Tag: ac contactor

Contactors are used in electric power, distribution and electricity applications. A contactor refers to an electrical appliance that uses a coil to flow through a current to generate a magnetic field to close the contacts in order to control the load in industrial electricity. There are many types of contactors according to their purpose and characteristics.

The contactor of CJX2 series we are going to use is type 4NO, type 3NO and type 2NO+2NC. The main contact point has different performance in 220V~660V. The control coil voltage is 110VAC, 220VAC, 24VAC and 24VDC, and the 220VAC is used this time.

A contactor is an electrical appliance that uses a current flowing through a coil to generate a magnetic field to close the contacts to complete the control of the load. As a kind of contactor, the AC contactor also controls the load, but there is an additional precondition on the original basis. The AC current flows through the coil. AC contactors have been widely used at present, high performance lighting contactors and 1 pole - 4 pole definite purpose contactors are popular AC contactors.

AC contactor is an intermediate control element, which can frequently turn on and off the line, and control large current with small current. Used in conjunction with thermal relays, it can also play a certain role in overload protection of load equipment. Compared with human manual opening and closing circuits, AC contactors are more efficient, can be flexibly used, and can open and close multiple load lines at the same time. The lock status continues to work.

The AC contactor has found wide applications in the motor-controlled circuit. It is no exaggeration to say that the electric drive of most motors cannot be separated from the control of the AC contactor. Many electricians are very familiar with the AC contactor for their frequency use or maintenance of it. How should we calculate the AC contactor rating for the motor or other equipment and make a right choice? Let us take a look at it.

Iron core of the AC contactor is usually laminated by silicon steel sheet, so as to reduce the eddy current and hysteresis loss generated by alternating magnetic field in iron core, avoid the iron core overheating. However, iron core in the DC contactor's coil would not generate eddy current and there is no heating problem in DC core, so the iron core can be made of a complete cast steel or cast iron. Coil of DC circuit has no inductance, so the coil has more turns, thus leading to large resistance and copper loss. In order to keep a good heat dissipation for the coil, the coil is generally made into a thin and cylindrical shape. Coil of AC contactor has less turns and small resistance, but the coil also gives heat, so the coil is generally made into a fat and short cylindrical shape. Meanwhile, a clearance is left to facilitate heat dissipation while avoiding the coils from being burned out. In order to eliminate vibration and noise generated by electromagnet, a short circuit ring is embedded on the surface of static iron core of the AC contactor, while the DC contactor doesn't need a short circuit ring.

Common fault for the iron core of an AC contactor is about the large noise. If it's caused by insufficient coil voltage after inspection, adjust the power voltage. If it's caused by bad contact between contact surfaces of dynamic and static cores, make contact surfaces smooth to ensure a good contact. If the noise is caused by the break of short circuit ring, replace or weld the short circuit ring. Another common fault is that the armature doesn't fall when powering off. This may be caused by small spring pressure between contacts, adjust the contact force please. If it's caused by block of armature or mechanical part, remover the barrier. There should be a clearance of 0.1～0.2mm in the central pillar of E-shaped core, if the clearance disappears due to iron core wear, the iron core may be stuck, repair the central pillar plane of the E-shaped core.

AC contactor is generally classified into class I, class II, class III and class IV according to the type of load, and they are respectively recorded as AC-1, AC-2, AC-3 and AC-4. AC-1 AC contactor corresponds to non inductive or micro inductive load as its control object, such as the filament lamp, resistor furnace. AC-2 AC contactor is used for starting and stopping of wound asynchronous motor. Typical application of AC-3 AC contactor is the operation of squirrel-cage asynchronous motor and the break in operation. AC-4 AC contactor is used for starting, reverse braking, reversing and jog of cage asynchronous motor. All ATO AC contactors with 24V/110V/220V coil operating at AC-3 380V or 660V.

As equipment to disconnect load power, selection of contactor should meet requirements of controlled equipment. Except that the rated operational voltage is the same with the rated operational voltage of controlled equipment, load power, usage category, control mode, operation frequency, working life, installation method, installation dimension and economy of controlled equipment are the basis of selection. How to choose a right contactor? The principles are as follows:

Contactor is an automatic electromagnetic switch for long-distance frequently connected or disconnected AC and DC main circuit and high-capacity control circuit. The main control object of a contactor is the motor, it can be used to control other loads as well.
According to the current types that through the main contacts, contactor is divided into AC contactor and DC contactor. The structure and working principle of both are basically the same, which mainly consists of three parts, electromagnetic mechanism, contact system and arc-extinguishing equipment. In the electrical control circuit of machine tool, AC contactor is mainly used. This article focuses on the basic structure of the AC contactor.