INTERPHASE INSULATION DIAGNOSING METHOD OF WOUND-ROTOR TYPE INDUCTION MOTOR

PURPOSE:To obtain a method for diagnosing easily whether a interphase insulation is good or not by separating a slip ring of each phase of three phases of an induction motor and a carbon brush contacting by pressing with said ring, opening a secondary winding, and thereafter, impressing the AC voltage to a primary winding, and measuring a current flowing to the secondary winding. CONSTITUTION:When primary voltage is impressed in a state that secondary windings 2u, 2v and 2w are opened, the secondary voltage is induced to each of the secondary windings 2u, 2v and 2w and impressed between layers. In this state, an electric conduction current of a leader line 6u by which a clamp meter 7 is clamped is read. Subsequently, the clamp meter 7 is detached from the leader line 6u, a leader line 6v is clamped, and its electric conduction current is read. Also, the clamp meter 7 is detached from the leader line 6v, a leader line 6w is clamped, an electric conduction current of the leader line 6w is read, and the interphase insulation is decided. In case when the insulation is normal, even in case of any leader line 6u, 6v and 6w, the current value becomes a state near zero. On the other hand, in such an abnormal case as an insulation resistance value of the layer insulation between slip rings 5u, 5v drops, a leakage current flows between the layers of its secondary winding, therefore, a larger leakage current than the normal time is read by the clamp meter 7, and failure of this layer insulation can be decided.