| 摘要 |
PURPOSE:To readily diagnose the damage by a simple circuit by comparing the frequency of a beat waveform obtained by demodulating a current flowed through a stator winding by an envelope circuit with the frequency of a beat calculated on the basis of a rotating frequency meter. CONSTITUTION:The stator current of a squirrel-cage induction motor IM is detected by a CT 1, and input to an envelope circuit 2. The circuit 2 full-wave rectifies the input current, filtered by an LPF, and the waveform of the beat frequency which does not contain a DC component is output through an insulat ing transformer. The output of the circuit 2 is input to a frequency counting display circuit 10 to display the beat frequency. The rotating speed obtained by a rotating frequency counter 11, the frequency of a commercial power source and the number of poles of the motor IM are input to a beat frequency counting display circuit 12 to calculate and display the beat frequency. If the output of the circuit 10 is 0, there is no damage of a rotor bar, and if the displays of the both display circuits are equal, there exists a damage. If the displays are different, there is a variation in loads. Thus, the damage can be readily diagnosed. |
