Q: My GIS is rated for 220 kV. Should I test it at the same voltage the factory used during their Type Test?
A: NO. Field test voltages are lower to avoid "Over-stressing" equipment that has already been shipped and handled.
The "80% Rule":
• Factory Test: The GIS is tested at the manufacturer at 100% of the standard withstand level (e.g., 460 kV for a 220 kV system).
• Field Test: We typically apply 80% of the factory test voltage (e.g., 368 kV).
• Duration: Usually 1 minute at the 80% level.
Why 80%? It is a balance. It is high enough to find any assembly errors or transport damage, but low enough that it won't cause permanent aging of the insulators if there's a minor imperfection.
