The motor control system consists of switches, fuses, main and auxiliary contactors, relays, temperature, induction devices, etc., and is relatively complex. There are various types of faults, which often require analysis and troubleshooting with the help of control schematic diagrams.
At ordinary times, pay attention to keeping the inside and outside of the control box clean and dry, without water or oil. Regularly (weekly) use a small fan to blow away the dust on the components, terminals and rows in the box, or use a brush dipped in electrical cleaner to clean them. , so as not to affect the operation or insulation of contactors and relays. For control boxes equipped with moisture-drying resistors, generally do not turn off the heating switch at will. The box should also be kept reliably grounded to prevent electric shock.
Regularly (monthly) check the tightening of wiring and screws in the box to prevent loosening of wiring and screws. Check whether components such as switches, contactors, and relays are damaged or burned, and whether the working status of each component and the start, stop, and interlock functions are normal. It is necessary to keep the dynamic and static contacts of the contactor closed and in good contact to avoid burning out of the motor due to phase loss due to poor contact contact. If the contact surface is good but only black, wipe it with a coarse cloth. Do not easily polish off the heat-resistant alloy layer on the surface, otherwise the life of the contact will be shortened. If the contact surface is severely ablated, use "0" sand paper to smooth it out. The moving and static contacts need to maintain line contact or surface contact, rather than point contact. The contact condition can be checked by placing a piece of paper between the moving and static contacts. If the clamp is not tight when closing, it means that the contacts or springs need to be adjusted or replaced. This point needs to be taken seriously. If it is light, poor contact will produce a large contact resistance (current), which means the load increases, causing the overload protection relay to trip. If it is serious, it will cause the motor to run out of phase and burn out.
When replacing relays and contactors, you need to pay attention to the working voltage of the electromagnetic coil to avoid burning the coil by replacing it incorrectly. Generally there are 24V, 220V and 380V. For time relays, in addition to paying attention to the coil voltage requirements, you must also clarify the time adjustment unit (hour, minute, second) and range of the time relay, and whether the setting current of the thermal relay is reasonable and appropriate.
For motors started using the star-delta (Y-△) method (the conversion delay is about 5 seconds), check whether the conversion and starting conditions are normal. Usually, the manufacturer has strict regulations on the starting cycle of the motor (that is, the number of starts per minute). There will be a warning label on the starting control box to remind users to prevent the motor from being damaged due to frequent starts. At the same time, it also prevents the starting control box from being damaged. Some electrical components (such as starting reactors, etc.) inside are heated and burned. Therefore, for motor control systems that start and stop frequently or have large currents, the inspection and maintenance period should be shortened. Regularly check the protection function of the thermal overload relay (you can turn the small red mark next to it) and its set action value should not exceed the rated current value on the motor nameplate to ensure that it can play the role of overload protection.
