage

For a 35kV busbar, the power frequency withstand voltage (AC, 50/60 Hz) is generally specified as 117kV for 5 minutes according to GB/T12706.4-2002 and IEC 60502-4 standards . This means the busbar insulation can safely endure 117kV RMS for a duration of 5 minutes without breakdown. This rating ensures that the busbar can tolerate temporary overvoltages and maintain operational safety.

Partial Discharge Level

The partial discharge (PD) inception voltage is an important parameter for medium-voltage busbars. For a 35kV system, the PD level is typically 45kV with discharge below 10pC . Maintaining PD below this threshold ensures long-term insulation reliability and prevents premature aging of the busbar insulation.

Standards and Testing

The withstand voltage values are defined and verified according to international standards:

• IEC 60502-4: Specifies testing procedures for medium-voltage cable accessories and busbar systems.
• GB/T12706.4-2002: Chinese standard equivalent for medium-voltage equipment.
• Testing involves applying the rated AC voltage for a specified duration (usually 5 minutes) and checking for insulation breakdown or excessive leakage current .

Practical Considerations

• The service voltage of the busbar is 35kV RMS, but the insulation is designed to handle significantly higher voltages (117kV) to provide a safety margin.
• Environmental factors such as humidity, pollution, and temperature can affect the effective withstand voltage, so creepage distances and clearances must comply with IEC or DIN standards .
• Busbar insulation materials, typically epoxy or composite insulators, are selected to meet these voltage ratings while providing mechanical stability and long-term reliability . In summary, a 35kV busbar is designed to withstand 117kV AC for 5 minutes, with partial discharge levels below 45kV, ensuring safe operation under temporary overvoltage conditions and compliance with IEC and GB standards .