The present invention relates to a three-phase motor protection circuit comprising: first, second, and third phase power input terminals respectively connected to three phase power input lines; A current transformer connection terminal connected to a current transformer installed for monitoring the current of a motor which is operated by receiving power from the three-phase power input line; And an overload setting variable resistor and a no-load setting variable resistor connected in parallel between the first phase power input terminal and the second phase power input terminal, wherein the overload setting variable resistor and the no- A delay angle setting unit for outputting a signal having a phase delayed by a predetermined angle with respect to a phase of the first phase power source; A transformer connected between the second phase power input terminal and the third phase power input terminal and having a center tap having a phase difference of 180 degrees with respect to the first phase power supply; And a first diode and a second diode which are connected in parallel to each other in a reverse direction between a line commonly connected to one of the center tap of the transformer and the current transformer connection terminal and a line connected to the other of the current transformer connection terminals A square wave converting unit for short-circuiting a voltage equal to or greater than a predetermined value obtained from the current transformer to convert an AC sine wave into a square wave; An amplifying unit amplifying the output of the square wave converting unit; An overload detection flip-flop for maintaining an output according to a parallax between a phase of a load current output from the amplifier and a delay angle set by the overload setting variable resistor for a wavelength; A load detecting flip-flop for holding an output according to a time difference between a phase of a load current outputted from the amplifying unit and a delay angle set by the no-load setting variable resistor for a wavelength; And an abnormality signal detecting unit for detecting and outputting an abnormality signal of the motor from the output of the overload detection flip-flop and the no-load detection flip-flop. According to the present invention, by detecting the motor abnormality by comparing the delay angle of the current due to the change of the inductance of the motor and the delay angle of the preset voltage, it is possible to precisely set the detection sensitivity regardless of the fluctuation of the amount of current of the load. There is an effect that the abnormality of the motor can be accurately detected even if magnetic saturation occurs.
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