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Cause analysis of electric hoist lack of phase and short circuit

Views: 4     Author: Site Editor     Publish Time: 2020-07-28      Origin: Site

The electric hoist frequently appears lack of phase during use; the wire in the control box is broken or loosened (open circuit or short circuit); then it is found that the main contact of the main contactor is frequently burnt, and the main contact that is newly replaced is basically maintained every time It was burned again in less than a week. And it directly caused the burning of the hoisting motor, and the main contactor and the intermediate relay as a transitional effect had jitter and jump phenomenon, and the motor started frequently.

Analysis of the cause of the failure: The electric hoist adopts a single-beam, dual-motor, and separate structure of hoisting and walking motors. At the same time, for safety reasons, the internal control of the electric hoist adopts a safety voltage of 36 V, and the two control boxes are fixed in Two sides of the electric hoist body. The large control box is equipped with two 100 A, 36 V Siemens AC contactors (3TF47); one 16A, 36 V Siemens AC contactor (3TB43); one 100 VA, 380 V/36 V control transformer. A 16A, 36V Siemens intermediate relay (3TH40) is installed in the small control box. The control element is fixed on a steel plate about 2 mm thick with M4 screws, flat washers and spring washers, and the steel plate is fixed in the control box with three M6 screws.

Simply replacing the components inside the control box and tightening the wires did not completely solve the fault. So the failure is divided into two obvious issues to discuss.

Wire failure inside the control box: After field observation, the electric hoist will be affected by various vibrations during use:

The vibration caused by the collision between the hopper and the protective ring of the acetylene generator when feeding;

Vibration generated when walking and lifting motors start and stop;

The vibration generated by the vibrator of the acetylene generator is transmitted to the electric hoist through the hopper and steel cable;

Vibration generated when the internal contactor of the control box is closed and released;

The bottom plate is fixed with M6 screws without spring pads. Only 3 of the 4 screws should be installed, and the screw holes are not completely aligned during processing.

It should be said that the vibration from all aspects of the electric hoist is the external cause of the loosening and disconnection of the internal wires of the control box, and the defects in the design, processing and installation of the fasteners are the internal reasons.

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