Greetings, esteemed readers! If you’ve ever found yourself inquisitive about the intricacies of Alternating Current (AC) contactors, you’re in for a treat. In this professional discourse, we will dissect the nuanced world of AC contactors, encompassing technical details, operational intricacies, and practical considerations. So, fasten your seatbelts, and let’s embark on a journey into the profound realm of electrical control.
What is an AC contactor
Contactor is an electrical component used to connect or break the AC main circuit, DC main circuit or large capacity control circuit with load. It mainly controls electric loads such as motors, transformers, etc. It can realize connecting or breaking circuits over long distances, support frequent operation, and work reliably. In addition, it also has zero-voltage protection, under-voltage release protection and other functions. Contactor electrical graphics and text symbols shown in Figure 1.
Contactor according to the type of contact current flowing through the different types of work, can be divided into AC contactor (CJ) and DC contactor (CZ) two categories, DC contactor structure and working principle and AC contactor is basically the same.
Structure of AC contactor
AC contactor is mainly composed of electromagnetic mechanism, contact system, arc extinguishing device and other parts, the structure is shown in Figure 2.
(1) Electromagnetic system
The role of the electromagnetic system is to manipulate the contact closure and breakage, which consists of static iron core, coil and armature three parts, iron core and armature shape are E-shaped, generally by the silicon steel sheet stacked riveted into the core to reduce the alternating magnetic field in the core of eddy current and hysteresis loss, to prevent the core from overheating.
The electromagnetic mechanism of the AC contactor in the actual operation process, the armature is not only subject to the role of the release spring and other institutional resistance, but also subject to the influence of the AC excitation current over zero, so that the armature vibration, noise.
Eliminate vibration and noise measures are installed in the iron core short-circuit ring, also known as vibration damping ring or demagnetization ring. After installing the short-circuit ring, a part of the alternating magnetic flux Φ1 passes through the short-circuit ring and generates an induction current in the short-circuit ring, which also generates a magnetic flux in the short-circuit ring, so that the magnetic flux in the short-circuit ring turns into Φ2, and the phases of Φ1 and Φ2 are different, i.e., Φ1 and Φ2 will not go over the zero level at the same time, and the electromagnetic forces F1 and F2 generated by them will not go to the zero level at the same time, which will make the core attract the armature all the time, and the vibration and noise will be reduced remarkably. The vibration and noise will be reduced significantly.
(2) Contact system
Contactor contacts are used to connect or disconnect the circuit, according to its contact situation can be divided into point contact, line contact and surface contact three kinds.
According to the different uses, the contacts are divided into main contacts and auxiliary contacts. The main contact is used to connect or disconnect the main circuit with a large current, generally composed of normally open contacts with a large contact surface. Auxiliary contacts are used to connect or disconnect small current control circuits, which are composed of pairs of normally open and normally closed contacts.
When the contactor is not working, in the disconnected state of the contact is called normally open (NO) contacts; when the contactor is not working, in the connected state of the contact is called normally closed (NC) contacts.
(3) Arc extinguishing device
AC contactor in the breaking of high-current circuits, will produce a strong arc between the moving and static contacts, the arc is between the contacts of the gas under the action of a strong electric field generated by the discharge phenomenon. Arc on the one hand will burn the contacts, on the other hand, will make the circuit cut-off time is prolonged, and even cause other accidents. Therefore, the arc is one of the main tasks of the contactor.
Arc extinguishing methods are generally used in the double-break structure of the electrodynamic arc extinguishing and semi-enclosed insulated grill terra cotta fire extinguishing cover. The former is suitable for contactors with smaller capacity (below 10A), and the latter is suitable for contactors with larger capacity.
The role of AC contactors
The role of an AC contactor is akin to that of a gatekeeper in an electrical system. It orchestrates the circuit’s closure or opening, permitting or restricting the flow of AC based on predetermined conditions. This meticulous control is imperative for maintaining the stability and integrity of the electrical network. Often used in electric motors as a control object, can also be used to control plant equipment, electric heaters, workhorses and various power units and other electrical loads.
The working principle of AC contactor
When the electromagnetic coil is energized to generate a magnetic field, so that the iron core generates enough suction to overcome the reaction spring and the reaction force of the spring plate of the pressure of the movable contact, the armature will be suction closed, and at the same time drive the transmission lever to make the movable and static contact state change, which the three pairs of normally open contact closure. In addition, the normally closed auxiliary contacts are first disconnected, followed by the normally open auxiliary contacts closed. When the electromagnetic coil is disconnected, due to the iron core electromagnetic suction disappears, the armature is released under the action of the reaction spring, and the contacts are also restored to the original state.
AC Contactor Rating Explained
Understanding the parameters of AC contactors is paramount in their appropriate selection for a given application. Parameters such as voltage rating, current capacity, and contactor size play pivotal roles in ensuring optimal performance within a designated electrical system. Selecting a contactor that aligns with these parameters is critical for longevity and efficiency.
(1) Rated voltage
The rated voltage on the nameplate of the contactor refers to the rated voltage of the main contact, and the rated voltage of the main contact should be selected to be greater than or equal to the rated voltage of the load circuit.
(2) Rated current
The rated current on the nameplate of the contactor refers to the rated current of the main contact, and the rated current of the selected main contact should be greater than or equal to the rated current of the motor.
(3) Rated voltage of the attracting coil
The rated voltage of the attracting coil is equal to the voltage of the control circuit. 36V, 110V, 127V, 220V, 380V are available for AC; 24V, 48V, 220V, 440V are available for DC.
(4) Rated operating frequency
The rated operating frequency of the contactor is the number of operations permitted per hour of the contactor
What are a1 and a2 on an AC contactor?
(1) Types of contactors
Select according to the type of motor or load current to be controlled, AC loads should use AC contactors, DC loads should use DC contactors. If the whole control system is mainly AC loads, and the capacity of DC loads is small, you can also use all AC contactors, but the rated current of the contacts should be appropriately selected larger.
(2) Rated voltage of contactor
Generally, the rated voltage of the contactor contacts is greater than or equal to the rated voltage of the load circuit.
(3) Rated current of main contacts of contactor
The rated current of the main contact of the contactor should be greater than or equal to the rated current of the motor or load. Since the rated current of the motor is related to its rated power, it can also be selected according to the rated power of the motor.
When the rated voltage of a three-phase motor is 380V, the rated operating line current of the motor.
In this equation, PN is the rated capacity of the motor (kW).
When the rated voltage of three-phase motor is 660V, the rated running line current of the motor.
For example, PN = 4kW and UN = 380 V. From the above equation:
IN = 4kW x 2A/kW = 8A, i.e., select the contactor main contact rated current greater than or equal to 8A.
When the contactor is used in frequent starting, braking and forward and reverse occasions, the contactor main contact rated current is generally reduced by one level or according to the maximum power of the motor can be controlled by halving the selection.
(4) Contactor coil voltage
Generally, the voltage of the contactor coil should be the same as that of the control circuit.
(5) Auxiliary contact of contactor
The rated current, quantity and type of auxiliary contacts of the contactor should be able to meet the requirements of the control circuit, if it can’t be met, an intermediate relay can be used to expand.
How to choose an AC contactor
A1 and A2 on an AC contactor are the two terminals of the contactor coil, through which the coil of the AC contactor is connected to the power supply, so that the coil of the contactor can be energized and the AC contactor can work, and these two terminals are connected to the control circuit.
Difference between AC contactor and DC contactor
While both AC and DC contactors share the overarching function of controlling electrical circuits, key differentiators lie in their design and compatibility. Here are the difference between AC Contactor and DC Contactor.
(1) Different control objects
AC contactors are used to control AC electrical equipment, while DC contactors are used to control DC electrical equipment.
(2) The core structure is different
The core of AC contactor is made of insulated silicon steel sheets stacked and riveted, often in E-shape to reduce eddy current loss; the core of DC contactor can be made of cast iron or cast steel, often in U-shape. AC contactor core often embedded in the short circuit ring to eliminate vibration and noise, while the DC contactor does not need a short circuit ring.
(3) Arc extinguishing system is different
AC contactor using the grid arc extinguishing device will be a long arc divided into a short arc; DC contactor using magnetic blowing arc extinguishing device, relying on the elongation of the arc and the cooling arc to extinguish the arc. Because the DC arc does not have a natural zero point, arc extinguishing relative to the AC arc is more difficult, so the DC contactor arc extinguishing device is usually more complex.
(4) Coil turns are different
AC contactor coil turns are less, resistance value is smaller, copper loss is smaller; DC contactor coil turns are more, resistance value is bigger, copper loss is bigger, and it becomes the main part of contactor heat. In order to good heat dissipation, the coil of DC contactor is usually long and thin cylindrical, no skeleton, and the distance between the core is small, in order to use the core to dissipate heat.
(5) Different operating frequency
AC contactors operate at a maximum frequency of about 600 times per hour, while DC contactors can operate at a frequency of up to 1,200 times per hour.
Can AC contactor be used for DC
The coil of AC contactor has fewer turns and smaller resistance, when the coil is energized with AC current, it will produce a larger inductive reactance, which is much larger than the resistance of the coil, and the excitation current of the coil mainly depends on the size of the inductive reactance. If the DC current is passed into the coil, the coil will become a pure resistive load, and the current flowing through the coil will be very large, making the coil hot, or even burned out. Therefore, AC contactors cannot be used as DC contactors.
AC contactor in emergency can be used as a substitute for DC contactor, suction time can not be more than 2 hours (because the AC coil heat dissipation is worse than DC, which is determined by their structural differences), really want to use for a long time it is best to string a resistor in the AC coil. On the other hand, DC can’t be used as a substitute for AC contactor; when the coil of DC contactor is connected to AC power: due to the long and thin coil, many turns, high resistance, it can’t be absorbed, or released when it is closed.
Where to buy ac contactor
Procuring AC contactors necessitates sourcing from reputable suppliers specializing in electrical components.
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There you have it—our deep dive into the AC contactor realm! We’ve covered everything from the nitty-gritty of electromagnetic mechanisms to choosing the right contactor for your electrical gig.
Remember, when it comes to AC contactors, understanding their ins and outs can make your electrical systems purr like a content cat. And hey, if you have any other questions, Derlicn’s got your back. Please do not hesitate to contact us, top-notch electrical gear and a support crew that knows their stuff – what more could you want?
So, buckle up, fellow electrical enthusiasts! Your journey into the fascinating world of AC contactors is just beginning. Happy wiring!
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