| 摘要 |
PURPOSE:To reduce maintenance cost and to extend the life of the brush and a cleaning period by using a brush near the optimum current density that minimizes its wearing amount. CONSTITUTION:When an induction motor 1 is rotated at a high speed, the secondary current of the motor is supplied through brushes 3X, 3Y to a con verter 8 of a power converter. When the motor 1 operates at low speed, a relay unit 20 receives an OFF control signal from a controller 19 to open a contact 20a. Thus, the brushes of energized state are only brush 3X group so that the number of brushes is reduced by half as compared with at high speed operation, but since the secondary current of the motor passing the brushes 3X group is approx. half of that at rated time, the brush current density becomes equivalent optimum value to that at rated time. The wearing amount of the brushes 3Y group through which a current does not flow consist of only mechanical wear, which is smaller compared with that at current flowing time. |
