Application of EOCR motor protector in lifting industry
The bridge cranes in large and medium-sized metallurgical enterprises in China are very old, and the failure rate is high. Accidents that burned the hoisting motor sometimes occurred. This paper describes a bridge crane winch motor overcurrent protector (EOCR-SS).
In bridge cranes, the only device that protects the hoisting motor is the overcurrent relay. In actual work, when the hoisting motor starts, the instantaneous current exceeds the rated current of the motor, and the inherent non-synchronization effect of the motor's hydraulic brake and the motor simultaneously starts, which increases the motor starting current and makes the overcurrent relay set the current. The adjustment is often several times higher than the rated current of the motor. If the crane is exposed to the following conditions during work, it is extremely likely to cause damage.
1. The hydraulic brake is faulty, and the brake that causes the chain reaction with the hydraulic brake cannot be fully opened or hung;
2. The human factor causes overload lifting and does not protect the current relay, so that the hoisting motor burns due to working for a long time exceeding the rated current.
The protector used in this circuit is manufactured by SAMWHA (Sanwa) Co., Ltd., and the model number is EOCR-SS. The current range of the product is: 05 type (0.5A ~ 5A), 30 type (3A ~ 30A), 60 type (5A ~ 60A), 100 type (10A ~ 120A), etc., can be selected according to the rated current of the motor, Optional 05 can also be used with current transformers.
The specific parameters are as follows:
Start delay time: adjust within 0.2s to 30s;
Accuracy: current error ± 5%, time error ± 5%,
Control voltage: 220V, 440Vl two.
Reset mode: manual reset
Ambient temperature: -20 ° C ~ +70 ° C,
Relative humidity: 45% to 85%,
Power loss: <2W.
Phase loss protection: action within 4 seconds,
Three-phase current unbalance protection; the phase-to-phase current difference does not exceed 50%, and the delay is 8 seconds.
Modification method:
1. Install an automatic air switch between the isolating switch and the main circuit contactor. The rated current is equivalent to the main circuit contactor.
2. Remove the three current relays on the original winch and replace them with two current transformers that match the 05 type, and install them in the original position;
3. Install the EOCR-SS protector in the appropriate position of the distribution box and connect the transformer. Adjust the delay time and the protection current of the protector according to the specific conditions, so that the steady current is 1~1.2 times of the rated current of the motor.
Operation: Press the start button ST, the AC contactor KM pulls in, and the motor M operates. When the stop button STP is pressed, the motor M stops operating. In the operation of the motor, if overcurrent or phase failure occurs, the signal is detected by the current transformer TA, and the KM coil voltage is automatically cut off after the delay. When the motor is started, the protector can escape the motor instantaneously through an effective delay. The current can be restarted by manual reset after the protector completes an action for troubleshooting.
