VLF vs. series resonant testing: which suits your cable?

Both methods prove that a cable can withstand an overvoltage after installation or repair. The choice depends on cable voltage, length and what the test specification allows.

When VLF fits

Very low frequency (0.1 Hz) testing is common for medium-voltage cable. The low frequency reduces the reactive power needed, so a portable unit can test long circuits.

When series resonance fits

For high-voltage cable and GIS, many specifications call for near power-frequency testing. A variable frequency series resonant system supplies only the losses, keeping the source small.