Do-it-yourself trial production of phase failure protection device

Working principle of phase failure protection device

By utilizing the characteristics of the star connection, when the three phases are unbalanced or a phase is lost, a voltage is generated between the star point and the ground. This voltage is used for control to cut off the three-phase power supply, thereby protecting the electrical equipment.

The circuit connection is shown in the figure. Three capacitors of the same specification are connected in a star shape and connected to the three-phase power line in front of the protected electrical appliance. A wire is drawn from the star point 0 and connected to one end of the coil through a diode D, while the other end is connected to the neutral line or the ground. The diode D here is added to ensure the reliable attraction of J1. The contact K1 of J1 is connected in series to the coil J2 of the three-phase AC contactor. K3 is a normally open push button switch. It is connected in parallel to both ends of a pair of contacts of K2 for starting.

During the working process, close the main switch K, press K3, the AC contactor is closed, the three-phase power is connected, and the load operates normally. If there is a fault in the line, the three-phase is unbalanced or the phase is broken, resulting in current in J1, K1 is attracted to cut off the current of J2, K2 disconnects the three-phase power supply, and the load is protected.

Component Selection

The three-phase AC contactor J2 depends on the load size. The capacitor c^~ce should be an AC capacitor with a non-polar withstand voltage of more than 400V and a capacity of about 1μF. The working voltage of J1 is about 10V, the coil current is more than 10mA, and the contact working current is determined by the power of the AC contactor. K3 is a normally open push button switch, as long as the insulation is safe. D is an ordinary rectifier diode.