Troubleshooting with AC Contactor
AC contactor is used for frequently connecting and disconnecting load. As it has magnetic coils, it belongs to electromagnetic switchgear. Main parameters of the ac contactor include: rated current and rated voltage, which are defined as above. The ac contactor and circuit breaker have a short circuit protection coordination relation. Specific definition is: When the circuit breaker breaks short circuit current, if contact welding occurs at the contactor, it belongs to type 1. Type 1 contactor must be replaced after short circuit. If contact welding doesn’t occur, it belongs to type 2.
Maximum overload capacity is generally defined by XX times of rated current. For the motor circuit breaking or starting directly, the overload capacity is 8 times. For positive and negative motor circuits, the overload capacity is 10 times.
AC contactor is an automatic control device used to connect or break up the main circuit with load frequently. AC contactor is used in the AC circuit. Common fault for the iron core of an AC contactor is about the large noise. If it's caused by insufficient coil voltage after inspection, adjust the power voltage. If it's caused by bad contact between contact surfaces of dynamic and static cores, make contact surfaces smooth to ensure a good contact. If the noise is caused by the break of short circuit ring, replace or weld the short circuit ring. Another common fault is that the armature doesn't fall when powering off. This may be caused by small spring pressure between contacts, adjust the contact force please. If it's caused by block of armature or mechanical part, remover the barrier. There should be a clearance of 0.1～0.2mm in the central pillar of E-shaped core, if the clearance disappears due to iron core wear, the iron core may be stuck, repair the central pillar plane of the E-shaped core.
When the ac contactor coil is overheated or burned out, check whether the rated voltage of the coil is consistent with the supply voltage, if not, replace a proper coil. Mechanical damage on the coil or partial short circuit caused by conductive dust may also cause above phenomenon, repair or change the coil, keep the coil clean. Frequent operation of ac contactor may also make it overheated or burned out, replace with a proper contactor. When the action part of contactor is stuck, above problems may also occur, please remove the obstacle timely.
If the armature can't be sucked after pressing the starting button, it may be caused by the break off or burned of coil, please repair or change a coil. It may also be caused by partial stuck or partial rust of the armature or mechanical parts, remove the obstacle and rust, lubricate or replace the parts.
AC contacts of the contactor may be welded due to excessive current, failure of arc extinguishing devices and arcing caused by circuit breaking.
Sometimes the ac contact can not be closed, please take out the fixed screws of arc extinguishing cover and open the arc extinguishing cover, check whether the top and bottom contact of main contact have serious burn. If it has, take the dynamic contact out and repair. A sandpaper can be used to polish the dynamic and static contacts, till their surfaces are smooth. But when the contact is seriously burnt to half of its original thickness, replace please. If there's no damage on the contact, check if there's mechanical stuck or measure with a multimeter if the voltage at coil terminal is too low, thus leading to insufficient magnetic adhesion.
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