A Electrical contactor is an electrical device which is used for switching an electrical circuit on or off.A contactor is also called an “electromagnetic contactor” although it is most often merely called a “contactor”.It is considered to be a special type of relay.
However, the basic difference between the relay and contactor is that the contactor is used in applications with higher current carrying capacity, whereas the relay is used for lower current applications.
Introduction
A contactor is a relay that is used for switching power.They usually handle very heavy loads like an electric motor, lighting and heating equipment and so on.
Though their output is used for switching very high loads, they are controlled by a circuit with very less power. According to the loads they handle, they vary in sizes from a small device to as huge as a yard.
There are various types of contactors, and each type has its own set of features, capabilities, and applications. Contactors can break current over a wide range of currents, from a few amperes to thousands of amperes, and voltages from 24 VDC to thousands of volts.
The most common application area of the contactor is high-current load. Contactors are known for their capability to handle currents of over 5000 amperes and high power over 100 kW. Heavy motor currents produce arcs when being interrupted. These arcs can be reduced and controlled using a contactor.
Contactors are available in two pole, three pole and four pole configurations. Both enclosed and open designs are common. The open design is intended for mounting in a customer’s enclosure. Most contactors are normally open although normally closed contactors are also available for specialized applications.
Working principle of Contactor
A contactor also has
- Contact
- Spring
- Electromagnet
The current passing through the contactor excites the electromagnet. The excited electromagnet produces a magnetic field, causing the contactor core to move the armature.
A normally closed (NC) contact completes the circuit between the fixed contacts and the moving contacts.
This permits the current to pass through these contacts to the load. When current is removed, the coil is de-energized and opens the circuit. The contacts of the contactors are known for their rapid open and close action.
The contacts are controlled by the electromagnet. These electromagnets give the initial force to the contacts and make them closed. Both these contacts and electromagnet are enclosed in a frame which is usually made of insulating materials.
The usually used insulating materials are Nylon 6, thermosetting plastics and so on. They are useful, as they completely insulate the contacts and help in preventing the touch of contacts.
For high-end contactors, an open-frame contactor is commonly used. This will provide a greater protection from oil, dust, weather and also from explosion.
Components of the contactor
- Coil or Electromagnet: This is the most crucial component of a contactor. The driving force that is required to close the contacts is provided by the coil or electromagnet of the contactor. The coil or electromagnet and contacts are protected by an enclosure.
- Enclosure: Just like the enclosures used in any other application, contactors also feature an enclosure, which provides insulation and protection from personnel touching the contacts. The protective enclosure is made from different materials, such as polycarbonate, polyester, Nylon 6, Bakelite, thermosetting plastics, and others. Generally, the open-frame contactor features an additional enclosure, which protects the device from bad weather, hazards of explosion, dust, and oil.
- Contacts: This is yet another important component of this electrical device. The current carrying task of the contactor is done by the contacts. There are different types of contacts in a contactor namely, contact springs, auxiliary contacts, and power contacts. Each type of contact has an individual role to play.
Purpose of Auxiliary contact and power contact
Auxiliary contact:
Auxiliary contacts, which would have a lower current rating than the main contacts, are available with most contactors. The auxiliary contacts are often used for the purpose of interlocking in control circuits or for the purpose of remote indication of contactor position.
Power contact:
Power contact have capacity to pass electric current as per their setting.The power contacts gains the power for the contactor.
Types of Contactor
Different types of contactor use as per their working.
Knife Blade Switch
It was probably the first ever contactor that was used to control (start or stop) electric motors. The switch consisted of a metal strip, which would drop onto a contact. This switch had a lever for pulling the switch down or pushing it up. Back then, one had to level the knife blade switch into the closed position by standing next to it.
However, there was a problem with this method of switching. This method caused the contacts to wear out quickly, since it was difficult to manually open and close the switch fast enough to avoid arcing. As a result of this, the soft copper switches underwent corrosion, which further made them vulnerable to moisture and dirt.
Manual Controller(Double break contactor)
Since the knife blade switch became potentially dangerous to use, engineers came up with another contactor device, which offered a number of features that were missing in the knife blade switch. This device was referred to as a manual controller. These features included:
Safe to operate
Non-exposed unit, which is properly encased
Physically smaller size
Single break contacts replaced with double break contact
As their name implies, double break contacts can open the circuit in two places at the same time. Thus, even in smaller space, it allows you to work with more current. Double break contacts divide the connection in such a way that it forms two sets of contacts.
The switch or button of the manual controller is not operated remotely and is attached to the controller physically.
The power circuit is engaged once the manual controller is activated by an operator. Once activated, it carries the electricity to the load. Soon, manual contactors replaced knife blade switches completely, and even today different variations of these types of contactors are being used.
Magnetic Contactor
The magnetic contactor does not require human intervention and operates electromechanically. This is one of the most advanced designs of a contactor, which can be operated remotely. Thus, it helps eliminate the risks involved in operating it manually and putting operating personnel in potential danger.
Only a small amount of control current is required by the magnetic contactor to open or close the circuit. This is the most common type of contactor used in industrial control applications.
Contactor Ratings
Ratings of a contactor are given according to the pole of the contactor. It also depends on factors like fault withstand current, coil voltage and so on. According to their rating, contactors are classified into the following.
AC1 – Non-inductive rows
AC2 – Contactors for starting of slip-ring motors
AC3 – Starting of squirrel-cage motors and switching off only after the motor is up to speed.
AC4 – Starting of squirrel-cage motors with inching and plugging duty.
AC11 – Auxiliary control circuits
Application of Contactor
Lighting Control Contactors are often used to provide central control of large lighting installations, such as an office building or retail building. To reduce power consumption in the contactor coils, latching contactors are used, which have two operating coils. One coil, momentarily energized, closes the power circuit contacts, which are then mechanically held closed; the second coil opens the contacts.
Electric Motor Starter Contactors can be used as a magnetic starter. A magnetic starter is a device designed to provide power to electric motors. It includes a contactor as an essential component, while also providing power-cutoff, under-voltage, and overload protection.
Contactor use with MCB(Miniature Circuit Breaker) to protect electrica circuit several field.
Frequently Asked Question (FAQ)
What is contactor?
A Electrical contactor is an electrical device which is used for switching an electrical circuit on or off.A contactor is also called an “electromagnetic contactor” although it is most often merely called a “contactor”.It is considered to be a special type of relay.
What is component of contactor?
Coil or electromagnet, Contact and enclosure
What is defference between contactor and relay?
The basic difference between the relay and contactor is that the contactor is used in applications with higher current carrying capacity, whereas the relay is used for lower current applications.
Why Contactor use in industrial application?
Contactor is special type relay,which is used switch current to an electric motor. Large motor can protect from overload by using overload contactor.
What is difference between AC and DC contactor?
Main difference is their arc extinguishing devices. AC contactor use grid arc extinguishing device while DC contacto adopts magnetic quenching arc extinguishing.
What is ampere and voltage rating of contactor?
Rating of Contactor is use as per application. Ampere and Voltage range of contactor is thousands times but applicability as per requirement.
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