AC contactor (electrical drawing code km) is the key household electrical equipment to operate switching power supply and load on / off in the power supply circuit, and it is also a common problem for welders in their daily work. In the work, Xiaobian often found that there were various omissions in the selection of AC contactors in some industries, which led to the poor selection of models, and the problems continued after the accident. Here, Xiaobian will show you four more common typical situations, hoping that you can take precautions.
1、 Some welders in the same industry choose compatible AC contactors according to the load, usually only according to the rated voltage of the load, so that the main contact of AC contactor often appears damage, melting and other conditions in the specific operation process! In the final analysis, this kind of common fault condition depends on that the way of selecting AC contactor (main contact capacity) according to rated voltage is only suitable for pure inductive load such as heating wire. For the rational load such as three-phase asynchronous motor, the starting current is about 4-7 times of the rated voltage due to different starting methods, dragging load types and starting frequency during the starting process before stable operation. Therefore, when selecting AC contactor, it is very critical and necessary to have the factor of load starting current.
2、 With the improvement of the concept of electricity safety and safety operation specification, and in order to reduce the occurrence of redundant personal safety accidents, it is an inevitable trend to choose the safety rated voltage (ac36v) as the priority of AC contactor coil working voltage at this stage. Therefore, in the process of design, selection and installation of AC contactor, we should first choose the products with coil rated voltage of ac36v. Minimize the coexistence of AC220V, AC380V and other coil rated voltage in the line.
3、 In order to reduce the total number of other auxiliary devices (such as small relays, etc.) and reduce the volume of the electronic control system, the selection of AC contactors should be based on the total number of auxiliary contacts that AC contactors often need in the route. For example, when there are many auxiliary contacts of AC contactors in the route, the selection of cjX series AC contactors that can add 2 pairs or 4 pairs of auxiliary contacts is more intelligent than cjt series AC contactors.
4、In addition to fully considering the above three levels of factors, the final compensation must show the difficulty of the operation method of AC contactor (coil). At present, industrial control automation such as PLC, which is conducive to centralized management and control, is increasingly widely used. In this process, there are many cases in the same industry that the coil of AC contactor is immediately led to the PLC output terminal, resulting in the destruction of PLC internal output devices (automobile relay, crystal triode, silicon controlled rectifier). The common fault condition is caused by the current in the coil closing process of AC contactor exceeding the current carrying capacity of PLC output device! Therefore, when PLC is used to control AC contactor, automobile relay should be used as control link.