One of the automatic control circuits that only allows the motor to run in one direction

90. In some places, the motor is only allowed to run in one designated direction. Even when the power phase sequence
is reversed for some reason (such as incorrect connection after external circuit maintenance), the motor must be guaranteed to run in the designated direction. Otherwise, personal and equipment accidents may occur
. For this purpose, a phase sequence discriminator can be used for control.
    The circuit is shown in Figure 3-90. When the phase sequence of the power supply is correct, that is, when the phase sequence is U, V, W, the neon bulb Ne does not light up, the relay
KA is closed, and the start button SBi is pressed, the contactor KMi is closed, and the motor starts running in the forward direction. If the power phase sequence
is wrong, Ne lights up and KA releases. Press the SBi, KMz suction table, change the phase sequence of the motor and then connect it to the power supply . The motor
will still start running in the forward direction.