It is generally the output of the three phase received three detection points, and then connected to the load, adjust the load phase sequence, so that the load turned to normal. At this time the phase sequence protection device is set up.

If there is a mistake in the maintenance phase, the output three-phase change, the protector will be disconnected, play a protective role.

The relay coil is represented by a rectangular box symbol in the circuit. If the relay has two coils, two parallel squares are drawn. At the same time in the box or rectangular box marked with the relay symbol "J". Relay contact has two ways: one is to draw them directly on the side of the box, this representation is more intuitive. The other is in accordance with the needs of the circuit connection, the various contacts were drawn to the respective control circuit, usually in the same relay contacts and coils were marked with the same text symbols, and contact group number, To show the difference.