A fault protection device incorporated in a transformer having a primary winding and at least two secondary windings connected to ground, and having a sensing coil to sense the fluxes generated by each of the secondary windings and generating a flux signal when an imbalance in the fluxes...http://www.google.fr/patents/US5847910?utm_source=gb-gplus-shareBrevet US5847910 - Fault protection device in a transformer
