Common fault analysis of AC contactors

Promulgator : TAIXIDate : 2018-11-03Views : 95

1. Coil fault

There are many reasons for coil burnout, such as high power supply voltage, over 110% of the rated voltage may burn the coil. On the other hand, the power supply voltage is too low, below 85% of the rated value may also burn the contactor coil, which is due to the contactor armature can not be closed, the coil circuit reactance is small, the current is too large. In addition, the frequency of power supply does not match the rated value, the mechanical part of the blockage can not be absorbed, the core pole surface unevenness causes the absorbed magnetic gap to be too large, environmental factors such as poor ventilation, excessive humidity, environmental temperature is too high, will cause this failure. The breakage of the coil is often caused by the overheating of the coil and may also be caused by external force damage. For different reasons, different countermeasures should be adopted. If the coil is faulty, replace the same type of coil. If the core of Din Rail Mounted Contactor has dirt or uneven pole surface, clean the pole surface or replace the core according to the situation.

2. Excessive noise of Household Contactor, too low voltage of power supply, too high pressure of contact spring and deflection of iron core can cause excessive noise. Din Rail Mounted Contactor produces loud noise. The main reason is that the coil is fed into AC and the suction is pulsating. Therefore, a short-circuit ring can be added on the pole surface to avoid noise. The breaking of the short-circuit ring will cause too loud noise. The way to exclude is to check the short circuiting ring, adjust the spring, clean or grind the iron core pole, etc. Of course, if the supply voltage is much lower than the required voltage, this phenomenon will occur. Therefore, the power supply should be checked.

3. Too fast contact burning of contactor has its own quality problems, and there are also reasons for improper selection of contacts causing too fast contact burning. In the case of this problem, first of all, we should check whether the load current exceeds the rated current of the contactor too much, or whether it is used in the occasion of frequent starting. In this case, we should replace the large capacity Household Contactor. If the controlled object is a three-phase motor, it is necessary to check whether the three-phase contact is synchronous. If there is no synchronization, the three-phase motor starts in short time, which leads to excessive starting current and should be adjusted. In addition, it is necessary to check whether the contact pressure is normal or not. If the contact pressure is too small, the contact resistance will increase and the contact will be heated seriously. The contact pressure can be measured by strip method. The method is to take a slightly wider strip than the contact and place it between the contacts. When the Household Contactor closes, if the strip is easy to pull out, the contact pressure is insufficient; if the strip is broken, the pressure is too high. Low capacity Din Rail Mounted Contactor can pull out the paper slightly and the paper is in good condition. Large capacity electrical appliances can pull out the paper slightly but with breakage, it is considered that the contact pressure is appropriate.

The treatment of oxide, cauterization, burr and fusion welding on the contact can be referred to as follows:
(1) When there is an oxide layer on the contact, if it is silver oxide, it is not necessary to remove it, if it is copper oxide, gently scrape it off with a knife; if there is dirt, it can be cleaned with gasoline or carbon tetrachloride.
(2) when contact burns or burrs, a knife or assorted file should be used to repair the contact surface. It is not necessary to make the contact smooth when repairing, because excessive smoothness will reduce the contact surface area. In addition, do not use sandpaper to repair the contact surface, in order to avoid gold and steel sand embedded in the contact, affecting contact.
(3) if contacts are fused, the cause must be identified and contacts should be replaced during repair. The causes of welding include short circuit of load side, unreliable or vibration of AC contactor due to low operating voltage, damage of arc extinguishing device and too small capacity of contactor.

4. In addition to mechanical faults, the main causes of the faults are too low power supply voltage, too large internal resistance and broken coil. The reasons for not releasing or slow releasing are that the contact spring loses elasticity or the elasticity is too weak to make the contact reset force insufficient, the contact fusion welding, the dirt on the core pole surface or the core guide groove, and the demagnetization air gap decreases when the core closes.