Short circuit detection device, and short circuit detection method for rotating electric machine

A short circuit detection method for a rotating electric machine comprising:

• an excitation step of applying an AC excitation current to field windings installed in the rotating electric machine at a predetermined frequency;
• a difference calculation step of calculating a difference value between a measurement value of a voltage or an impedance in the field windings to which the AC excitation current is applied and a value when the AC excitation current is applied while the field windings are in a sound state;
• and
• a short circuit state analysis step of estimating a short circuit resistance based on the difference value, the short circuit resistance being an index of a degree of a short circuit that occurs between layers of the field windings, wherein,
• in the short circuit state analysis step, the difference value when the AC excitation current is applied at a first frequency is compared with a threshold value, the short circuit resistance is estimated from the difference value based on data indicating a relationship between the short circuit resistance and the difference value at the first frequency when the difference value is smaller than the threshold value, the excitation step is caused to execute at a second frequency that is lower than the first frequency when the difference value is equal to or greater than the threshold value, and the short circuit resistance is estimated from a difference value obtained by the AC excitation current at the second frequency based on data indicating a relationship between the short circuit resistance and the difference value at the second frequency.