There are two main methods of testing large capacitive loads: Variable Inductance (VI) Series Resonant Circuits and Variable Frequency (VF) Series Resonant Circuits.

In the first case the frequency is fixed at 50Hz or 60Hz and in the second case the Inductance value is fixed. Both methods result in the load being tuned to the source impedance to achieve series resonance.

In the of VF systems test frequencies can go down to 20Hz to achieve maximum load. In the case of VI systems test frequencies are fixed at the source frequency.

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