Under the circumstances of three phase opening and three phase seriously unbalance, the circuit can cut off the loaded electric power supply automatically, give light as siren with LED, and indicate the cause of leading to protection, and when the three phase electric supply source having recover to the range from 180V to 260V, it will again supply the electricity.

In order to insure electric-motor running safely,and to be immune to burn-up while lost its phase,besides of general safe considerations,some other protections should be taken into account such as lack-phase protection,so the rest of this paper will depict why an electric-motor lost its phase and how to deal with the problem.

With the advantages of simple,safe and reliable structure,flexible application,it can be applied to the power protection against the faults including over-current, over-voltage and lack-phase.

Improvement of three-phase asynchronous motor open-phase protect function;

After power-flow calculation of 110 kV transmission line with open-phase fault, this paper addresses the precautions during long time operation of open-phase transmission line and main transformer, and analyzes the feasibility of load transfer of open-phase line in closed loop network.

In this paper,the damage of three-phase asynchronous motor open-phase and overcurrent is introduced.

Improvement on Lack Phase Protection Circuit of TV Transmitter;