The control system of the motor is composed of switches, fuses, main and auxiliary contactors, relays, temperature, induction devices, etc., which is relatively complex. There are many kinds of faults, and it is often necessary to analyze and troubleshoot with the help of control schematic diagrams.
Usually, you should pay attention to keeping the inside and outside of the control box clean and dry, without water or oil stains. Regularly (weekly) use a small fan to blow away the dust on the components and terminals and rows in the box, or use a brush dipped in electrical cleaner to brush them clean, so as not to affect the operation or insulation of the contactor and relay. For control boxes with drying resistors, generally do not turn off the heating switch at will. The box should also be grounded reliably to prevent electric shock.
Check the tightness of the wiring and screws in the box regularly (monthly) to prevent the wiring and screws from loosening. Check whether the components such as switches, contactors, relays, etc. are damaged or burned, and whether the working status of each component and the start, stop, and interlocking functions are normal. Keep the moving and static contacts of the contactor closed and in good contact to avoid burning of the motor due to poor contact. If the contact surface is good and just blackened, you can wipe it with a coarse cloth. Do not easily polish off the heat-resistant alloy layer on the surface, otherwise it will shorten the life of the contact; if the contact surface is severely ablated, you can use “0″ sandpaper to smooth it. The moving and static contacts need to maintain line contact or surface contact, not point contact. The contact condition can be checked by placing a piece of paper between the moving and static contacts. If it is not clamped tightly when attracted, it means that the contact or spring needs to be adjusted or replaced. This point needs to be taken seriously. In mild cases, poor contact will generate a large contact resistance (current), which means that the load increases, resulting in the overload protection relay tripping. In severe cases, it will cause the motor to run in a phase-deficient manner 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 due to wrong replacement. 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; whether the setting current of the thermal relay is reasonable and appropriate.
For motors that are started using the star-delta (Y-△) method (conversion delay of about 5 seconds), check whether the conversion start is normal. Usually, manufacturers have strict regulations on the starting cycle of the motor (i.e. the number of starts per minute), and there will be warning labels on the starting control box to remind users to prevent the motor from being damaged due to frequent starting. At the same time, it is also to prevent some electrical components in the starting control box (such as starting reactors, etc.) from heating and burning. Therefore, for motor control systems that start and stop frequently or have large currents, the inspection and maintenance cycle should be shortened. Regularly check the protection function of the thermal overload relay (you can turn the small red color system 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.
Post time: Aug-14-2024
