Maintenance of AC contactor

 (1) common faults of AC contactor


　　　1) Abnormal noise. Contactor at the normal work condition buzzes, similar with transformer in work. Big noise indicates that the contactor has faults. The reasons are that the circuit voltage is less than 85% of rated voltage, that pressure among contact is improper, that short-circuit ring is broken, that magnetic yoke and the pole face is not level, that air gap of polar front in the center of E-shape iron core,that bolts of fixed magnetic yoke and terminal stud is loose, that loop overloads, that armature iron is clamped,and that rotating shaft and axle hole abrades too heavy.


　　　2) Contact is overheated or burning, which is caused by many reasons such as over-low circuit voltage, small pressure among contacts, small over travel, bad contact or dirt. Three contacts do not contact at the same and the difference exceeds 0.5mm. Contactors are burnt or loose. Movable parts are clamped. After wire loop is power off, the armature iron begins the second contact or manipulation of controller is too fast, which leads to loose terminal.


　　　After line power down, armature iron can not drop off. For this, there are many reasons. Over travel or pressure is too small. Released force is not enough. Dirts are between magnetic yoke and armature iron. Pole face air gap is less than 0.2mm, and silicon steel sheet is bad-quality. Installation of the contactor is wrong ( angle of inclination is less than 5). And movable parts are clamped, and wire loop circuit has short circuits. And the spring is broken or the contact is therm welded.


4) Wire loop of the contactor is overheated. The reasons are like wire loop overloading, bad contact of armature iron and magnetic iron, dirt and clamp, oversize pressure of contacts, short-circuit ring damaging, abnormal power, bolts of armature iron loose.


　　　5) The contactor runs slowly. Reasons are long distance of armature iron and magnetic yoke, the upper of soleplate outstanding compared to the bottom, movable parts clamping, and inclination of contactor oversizes.


　　　6) The contactor moves when the crane is in operation, which may be caused by lack of pressure, burn, and dirt among contacts, and overload and unlevel track.

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