ROTARY TRANSFORMER

PROBLEM TO BE SOLVED: To provide a rotary transformer which can surely supply power to the rotating side, transmit a detection signal on the rotating side to the fixed side, and in particular, can be suitably applied to a field ground fault detecting apparatus of an AC generator. SOLUTION: A rotating side power source coil 21 and a fixed side power source coil 24 are wound around a rotating shaft 22, and a voltage to be applied to the coil 24 is made to be induced in the coil 21. A rotating side signal transfer coil 26 and a fixed side signal transmission coil 27 are made to face each other in a part of a rotor core 23 and a part of a stator core 25, and are wound around a shaft rectangular to the rotating shaft 22. A voltage, based on a signal supplied to the coil 26, is made to be induced in the coil 27, thereby making perform it signal transmission.