People are increasingly using high-voltage devices in everyday life, for example, generators as a power source, transformers, etc. Therefore, it is often necessary to control the level of current flow in the circuit. It is in this control that the purpose of the relay lies.
Content
- Relay classification and purpose
- Relay design
- Application in production and in everyday life
- Advantages and Disadvantages of Switches
A relay is an electrical switch designed to connect and disconnect a circuit under certain conditions. This device belongs to the category of devices that regulate the operation of controlled objects when a signal is received. The relay regulates an electrical circuit that is controlled. And the circuit through which the signal passes is the control circuit.
Relay classification and purpose
There is a basic classification of types of relays, according to which, it is customary to subdivide them into the following categories and types.
By purpose, the following types of relays are distinguished:
- Control relay. They are used in low-voltage devices as component elements, as well as as independent control elements;
- Protection relay. Designed to protect devices with thermal contacts, for example, electric motors, fans;
- Signaling. They are used in cars, houses, organizations, to protect the territory of the private sector, in production, etc.
By the principle of action, they are divided into:
- Electromagnetic. They are more complex devices and are used in automation and control systems;
- Magnetoelectric. They function only if direct current is present;
- Induction relay devices work on the principle of interaction of magnetic fluxes with induced currents;
- Thermal fuses are used as fuses in electric motors to protect against overheating;
- Solid state or solid state relays are effectively used in precision temperature control systems.
The controlled value can be:
- Current, that is, the principle of operation of such devices is based on the flow of current to a certain structural element, most often an armature or a coil acts as such;
- Power relay. The device operates under the influence of a certain force that is generated in a controlled environment;
- Devices operating under the influence of any frequency on the winding;
- Functioning under conditions of a certain voltage.
According to the method of influencing the control element, they are distinguished:
- contact, as the name implies, such relays use contacts that create a force field in contact with each other;
- contactless relays, in which the circuit is closed and opened by changing one of the circuit parameters.
By design, they are divided into:
- electrical - used to turn on and off the circuit in devices that require a large load;
- reed switches - in their design they have a reed switch with a coil, that is, a small vacuum cartridge that is filled with gas;
- electrothermal, the principle of operation of such relays is based on the linear expansion of metals.
There are many other types that are used in highly specialized fields. Time relays, voltage relays, intermediate relays and others can be cited as an example.
Relay design
Relay devices of a simple circuit consist of magnets, an armature and contacts. Closing the circuit in such a device occurs by supplying current to the magnet, which then closes the armature with the contact. That is, the closure of the circuit is the result of the closure of the armature. Opening the circuit occurs in the reverse order. When the supply of current to the magnet decreases, the armature returns to its original state, that is, it opens, and then opens the circuit.
In addition to the components listed above, resistors may be included in the design of relay switches. They provide more accurate and stable operation of devices, and also act as capacitors to prevent sparks in the wire and sudden voltage surges.
As for the electromagnetic type relays, they are more complex devices both in principle of operation and in design. They consist of the following elements:
- contacts;
- anchors;
- flat spring;
- windings;
- core;
- yoke;
- frame;
- grounds.
The device turns on when an electric current is applied to the winding. When the amount of current required to create an electromagnetic wave is reached, the spring begins to move to the surface of the yoke, while the spring bends slightly under the influence of the magnetic wave. The action of the armature drives the contact, which affects the external contact. And it comes into contact with the conductor and the circuit is closed.
The stable operation of the relay directly depends on the amount of electric current supplied to the winding. If it is not enough, then the magnetic wave cannot be formed, and without it the armature cannot work. Therefore, even with a slight reduction in the current supply, the device stops working and turns off.
Some of these devices are equipped with multiple pairs of contacts, allowing multiple electrical circuits to be made and broken at the same time.
Application in production and in everyday life
Electromagnetic switching devices are the most common. They are often used in the field of power generation. They provide protection for high voltage lines and maintain a fail-safe operation of all connected devices.
The control elements of the relay design allow working with high voltages up to several hundred thousand volts.
The popularity of electromagnetic relays is explained by the following:
- elements that are part of the design have a long service life;
- have an instant response to deviations of the parameters of the connected devices from the norm;
- can function in conditions of high voltage magnetic fields and exclude the formation of extraneous electrical potentials.
Electromagnetic switches are used to back up power lines and to remove the damaged section from the network. Relay devices, namely the protection they provide today, are considered the most effective.
They are also used in production control conveyor systems. Because in such systems, parasitic potentials of high power are often formed, which can easily damage solid-state relays and other equipment connected to them. Semiconductor systems fail due to high static electricity, which can cause damage. Therefore, they were replaced with electromagnetic relays, and they are neutral to static electricity.
Devices of switching electromagnetic type are effectively used in devices with remote control and even computers as elements that perform elementary logical operations. It was thanks to the use of such switches that computers surpassed the reliability of computers that appeared later.
Examples of using relays can be cited from life. All people use household appliances, refrigerators, washing machines, TV sets and other appliances in their activities. Their principle of operation is based on the operation of electromagnetic relays.
Advantages and Disadvantages of Switches
The widespread use of electromagnetic relays in various fields of activity is due to the presence of a number of advantages over semiconductor and other types. Among the advantages are:
- the ability to close and open circuits with a total power not exceeding 4 kilowatts, with a volume of not more than 10 cubic centimeters;
- resistance to the conditions of a sharp change in the voltage level in the networks, which may arise due to a lightning discharge or when working with high-voltage equipment;
- a design feature that provides electrical insulation,
- the ability to generate a small amount of heat at low voltage;
- are much cheaper than solid state relays.
Among the disadvantages are:
- low speed of work;
- the presence of restrictions regarding the resource, both mechanical and electrical;
- the formation of interference in radio waves during switching processes;
- presence of serious problems during the closing and opening of high-voltage and inductive DC circuits.
Electromagnetic relays are used in the control of production lines, conveyors, in areas with increased parasitic potentials, where semiconductor elements cannot be used.
