Patent ID: 6888709

Claim:
A an apparatus for suppressing transient voltage surges in a three-phase power supply bus, said power supply bus comprising at least a first, second and third power line, each power line corresponding to a respective phase of the three-phase power supply bus, comprising: a) a reference node; b) an interface having an input side and an output side, said input side coupled to at least said first, second and third power lines and said output side of said interface having a first, second and third output nodes; c) a first transformer having a primary side and a secondary side, said primary side having a first primary terminal and a second primary terminal, said first primary terminal coupled to said first output node of said interface and said second primary terminal coupled to said reference node, said secondary side of said first transformer having a first secondary terminal and a second secondary terminal; d) a second transformer having a primary side and a secondary side, said primary side having a third primary terminal and a fourth primary terminal, said third primary terminal coupled to said second output node of said interface and said fourth primary terminal coupled to said reference node, said secondary side of said second transformer having a third secondary terminal and a fourth secondary terminal, said fourth secondary terminal coupled to said first secondary terminal; e) a third transformer having a primary side and a secondary side, said primary side having a fifth primary terminal and a sixth primary terminal, said fifth primary terminal coupled to said third output node of said interface and said sixth primary terminal coupled to said reference node, said secondary side of said third transformer having a fifth secondary terminal and a sixth secondary terminal, said sixth secondary terminal coupled to said third secondary terminal; f) a resistor, coupled between said second secondary terminal and said fifth secondary terminal; wherein the circuit formed by said resistor and said secondary sides of said first, second and third transformers is not electrically connected to said reference node.