Contactor

Contactor

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A contactor is an automatic electromagnetic switch for long distance frequently turned on or off the main circuit and AC-DC high-capacity control circuit. Its main target is to control the electric motor can also be used to control other loads. It not only enables remote automatic operation and under voltage release protection, but also control a large capacity, reliable, high operating frequency, long life and other advantages.

Current Category contactor main contacts by the press, contactors, AC and DC contactors two kinds. In the machine tool electric control circuit, mainly used in AC contactor.

First, exchanges and contacts

working principle

1. Electromagnetic System

Mainly composed of three parts AC contactor system consists of an electromagnetic coil, static core and the armature (movable core). Its role is to use the power on or off the electromagnetic coil, the armature and static core pull or release, thus boosting the dynamic contact with the stationary contact closure or breaking achieve the purpose of turning on or off the circuit.

In order to reduce the work process alternating magnetic field eddy current and hysteresis losses generated in the core, to avoid overheating of the core, AC contactor core and the armature is generally used as the E-shaped silicon layers riveting. Nevertheless, the core is still a major part of the heat exchanges and contacts. To increase core cooling area, avoid direct contact with the coil and the core burning heat, AC contactor coil generally made of thick and short cylindrical shape, and is wound around the insulating housing, the iron core and coils there is a certain gap between. Further, the end surface of the column left for an E-shaped core 0.1mm ~ 0.2mm air gap, to reduce the impact of remanence to avoid sticking of the armature coil power can not be released.

a) linear motion armature formula; b) armature pivoting retractable row

AC contactor during operation, the coils pass into the alternating current generates an alternating magnetic flux in the core, and therefore suction between the core and the armature is varied. This causes the armature to vibrate, making noises. To eliminate this phenomenon, the AC contactor cores and two different ends of the armature of the opening of a groove, a groove fitted with embedded copper, constantan or nickel-chromium alloy material short-circuit ring, also known as damping after the loop or sub-ring, the core device short-circuit ring, when alternating current is passed through the coil, the coil current produces a magnetic flux Φ1, Φ1 passes through part of the short-circuit loop, generating induced current in the ring, and then generates a magnetic flux Φ2, known by the law of electromagnetic induction, Φ1 and Φ2 different phases, namely Φ1 and Φ2 are not zero simultaneously, and by the electromagnetic force Fl Φ2 Φ1 generated and F2 are not zero simultaneously, which ensures the core and the armature at any time has a suction armature will always suck, vibration and noise will be significantly reduced.

2. Contact system

Press contact exposure can be divided into point contact, line contact and surface contact type three

a) point contact; b) line contact; c) surface contact

a) double-break contact bridge; b) finger contacts

AC contactor is generally double break contact bridge.

Divided by breaking capacity AC contactor is divided into the main contacts and auxiliary contacts. Off the main contact for the main circuit current is high, generally consists of three large contact surface make contact components. Auxiliary contacts for on-off control circuit current is small, generally consists of two pairs and two pairs make contact break contact components.

3. Extinguishing device

AC contactor off when large current or high-voltage circuit, the move will have a strong electric arc between the stationary contacts. Arcing, on the one hand it will burn contacts, reducing contact life; the other hand, the circuit would cut prolonged arc short circuit or even cause a fire accident. Capacity of 10A or more contactors are equipped with interrupter device. AC contactor There are several commonly used extinguishing methods:

(1) electrical power interrupter device double fracture electric power interrupter double fracture structure. This interrupter method is to split into two entire arc, while taking advantage of the contacts of the circuit itself, the electric force F on both sides of the arc to elongate the arc heat in the process of distributing the elongated, cooling off.

(2) longitudinal seam longitudinal joints interrupter interrupter device shown in Figure 5-30b. Within the arc-proof clay, asbestos cement and other materials interrupter cover each phase has one or more longitudinal seam, the lower seam is wider in order to place contacts; an upper seam is narrow, so as to compress the arc, the arc on and off arc wall has nice touch. When the contact breaking arc is blown into an external magnetic field or electric power within the joints, which heat is transferred to the interrupter chamber wall, the arc is cooled rapidly extinguished.

a) double fracture electric power interrupter; b) longitudinal seam interrupter

(3) gate films interrupter gate films interrupter device structure and working principle. Sheet metal gate by a copper or galvanized iron sheet made of the general shape of a chevron shape, the strips inserted in the arc chute, insulated from each other between the sheets. When the movable contact and the stationary contact breaking arc is generated between the contacts, the arc current produces a magnetic field around it. Since the sheet metal gate reluctance is much smaller than the reluctance of air, the upper portion of the arc and therefore the magnetic flux through the sheet metal gate readily closed magnetic circuit is formed, which resulted in the magnetic field around the arc air under close sparsely. The magnetic field on the arc upward force will pull the gate chip arc gap, the gate chip arc divided into several series of short arcs. Each gate electrode sheets become short arc, the total pressure drop is divided into paragraphs arc, arc voltage between the gate sheet are below the arc voltage, while gate films absorb the heat of the arc for distributing the arc is rapidly cooled, prompting the arc as quickly as possible off.

4. Accessories

AC contactor accessories counterproductive spring, buffer spring, the contact pressure springs, transmission and chassis, terminal and so on. Counterproductive action of the spring coil power is to promote the release of the armature so that the contacts restore the original state. Buffering action of the spring in a buffer armature energisation of static core and shell impact. Increasing the contact pressure spring is dynamic, static pressure between the contacts, thereby increasing the contact area, to reduce the contact resistance. The role of the transmission mechanism in the armature or counterproductive action of the spring, the movable contact driven to achieve and static contact or breaking.

AC contactor works when the contactor coil is energized, the current flowing through the coil generates a magnetic field, the iron core generate enough suction to overcome the reaction of the reaction force of the spring, the armature pull, driven by three pairs of main transmission mechanism moving together contacts and auxiliary contacts are closed, the auxiliary contact being broken off. When the contactor coil power or voltage drops significantly, due to electromagnetic suction disappeared or too small, the armature in the reaction of the spring force of the reset to drive the contacts restored to its original state.

Common CJ0, CJ10 series AC contactor at 0.85 to 1.05 times the rated voltage, to ensure reliable pull.

a) coil; b) the main contacts; c) moving together auxiliary contacts; d) moving off auxiliary contacts

Second, the DC contactor

Its structure and working principle is basically the same with the exchanges and contacts, but there are some differences.

(A) Structure

DC contactors electromagnetic system is composed of three parts, the contact system and the arc extinguishing device component
1. Electromagnetic System

DC contactor system consists of an electromagnetic coil, core and armature components. The system uses electromagnetic angular rotation of the armature winding Clapper. Since the direct current through the coil, the core will not produce eddy current and hysteresis loss and fever, so the core piece of steel or cast iron can be used, also without core end face is fitted short ring. To ensure that the coil power can be reliably release the armature, the magnetic circuit pads often have a non-magnetic spacer, in order to reduce the impact of remanence. DC contactor coil turns than the exchanges and contacts, the resistance value is large, a large copper loss is the main component contactor fever. To make good heat coil, the coil is usually made in long, thin cylindrical; skeleton not provided, so that the coil and the core spacing is small, in order to distribute the aid to the core part of the heat.

DC contactors double winding coil wiring diagram

2. Contact system

Since the main contact switching on and off of the current is large, the use of rolling contact finger contacts, to extend the service life of the contacts. Contact closure process, the first movable contact and the stationary contact in the contact point A, then by B to C transition point slide. As in the opposite direction when the opening movement, thus automatically remove the oxide film on the contact surface to ensure reliable contact.

Auxiliary contacts off current is small, the use of double-break contact bridge, may have several pairs.

In order to reduce run-time coil power consumption and prolong the life of the attraction coil, large capacity DC contactor coil in series often double winding. Contactors a break contact with the holding coil in parallel. In the circuit just turned moment, holding coil passive break contacts short circuit, it can get a larger starting coil current and suction. When the contactor operation, and maintenance of coils in series starting coil is energized, the voltage constant, so the current is small, but still maintain the armature is energized, so as to achieve the purpose of saving.

3. Extinguishing device

DC contactors generally use magnetic blow interrupter device in combination with other methods interrupter interrupter. Magnetic blow interrupter device consists of a magnetic coil blow, core, two plywood permeability, arc angle and arc chute components

Works magnetic blow interrupter device: When the contactor dynamic and static contact breaking arc is generated between the contacts, a short arc by itself remains load current continues to exist, then the current will be in the arc is not extinguished prior to the formation of two magnetic fields. A magnetic field is formed around the arc current, the ampere given directions available is determined, as shown in Figure 5-36. In addition, in an arc around the same time there is a flow of current through the magnetic field by the magnetic blow between two magnetic coils in plywood formed through the magnetic core from a magnetic plywood through the air gap between the plywood into another piece of lead cleats, forming a closed magnetic circuit. Obviously outside a magnetic field direction is into the plywood on the paper. Visible in the top of the arc, the magnetic field direction of the magnetic field around the arc and plywood between opposite magnetic field strength weakening; the same in both directions at the bottom of the arc magnetic field, the magnetic field intensity increased. Accordingly, the arc is drawn from the magnetic field strong side to weak side; then the arc upward movement. The arc is elongated in the process of rapid upward movement of air and relative motion, the arc temperature. At the same time the arc is blown into the arc chute unit, heat of the arc to the arc chute has been passed, further reducing the temperature of the arc, prompting the arc quickly extinguished. In addition, during the upward movement of the arc, on the stationary contact of the arc root will be gradually transferred to the arc angle, thereby reducing the contact burns. Arc angle guide the upward movement of the arc root and continued to lengthen the arc when the supply voltage is not sufficient to maintain the arc burning, the arc extinguished. Thus, arc magnetic blow interrupter device is blown by the effect of magnetic force of the arc elongated and rapid cooling in air and arc chute, so that the arc quickly extinguished.

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