Despite the continuous advancement of technology over the years, the main method of controlling the circuit has not changed. Including contactors, this article studies different types of contactors and how they work. In addition, it compared AC contactors and DC contactors.
1. What is a contactor?
An electromechanical contactor is a device that connects the power supply to the load by making or breaking a connection. The contactor is electrically controlled and is usually powered at a much lower level than the switching circuit. For example, you have a 24 volt coil solenoid to control a 230 volt motor switch.
Applications for contactors include controlling motors, thermal evaporators, lighting, capacitor banks, heating and other electrical loads. The size and capacity of the contactors vary. You can easily lift them to the side about a meter high with your hands. You also have those circuit breakers with currents ranging from a few amperes to thousands of amperes and those from 24V DC to many kilovolts.
2. Type of contactor
It is the oldest type of contactor, using ON and OFF motors. The blade switch consists of a long bar and a lever. The function of the lever is to pull the metal sheet up and down, so that the contactor is manually operated. It has several shortcomings, which led to its discontinuation. These challenges include
- High arc occurrence rate, resulting in short contactor life
- There is a security risk
- Vulnerable to moisture and dust
- Double break
The contactor is the replacement and improvement of the blade switch. However, it still features manual operation. Other main features are
- Double-open contact, which can break the circuit in two places at the same time, providing more current in a smaller space.
- Properly enclosed unit protects internal components
- Safe operation
- Smaller size
This is the latest contactor design and the most advanced of all designs. Because of its characteristics, it is often used in industrial applications
- Automatic work
- Provide the safest operation
- Use the least control current to disconnect and close the circuit.
3. How does the contactor device work?
To understand the working principle of the contactor, you need to understand the various parts of the contactor. The contactor has three basic components;
- Rack or shell
Coil or electromagnet
The coil provides the driving force in the contactor that closes the contact. It is characterized by a coil wound around an electromagnetic core, so it behaves like an electromagnet. The coil has two parts, one is the fixed part and the other is the movable part. The two parts are connected by a spring. Structures such as this function as spring return mechanisms.
The moving part is attached to a rod, called an armature. When the force of the coil is greater than the force of the spring, the two contacts are connected. When the force of the spring is greater than the force of the coil, the contact will open.
The input of the contactor coil can be AC or DC. This current comes from the external control circuit of the contactor and is used to excite the electromagnetic core. For AC contactors, soft laminated iron is the electromagnet core material. It helps reduce eddy current losses. In the DC contactor, since there is no eddy current problem, the material of the electromagnet core is solid steel.
The contacts perform a current-carrying function in the contactor. There are different types of contacts in the contactor. They are: auxiliary contacts, power contacts, and contact springs. There are two types of power contacts; fixed and mobile contacts.
The material used to make the contacts must have high welding resistance and stable arc resistance. This material should also be able to withstand erosion and mechanical stress. In high current and DC applications, the material is silver tin oxide, while in low current applications, the material is silver nickel oxide and silver cadmium oxide.
As the name suggests, the housing protects the internal components of the contactor. It can protect the contacts from dust, bad weather, explosion hazards and oil. It also prevents people from touching the contacts.
4. Simply put, the working principle of the contactor is as follows
The current from the external control circuit passes through the contactor to excite the electromagnet core. An electromagnetic field is created by the coil/electron, which then moves the armature. A normally closed contact completes the circuit between the fixed contact and the moving contact.The current can then pass through these contacts to the load.
When the current is removed, the coil will be de-energized and the magnetic force will drop to zero. Therefore, the spring force is higher and pulls back the armature, opening the circuit. The design of the contactor is conducive to rapid on-off action.
5. The difference between AC contactor and DC contactor
The difference between AC contactor and DC contactor is mainly reflected in five aspects;
- The electromagnet core of the AC contactor is made of silicon steel sheet, and the electromagnet core of the DC contactor is made of mild steel.
- The electromagnet core of the AC contactor is usually E-shaped, while the electromagnet core of the DC contactor is usually U-shaped.
- The AC contactor has a short-circuit ring at the end of the static iron core. It helps to eliminate vibration and noise from the electromagnet. The DC contactor does not have a short-circuit ring because it does not need it.
- The AC contactor has a high starting current, and the maximum operating frequency is 600 times/hour. The contact frequency of the DC contactor is about 1200 times/hour.
- The DC contactor uses magnetic arc extinguishing, and the AC contactor uses grid arc to extinguish the fire.
6. Contactors and relays
Since contactors and relays are often confused with each other, comparing contactors and relays will help you distinguish and know which one to choose.
Size: The contactor is relatively large compared to the control relay
Current switching capacity: the relay load does not exceed 10A, and the contactor load exceeds 10A.
Purpose: Relays are usually used in single-phase control circuits, while contactors are used in three-phase control circuits.
System voltage: The rated voltage of the relay is usually only 250V, which is less than the rated voltage of the contactor, which is usually as high as 1000V.
The normally open/closed contact standard is pretty much the norm among contactors On the other hand, according to the expected function, the relay has two types: normally open and normally closed.
Safety features: Relays have low power and therefore usually do not have safety features, while contactors have safety features such as arc suppression and spring-loaded contacts because they carry higher loads.
Maintenance: Contactors are easier to maintain than relays, and relays are often even impossible to repair.
Finally, compared with the connector, the relay has a faster switching action.
The contactor is an indispensable device in circuit control and has additional safety functions. For every electronic device, making sure you find one that meets your needs and functions is crucial. You also need a reliable supplier like Chint to provide Chint products that comply with international standards, such as IEC.
In addition, you want more options in terms of design and utility, as well as professional support. These factors can help you determine a suitable gadget, improve security, and make your money worthwhile.