An example of troubleshooting the hottest low volt

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Troubleshooting of low-voltage distribution board an example

1 fault phenomenon

a stone processing plant, the main machine stopped due to the failure of the control board. The host is a 30kw4 pole asynchronous motor, which adopts y/△ step-down starting and thermal relay for overload protection. After shutdown, the worker on duty did not ask the electrical worker for maintenance. After 10 minutes of formula (15), the motor was restarted and operated normally. The three-phase voltage and current on the observation panel are normal and do not exceed the set value. After running for more than an hour, it suddenly stopped

2 fault cause analysis and treatment

refer to the electrical schematic diagram and check whether the contacts, coils and connecting wires of the control circuit relay are loose or have poor contact. Check whether the fuse and stop button are connected and the contacts are in good condition with the line lamp. Press the armature of the intermediate relay, and its dynamic contact is connected normally. At the same time, manually operate the time relay, and the delay contact is connected normally. The interlocking contact of the AC contactor is in good contact. Use a multimeter to measure that the coils of relevant relays and AC contactors are in good condition. Check the connecting wires, and no problem is found. Therefore, it is certain that the secondary control circuit is normal. Continue to check whether the connecting wire and @b run normally at all speeds. It was found that there was electric burn at the connection between the small aluminum bar and the thermal relay. Check with a large screwdriver and find that the screw is not loose. You can preliminarily determine the problem. Due to the loose connector, the contact resistance increases and heats up, and the heat is transferred to the interior of the thermal relay, causing the thermal relay to act after a period of operation, and the host machine stops. Remove the aluminum bar, polish it with emery cloth, replace the screws, and then fix it. At the same time, check all the connecting contacts, and start the host to return to normal

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