Basic working principle of AC contactor

When the coil is energized, the static iron core generates electromagnetic attraction, which attracts the moving iron core. Since the contact system is linked with the moving iron core, the moving iron core drives the three moving contact pieces to move at the same time. The main contact is closed and the main contact is closed. The auxiliary normally closed contact mechanically connected to the contact is disconnected, and the auxiliary normally open contact is closed, thereby turning on the power supply.

When the coil is de-energized, the suction force disappears, and the moving iron core linkage part is separated by the reaction force of the spring, so that the main contact is disconnected, the auxiliary normally closed contact mechanically connected to the main contact is closed, and the auxiliary normally open contact is disconnected , Thereby cutting off the power.

The AC contactor can only be used in the AC line. If the AC contactor is forced to be connected to the DC, the result is bound to burn the line and even the equipment.

Main components of AC contactor

(1) Electromagnetic system, including attraction coil, moving iron core and static iron core;

(2) The contact system, including three groups of main contacts and one or two sets of normally open and normally closed auxiliary contacts, which are connected to the moving iron core in linkage with each other;

(3) Arc extinguishing device. Generally, AC contactors with larger capacity are equipped with arc extinguishing device to cut off the arc quickly and avoid burning the main contact;

(4) Insulating housing and accessories, various springs, transmission mechanisms, short-circuit rings, terminals, etc.

AC contactor wiring method

There are marks on the contactor (subject to actual conditions)

1L3L5L corresponds to 2T4T6T and is connected to the main contact

The corresponding coil has terminal A1A2

There are auxiliary contacts that can be connected

13 and 14 represent the auxiliary contacts of this contactor, NO represents normally open, that is, 13 and 14 are open when there is no power, and 13 and 14 are closed after power is applied. Put it in the control circuit part and use the self-lock (connected in parallel with the start button) to achieve the purpose of continuous operation.

Debugging of Motor Reversible Operation Control Circuit

1. Check whether the wiring of the main circuit is correct. In order to ensure that the phase sequence of the motor can be reliably exchanged when the two contactors are in action, the upper connection of the contactor should be kept consistent when connecting, and the phase should be adjusted at the lower connection of the contactor.

2. After checking that the wiring is correct, conduct a power-on test. To prevent accidents during the power-on test, disconnect the motor wiring first. Pre-processing of failure phenomena;

1. It does not start; one of the reasons is to check whether the control fuse FU is open, whether the FR contact of the thermal relay is used incorrectly or is in poor contact, and whether the normally closed contact of the SB1 button is bad. The second reason is that the wiring of the button interlock is wrong.

2. When starting, the contactor "patter" will not suck; this is because the contactor's normally closed contact interlocking wiring is wrong, the interlocking contact is connected to self-locking, and the normally closed contact is open contact when starting After the electric pull-in contactor of the coil is closed, the normally closed contact is disconnected, the contactor coil is de-energized and released, the normally closed contact is released, and the contactor is closed and closed again, and the contact is disconnected, so a "pet" will appear. "The phenomenon that the contactor does not pull in.

3. The contactor will be disconnected as soon as it cannot be self-locked. This is because the self-locking contact is connected incorrectly. Motor reversible operation control circuit. In order to enable the motor to rotate forward and reverse, two contactors KM1 and KM2 can be used. The phase sequence of the three-phase power supply of the motor, but the two contactors cannot be closed. If they are closed at the same time, it will cause a short circuit accident of the power supply. In order to prevent such accidents, a reliable interlock should be adopted in the circuit.

1. Positive start:

1. Close the air switch QF to switch on the three-phase power supply

2. Press the forward start button SB3, KM1 is energized and attracted and self-locked, the main contact is closed and the motor is turned on. The phase sequence of the motor at this time is L1, L2, L3, that is, forward running.

2. Reverse start:

1. Close the air switch QF to switch on the three-phase power supply

2. Press the reverse start button SB2, KM2 is energized and attracted and self-locked through the auxiliary contact. The normally open main contact is closed and the three-phase power phase sequence of the motor is changed. At this time, the phase sequence of the motor is L3, L2, L1 , That is, reverse operation.

3. Interlocking link: It has a prohibition function and plays a safety protection role in the line

1. Contactor interlock: KM1 coil circuit is connected to the normally closed auxiliary contact of KM2, and KM2 coil circuit is connected to the normally closed contact of KM1. When the KM1 coil of the forward rotation contactor is energized, the auxiliary normally closed contact of KM1 disconnects the KM2 coil circuit. If KM1 is energized and closed, KM2 must be de-energized and released, and its auxiliary normally closed contact is reset. This prevents KM1 and KM2 from being pulled in at the same time and causing a short circuit between phases. This circuit link is called an interlock link.

2. Button interlock: The positive and negative transmission control circuit of the control button operation is adopted in the circuit. The buttons SB2 and SB3 have a pair of normally open contacts and a pair of normally closed contacts. These two contacts are respectively connected with KM1 and KM1. KM2 coil circuit connection.

For example, the normally open contact of the button SB2 is connected in series with the coil of the contactor KM2, and the normally closed contact is connected in series with the coil of the contactor KM1. The normally open contact of the button SB3 is connected in series with the coil of the contactor KM1, and the normally closed contact presses the KM2 coil circuit in series. In this way, when SB2 is pressed, only the coil of contactor KM2 can be energized and KM1 is powered off. When SB3 is pressed, only the coil of contactor KM1 can be energized and KM2 is powered off. If SB2 and SB3 are pressed at the same time, two None of the contactor coils can be energized. This acts as an interlock.

4. After the motor starts running in the forward (or reverse) direction, it is not necessary to first press the stop button to stop the motor. You can directly press the reverse (or forward) start button to make the motor run in the reverse direction.

5. The overload protection of the motor is completed by the thermal relay FR.

The purpose of AC contactor

AC contactor is the most common low-voltage control electrical appliance used in electric drive and automatic control systems. As an actuator, it is used to connect or disconnect lines, or frequently control the operation of motors and other equipment. It is composed of moving and static main contacts, arc extinguishing cover, moving and static iron cores, auxiliary contacts and bracket shell.

After the electromagnetic coil is energized, the moving iron core is attracted under the action of electromagnetic force, and the moving contact is contacted with the static contact directly or through a lever transmission, and the circuit is connected. After the solenoid coil is powered off, the moving iron core automatically returns under the action of the return spring, commonly known as release, the contacts are separated, and the circuit is broken. AC contactor is the most common low-voltage control electrical appliance used in electric drive and automatic control systems. As an actuator, it is used to connect or disconnect lines, or frequently control the operation of motors and other equipment. It is composed of moving and static main contacts, arc extinguishing cover, moving and static iron cores, auxiliary contacts and bracket shell. After the electromagnetic coil is energized, the moving iron core is attracted under the action of electromagnetic force, and the moving contact is contacted with the static contact directly or through a lever transmission, and the circuit is connected. After the solenoid coil is powered off, the moving iron core automatically returns under the action of the return spring, commonly known as release, the contacts are separated, and the circuit is broken.

AC contactor composition

Main contact, auxiliary contact, coil; the contactor uses the main contact to open and close the circuit, and the auxiliary contact to conduct the control loop. The coil voltage is to supply power to the control loop.

AC contactor used in conjunction

The AC contactor does not have the overcurrent protection function, so it needs to be used in conjunction with the electrical appliances with overcurrent protection function when used in the circuit. Such as matching fuses, circuit breakers, thermal relays, etc. Used in small current to control large current, or low voltage to control high voltage. The main contact is connected to the incoming and outgoing wires, A1A2 is connected to the coil, and the auxiliary contact is used for self-locking, interlocking, signal lamp display or alarm indication, etc. Contactor is often encountered, its main function is to connect and disconnect the load. At the same time, self-retaining, chaining, etc. can also be realized. If used in conjunction with other electrical appliances, such as thermal relays, overload protection can also be achieved. It can be said that this is the most common electrical appliance. It is also very common.

What is the difference between AC contactor and DC contactor

The function of the contactor, in terms of function, is to isolate and cut or pull in electrical circuits. In essence, the AC and DC contactors are the same in terms of contacts, but the coil design is different and the voltage used is different.

The AC contactor is composed of an electromagnetic system, a contact system, an arc extinguishing device, and a housing base. The AC contactor has the following characteristics: ①The iron core and the armature are made of silicon steel sheets;

② The AC voltage pull-in coil has a larger impedance;

③Short-circuit rings are embedded on both the moving armature and the static armature;

④It has main contacts that can be turned on or off and auxiliary contacts of varying numbers. The main contacts are equipped with arc extinguishing devices.

How to choose and consider the factors of AC contactor

1. When choosing a contactor, we should proceed from the working environment, mainly considering the following factors

①The AC contactor should be used to control the AC load, and the DC contactor should be used for the DC load

②The rated working current of the main contact should be greater than or equal to the current of the load circuit. It should also be noted that the rated working current of the main contact of the contactor can be normal under the specified conditions (rated working voltage, use category, operating frequency, etc.) The working current value, when the actual use conditions are different, the current value will also change accordingly.

③The rated working voltage of the main contact should be greater than or equal to the voltage of the load circuit.

④The rated voltage of the coil should be consistent with the voltage of the control circuit

2. The specific steps of contactor selection

①Select the type of contactor, you need to select the type of contactor according to the load type

Load types: Class I, Class II, Class III, Class IV

Tag name: AC-1, AC-2, AC-3, AC-4

Control object: non-inductive or symptomatic load, asynchronous motor start and stop, cage asynchronous motor operation and operation, cage asynchronous motor start, reverse braking, reverse rotation and jog,

②Select the rated parameters of the contactor

According to the controlled object and working parameters, such as voltage, current, power, frequency, etc., determine the rated parameters of the contactor.

(1) The coil voltage of the contactor should generally be lower, so that the insulation requirements for the contactor can be reduced and it is safer to use. When the control circuit is simple and the use of electrical appliances is relatively small, the voltage of 380V or 220V can be directly selected. If the circuit is complicated. When the number of electrical appliances exceeds 5, coils with a voltage of 36V or 110V can be used to ensure safety. However, in order to facilitate and reduce equipment, it is often selected according to the actual grid voltage.

(2) The operating frequency of the motor is not high, such as compressors, water pumps, fans, air conditioners, etc., and the rated current of the contactor is greater than the rated current of the load.

(3) For heavy duty motors, such as machine tool main motors, lifting equipment, etc., when selecting, the rated current of the contactor is greater than the rated current of the motor

(4) For special purpose motors. When often running in the state of starting reverse, the contactor can be roughly selected according to the electric life and starting current, and CJ10Z, CJ12,

(5) When using a contactor to control a transformer, the magnitude of the surge current should be considered. For example, for electric welding machines, contactors, such as CJT1, CJ20, etc., can generally be selected at twice the rated current of the transformer.

(6) The rated current of the contactor refers to the maximum allowable current of the contactor under long-term operation, and the duration is ≤8H, and it is installed on an open control board. If the cooling condition is poor, the rated current of the contactor when the contactor is selected The current is selected according to 1.1-1.2 times of the rated current of the load.

(7) Choose the number and type of contactors. The number and types of contacts should meet the requirements of the control circuit.

Selection scheme of anti-shake AC contactor

1. What is electric shock?

During the operation of the power system, due to lightning strikes, short-circuits to ground, fault reclosing, automatic standby switching, abnormal grids, large equipment startups, etc., the grid voltage instantly drops and returns to normal, which causes the voltage to fluctuate greatly or The phenomenon of power failure and recovery is called "power shaking".

2. The reason for the electric shock?

The power grid is composed of substations at various levels, especially the user distribution points in the 10KV loop are wide-ranging, and it is extremely prone to short-circuit or over-current faults. After a circuit fails, the relay protection device of the circuit will act and remove the fault circuit. The time from the occurrence of the fault to the removal of the fault is about 500-1200ms. During this period, the voltage of other normal circuits will cause temporary power sloshing. In addition, summer is a season of frequent thunder and lightning, and lightning strikes will also cause temporary power swaying in the grid voltage.

3. The impact of electric shock?

Electric shock causes the AC contactor to trip and shut down

AC contactors are widely used in low-voltage motor control systems and occupy a large proportion. Due to the working principle and characteristics of electromagnetic AC contactors, when the power grid appears to be shaken, the working coil of the electromagnetic AC contactor will be disconnected for a short time. Electricity or voltage is too low, resulting in that the suction force of the moving and static iron cores maintained by the current is less than the elastic force of the release spring to cause the contactor to trip. This is an important reason for the contactor to trip and stop. The operating characteristics of the electromagnetic AC contactor are in accordance with the international IEC standards, and the contactor should be reliably closed between 85% and 110% of the rated control power supply voltage. The release operating voltage range is between 20% and 75% of the rated control power supply voltage. In field use, the electromagnetic AC contactor is generally released at 50% of its rated control power supply voltage, and the electric shock causes the electromagnetic AC contactor to be uncontrolled and naturally trip and shut down. Therefore, the working principle of the electromagnetic AC contactor determines that it cannot avoid the "electric shock" phenomenon on the power grid.

The influence of electric shock on the control circuit of the power supply loop

With the development of the power grid, the continuous expansion of capacity and scale, the frequency of electricity swaying phenomenon is increasing. Due to the increasing scale of modern industrial and mining enterprises' production equipment, although the duration of electricity swaying is relatively short, it has an impact on production. It's huge. Instantaneous voltage fluctuations will cause hundreds of motors to trip and equipment to stop. After the grid voltage is restored, the motors cannot resume operation by themselves, leading to disorder in the continuous production process and possibly causing production and equipment accidents. For large-scale installations, it will take a long time to recover manually. For an unattended field installation, the recovery time will be longer. For continuous production installations such as petroleum, chemical, pesticide, etc., it will take a long time. A series of losses such as safety, environmental protection, waste products, waste of raw materials, reduced output, and low efficiency are very huge.

Fourth, the solution to the electric shock

First of all, it needs to be clear that all current anti-shake technologies are remedial measures when the electric shock occurs, that is, when the electric shock occurs, the best method is used to avoid the loss or harm caused by the electric shock. It is currently impossible to fundamentally control and avoid the occurrence of electric shock.

1. Because the short-circuit capacity of the power supply system is too large, if compensation is performed from the primary system, it can theoretically be realized: each 10KV circuit must be equipped with current-limiting compensation equipment. However, the investment of a 10KV circuit will be hundreds of Therefore, the investment is quite large. For this item, the investment of a substation is tens of millions, and at the same time, it also occupies several times the area of the substation. Therefore, the use value of a system compensation is not high for the general enterprise. Not easy to achieve.

2. Take measures on the secondary circuit of the electrical system

At present, anti-shake measures are generally taken on the secondary circuit of the electrical system. That is, when a power sway occurs, the voltage of the secondary circuit is basically unchanged, or the control appliance of the primary circuit is disconnected with a delay to ensure that it is normally closed after the power sway, so as to avoid the impact of the instantaneous low-voltage accident of the power supply system. At present, there are mainly the following methods in the market:

①The anti-shake and restart scheme: when the circuit system has electric shock, the voltage drops to release the contactor; if the voltage recovers within the anti-shake time set by the restart device, the restart device relay contact is closed to make the contactor re-engage Together, it ensures that the power supply circuit continues to work.

Disadvantages: If it is a heavy-duty motor, the electromagnetic energy stored in the motor is quickly consumed by the load when the power is shaken, the motor speed has dropped to 0 when the voltage is restored, and the restart device starts when the contactor is closed. 5 to 8 times the rated current of the motor, and the starting current is too large. If it is a light-load motor, the motor speed may not be 0 when the voltage is restored when the power is shaken. When the restarting device starts the contactor to close, due to the residual voltage of the motor, it is easy to cause the reverse phase closing, causing a larger closing shock.

②The anti-shake protection scheme of the AC contactor: that is, when the electric shock occurs, the contactor is not released, so as to ensure that the power supply circuit continues to work. For the motor, this process is only a short-term undervoltage operation process, and there is no large starting current or closing shock.

Therefore, these two schemes give priority to the electric shock retention type,

The anti-shake protection scheme is further divided into an additional delay disconnect module and a permanent magnet anti-shake electric contactor.

The time-delay disconnect module is mainly used as the power supply to protect the contactor, that is, the power supply of the control loop is connected to the time-delay module, and the time-delay module then supplies power to the contactor. Therefore, the requirements for modules are relatively high. First of all, the capacity of the module must be large enough to meet the requirements of the capacity of the contactor being powered, otherwise it will cause the module to generate heat and affect its life; secondly, the module must have the function of exiting when the module fails, that is, when the module itself fails, the module itself To automatically exit the operation, but can not affect the normal breaking and closing of the contactor.