| 摘要 |
PURPOSE:To contrive a controlling device with its overall size compact by a method wherein a thyristor is provided making and breaking the electric motor main circuit and electric currents detected by current transformers are used to decide on an excessive load, open phase, or inverted phase, for the controlling of the gate of said thyristor. CONSTITUTION:A triac 16, a double-throw thyristor, is connected to the R and T phases of a 3-phase iduction motor IM, and each of the three phases is provided with a current transformer CT whose output is supplied to an excess current decision circuit 18 of a 3E relay or the like detecting an excess load, open or inverted phase. The output of the decision circuit 18 triggers the gate G of the triac 16 to break the power supply. The device being thus constructed, the motor IM is protected with an extremely compact device without using such a complicated means as an electromagnetic contact means, which results in a great reduction in the space a controlling board occupies. |
