AC contactor basics - Solutions - Huaqiang Electronic Network

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

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1 Classification of uses

The contactor is an automated control appliance. The contactor is mainly used to frequently switch on or off the AC and DC circuits. It has large control capacity and can be operated at a long distance. It can realize timing operation, interlock control, various quantitative control, voltage loss and undervoltage protection with the relay. In the automatic control circuit, the main control object is the motor, and can also be used to control other electrical loads, such as electric heaters, lighting, electric welders, capacitor banks, and the like.

The contactor can be divided into an AC contactor and a DC contactor according to the type of the controlled current. Here we mainly introduce the commonly used AC contactors. AC contactors can be divided into electromagnetic and vacuum.

2 Model Description

(1) The above models are standard models. In recent years, B series AC contactors have been newly developed, and their models are BXX.

(2) The AC contactor model is CJ. The DC contactor model is CZ.

3 Electromagnetic AC contactor structure and working principle

Principle, selection and connection of AC contactors

AC contactors are widely used as breaking and control circuits for electric power. It uses the main contact to open and close the circuit, and the auxiliary contact to execute the control command. The main contacts generally have only normally open contacts, while the auxiliary contacts often have two pairs of contacts with normally open and normally closed functions. Small contactors are often used as intermediate relays in conjunction with the main circuit.

The contact of the AC contactor is made of silver-tungsten alloy and has good electrical conductivity and high temperature ablation resistance.

The AC contactor is mainly composed of four parts: (1) electromagnetic system, including attracting coil, moving iron core and static iron core; (2) contact system, including three main contacts and two normally open and two normally closed Auxiliary contact, which is connected with the moving iron core and interlocked with each other; (3) Arc extinguishing device, generally large-capacity AC contactor is provided with arc extinguishing device, so as to quickly cut off the arc and avoid burning the main touch Head; (4) Insulating housing and accessories, various springs, transmission mechanisms, short-circuit rings, binding posts, etc.

working principle:

When the coil is energized, the static iron core generates electromagnetic attraction, and the moving iron core is sucked. Since the contact system is linked with the moving iron core, the moving iron core drives the three movable contact pieces to operate at the same time, and the contacts are closed, thereby being connected. power supply. When the coil is de-energized, the suction force disappears, and the moving iron core linkage portion is separated by the reaction force of the spring, so that the main contact is disconnected and the power is cut off.

AC contactor selection:

(1) Equipment that is continuously running. The contactor is 67-75%. That is, the 100A AC contactor can only control devices with a maximum rated current of 67-75A or less.

(2) Equipment that runs intermittently. The contactor is 80%. That is, the 100A AC contactor can only control devices with a maximum rated current of 80A or less.

(3) Equipment that repeatedly works for a short time. The contactor is calculated at 116-120%. That is, the 100A AC contactor can only control devices with a maximum rated current of 116-120A or less.

Also consider the working environment and the structural form of the contactor.

One point to note is that due to fierce market competition, some domestic manufacturers are already cutting corners to reduce costs. For example, in the production of coils, the wire diameter is reduced or even less, and the materials that do not conform to the national standard are used on the contacts. Thickness and section are not enough. This situation is not only reflected in the contactor, but also in other products such as short circuits. In actual use, the target is 100A contactor or short circuiter, the actual load can only be 80A or even lower, the failure rate is very high. Therefore, there is a popular saying now: use domestic low-end products, you must use the nominal capacity of the nameplate to play 30% off!

Connection:

A: The general three-phase contactor has a total of 16 points, three inputs, three outputs, two sets of normally open auxiliary contacts, two sets of normally closed auxiliary contacts, and two control points (contactor coils). The output and input are corresponding and can be easily seen. If you want to add a self-locking, you need to connect the line from the normally open auxiliary contact to the control point.

Second: First of all, you should know the principle of the AC contactor. He uses an external power source to apply to the coil to generate an electromagnetic field. After the power is applied, the contact point is disconnected after the power is turned off. Knowing the principle, you should figure out the contact point of the external power supply, that is, the two contacts of the coil, generally in the lower part of the contactor, and on each side. The other few inputs and outputs are generally in the upper part and are known at a glance. Also pay attention to the voltage of the external power supply (220V or 380V), which is generally marked. Also note that the contact point is normally closed or normally open. If there is self-locking control, the line can be based on the principle.

(1) Structure:

The contactor is mainly composed of an electromagnetic system, a contact system, an arc extinguishing system and other parts.

1 Electromagnetic system: The electromagnetic system consists of an electromagnetic coil and a core. It is an important part of the contactor, and it relies on it to drive the closure and disconnection of the contacts.

2 contact system: The contact is the actuator part of the contactor, including the main contact and the auxiliary contact. The main contact functions to switch the main circuit on and off, controlling the large current, and the auxiliary contact is in the control loop to meet the requirements of various control methods.

3 arc extinguishing system: the arc extinguishing device is used to ensure that the arc generated when the contact breaks the circuit is reliably extinguished, and the damage of the arc to the contact is reduced. In order to quickly extinguish the arc at the time of disconnection, the contactor is usually equipped with an arc extinguishing device, generally adopting a semi-sealed longitudinal joint ceramic arc extinguishing cover and a strong magnetic blowing circuit.

4 other parts: there are insulating shell, spring, short circuit ring, transmission mechanism and so on.

(2) Working principle:

When the contactor solenoid is not energized, the reaction force of the spring and the self-weight of the armature core keep the main contact in the open position. When the electromagnetic coil is connected to the control voltage (generally the rated voltage) through the control loop, the electromagnetic force overcomes the reaction force of the spring to attract the armature to the static iron core, drives the main contact to close, turns on the circuit, and the auxiliary contact moves accordingly.

4 AC contactor selection and operation and maintenance

(1) Selection:

1 The rated current of the main circuit contact should be greater than or equal to the rated current of the controlled device. The contactor of the control motor should also consider the starting current of the motor. In order to prevent frequent contact of the contactor main contacts, the frequently operated contactor rated current can be reduced.

2 The rated voltage of the electromagnetic coil of the contactor is 36V, 110V, 220V, 380V, etc. The electromagnetic coil is allowed to be used within the range of 80% to 105% of the rated voltage.

(2) Operation and maintenance: 1 In-service inspection items: 1) Whether the passing load current is within the contactor rating;

2) The split signal of the contactor indicates whether it matches the state of the circuit;

3) Is the running sound normal, and whether there is a discharge sound due to poor contact;

4) Whether the electromagnetic coil is overheated or not, and the short circuit of the electromagnet is abnormal.

5) Whether the arc extinguishing cover is loose or damaged;

6) Whether the auxiliary contacts are burnt or not;

7) Whether the transmission part is damaged or not;

8) Whether there are adverse operating factors in the surrounding operating environment, such as excessive vibration, poor ventilation, and excessive dust.

2 maintenance:

When performing maintenance work on electrical equipment, maintenance work should be performed on the contactor.

1) External maintenance:

a. Clean up external dust;

b. Check whether the fasteners are loose, especially the conductor connection parts, to prevent loose contact and heat;

2) Contact system maintenance:

a. Check whether the position of the moving and static contacts is aligned, and whether the three phases are closed at the same time. If there is any problem, adjust the contact spring;

b. Check the degree of contact wear, the wear depth should not exceed 1mm, the contact burns, when the welding is off, it must be replaced in time; when it is slightly burnt, it generally does not affect the use. Sandpaper should not be used when cleaning the contacts, and plastic files should be used;

c. Measuring the insulation resistance between phases, the resistance is not less than 10MΩ;

d. Check whether the auxiliary contact action is flexible. The contact stroke should meet the specified value. Check whether the contact is loose or not. When the problem is found, repair or replace it.

3) Core maintenance:

a. Sweeping dust, especially between moving parts and core contact surfaces;

b. Check the tightening of the iron core, and the loose iron core will cause the running noise to increase;

c. If the iron core short-circuit ring is detached or broken, it should be repaired in time.

4) Electromagnetic coil maintenance:

a. Measuring the insulation resistance of the coil;

b. Whether the coil insulation has discoloration or aging, and the surface temperature of the coil should not exceed 65 °C;

c. Check the coil lead connection. If there is open welding or burning, it should be repaired in time. 5) Partial maintenance of the arc extinguishing cover:

a. Check if the arc chute is damaged;

b. Whether the position of the arc extinguishing cover is loose or positional;

c. Remove metal particles and debris from the gap of the arc chute.

5 vacuum AC contactor working principle

The vacuum contactor uses vacuum as the arc extinguishing medium, and its main contact is sealed in a special vacuum arc extinguishing tube. When the operating coil is energized, the armature pulls in, and the contact closes under the action of the contact spring and the self-closing force of the vacuum tube; when the operating coil is de-energized, the reaction force spring overcomes the self-closing force of the vacuum tube to release the armature and the contact is broken. When the contactor breaks the current, platinum scale formed by the metal vapor is formed in the contact gap, which affects the service life of the contactor.