| 摘要 |
PURPOSE: A motor protection relay is provided to prevent the entry of foreign materials inside a terminal box by adopting a contactless switching unit. CONSTITUTION: A motor protection relay comprises a current transformer(210), a burden resistive unit(230), a contactless switching unit(350) and a controller(310). The burden resistive unit changes the current generated by the current transformer into the voltage. The burden resistive unit has a plurality of resistors with different resistances. The contactless switching unit selectively connects the current transformer to each path of the burden resistive unit and includes at least one of transistor, an FET(Field Effect Transistor), a thyristor, and an analog switch. The controller controls the switching of the contactless switching unit.
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