The invention relates to an air-gap field detecting device of an alternating-
current generator, comprising a detecting coil and a
signal detecting and
processing circuit, wherein the detecting coil is arranged on a rotor of the alternating-
current generator and surrounds one zone on the inner surface of the
stator, and the
induced voltage of the detection coil is relevant to the strength of an air-gap field in the zone surrounded by the detecting coil, as well as the distribution condition and the changes of the air-gap field; the
signal detecting and
processing circuit is connected with the detecting coil and used for detecting and
processing the
induced voltage of the detecting coil; the
signal detecting and processing circuit can be used for detecting and processing the fundamental
waves or the
harmonic waves of the
induced voltage of the detecting coil, or detecting and comparing the induced voltages of different detecting coils, and the detection and processing result can be used for the monitoring of the states of the generator, including the faults of
stator and rotor windings, the decentraction of a
stator and a rotor, axial and opposite shift of the stator and the rotor,
magnetism loss, overload, external
short circuit and circuit breakage and the like; and the detection and processing result of signals can also be used for the operation control of the generator.