As an electromagnetic relay commonly used in electrical control systems, contactors have many specifications. Generally, the contactor controls the closing and breaking of the main contact by controlling the energization and de-energization of its coil. We will find that the voltage specifications of the contactor coil are less than the rated voltage of the main contact of the contactor. For example, take the AC contactor as an example. When the rated voltage of the main contact of the AC contactor is 380V, then Its coil voltage specifications can have five specifications: 36V, 110V, 127V, 220V and 380V. In this way, we can know that it is an automatic control device for low voltage control high voltage.
In terms of controlling current, the current that the main contact of the AC contactor can pass through can pass 10A, 20A, 40A, and 60A or even more. The auxiliary contact of the AC contactor generally does not allow more than 5 amperes of current. In this respect, it is an electromagnetic relay with a small current to control a large current. One of the main purposes of this is to ensure the safety of the operation of the control circuit and ensure the safety of the operator. It is especially important for controlling high voltage and large current. Therefore, using the low voltage and small current of the contactor to control the high voltage and large current is our consistent method in electrical control.
In my understanding, the main function of contactors and intermediate relays should be to realize the breaking control of low voltage to high voltage, rather than small current to control large current! The original intention of the invention of contactors or electromagnetic relays should be to enable people to It is safer to operate the energization and de-energization of equipment with higher voltage levels! --The relationship between electricity and magnetism has well realized this idea or requirement of people, or the low voltage control circuit current coil generation The magnetic field, the magnetic field makes the armature pull in, so that the circuit of the high voltage part is connected, and then the high voltage equipment is operated!
In fact, the most important thing here is electromagnetism. The magnetic field is distributed in the air. Through the enameled wire, the isolation between the control circuit and the circuit to be broken is realized. This isolation can be said to be electromagnetic isolation, and this isolation is also for personal safety. The main guarantee!
The concept of isolation is important to safety, such as common electromagnetic isolation and photoelectric isolation. For example, some PLC input points, many of which are optically isolated. The signal points on the equipment site are connected to the PLC, and the electrical signals are first converted into optical signals, and the optical signals are converted back to electrical signals. Such a process is photoelectric Isolation, the signal does not change, but the two sides are isolated electrically
It is also because relays such as contactors meet the electrical isolation characteristics between the electrical high-voltage equipment circuit and the low-voltage control circuit, so they are safe and can be used so widely!
The above is a little bit of my personal opinion, I hope it can help you a little! If you understand the original intention of a thing being invented, many problems will be easier to understand, so whether it is low voltage control high voltage, or small current control large current , The reason is the same, they are all based on the principle of electromagnetic induction, with the enameled wire, to achieve the isolation of the primary circuit and the secondary circuit, this is the point!
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