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Q:What are the common electrical faults of 5t overhead cranes


European Standard double  girder hoist crane .jpg

(1) The main contactor KM does not attract
    This failure may be the knife switch QS or the emergency switch SA1 is not closed, check the switch. If it is not a switching problem, the fuse FU1 may be blown or the line may be without voltage. If there is no problem with the power supply, check the cam controller. It may be that the cam controller has not returned to zero position. It may also be that the contacts of the cam controller are damaged and should be replaced or repaired. The open circuit of the contactor KM coil can also cause the KM to not pick up. If the power is turned on and the voltage is normal, you should listen to the contactor for electromagnetic noise and feel if there is slight jitter. If yes, the contactor is stuck.
    (2) When the cam controller is closed but the motor does not rotate
    The cause of the failure may be a loose wiring line or open circuit leads to no voltage, which can be repaired according to the situation. When the motor rotor circuit is open or the resistor is open, the motor cannot rotate. Open circuit between the motor's slip ring and the corresponding brush will also affect the rotation of the motor. The cause of the malfunction may also be a poor contact of the cam controller contacts. In this case, check whether the contact of the cam controller to the motor stator circuit is connected. The cause of the fault may also be the open circuit of the motor stator common connection line, which may cause the motor to run out of phase and cannot run. Observe whether the motor has a missing “click” sound and slight jitter when starting the motor. If any, find the open section and repair it. .
    (3) After the main contactor KM is pulled in, the overcurrent relay immediately trips.
    First, it may be considered that the setting value of the overcurrent relay is not suitable, resulting in malfunction, and the overcurrent relay setting value can be adjusted to try again. After troubleshooting, the overcurrent relay should be removed and sent to the relevant department for precise adjustment. Problems with the motor can occur if the stator circuit of the motor is shorted to ground or the motor leads are shorted or the mechanical parts are stuck.
    (4) The motor output power is reduced, and the number of revolutions is significantly slowed down
    At this point check that the brake is completely loose or check the controller for bad contact. This can also be caused by too low line voltage or stuck mechanisms.
    (5) The motor can only run in one direction
    This may be due to the failure of the control loop to fail to open contacts or pressure springs. If the contact wear is too large, it cannot be turned on and it should be replaced. Damage to the cam in the controller can also cause this. The cause of the failure may also be an open limit switch, which should be found and repaired.
    (6) Motor starting shock is large and speed adjustment is abnormal
    This kind of fault is usually a short circuit in the rotor circuit of the motor, and it may also happen that the speed regulating resistor cannot be removed by normal stages. Therefore, check the rotor circuit. The inspection method is: Cut off the power, remove the three wires connecting the resistors of the motor slip ring terminals, measure the resistance between them and find the short circuit point. Sometimes the short circuit point may also appear on the brush device, because the conductive dust accumulates on the brush holder, it may also cause two-phase short circuit or insulation breakdown of the brush bar to form a two-phase short circuit. If you find out that the cause of dust accumulation can be cleaned, if it is a problem with the brush stem, it should be repaired.
    Sometimes the collector ring can also cause a short circuit. If it is dust, clean it. If it is damaged, repair it or replace it.

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