When performing electrical work on high-voltage lines, when connecting powerful consumers of electrical energy and industrial equipment, an electrician inevitably encounters a device such as a contactor. A professional has no doubts why a contactor is needed and what functions it performs, but a person who is far from electrical engineering or who is just starting to learn the electrical specialty sooner or later has to face this concept. The contactor is a very convenient device, but in order to understand why it is needed, you will have to figure it out a bit.
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What is a contactor and why is it needed
In electrical networks, you constantly have to turn on or off various loads or control their operation. As we know, in everyday life there are mechanical switches and knife switches for these purposes.But such devices have a very limited durability resource, and for large electrical systems, control by means of mechanical switches is an inconvenient and inefficient way. That is why such a device was created, which has a huge service life, allows you to cycle on and off up to several thousand times per hour, and most importantly, makes it possible to control the load remotely. In simple words, this is a switch.
Contactor - This is an electromagnetic device designed for frequent switching on and off of electrical circuits remotely.
Electromagnetic contactors are used in all spheres of our life. They turn on street lighting, control the shutdown of high-voltage power lines, lines of transport systems (tram, trolleybus, railway), are widely used in construction and industry to start powerful power plants, engines, machines and other equipment.
Moreover, such switching devices are also used in residential buildings for various purposes, such as switching on electric heaters or water heaters, for controlling ventilation systems, water or sewage pumps. Progress does not stand still, and at the moment, smart home systems controlled by contactors or groups of such devices are already gradually entering the lives of ordinary people.
These devices play a huge role in electrical safety and, as a result, in preventing fires from igniting electrical equipment or power lines.
These devices have a number of advantages over various modular devices:
- Can connect to any network;
- They have compact dimensions;
- Absolutely silent in operation;
- Can be used at high powers and high currents;
- Easy to operate and easy to install;
- They can work in any conditions.
Device and principle of operation
The contactor is a two-position electromagnetic device, which is controlled by an auxiliary circuit of electric current passing through the contactor coils. During the passage of electric current, the armature is attracted to the core, and the group of contacts closes. In the normal state, the contacts in such a device are always open - this is an important rule for electrical safety and ease of use.
In simple terms, a contactor is a switch when voltage is applied to which its contacts close and the load turns on, and if there is no voltage on the contactor, it opens the electrical circuit.
Structurally, this electromagnetic switch consists of a system of auxiliary contacts, arcing, contact and electromagnetic systems.
For those who are familiar with electrical diagrams and the principles of operation of the switches, these circuits will be clear. To the coil A1 - A2 an auxiliary voltage is applied, while in order to create a mechanical force and close the contacts, the solenoid is retracted and turns on those contacts that are necessary. Depending on the type of contactor and its design, it can include both one group of contacts, and several at the same time or in a certain sequence. In order to safely and quickly open the contactor, there is a spring in its design, through which the contacts, in the absence of voltage, instantly open.
Despite the fact that in appearance this device seems very complicated, and in many cases (when controlling power lines up to 600V and currents up to 1600A) large in size, everything is quite simple in its design:
- a group of contacts made of high-quality copper;
- housing made of dielectric materials;
- a contact strip connected directly to the electromagnet;
- electromagnetic coil;
- arcing elements, which are necessary when controlling high currents.
The contactor is controlled by an auxiliary circuit, the voltage of which must be lower than the operating current voltage and can correspond to 24, 42, 110, 220 or 380V.
Main types and types of contactors
To fulfill various working conditions, tasks and control various types of electrical systems and equipment, there are contactors with a variety of functionality.
By type of electric current switching devices are:
- direct current – designed for network switching direct current;
- alternating current - working and performing their task in alternating current networks.
By type of construction these mechanisms differ in the number of poles. The most widely used single pole and double pole devices, less tripolar.
Three-pole devices are used in three-phase AC electrical networks to control powerful electric motors and other devices. In industry, multi-pole contactors are produced and used, but such mechanisms are used extremely rarely and perform specific tasks.
By the presence of additional systems:
- without arc extinguishing system;
- having an arc extinguishing system.
The presence of an arcing system, which was mentioned above, is not a mandatory construct for 220 V networks, but it is necessarily used in devices and in high voltage networks (380V, 600V). Such a system extinguishes the electric arc, which invariably occurs at high voltage, using a transverse electromagnetic field in special chambers.
By type of contactor control:
- manual (mechanical) – the operator himself turns on or off the device;
- using a weak line – switching takes place remotely;
Drive type switching devices are electromagnetic and pneumatic. The most common and effective are mechanisms that work with the help of electromagnetic induction. Pneumatic are mainly used in railway transport (e.g. in train locomotives) where there are compressed air systems.
By type of installation apply frameless and corps contactors. The former are mounted in electrical panels or inside electrical installations and are not protected from moisture and dust, while the latter can be mounted anywhere and very often have good moisture and dust protection.
Contactor characteristics
To choose the right device for your needs, you need to know what characteristics this type of device has and how they differ. As a rule, electromagnetic contactors have the following important characteristics:
- Limit and rated voltage;
- The ratio of work with various circuit breakers (short circuit protection);
- Parameters and types of regulators of accelerations of automatic switches;
- Characteristics and type of resistance;
- Type and nature of relays and releases and other elements in its composition.
What is the difference between a contactor and a magnetic starter
Contactors are often confused with magnetic starters and this is justified, since in fact they are one and the same. These types of devices are structurally made almost identically. The difference between these devices is in the purpose: if the contactor is a monoblock device, it is a switch and mainly serves to switch circuits, then the electromagnetic relay (actuator) also performs a protective function, for example, by urgently opening the circuit in case of overheating, and incorporates several contactors, protective devices and control elements.
There is such a type of switching device as an intermediate relay - this is a small power device that serves for switching in low-current circuits and can withstand many more opening cycles than a contactor.
Contactor connection diagrams
Contactors are produced by many manufacturers of electrical products and have different types and designs. When connecting such a device, it is important to strictly follow the manufacturer's recommendations and regulatory electrical documentation. In the instructions and on the body of the device itself, the connection diagram of this mechanism and its main characteristics will be mandatory. Understand this wiring diagram a professional electrician will not have any difficulty, but a non-specialist will have to try a little.
Note! For performance scheme a normally open contactor contact is used to realize self-retaining positioned parallel start button.
Regardless of how the contactor is connected in the system, two types of network are necessarily used: power and signal. The signal line starts the contactor itself, and it in turn closes the power line.
When connecting to powerful asynchronous motors, it is important to connect in series with the contactor thermal relay, to protect the engine from overheating and automatic to protect against short circuit.
It was not at all difficult to understand the purpose, design and principles of operation of this complex device. It is important to remember that a properly connected device is the key to a long and safe contactor service. When connecting, it is necessary to work only with the power off, remember the electrical safety measures and general labor protection rules, and strictly follow them. And if something in the operation or connection of this device is still unclear to you, then the best option would be to contact professional electricians to connect this device.
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