| 摘要 |
PURPOSE: To prevent an electric motor from being damaged by a fire by a method wherein the operating point of an overload protective device with reference to the load current of an inverter is made variable in a direction in which the operating point is lowered in a region in which an inverter output frequency is low. CONSTITUTION: A command value 81a at an inverter output frequency is input to an overload protection point setter 833, and an overload protection point is changed according to the input command value 81a at the inverter output frequency. That is to say, since the operating point of the setter 833 is set at 105% of a rated current, the operating point is made variable in a direction in which it is lowered at the frequency or lower. Thereby, it is possible to prevent a drawback that an electric motor is damaged by a fire or the like, and a cooling effect can be made good. |
