AC contactor common fault handling method

AC contactors are commonly used in electromechanical device control circuits to turn the power on or off. It can frequently turn the AC circuit on or off and enable remote control. The contactor is mainly composed of a contact system and an electromagnetic system. The failure of the AC contactor generally occurs at the coil circuit, the mechanical part, and the contact portion.

First, the noise is too large

(1) When the power supply voltage is too low during operation, only the contactor can be kept in contact. When a large-capacity motor is started, the circuit voltage drop is large, and the corresponding contactor noise is also large, and the noise is reduced when the starting process is completed. Try to increase the voltage of the operating loop.

(2) The magnetic system is improperly assembled or shaken by the vibration or the needle is stuck, so that the iron core cannot be absorbed, and noise is generated. The magnetic system should be adjusted during processing to identify and eliminate the cause of the mechanical jam.

(3) Due to the breakage of the short-circuit ring, the static iron core vibration causes noise, and the iron core or short-circuit ring should be replaced.

(4) Electromagnet noise is generated due to excessive contact spring pressure. Usually adjust the contact spring pressure.

(5) There is dirt and debris between the contact surface of the static iron core and the moving iron core. Because the distance between the pole faces becomes large, the reaction force of the recovery spring cannot be overcome, and vibration is generated. If the contactor vibrates for a long time, it will cause the coil to burn out. At this point, the core face should be cleaned.

(6) The pole face of the iron core is excessively worn and uneven. The core should be replaced.

(7) Short circuit between turns of the coil. Usually the coil can be replaced.

Second, the main contact is overheated or welded

(1) Since the contactor is too slow or stagnant, the contact is in a position like contact non-contact, and it can be treated according to the "AC contactor is not normal" treatment method after the identification.

(2) The surface of the contact is severely oxidized and burned, causing the contact resistance to increase, causing the main contact to overheat. The treatment first removes the oxide layer on the surface of the main contact, and then gently flattens it with a file to make the contacts in close contact.

(3) Due to the frequent starting of the device, the main contact is overheated or welded by the impact of the starting current multiple times. Avoid frequent starts at this time, or choose a contactor that can accommodate the operating frequency and power-on duration.

(4) The main contact is overheated or welded due to excessive load current for a long time. In this case, reduce the load on the transmission equipment to operate under rated conditions, or re-select the appropriate contactor according to the operating current of the equipment.

(5) The three-phase main contact of the contactor is not synchronized when it is closed, and the two-phase main contact is impacted by a large starting current, causing the main contact to be welded. In this case, the main contact closure condition should be checked, and the gap between the moving and stationary contacts should be adjusted so that the three-phase main contacts are in synchronous contact.

(6) The main contact itself has poor resistance to melting, such as pure silver contacts that are easily welded. This type of contact should be replaced. A silver-based alloy contact with strong anti-melting ability can be used as the main contact of the contactor.

(7) The overtravel of the contact is too short, and the contact overtravel or the replacement of the contact should be adjusted.

Third, the core can not be released after the coil is powered off

If the core cannot be released after the AC contactor coil is de-energized, the device will be out of control and threaten the safety of the person and equipment. Therefore, in the event of such a failure, it should be immediately shut down for maintenance, which can generally be handled from the following aspects:

(1) The installation does not meet the requirements, or the anti-rust oil on the surface of the new contactor core is not cleaned. If it is the former, it can be reinstalled so that the inclination does not exceed 5°; if it is the latter, the oil can be wiped clean.

(2) In the long-term operation of the contactor, due to frequent impact, the pole surface of the iron core is deformed, and the gap on the middle magnetic pole surface of the "convex" type core is gradually disappeared. Therefore, after the coil is de-energized, there is a large surplus on the iron core. Magnetically, the moving iron core is adhered to the static iron core.

The method of treatment is to carefully trim the iron core contact surface with a file, and keep the core magnetic pole contact with an anti-remaining magnetic gap of not more than 0.2 mm. In addition, the "convex" type core contact surface is placed on the grinding machine to be smooth and smooth, so that the middle magnetic pole surface of the iron core is lower than the two side magnetic pole faces by 0.15-0.2 mm, and this failure can also be prevented.

(3) Too much oil and dust on the magnetic pole surface of the iron core, or the spring pressure of the moving contact is too small. For the former, the oil can be removed; for the latter, the spring pressure can be adjusted and a new spring can be replaced if necessary.

(5) The contact of the contactor is welded, so that the core cannot be released after the contactor coil is de-energized, and it can be treated according to the "AC contactor main contact overheating or fusion welding" treatment method.

4. After the power is turned on, it cannot be sucked or pulled and then disconnected.

(1) Test whether there is no rated voltage at both ends of the electromagnetic coil. If there is no voltage, it indicates that the control loop is faulty. It should be inspected according to the specific circuit; if there is voltage, but lower than the rated voltage of the coil, it is generated after the electromagnetic coil is energized. The electromagnetic force is not enough to overcome the reaction force of the spring. In this case, the coil should be replaced or the circuit should be replaced. If there is a rated voltage, the coil itself may be open, and the ohmmeter of the multimeter can be used for measurement. (If the wiring bolt is loose, it should be tightened; If the coil is broken, replace the coil).

(2) Check whether the action mechanism and the moving contact of the moving part of the AC contactor are stuck. If the resistance is blocked, the action mechanism can be trimmed, the arc extinguishing cover can be corrected, the position of the contact and the arc extinguishing cover can be adjusted, and the friction phenomenon of the two can be eliminated.

(3) Check if the shaft is rusted or skewed. If rust or skew occurs, the shaft should be disassembled for cleaning, and if necessary, the parts should be replaced to make the shaft rotate flexibly.

If the contactor is disconnected after the suction, it may be that the auxiliary contact in the self-locking circuit of the contactor is not connected or the contact is bad, which makes the self-locking link of the circuit lose its function. At this point, the moving auxiliary contact can be refurbished to make it in good contact.