Application of steering circuits in the electrical industry

Application of steering circuits in the electrical industry

Application of steering circuits in the industry

Application of steering circuits in the electrical industry Various devices are used in electrical circuits, the most important of which is the contactor or magnetic switch. Application of steering circuits in the electrical industry In electrical circuits, various devices are used, the most important of which is the contactor or magnetic switch. The use of this contactor in control circuits creates a variety of different designs. Safe and uninterrupted operation of electrical installations and power generation centers and supply of electrical energy required for electrical equipment of industrial plants and economic centers depends to a large extent on the characteristics and operation of switches and circuit control devices. Creates different designs. The safe and uninterrupted operation of electrical installations and power plants and the supply of electrical energy required for the electrical equipment of industrial plants and economic centers depend to a large extent on the characteristics and operation of switches and circuit control devices.

Estimated study time
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Application of steering circuits in the electrical industry

Safe and uninterrupted operation of electrical installations and power generation centers and supply of electrical energy required for electrical equipment of industrial plants and economic centers largely depends on the characteristics and features and operation of switches and circuit control devices.

Application of steering circuits in the electrical industry

In electrical circuits, various devices are used, the most important of which is the contactor or magnetic switch. The use of this contactor in control circuits creates a variety of different designs.

In order to design control circuits and work with them, it is necessary to fully know the components and make them familiar with the principles of construction and the use of these devices.

Application of steering circuits in the electrical industry

The devices used in the command circuits are as follows:

  • The contactor (magnetic switch)
  • Stop starter knob
  • Electric relay
  • Magnetic relay
  • Signal lamps
  • Fuses
  • Limit switch
  • Function switches
  • Floating switches
  • Electric valves (sensors)
  • Timmers
  • The timer types

Application of steering circuits in the electrical industry

In the case of a contactor, it can be said that it is a magnetic switch that, when the desired voltage is applied to it, closes a series of open contacts (or switches) and opens a series of closed contacts; Using this property of different circuits, many circuits can be designed.

Contactor building:

Application of steering circuits in the electrical industry

When the coil is connected to the power supply, it uses the magnetic property to neutralize the spring tensile force and connect the upper core to the lower core, causing a number of insulated contacts to be connected to the input and output terminals of the switch or to open the contacts. Contactor package Closed contactor package.

If the contactor coil supply circuit is interrupted, the moving core returns to its original position due to the spring force inside the switch.

Advantages of using contactors Contactors have the following advantages over industrial manual switches:

  • The consumer can be controlled remotely.
  • The consumer can be controlled from several places.
  • It is possible to design an automatic control circuit for different stages of consumer work.
  • The speed of disconnecting and reconnecting the key is high and its depreciation is low.
  • They are safer in terms of protection and have more secure and complete protection.
  • They have a longer effective life.
  • When the power goes out, the consumer circuit is also cut off and restarted; As a result, it avoids the dangers of sudden device connection.

Application of steering circuits in the electrical industry

The contactor is made for AC and DC currents. The difference between the two contactors is that AC contactors use a short circuit to prevent vibration from the power frequency. The tensile force of an alternating current electric magnet is proportional to the square of the current passing through it and therefore proportional to the square of the magnetic induction. Because the value of the instantaneous current with respect to the relation i = ImaxSIN wt decreases, the magnetic tensile force is also equal to

F=Fmax sin^2( wt)

Application of steering circuits in the electrical industry

The number of times this force is maximized and zero will be doubled by the frequency of the network. As a result, at the moment when the amount of tensile force is more than the resistive force of the contactor springs, the contactor core is absorbed and at the moment when the amount of tensile force is less than the amount of spring force, the moving core of the core is released and returns to its original position.

In this way, vibration and sound will be created in the moving core. These oscillations can be placed by a closed-loop on the surface of the poles and cover about half to 2.3 of the surface of each pole and eliminate its vibration.

The operation of this loop is that, like the secondary winding of a short-circuit transformer, an inductive current passes through it, causing a sub-magnetic eruption in the core circuit.

This sub-eruption has a phase difference with the atomic eruption, and when the tensile force from the atomic eruption is zero, the tensile force from the atomic eruption will be maximum, and if the force from the maximal eruption is zero, and because The sum of these two forces acts on the moving core, the tensile force will be greater than the spring resistance force at any moment.

Application of steering circuits in the electrical industry

The power supply voltage of the coil varies and is made from 24 to 380 volts. In most industrialized countries, the contactor coil is fed below the shielded voltage (65 volts) for extra protection; Or they use a separate transformer to power the control circuit.

Recognition of contactor specifications

Contactor type


Depending on the type of consumer and operating conditions, contactors have a certain power and current flow for different voltages; Therefore, sufficient attention should be paid to the table and specifications of the contactor and the selection of the contactor. According to the required specifications.

To connect the consumer to the network, a switch or contactor with appropriate specifications must be used, whose contacts can withstand the starting current and constant current, and also in case of short circuit, the current of many moments that pass through the circuit; Or the spark generated when connecting the circuit does not damage the switch.

For this purpose, and in order to be able to select the appropriate contactor to connect the consumer to the network after designing the circuit, we must be familiar with the nominal values ​​of the contactor.

Tables can be used to select contactors at different powers.

Stop-start knob and steering wheel selector

Application of steering circuits in the electrical industry

Knobs are steering devices that are stimulated by hand and are designed in different types and for different applications.

The knobs that disconnect the two contacts after excitation are called the stop and the knobs that connect the disconnect after the excitation of the two contacts are called the start knob.

Knobs that perform both operations at the same time are known as start-stop or double knobs, meaning that two open contacts close and two closed contacts open with the push of a key.

Overload relay (thermal or bimetal):

Electrical appliances must be protected against potential hazards and errors. One of the ways to protect electric motors is to use thermal relays and magnetic relays. The thermal relay protects the motor against overload.

Overload relay is used to control the current of electric motors and is a type of protection relay.

This relay is composed of two different metals that have different coefficients of longitudinal expansion. Around the two metals glued together, a series of wires carrying a complex electric current was adjusted so that the device could not be cut off for no reason and quickly due to low current increase.

Using these curves, it can also be adjusted so that the time Cut off too much and does not allow excess current to pass through the device.

The operating conditions of these relays vary from (-20) to (+60) degrees Celsius.

Magnetic relay

Magnetic relays are also used to control the current. The working principles of this relay are based on the magnetic phenomenon.

This relay is used to cut short circuit currents. We know that a short circuit must be disconnected quickly, so in such a situation it is not possible to use an overload (thermal) relay because the bimetal heating of the relay requires a relatively long time.

The relay consists of a magnetic core wrapped around several turns of wire. The passage of the short-circuit current causes the magnetization and absorption of the lever to be cut off. These relays are rarely used as conduits and are used in automatic switches with thermal relays.

Signal lamps:

Signal lamps or signal lamps are used in all industrial devices and distribution panels and control panels. The type of use of this lamp is different. This lamp is used as a news lamp and can indicate whether the device is on, off or faulty, and so on.

The lights used in the steering circuit are low power lamp (1.2 to 5 watts) that works with different voltages from 24 to 220 volts. These lights are usually made in three standard colors of red, green, and orange.

For example, in a factory where a large number of motors are running at the same time and the distances to the control panel are relatively large, they use a red light that is turned on by the game contact from the main motor contactor. Using the open contacts of the contactor, the green light that indicates the off state of the circuit can be turned on. In maps to display the signal light from the letter h. Is used.


Fast-acting fuses have a shorter cut-off time than slow-acting fuses and are therefore used in lighting applications. Slow-acting fuses have a longer cut-off time and are therefore used to start electric motors. The tolerance of the motor starting current is about 3 to 7 times the rated current that is written on all fuses with their rated current. This current is less than the maximum current of the fusing bearing.

Fuses are made in different types of cartridges, automatic (alpha), miniature, box, card (blade), glass or cartridge, and high-pressure fuses.

Usually, the fuses used in the power circuit protect the contactor circuit against short circuit; That is, it actually protects the interface wires; Therefore, in circuits where, for example, a 25 amp fuse is used, one or one and a half wires may be used in their control circuit. Therefore, it is necessary to protect the control circuit with a separate fuse.

Automatic fuses, or alpha fuses, are a type of automatic fuse through which an overcurrent can cause a circuit breaker; But again, you can push the knob inward to communicate. Some automatic fuses control both high current and high load operations in the circuit; However, after disconnection, the corresponding knob must be pressed again after a short time to connect the circuit.

In automatic fuses, there are two magnetic and thermal elements, the magnetic part of which breaks the short circuit or high current and the thermal part of which (bimetal) breaks the high load (gradual current increase).

The miniature switch is a type of automatic fuse that is similar in structure to the alpha fuse and consists of three parts: magnetic relay (high current fast relay), thermal relay or bimetal relay (delayed high current relay) and switch. This set is also called the engine key. These keys are made in two types L. and G. Type L. is used for lighting and is fast (LIGHT) and type G. is used to start motor vehicles and is slow. These switches are made in single-phase, two-phase and three-phase types.

Restrictive keys:

The limit switch (LIMIT SWITCH), sometimes called the microswitch, is the key used to disconnect and connect a linear or rotational motion or to change the direction of rotation of a moving object.

This key has a lever that cuts off contact when the moving handle hits it. The contact itself is a command factor for the machine it is intended to control. As the name implies, this key is used to restrict the movement of moving objects. For example, in an overhead crane that moves in several directions, when the slider reaches the end of each part of its path, it activates a key limiting the travel circuit and provides the return circuit.

Types of simple limit switches:

  • End pressure limit switch
  • Pulley limiter switch
  • General one-way pulley limiter from the left
  • One-way pulley limiter key from the right
  • Two-way pulley limiting switch
  • Two-way antenna limiter

Pressure function key (gas keys)

These switches are used to control the gas level inside the tanks and compressors, adjust the water pressure inside the pipes and turn these devices on and off automatically. To take. The command of this switch is the pressure of gas or liquid inside the tank.

The reason for disconnecting and connecting this gas switch is the principle of operation is that the effective gas pressure on each plate creates a force equal to F = P.A (P pressure and A. are the cross-sections of the plate). In relays, F. causes the plate to move. This displacement is transmitted through a lever and disconnects and reconnects the contact. The turning force is created by the spring under the plate. So by selecting different springs, you can apply more or less pressure on the plate and adjust the disconnect and connect the contact as desired.

Floating keys:

Float switches are used to control water levels or inputs in springs, pools, and reservoirs. The construction of this switch consists of a balanced weight, a floating part, and a micro switch.

When the floating part is adjusted, by changing the liquid level inside the floating tank, it moves to the microswitch inside the control key and causes the circuit to be disconnected and connected.

Electric springs (sensors)

This switch is a type of command switch that reacts without physical contact with the hand or any other device by the electric eye system from a distance of at least one millimeter and at most 8 meters and issues the command also by the relay used inside it. Opens or closes contacts and thus commands the desired devices. This key is widely used in industrial machines and production lines.

Timer relay and its types:

One of the command devices of automatic control circuits is timers or time relays that are responsible for controlling the circuit for a certain period of time.

The working principles of relays are the same as contactors, except that in relays:

  • All contacts are similar in appearance and participate in command circuits.
  • Contacts may be disconnected momentarily or with a time delay depending on work requirements. In this case, the name of the relay will be instantaneous relay or time delay relay.
  • Relays may also have instantaneous or time-delayed contacts. Of course, time delay means the time interval between the contact operation (whether opening or closing) from the moment the relay coil is connected to the voltage.

Motor or electromechanical time relay

This relay operates on a clock-driven by asynchronous motors and most motors with slotted poles. The principle of operation is that the engine speed is reduced by a gear system so that eventually, the last gear closes or closes the contact very slowly. The start time of the relay is from the moment the motor is started.

This relay can set times from about seconds to about hours, and even days and weeks.

The location of the disc is adjustable at the moment of starting, and after setting the time (by external output) and feeding the timer, the motor starts at a constant speed and the timer time starts with the rotation of the motor.

After rotation, it stops due to a collision with the disc protrusion and commands the built-in micro-switch, and the timer contacts operate and are automatically disconnected, causing the motor or any other device to fail.

Of course, there are new relays that close the game contact and open the closed contact during operation, and the motor can be turned on or off or the power can be transferred from the mains motor to another motor.

Electronic time relay

Electronic timers are used to set times from less than a second to several seconds. In the construction of these timers, circuits and electronic components are used.

In one of these timers, a small relay is excited by charging and discharging a coil capacitor. The principles of electronic relay construction are based on the RC circuit (capacitor and resistor) and in terms of time delay. Setting these types of timers depends on the resistance of the capacitor.

In the simplest type of electronic timer in the capacitor type timer, the relay is connected when the capacitor is charged and its double voltage is equal to the voltage of the relay connection. After connecting the relay, it is discharged by storing it in the capacitor on the resistor that is connected to both ends of the capacitor by the open contact of the relay. In this type, by changing the capacitance of the capacitor, the timer time can be set.

New Matic time relay

These relays use air storage and compression properties. In this way, the relay is released very easily when released. When the spool absorbs the excitation of the moving part, the lever will push the piece, which is in the shape of a forging tail.

The tail air comes out through a one-way valve. When the coil comes out of the stimulus, it expands the tail spring. The tail is filled with air through an adjustment valve.

The expansion rate of the tail varies with respect to the adjusting screw. When the tail returns to normal, the contacts operate; Therefore, by adjusting the adjusting screw, the operation of the contacts can be reduced.

This timer works like a motor timer; The difference is that the motor timer starts working after adjusting and connecting its coil to the voltage, but the neural timer starts working after disconnecting its coil from the voltage.

Bimetal or thermal time relay (thermal timer)

This type of timer works using bimetal property and is made in various types of melting relays, bimetal thermal relays, and reflective thermal relays. When the current passes through the bimetal, it heats up and after a while, due to the deformation of the shape, the circuit breaks or connects. The accuracy of this type of timer is not high and the ambient weather affects it.

In general, time relays can be divided into two categories:

A. ON-DELAY Relays: Relays are said to energize the relay and then operate the relay to open or close the contact; Like a motor time relay.

B. OFF-DELAY Relay: A relay that operates to open or close contact after a power failure; Like New Matte Relay.

Hydraulic time relay

In these relays, a hydraulic system is used to delay the circuit. It works in such a way that when an electric current is connected to the relay, some oil is transferred inside it.

To return the oil to its original location, it is necessary to consider this time as the timer time. These relays are used in various circuits. If any of your friends have more explanation about this relay, please provide it to make the content more complete.


A thermostat is a type of thermal relay that is sensitive to the heat of the environment and operates. This device is widely used in various industrial devices and is responsible for the thermal balance of the device. If the temperature exceeds the set limit, the operated switch closes an open contact or opens a closed contact. Thermostats are mostly used in heating and cooling appliances such as radiators, refrigerators, and chillers.

Remote function keys (centrifugal):

Round function switches are used in some single-phase electric motors to remove the auxiliary coil from the circuit and in others such as reverse current braking. Their structure consists of an axis and two weights that move around the axis by a collar and a spring, and as the speed of the motor or rotating device increases and decreases, the weights on both sides move closer or farther to the axis; In this way, the collar moves on the axis and causes the key to be disconnected and connected.

Source: Electrical Articles Reference



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