CJX2 AC contactor is a kind of main control electrical apparatus, which can complete the function of connecting and disconnecting the strong current main circuit with load under the control of button or relay by driving the closing and separation of contact and static contact with electromagnet. Generally, it is used to control motors, welding machines, capacitor banks, electric heaters and so on. It has the advantages of rapid action, safe and convenient operation, and frequent operation. It has been widely used in rural distribution network.

Although CJX2 AC contactor is easy to operate, it can not prevent the occurrence of defects in the harsh environment of dust, strong corrosion, high temperature and high humidity. Frequent faults will cause the damage of CJX2 AC contactor, and even affect the reliability of low-voltage power supply and the production life of users.

After careful inquiry, analysis and research, we finally solved this problem by improving the self-locking circuit in the control circuit, which provides a feasible way to reduce the failure rate of CJX2 AC contactor in special environment.

1 event Brief

CJX2 AC contactor controls the main circuit of the distribution board. Any fault will affect the normal power supply

(1) According to the "ten promises" of SGCC, the reliability rate of power supply in rural areas (RS-3) should not be less than 99.5%.

(2) Many faults seriously affect the service life of CJX2 AC contactor.

(3) Users want to minimize the impact of substation faults on production days.

2 status inquiry

The causes of the faults of CJX2 AC contactors in recent 22 times were analyzed from five aspects: poor touch of auxiliary contact, coil damage, stuck moving part, failure of reaction tension spring, and interphase insulation damage. The results showed that: 1) poor touch of auxiliary contact accounted for 68.18%; 2) coil damage accounted for 13.63%; 3) failure of action tension spring accounted for 9.09%; 4) stuck moving part accounted for 4% 54%; 5) phase to phase insulation damage accounted for 4.54%.

It can be seen from the above that the poor touch of auxiliary contact is the primary reason for the faults of CJX2 AC contactor in special environment.

3. Cause analysis

After on-site inquiry and careful analysis, the team members analyzed, summarized and sorted out the causes of poor touch of auxiliary contact of CJX2 AC contactor from five aspects of personnel, equipment, materials, methods and environment, and obtained the following cause and effect diagram and found five reasons.

Lack of sense of responsibility of protection personnel: some electricians are lack of sense of responsibility, and the protection of distribution equipment is not in place, but only individual phenomenon. I really think it's necessary.

Poor manufacturing process: the manufacturing process of some manufacturers is not high, and the product quality is unqualified. But we should choose famous brand products from famous manufacturers first. I really think it's necessary.

Small touch area of auxiliary contact: the small touch area of auxiliary contact directly constitutes a high probability of poor touch. I really think it's the cause.

Nonstandard installation and use: the installation is not firm or the inclination exceeds 5 degrees, which has a certain impact on the fault composition. Frequent opening and closing operation has certain influence on the contact, but it is not the primary cause of bad touch. I really think it's necessary.

Temperature and humidity overrun, dust, corrosive gas: too high temperature, contact deformation; dust will directly constitute poor touch, strong corrosion and high humidity, contact oxidation. Many distribution areas are in bad operating conditions. I really think it's the cause.

4. Adopt countermeasures

In view of the poor touch of auxiliary contact, we have adopted detailed countermeasures and implemented them.

4.1 analyze the operation principle of conventional CJX2 AC contactor

CJX2 AC contactor consists of the following system

(1) Electromagnetic system: including attracting coil, static core and armature.

(2) Contact system: including main contact and auxiliary contact. The main contact is three pairs of normally open contacts, which are used to connect and disconnect the main circuit; the auxiliary contact is used to connect and disconnect the control circuit and signal circuit, which is composed of normally open contact and normally closed contact.

(3) Arc extinguishing cover: install an arc extinguishing cover on the main contact to reduce the burn of the main contact caused by the arc.

4. Tension spring system and base.