Motor phase loss automatic time delay protection circuit

Circuit working principle: The motor phase loss automatic delay protector circuit (Figure 1-16a
) is composed of capacitor C. ~c8, diode VD, resistor Rl-Rs, Zener diode
vs. , light-emitting diode LED, single-junction transistor vu and relay KA. Close
the knife switch Qs and press the start button SB2, then through L2, phase, relay KA,
thermal relay FR, SB. The normally closed contact and the KM coil of the AC contactor form a circuit for
electrical action. When the three main contacts connected in series in the main circuit are closed, turn on the three-phase power supply
to make the motor rotate, release SBz, and it will return to the off position under the elastic force of the spring.
When the auxiliary contact and the main contact of the AC contactor in parallel with SB2 are closed at the same time, the KM
coil is still energized and self-locking. When it is time to stop, press SB again. , once the moving contact is disconnected, the auxiliary contacts and main contacts
of the contactor are all disconnected, and the motor cuts off the power supply and stops running.