Series Resonant capacitor used in high-power Medium Frequency Induction Furnace for Silicon Melting or steel melting. 
For an efficient solid state power sources for induction furnace, usually have the induction heating load driven at its natural resonant frequency. 
The furnace coil and a capacitor form a resonant tank circuit. The metal to be heated in the coil which resulting in shift in the frequency. The resonant tank circuit is returned via frequency control circuit to achieve resonance and to enable maximum power transfer to the load at all time.