The resonance testing system is widely accepted in any high-voltage testing application with high load, low capacitance, and low loss. For example, power cables, power factor correction capacitors, coupling capacitors, gas insulated switchgear, generator windings, voltage testing applied to transformers, and insulators can be equipped with a complete variable frequency series resonance testing system for factory testing in the laboratory, or installed on trailers or trucks, providing flexibility for on-site testing of installed power lines or other installed HV equipment (such as generators or switchgear).

The difference between a variable frequency series resonant system and a variable inductance resonant system is that it is tuned to a given capacitive load by adjusting the frequency of the test voltage, rather than by adjusting the inductance at a fixed frequency. The advantages are:

The system has no active components

There are no mechanical systems to maintain

Magnetic cores can be designed with distributed gaps to reduce size and weight

Power electronic devices allow three-phase input connections to achieve balanced loads

By reducing the frequency, it is possible to test capacitive loads larger than the power frequency

Compared to the VI system (25:1), the VF system has a wider adjustment range (100:1)

The variable frequency series resonant system has the advantages of a variable inductance system:

The system loses resonance during flashover to prevent current from following the load

The operation has a high quality factor, which can reduce the input power demand

The harmonic distortion of the test output voltage waveform is very low

The system inductance acts as a natural filter for PD on the main power supply