Circuit for suppressing transients occurring in either common or transverse modes

Claim 1

A circuit for suppressing coupling of common mode and transverse mode transients on an a.c. power line to a load comprising a transformer having: (a) a primary winding adapted to be connected to the power line, (b) a secondary winding having a pair of output terminals adapted to be connected to the load, (c) inductive leakage reactance, (d) an electrostatic shield separating the primary and secondary windings, and (e) a structure electrically connected to the shield and arranged so that the common mode transients are shunted to the structure from the primary winding and the shield via electrostatic coupling between the primary winding and the shield; a low pass filter transverse mode transient suppression network including as its only inductive reactance the transformer leakage reactance to substantially prevent core losses and core saturation and insert substantial reactive impedances in series with the load, and a shunt circuit across one of said windings, the shunt circuit including in series a capacitor and bi-directional breakdown means having a predetermined dead band threshold, the component values of the suppression network being such that the power line frequency is passed thereby without substantial attenuation and high frequency components of the transverse mode are substantially attenuated thereby after achieving the dead band threshold.