Causes of burning loss of contact of AC contactor
In the use of AC contactors, one of the problems that users always pay attention to is that the contact burns too fast. What are the reasons for the contact burn too fast? The manufacturer of AC contactor explains for you!
It has its own product quality problem that the contact of AC contactor burns too fast, which may also be the reason why the contact burns too fast due to improper selection. In case of such phenomenon, it is necessary to check whether the load current exceeds the rated voltage of the contactor, or whether it is used for frequent start-up. In this case, the AC contactor with large capacity shall be replaced. If the controlled object is a three-phase motor, check whether the three-phase contacts are in the same step. If the three-phase motor starts in different steps, it belongs to phase breaking operation in a short period of time, resulting in excessive starting current, adjustment shall be carried out. On the other hand, it is also necessary to check whether the working pressure of the contact is normal. If the working pressure of the contact is very small, the contact resistance of the contact will expand, which will cause the contact to burn seriously. The working pressure of the contact can be measured by using a small paper strip, which is a little wider than the contact, and put it in the middle of the contact. When the AC contactor is closed, if the small paper strip is very easy to be pulled out, it indicates that the working pressure of the contact is not enough; if the small paper strip is pulled off, it indicates that the working pressure is too large. Small capacity AC contactor with a little effort can pull out the small paper and the small paper is intact. Large capacity household appliances with a little effort can pull out the small paper but it is damaged, so the working pressure of the contact is suitable.
For the solution of oxide layer, burning or burr, fusion welding and other phenomena on the contact, please refer to the following:
(1) when there is oxide layer on the contact, if it is silver oxide, it need not be removed. If it is copper oxide, use a knife to gently scrape it off; if there is no stain, use towel to clean it with gasoline or carbon tetrachloride;
(2) when the contact is burned or has burrs, the surface of the contact shall be trimmed with a small knife or assorted file. It is not necessary to finish the contact very smooth, because too smooth will reduce the total area of contact surface. On the other hand, do not use abrasive cloth to repair the contact surface to prevent steel sand from being put into the contact and damaging the contact.
(3) if there is no fusion welding on the contact, it is necessary to find out the cause and replace the contact during maintenance. The causes of welding include short circuit fault at load side, unreliable or vibration of AC contactor due to low operating voltage, destruction of arc extinguishing equipment and too small contactor capacity.
