The control system of the motor is composed of switches, fuses, main and auxiliary contactors, relays, temperature, and sensing devices, which are relatively complicated. There are many kinds of faults, and it is often necessary to analyze and troubleshoot with the help of control schematic diagram.
At ordinary times, attention should be paid to keeping the inside and outside of the control box clean and dry without water or oil stains. Regularly (weekly) use a small air blower to blow clean the components, terminals and dust in the box, or use a brush dipped in electrical cleaner to clean it, so as not to affect the work or insulation of contactors and relays. With the control box of the drying resistance, generally do not turn off the heating switch at will. It should also maintain reliable grounding of the cabinet to prevent electric shock.
Check the fastening of wiring and screws in the box regularly (monthly) to prevent the wiring and screws from loosening. Check whether the switch, contactor, relay and other components are damaged or burned, and whether the working state of each component and the start, stop and interlock functions are normal. The moving and static contacts of the contactor shall be kept in good suction and contact, so as to avoid burning out of the motor caused by poor contact of the contacts. If the surface of the contact is good and only black, wipe it with coarse cloth. Do not polish off the heat-resistant alloy layer on the surface easily, otherwise the life of the contact will be shortened. If the surface of the contact is seriously ablated, it can be smoothed with “0” sand paper. 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 during suction, the contact or spring needs to be adjusted or replaced. This point needs to be paid attention to. When it is light, a large contact resistance (current) will be generated due to poor contact, which means that the load will increase, causing the overload protection relay to trip, and it will cause the motor to run without phase and burn out.
When replacing relays and contactors, it is necessary to pay attention to the working voltage of the electromagnetic coil to avoid changing the wrong coil to burn out. Generally, there are 24V, 220V and 380V. For time relays, in addition to paying attention to the coil voltage requirements, it is also necessary to find out the time adjustment unit (hours, minutes, seconds) and range of the time relay. Whether the setting current of the thermal relay is reasonable and appropriate.
For the motor started by the star-triangle (Y-△) method (the conversion delay is about 5 seconds), check whether the conversion start is normal. Usually, the manufacturer has strict regulations on the starting cycle of the motor (that is, the number of starts per minute), and there will be warning labels on the starting control box to remind the user to prevent the motor from being damaged due to frequent starting, and at the same time, to prevent the starting control box Some electrical components (such as starting reactors, etc.) are heated and burned. Therefore, the motor control system with frequent start and stop or large current should shorten the inspection and maintenance cycle. Regularly check the protection function of the thermal overload relay (the small red code color system can be toggled next to it) and its set action value shall not exceed the rated current value of the motor nameplate to ensure that it can play the role of overload protection.