A 35kV busbar typically requires a power-frequency withstand voltage of around 70–75 kV RMS for 1 minute, with higher impulse voltages for lightning or switching tests.

Power-Frequency Withstand Voltage

For a busbar rated at 35kV, the IEC 62271-1 standard recommends that the busbar insulation be capable of withstanding approximately 2.0 to 2.2 times the rated voltage for a 1-minute AC test. This translates to a power-frequency test voltage of roughly 70–75 kV RMS between phase-to-phase and phase-to-ground under standard test conditions. This ensures that the busbar can safely operate without dielectric breakdown during normal and transient overvoltages .

Impulse Withstand Voltage

In addition to AC testing, busbars are often subjected to lightning impulse tests. For a 35kV system, the standard impulse withstand voltage is typically 150–170 kV peak, depending on the insulation design and environmental conditions. This protects against transient overvoltages caused by lightning strikes or switching surges .

Clearance and Creepage Considerations

The physical spacing between busbars and between busbars and ground is critical to achieve the required withstand voltage. IEC 62271-1 provides minimum clearances for phase-to-phase and phase-to-ground distances, which are designed to prevent flashover under rated and overvoltage conditions. Proper selection of insulators and supports ensures mechanical and electrical integrity .

Summary

• Rated voltage: 35 kV
• Power-frequency AC withstand voltage: ~70–75 kV RMS for 1 minute
• Lightning impulse withstand voltage: ~150–170 kV peak
• Standards: IEC 62271-1, ANSI C37.23
• Design considerations: Adequate phase-to-phase and phase-to-ground clearances, proper insulator selection, and mechanical support to withstand electrodynamic forces during faults . These values provide a safe margin for insulation performance, ensuring reliable operation of the 35kV busbar under both normal and transient conditions.