1, Introduction
AC contactor is a kind of electrical appliance used to automatically connect or disconnect the high current circuit, which can frequently connect or disconnect the AC circuit, and can realize the long-distance control. Its main control object is the motor, can also be used for other loads, has a large control capacity, overload capacity, long life, simple and economical equipment, etc., so it is widely used in electrical control.
However, because of its special working environment, AC contactors will inevitably occur a variety of faults, if you can not timely and effectively find faults and eliminate them, will inevitably have an impact on the normal operation of electrical equipment, and even lead to the serious consequences of electrical equipment burned.
2, AC contactor common failure
2.1 common failure analysis
(1) coil failure
Coil failure can be divided into overheating burnt and broken wire. There are many reasons for coil burnout, such as too high or too low voltage. In addition, the power supply frequency does not match the rated value, the mechanical part of the jam resulting in can not be suction, the core pole surface is not flat resulting in suction gap is too large, environmental factors such as poor ventilation, excessively humid, the ambient temperature is too high, can cause this kind of failure.
(2) AC contactor ringing sound
The power supply voltage is too low, the contact spring pressure is too large, the core is skewed can be caused by the ringing sound is too large. AC contactor produces a large ringing sound, the main reason is that the coil passes into the alternating current, suction is pulsating, so you can add a short-circuit ring on the pole surface to avoid the noise, and the short-circuit ring breakage will cause excessive ringing sound.
(3) contactor contacts burn too fast
There is the quality of its own problems, but also the selection of improper causes contact ablation too fast. Encountered this problem, the first should check whether the load current exceeds the rated current of the contactor is too much, or whether it is used for frequent starting occasions, this is the case, it should be replaced with large-capacity AC contactors. In addition, should also check whether the contact pressure is normal, the contact pressure is too small, will cause the contact resistance increases, causing serious contact heating.
(4) suck on or not release
Suck on or suck insufficient cause in addition to mechanical failure, the power supply voltage is too low, internal resistance is too large, the coil broken wire, etc. is the main reason for this failure. Do not release or release slowly due to contact spring loss of elasticity or elasticity is too weak so that the contact reset force is insufficient, contact welding, core pole surface or core guide groove with dirt, core closure of demagnetization air gap is reduced and so on.
Contact no matter what kind of failure, should be the first to determine the type of failure and the cause of the failure may arise, and then in accordance with the principle of the first easy to check the coil, and then check the power supply and mechanical parts, and finally adjusted, grinding, etc., to avoid blind disassembly, artificially expanding the workload of the maintenance and even artificial recreation of the fault.
2.2 Fault judgment
How to determine whether a contactor is normal? Generally should start from the following aspects:
(1) electrical inspection
Contact coil should be maintained between the two terminals on state. When measured with a resistance gear, there should be a resistance of ten to tens of ohms. If the resistance value exceeds 2kΩ or more, you should check whether the coil circuit has poor contact or broken wire phenomenon. When the resistance value is too low, such as small contactors only a few ohms or zero point a few ohms, should check whether there is a short circuit phenomenon. If there is a short circuit between the turns, the coil often has a burnt or localized burnt, at this time only to replace the coil.
The movable closing contact and movable breaking contact should be able to reliably connect and break the circuit when the contactor is engaged.
(2) mechanical part
check with a hand or other tools to promote the armature, the action should be able to be flexible and free, no stagnation phenomenon. Contacts contact and then force, there should also be a certain amount of travel, hand release, the contacts can quickly reset. The action of the contacts should be synchronized.
(3) energized check
The rated voltage is added to the coil, the contactor should be able to operate reliably; there is no obvious ringing after suction, and the reset is rapid when the power is off.
3, case study
A CJ10-100 AC contactor installed in the control box, in the initial wiring, the phenomenon of jumping after power.
Analysis: the contactor quickly and evenly release and suction, in general, is due to the contactor wiring error caused by, such as the coil circuit is connected in series with the contactor's movable break contacts, etc.. Possible causes of failure in this case are power supply problems, coil problems and wiring problems.
The overhaul: the most likely problem in this case is a wiring problem, so first check the wiring. Although the wiring is relatively simple, but repeated checks, can not find the problem. Finally, in the contactor coil terminal another two wires, direct access to the power supply, but the contactor is still jumping, it seems that the power supply may be a failure. In order to confirm this phenomenon, take another contactor, access to the same power supply. The contactor action is dry, good absorption, indicating that the power supply is normal. Therefore, the problem is in the contactor coil circuit. Disconnect the power supply, measure the coil circuit resistance, resistance value is normal. Check the coil and shell insulation resistance, for infinity, indicating good insulation. Double-check the coil circuit, found that the coil to the terminal section of the connecting wire has broken skin and burned black phenomenon. So far to find out, the lead due to external forces and moved to the core section. In the contactor action, due to the armature force is large, the wire insulation by the armature broken, so that the wire and the contactor core short circuit, and the contactor is fixed in the control box, the control box is reliably connected to the earth, resulting in a short circuit of the coil lead and the zero line. This short circuit again occurs only when the armature is absorbed. Thus, when the contactor is suctioned, the coil circuit is shorted, the coil is de-energized, the armature is released, and the short-circuit fault is eliminated. The coil was re-energized, the armature was again suctioned again, the coil was shorted again, and so on and so forth. The wire will be wrapped and pushed into the original position, the power test, the fault is eliminated.
Description: this kind of failure is relatively rare, this case at the same time there are the following conditions: (1) the use of voltage 220V alternating current; (2) coil breakers for the firewire; (3) armature reliable grounding; (4) broken skin with the armature short-circuit rather than with the fixed iron core.
Short circuit. The absence of one of these conditions will not produce such a failure. In practice the power cord is too thin and too long, limiting the short-circuit current and contributing to this fault.
References
[1]Feng Ping. Failure analysis of common AC contactors[J]. China Science and Technology Expo,2010,(30):57-57.
[1]Bian Chaozhao,He Jian,Liu Feng et al. Failure analysis and treatment of AC contactor[J]. China Equipment Engineering,2005,(10):24-25.
[2]Wu Buxin.Failure analysis and solution of three-phase AC contactor of SS4 electric locomotive[J]. Science and Technology Wind,2011,(6):76.
[3]Wang Rujun. The maintenance of AC contactor[J]. Science and Education Magazine,2011,(36):128-128,185.
[4]Zhang Q. Failure repair analysis of high voltage AC contactor of CT machine[J]. Medical Equipment Information,2005,20(5):73,75.
[5]Feng Hongjun. AC contactor contact absorption failure and treatment[J]. Coal Mining Machinery,2010,31(5):249-250.
[6]Wang Feifei,Liu Guangzhao. Common Failures and Maintenance Methods of AC Contactors[J]. Machine Tool Electric Appliance,2010,37(1):56-57.
[7]Ma Yingli. Analysis of common causes of failure and treatment of AC contactors[J]. Value Engineering,2011,30(20):22-22.
[8]Zhan Xiuying. Maintenance method of common failure of AC contactor[J]. Applied Energy Technology,2004,(5):28-29.
[9]Huang Bo. The use of AC contactors[J]. Shanxi Architecture,2004,30(12):100-101.