Fault current limiter

A current limiting circuit for insertion in a power line between an AC power source and a load, comprising first and second series resonant branch circuits,

• a capacitor and an inductor in each of said branch circuits tuned to the AC power frequency, and having a common circuit node therebetween, whereby substantially no impedance is offered to the power line by the branch circuits at resonance,
• means for switching connected between said common circuit nodes in said first and second branch circuits, said means for switching being actuated in response to a fault current in the power line, and operating when actuated to detune said first and second branch circuits, whereby high impedance occurs and fault current in the power line is limited, and
• a resistance in parallel with each of said capacitors, whereby switching transients and voltage oscillations thereacross are reduced, said resistance comprising a voltage divider, first and second junctions on said voltage divider, said means for switching comprising a first switch connected between said common node in said first branch circuit and said first junction, and a second switch connected between said common node in said second branch circuit and said second junction.