Multifunctional protection circuit for detecting harmonic current

It has phase failure and overload protection functions.
    This circuit uses two sets of current transformers, 1TA1, lTA2, and lTAs are out-of-phase signal detection components; 2TA1,
2TAz, and 2TA3 are overload signal detection components. Adding winding ∞2 to the contactor KM coil instead of a transformer can save a
step-down transformer.
    In the figure, the capacitor Cs acts as a delay for several seconds to avoid malfunction due to current impact during startup and to avoid
short-term overload current that occurs during normal operation of the motor.
    Both sets of current transformers can be made of manganese-zinc MX0-2000 type magnetic surround. The secondary winding is wound with
about 500 turns of lacquered wire with a diameter of 0.2mm, and the primary winding is wound with 2 to 3 turns of power wire.