Overhead crane operation to prevent motor phase protection circuit

Large-scale industrial enterprises of all types in the room, are generally fitted with  overhead bridge crane s.  bridge crane  on the power of the motor is achieved by collector trolley line in sliding contact angle powered, long-term operation of the crane, because the collector badly worn, or severe localized corrosion trolley line, trolley line will appear poor contact, resulting in missing motor phase operation. In addition, the causes of accidents caused by the wear of the motor lead disconnected, or inverse time overcurrent relay settings unreasonable, etc., will cause an accident. For example, I plant 101 workshop fire pressure Kobo l0 ton bridge cranes, bridge on the slip line collector severe wear, when the car walking, gliding to a fixed collector trolley line of porcelain at the time, met individually porcelain collector after shave or off from the trolley line, causing the motor phase operation, the crane has burned for this reason has been a platform trolley travel motors and one hook motors.

To prevent the bridge crane runs on electric motor to burn out due to lack of phase, we designed a protection circuit. The circuit shown in Figure 1. In total angle trolley line into the line at the creation of a power station AC contactor KM, the trolley line power supply terminal and the motor terminals of each resistor Rl, R2 connected in star symmetrical loads, their midpoint through the bridge rectifier, DC relay KA attract receiving coil, KA is a normally closed contact in series with the KlVl control loop.
In the normal state, the voltage of three-phase power are balanced throughout and symmetric, two star resistive load midpoint voltage between 0l and 02 is 0, the relay does not operate KA. If the trolley line 81 and 3
Office or soft wire cl-c3 off at any point, or collector bl ~ b3 either an accidental fall, 01 point and 02 point special produce a voltage, current through the rectifier DC power supply to the relay coil to attract KA KA action, it normally closed contact breaking, contactor KM moves to cut off power to prevent the motor single phase operation.
If you prevent the power phase of the main part of the bridge on the crane, it may not add contacts KIVl, only the normally closed contact relay KA series with the crane master loop can be. When supply phase failure, KA special equipment normally closed contact of the main circuit power supply cabinet starter contactor is disconnected, to prevent motor single-phase operation.