| 摘要 |
PURPOSE:To alleviate a mechanical shock at switching time by varying a time from power source OFF during high speed operation to power source ON during low speed operation according to a load when the speed is switched from high to low speeds. CONSTITUTION:When high speed operation switching units 2, 3 are opened, a time limiter TB operates by a time limit specified by a load detector 8 for calculating a load amount on the basis of a current transformed by a current transformer 7 with the open of the units 2, 3 as a starting time, and the second switching unit 1 is closed for low speed operation. Accordingly, the time limit until the second unit 1 is closed is the time limit in response to the load of a pole change conversion motor 4, the speed of the motor 4 at energizing time becomes coincident to the speed at low speed operation time or near the speed, thereby alleviating the mechanical shock. |
