Sewerage

Description of electrical elements and apparatuses. Electrical apparatus

Section 2. Low voltage electrical apparatus

Topic 2.1 Electric hand-operated devices

1. Knife switches - purpose, device, features of work and design, application

2. Command devices - classification, purpose, device, features of work and design, application.

3. Resistors and rheostats - purpose, device, features of work and design, application

The choice of knife switches, package switches

Question 1. Knife switches

knife switch- the simplest manual control device, which is used to switch electrical circuits at voltages up to 660 V AC and 440 V DC and currents from 25 to 10,000 A.

Knife symbol on electrical diagrams: -single-pole

Three-pole

Knife switches are designed for switching circuits and are designed to create a visible break in electrical circuits. The mechanical resource of knife switches is up to 10,000 operations.

Knife switches are made one-, two- and three-pole. Their main elements are: fixed cut-in contacts, movable contacts hinged in other fixed contacts. Knife switches are mounted on insulating parts, plates, frames. The design of the knife switch can be made for connecting wires from the back or front.

Arc quenching direct current at low currents up to 75 A, it occurs due to its mechanical stretching by diverging knives. At high currents, extinguishing is carried out mainly due to the movement of the arc under the action of the electrodynamic forces of the current circuit (details of the knife switch, etc.).

When installing circuit breakers in distribution boxes or closed switchgear of small volume, it becomes very important to limit the size of the arc. It is necessary that the ionized gases remaining after the extinction of the arc do not cause overlap on the case or between current-carrying parts. In such cases, the circuit breakers are equipped with various kinds of arc chutes.

Fig. 2.1. Two-pole changeover knife switch

Structural designation of the knife switch:

Task 1. a). List the positions of the knife switch in Figure 2.2.

Question 2. Command devices

Pushbutton switches (buttons)– electrical hand-operated devices designed to give the operator a control action when controlling various electromagnetic devices (relays, starters, contactors, etc.), as well as for switching control circuits, signaling, electrical blocking of DC and AC circuits. They consist of a body or base, buttons, make and break contacts. Several buttons installed on a common panel or in a common housing is called a button post.

STOP button, START button

Example symbol of the push-button post KE

KE XXX XXXX:

KE- series designation;

XX- execution according to the type of control element and the presence of special devices: from 0.1 to 21;

X- number of contact elements: 1-1 or 2; 2 - 3 or 4;

XXX- climatic version according to GOST 15150-69: U, HL, T - for switches of the Kamenetz-Podolsk Electromechanical Plant; У, В - for circuit breakers of the plant of ballasts "Rheostat";

The device of push-button switches (Fig.2.3.)

Fig. 2.3. Device and symbol of push-button switches

Buttons have fixed contacts 1 , contact bridge with moving contacts 2 , spring 3 , to return the bridge.

A- button with make contacts ( "start");
b- button with break contacts ( "stop").

Task 2. a). Answer the question: what materials are the contacts of pushbutton switches made of?

Batch breakers and switches(Fig. 2.4) - manual control electrical devices, designed for switching control and signaling circuits in electric motor reverse start circuits, as well as 380 V AC and 220 V DC electrical circuits of low power under load.

Fig. 2.4. General view of the package switch

Symbol for any switch:

Basically, the switches are of the following design: switching packages (contacts) of identical design are assembled on one shaft, which are held in the assembled position by a locking mechanism. Turning the switch handle rotates the shaft, and with it the cams of the switching devices, which close or open the contacts.

The switching device has one or two contact systems, electrically isolated or connected by a jumper, depending on the electrical circuit, and consists of a body, fixed contacts, contact bridges, pushers, cams, springs.

Universal switches. (Fig. 25.) Switches can be divided into two groups: with rotary moving contacts of the MK and PMO series and cam UP5300, PKU.

Universal switches in the normal version are produced in the UP5300 series; waterproof - series UP5400; explosion-proof - UP5800 series. They are distinguished by the number of sections, as well as by the fixed positions and angle of rotation of the handle, its shape and other features.

Fig. 2.5. General view of universal switches

The switches can have 2, 4, 6, 8, 10, 12, 14, 16 sections. In switches with a number of sections from 2 to 8, the handle is fixed in each position or a handle with a self-return to the middle position is used.

The number of fixed positions and the angle of rotation of the handle are indicated by the corresponding letter in the middle of the nomenclature designation of the switch. The letters A, B and C indicate the design of the switch with self-return to the middle position without fixation. Moreover, the letter A indicates that the handle can be rotated 45 ° to the right (clockwise) and to the left (counterclockwise), B - only 45 ° to the right, C - 45 ° to the left. The letters G, D, E and G indicate that the design of the switch is with fixation in positions through 90 °. Moreover, the letter D indicates that the handle can be rotated to the right by one position, D - to the left by one position, E - by one position to the left and right, F - can be in the left or right position at an angle of 45 ° to the middle (in the middle position the handle is not fixed).

The letters I, K, L, M, N, C, F, X show that the switch is latched in positions through 45 °. The letter AND indicates that the handle can be rotated to the right by one position, K - to the left by one position, L - to the right or left by two positions, M - to the right or left by three positions, H - to the right by eight positions, C - to the right or left by one position, Ф - to the right by one position and to the left by two positions, X - to the right by three positions and to the left by two positions.

The handle can have an oval and revolver shape. Typically, switches, in which up to 6 sections, inclusive, with circular rotation (for eight positions), have an oval handle.

The designation of each switch contains the abbreviated name, the conditional number of this design, the number indicating the number of sections, the type of retainer and the switch diagram number in the catalog. For example, the designation UP5314-N20 stands for: U - universal, P - switch, 5 - unregulated command device, 3 - railless design, 14 - number of sections, H - type of latch, 20 - catalog number of the diagram.

The main part of the UP5300 switch is the working sections tightened with pins. A roller passes through the sections, at one end of which there is a plastic handle. To fix the switch on the panel, three protrusions with holes for the set screws are made in its front wall. Switching of electrical circuits is carried out by existing contacts.

Small Switches intended for installation on switchboard panels, can be used for remote control of switching devices, in signaling, measurement and automation circuits of alternating current with voltage up to 220 V and are rated for a rated current of 6 A.

Each switch has its own switching circuit and contact closure diagram.

Small-sized switches of the series are designed for installation on control panels. They are used for remote control of switching devices (relays, electromagnetic starters and contactors) and in signaling, measurement, automation circuits at AC and DC voltages up to 220 V. Switch contacts are designed for a current of 3 A.

Switches consist of 2, 4 and 6 contact packages. Packet cam universal switches PKU are used in electric motor control circuits in manual, semi-automatic and automatic modes. They are rated for 220 V DC and 380 V AC.

Switches of the PKU series are distinguished by the method of installation and fastening, the number of packages, fixed positions and the angle of rotation of the handle. The letters and numbers that are included in the designation of the switch, for example, PKU-3-12L2020, mean: P - switch, K - cam, U - universal, 3 - standard size, determined by a current of 10 A, 1 - version according to the type of protection (without a protective shell), 2 - version according to the method of installation and fastening (installation behind the shield panel with fastening by the front bracket with the front ring), L - fixing the position through 45 °, 2020 - catalog number of the scheme and diagram.

Task 2. b). What are the positions of the batch switch shown in Figure 2.6.

Fig.2.6. Packet switch

toggle switches designed for manual switching of low-voltage electrical circuits of low power that do not require frequent switching.

Rice. 2.7.Toggle switch

Task 2.c). What are the approximate overall dimensions of the toggle switch.

Controller- a switching device that starts and regulates the speed of the electric motor. Multi-circuit electric apparatus with manual or foot drive for direct switching of power circuits of electric motors. By design, they are divided into cam, drum, flat and magnetic.

Controllers come in three types : flat, drum, cam.

Flat controllers can be performed on a larger number of steps compared to drum and cam, but their switching capacity is less. Their design is carried out according to the principle of switching devices of rheostats

Drum controllers are used to control motors up to 75 kW. Their switching ability is small. They allow up to 120-240 switchings per hour.

Cam controllers allow up to 600 switchings per hour. Their contact device works similarly to the contact device of contactors, i.e. each switching element has an arc extinguishing system.

Task 2. d). Name the position of the controller Fig.2.8.

Fig 2.8. Power controller

Fig.2.9. Types of resistors

Resistors on a heat-capacitive frame are made in the form of a cylinder or tube made of heat-resistant material (porcelain, fireclay), on which a wire with a high resistivity is wound (constantan, fechral, cast iron, steel, nichrome, ferronichrome). To improve heat transfer and prevent the wire from slipping, the resistors are coated on top with a layer of enamel or glass.

Frame resistors consist of a steel plate, on the side ribs of which porcelain or steatite insulators are fixed, having recesses into which a wire or resistance tape is placed. Step leads are made in the form of clamps or soldered copper tips.

Cast iron and stamped steel resistors are made in a zigzag shape with ears for fastening.

Rheostat- this is an apparatus consisting of a set of resistors and a device with which you can adjust the resistance of the included resistors.

Conditional graphic representation of a rheostat. The dimensions of the rectangle are 8x4.

Depending on the purpose, the following types of rheostats are distinguished:

Starters for starting ED direct and alternating current;

Ballasts for start-up and speed control of EM;

Excitation rheostats - for regulating the excitation current in the excitation windings of electrical machines (Fig. 2.10.);

Fig.2.10. Structural diagram of the excitation rheostat

Load or ballast - for absorption of electricity.

Task 3. a) Try, looking at figure 2.11, to find out for yourself in which direction you need to move the engine in order to:
a) increase the resistance included in the circuit?
b) reduce resistance?

Fig.2.11

Task 4. Checking the degree of assimilation of the studied information on questions 1,2,3

topics 2.1 "Electric devices for manual control"

a) name the devices shown in figure 2.12.

Fig.2.12.

b) List the elements that all manual switching devices have:

Table 2.1. Choice of knife switches, batch switches

Task 5. Choose a main three-phase switch installed in the power board with an input voltage of 380 V. The power transmitted by the circuit is 20 kW. Estimated value of maximum short-circuit current equals 11.5 kA. Technical data of three-phase circuit breakers are presented in table 2.2. Decipher the brand of the accepted knife switch

Solution: 1. We determine the calculated value of the circuit breaker current

2.Fill in table 2.1 taking into account the data and table 2.2. (continue on your own)

Table 2.2. Technical data of circuit breakers

Breaker type	R-25	RPS-1 (with fuse, side shifted)	RTs-1(with central handle)	RB
Rated voltage, V
Rated current, A		100,250,400,630	100,250, 400	100,250,400
Electrodynamic resistance, kA	2,8	20,20,30,32	1,2; 3,0; 4,8	1,5; 2,5; 4,5
Thermal resistance, kA 2 s
execution	single-pole	tripolar	tripolar	tripolar
Mechanical durability		At least 2500 VO cycles	At least 2500 VO cycles	-

Task 6. Theme "Manual control devices"

Choose the correct answer:

Homework assignment. Finish completing assignments.

Question 3. Contactors

Fig. 2.2.1. Section and diagram of the friction clutch

The principle of operation of the friction clutch. Voltage is applied through slip rings to the excitation winding mounted on the driven shaft. This winding creates a magnetic flux F, which closes through the armature of the clutch. The resulting electromagnetic force moves the armature to the left and through the friction surface, the driving and driven parts of the shaft engage. When the voltage is removed and the magnetic flux disappears, the return spring moves the armature to the right and the clutch disengages. Friction surfaces (friction discs) are made of wear-resistant materials with a high coefficient of friction. Conventional materials can be used: steel on steel, steel on cast iron, steel on bronze, etc. The most advanced are metal-ceramic materials (copper 68%, tin 8%, lead 7%, graphite 6%, silicon 4%, iron 7%).

The excitation winding can be powered by direct and alternating current. In the case of AC power, there are differences in the design of the coupling in terms of the manufacture of the magnetic circuit. The magnetic circuit is made of laminated electrical steel.

Ferro-powder couplings are two concentric steel parts with flat surfaces facing each other, between which there is a small air gap. One part is rigidly connected to the drive shaft, the other to the driven shaft of the drive. If the space between the flat surfaces is filled with a very fine ferromagnetic powder, then in the presence of a magnetic field in the air gap, the powder particles form mechanical chains-ligaments, which will create the adhesion force of one part to another. As a result, rotation will be transmitted from one part to another. When the magnetic field is removed, the ligaments will disintegrate, the mechanical connection will be broken, and the system will stop rotating. The magnetic field is created by a winding with a core rigidly fixed in space. The magnetic flux is coupled by the magnetic materials of the coupling (steel part, ring, ferromagnetic powder, rotor)

For ferro-powder couplings, carbonyl, silicon, vortex iron is used. The powder is obtained by decomposition of iron pentacarbonyl (ferum (CO) 5 = ferum + 5 CO). Ferromagnetic powder is used in an equal mixture with graphite separator, zinc oxide, talc, etc. It is designed to prevent the powder from sticking together, the formation of lumps.

Special seals are created in the couplings so that the powder does not go beyond the air gaps, and magnetic traps that attract powder particles that have left the coupling.

In a drum-type ferro-powder clutch (Fig. 2.2.2), the drive shaft 1 is connected through non-magnetic flanges 2 to a ferromagnetic cylinder (drum) 3. An electromagnet 4 is located inside the cylinder, connected to the driven shaft 6. The winding 5 of the electromagnet is powered through contact rings (not shown in the figure). The inner cavity 7 is filled with ferromagnetic powder (pure or carbonyl iron) with grains ranging in size from 4-6 to 20-50 microns, mixed with dry (talc, graphite) or liquid (transformer, silicone oils) filler. When the winding is de-energized and the driving part (drum) rotates, the electromagnet and the driven shaft remain stationary, since the ferromagnetic grains of the filler move freely relative to each other. There is some friction between the drum and the electromagnet, but it is relatively small.

Rice. 2.2.2. Drum type electromagnetic ferro-powder clutch

When voltage is applied to the electromagnet, the grains of the ferromagnetic powder lose their freedom of movement under the influence of the magnetic field of the winding. The viscosity of the medium in the drum increases dramatically. The friction force between the drum and the electromagnet increases. A torque appears on the driven shaft.
At a certain value of the excitation current, the ferromagnetic powder and the filler completely solidify. The drum and the electromagnet become rigidly connected. It is possible to consider the transmitted moment as the moment from the frictional force acting between the powder and the inner cylindrical surface of the drum.

Due to the fact that the gap between the drum and the electromagnet is filled with a ferromagnetic mixture, its magnetic conductivity is very high, which makes it possible to reduce the required MMF of the winding and increase the clutch control coefficient, which is equal to the ratio of the transmitted power to the control power (magnet power).

It is expedient to use ferro-powder couplings where high speed, high switching frequency and smooth speed control of the driven shaft are required. The disadvantage of ferro-powder clutches is the lower transmitted power with the same overall dimensions with a friction clutch.

The advantage of powder clutches is their speed, which is 10 - 15 times higher than that of frictional electromagnetic clutches.

In hysteresis couplings(Figure 2.2.3) The mechanical adhesion forces between the driving and driven parts are created by using the phenomenon of residual magnetization of hard magnetic materials. The magnetic system consists of two parts: one is connected to the drive shaft, the other to the driven one. The magnetizing winding is located on the drive shaft. The magnetic flux created by the winding will cross the magnetic systems of the shafts, and its path will lie along the sections with the lowest magnetic resistance, as a result of this, the hysteresis magnetic disks of the driven shaft will be attracted to the teeth of the drive shaft core (the principle of operation resembles the principle of the IM, only there is no winding on the rotor)

Fig.2.2.3. General view of the hysteresis clutch

Electromagnetic braking devices- electromagnetic remote control devices designed to fix the position of the mechanism when the electric motor is turned off. They are divided into shoe, disk and tape.

Task 2.a) Make a logical chain of the principle of operation of the friction clutch.

Task 2.b) Try to name the elements of the coupling shown in Figure 2.2.4.

Fig.2.2.4.

Task 2.c) Complete the sentences:

The clutch is..

The electromagnetic clutch is...

Ferromagnetic powder is...

Advantages of Powder Couplings…

The principle of operation of the hysteresis clutch is based on ...

Glossary

Law of electromagnetic induction: Crossing a conductor by a magnetic field induces an emf in the conductor.

Law of electromagnetic force: the interaction of current in a conductor with a magnetic field causes the creation of an electromagnetic force acting on this conductor.

Hysteresis- delay in the change in a physical quantity characterizing the state of magnetization of a substance, in particular steel

Relay characteristics

The main characteristics of the relay are determined by the dependencies between the parameters of the output and input values.

There are the following main characteristics of the relay.

1. Relay actuation value Хср– value of the parameter of the input value, at which the relay is switched on. The amount of operation to which the relay is adjusted, called setpoint.

2. Actuation power Rav relay- the minimum power that must be supplied to the perceiving organ to transfer it from a state of rest to a working state.

3. Controllable power Rupr is the power controlled by the switching elements of the relay during the switching process. According to the control power, there are relays of low power circuits (up to 25 W), relays of medium power circuits (up to 100 W) and relays of high power circuits (over 100 W), which belong to power relays and are called contactors.

4. Relay response time tav– the time interval from the input of the Xav signal to the relay input until the start of the impact on the controlled circuit. According to the operating time, normal, high-speed, delayed relays and time relays are distinguished. Usually for normal relays tav = 50…150 ms, for high-speed relays tav 1 s.

Task 3: A) Make a classification of the relay

Fig.2.2.5

The receiving part consists of an electromagnet 1, which is a coil put on a steel core, an armature 2 and a spring 3.

The executive part consists of fixed contacts 4, a movable contact plate 5, through which the receiving part of the relay acts on the executive part, and contacts 6.

Fig.2.2.6

Fig.2.2.7.

Question 3. Contactors

Contactors- these are remote action devices designed for frequent switching on and off of power electrical circuits during normal operation. The contactor is perhaps the oldest device that was used to control electric motors. Electromagnetic contactors are the most widespread all over the world. They are the main switching devices of circuits with currents over 50 A.

Contactor classification

All contactors are classified:

by the nature of the current of the main circuit and the control circuit (including coils) - direct, alternating, direct and alternating current;

by the number of main poles - from 1 to 5;

by rated current of the main circuit - from 1.5 to 4800 A;

according to the rated voltage of the main circuit: from 27 to 2000 V DC; 110 to 1600 V AC 50, 60, 500, 1000, 2400, 8000, 10,000 Hz;

according to the rated voltage of the closing coil: from 12 to 440 V DC, from 12 to 660 V AC with a frequency of 50 Hz, from 24 to 660 V AC with a frequency of 60 Hz;

by the presence of auxiliary contacts - with contacts, without contacts.

Fig.2.2.8. General view of the contactor

The contactors consist of a system of main contacts, an arcing system, an electromagnetic system and auxiliary contacts.

Fig.2.2.9. Scheme of electromagnetic contactor

2.2.10. The device of the electromagnetic contactor: a) general view, b) arcing system and contact system, c) electromagnetic system

A core 2 of a magnetic circuit with a coil 4 is fixed on a metal rail 5 with a bracket 17. The core 2 has a short-circuited coil 3 and is damped by a spring 18. Three blocks 1 of the poles are attached to the rail through an insulating block 15, having fixed contact parts 9 and an arc quenching coil 16. The movable contactor system is installed on an insulated shaft 7 and rotates in the bearing x 6. The movable contact part 11 is fixed in the contact holder 13 and spring-loaded with a spring 12. The connection with the contact bolt is provided by a flexible connection 14. Each block has an arc chute 10. Auxiliary contacts 8 are also installed on the shaft.

Main contacts carry out the closing and opening of the power circuit. They must be designed for long-term conduction of the rated current and for the production of a large number of switching on and off at their high frequency. The position of the contacts is considered normal when the retracting coil of the contactor is not energized and all available mechanical latches are released.

The main contacts can be made of lever and bridge type. Lever contacts assume a rotary movable system, bridge contacts - a straight-way one. Figure 2.2.11 shows sequentially the kinematics of contactor contact movement during closing.

Fig.2.2.11.

As a rule, for lever contacts, the axes of rotation of the contact do not coincide. In addition, the contacts touch before the movable system reaches the end position. As a result, when closing and opening, the moving contact rolls and slips over the fixed one. Therefore, the starting point of contact during closing and the end point of contact and, accordingly, the point where an arc occurs when opening, turns out to be displaced with respect to the point of final contact of the contacts. Due to this, the surfaces that provide long-term current conduction and which determine the contact resistance are distant from the point of origin of the arc. Well, the slippage of contacts with sufficient contact pressure leads to the erasure of the oxide film and various accumulated dirt from the contact surface, i.e., self-cleaning of the contacts occurs. Since the contacts in switching devices are perhaps the weakest parts of the device, we see that in this case, the very design of the power contacts of the contactors allows for a long time to maintain stable transient contact resistance, which in turn greatly affects the reliability and failure-free operation of the contactor as a whole. But nothing is perfect, so this lever contact has its drawbacks. Slippage with the roughness that contact surfaces usually have (especially working ones) causes additional contact bounce during closing, and hence increased wear. Well, a complete rejection of slippage and with insufficient pressure will lead to rapid overheating of the contacts due to their oxidation. Therefore, here you have to choose the lesser of the spirit of evil.

Task 4.a) Name three advantages of the lever contacts shown in fig. 2.2.11

Lever contacts require a flexible connection for connection to the conductor, but in some cases a flexible connection is a weak point of the contact system. It is difficult to carry out high currents and its mechanical wear resistance is lower than other parts.

Next, we will deal with the purpose and possible designs. arc extinguishing system contactors. The arc extinguishing system provides extinguishing of the electric arc that occurs when the main contacts open. The methods of arc extinguishing and the design of arc extinguishing systems are determined by the type of current of the main circuit and the operating mode of the contactor. The arc extinguishing systems of DC contactors differ from the arc extinguishing systems of AC contactors due to the fact that the principles of arc extinguishing at direct and alternating current are different.

Arc quenching chambers of DC contactors are built on the principle of extinguishing an electric arc by a transverse magnetic field in chambers with longitudinal slots. The magnetic field, in the vast majority of designs, is excited by an arcing coil connected in series with the contacts. In the 60s of the last century, structures with permanent magnets were created in the USSR, but they did not receive distribution. Chambers with narrow slots, which can be straight and zigzag, significantly increase the breaking capacity and limit the size of the arc and its flame outside the chamber, however, complete extinguishing of the electric arc in the volume of the chamber cannot be achieved using this chamber.

AC contactors are made with deionic grid arc chutes. When it occurs, the arc moves to the grid, breaks into a number of small arcs, and goes out at the moment the current passes through zero. It is, in principle, easier to extinguish the arc on alternating current than on direct current, therefore, direct current contactors have a more complex arc extinguishing system.

Contactor Electromagnetic System provides remote control of the contactor, i.e. switching on and off. The design of the system is determined by the type of current and control circuit of the contactor and its kinematic scheme.

The electromagnetic system consists of a core, armature, coil and fasteners. Figure 6 shows a diagram of switching on an electric motor using an electromagnetic contactor.

Auxiliary contacts. Switching is carried out in the control circuits of the contactor, as well as in the blocking and signaling circuits. They are designed for long-term conduction of a current of not more than 20 A, and a current cut-off of not more than 5 A. Contacts are made both making and breaking, in the vast majority of cases of a bridge type.

Task 4.b) Fill in table 1

Table 1

The principle of operation of the contactor. In the initial disconnected position, when the voltage is removed from the coil, the movable system is in the normal position under the action of the spring. The contactor is switched on by pressing the "Start" button. A magnetic flux is created in the coil, which attracts the armature to the core. Simultaneously with the main contacts, additional (auxiliary) contacts are closed, which block (shunt) the contacts of the Start button. Contact pressing is carried out by a spring. A gasket made of non-magnetic material is installed on the anchor, which reduces the force of attraction and when the voltage is removed from the coil, the anchor immediately leaves and does not stick.

Task 4.c) Build a logical chain of operations of the principle of operation of the contactor (seven points in total)

PME series starters

Contactors and magnetic starters - purpose, application categories, basic parameters. Series of direct and alternating current contactors, their designs and working conditions. Vacuum contactors. Magnetic starters, their operating conditions and design. Schemes of non-reversing and reversing starters. Selection of contactors and starters .

Automatic switches. Purpose, device and principle of operation of universal and installation machines, types of releases, the role of the free trip mechanism. Fast automata. Field extinguishers. Choice of machines.

Breakers and switches.

Fuses of low and high voltage The principle of operation and operating conditions of fuse-links. Fuse designs, time-current characteristic. High-speed fuses for protecting semiconductor devices. Choice of fuses. High voltage fuses ..

Controllers, command devices and rheostats - purpose, designs, schemes. Types of resistors and their choice.

Electromagnetic clutches - friction, ferro-powder, hysteresis and induction.

7.1. Guidelines

When studying each type of electrical apparatus, it is necessary to learn the following range of questions: the purpose and principle of operation of the apparatus, its varieties, device and electrical circuit; requirements for it; designation of the apparatus and its elements on the diagrams; purpose and arrangement of individual units of the device; materials used for the manufacture of critical parts; the main parameters of the device, technical data, operating modes, its advantages and disadvantages; equivalent circuits, characteristics (in a graphical representation); the main quantitative dependencies (formulas) characterizing the operation of the apparatus and its properties.

It is also necessary to pay attention to the differences between some devices from others, for example, automatic machines from contactors, controllers from power controllers, rheostats from resistors. It is necessary to understand the interaction of devices used in automatic control circuits, for example, contactors - with command devices, relays, resistors.

Attention should be paid to command devices based on the use of reed switches and optocouplers.

It is also required to become familiar with the device of at least one industrial design of each type of apparatus (DC contactor, magnetic starter, controller, etc.) according to drawings and drawings from the literature, catalogs for industrial electrical equipment.

No need to try to memorize the numerical values of the parameters of the device from the reference and catalog data, it is enough to have an idea about the order of these values.

The concept of an electrical apparatus is very voluminous, since it includes a huge number of industrial and household devices.

Electrical apparatus - an electrical device used to control non-electric and electrical objects, as well as to protect them in the event of abnormal operating modes.

Classification of electrical apparatus

The classification of electrical devices is carried out according to a number of criteria - scope, type of current, principle of operation, purpose (the main functions that this electrical device performs), design features, degree of protection from environmental influences and other features. The main one is classification by purpose.

Depending on the purpose, electrical devices are divided into the following groups:

Switchgears of switchgears- this group of electrical devices is used to connect and disconnect electrical circuits. This group includes load switches, knife switches, package switches, separators, short circuiters, fuses,. These devices are characterized by relatively rare switching on and off, however, there are cases when electrical devices of this group often perform switching processes (for example, a high-voltage switch that feeds an electric furnace).
Restrictive apparatuses- their main purpose is to limit short-circuit currents (reactors) and overvoltages (). In a normally designed mode, overvoltages and short circuits are rare, so these electrical devices are little exposed to maximum loads.
Ballasts- are designed for starting, regulating current, voltage, rotational speed of electrical machines or other consumers of electrical energy. This group includes controllers, controllers, contactors, rheostats and starting resistors. This group is characterized by frequent switching on and off.
Controlling devices- their main function is to control the specified non-electrical or electrical parameters. This group of electrical devices includes sensors and relays. If, with a smooth change in the measured (or input value), the value of the device changes abruptly, we are dealing with a relay. The output signal is usually . The sensor converts continuous changes in the input quantity into converted output values (for example, speed into an electrical signal). Sensors are capable of monitoring both electrical quantities and non-electrical quantities. As a rule, sensors produce a smooth signal conversion, although options are also possible with a stepwise conversion of output signals with a smooth change in input (relay-sensors).
Measuring apparatus– these products isolate the primary switching circuits (main current) from protective and measuring devices. They convert the measured value to a standard value that is convenient for measuring with conventional instruments. These include capacitor voltage dividers.
Regulating devices- they are designed to regulate a given parameter according to a certain, previously set law. Such regulators serve to maintain voltage, frequency, temperature, current and other values at a given level.

By regions, the division of electrical devices is more conditional. Electrical devices that serve electrical systems and power supply systems are combined into a group of high and low voltage switchgear devices.

A huge group of electrical devices is used for maintenance and industrial automation, which is conveniently combined into a group of control devices. However, the same devices can be found among control devices and switchgears, for example, package switches, relays, current and voltage transformers, knife switches and other devices.

By voltage, electrical devices are divided into two groups - low voltage electrical devices U P ≤ 1000 V and high voltage U P > 1000 V.

To protect workers from touching moving or live parts, as well as from foreign bodies entering the electrical apparatus, special protective sheaths are installed.

The protective properties of the shell are indicated by the letters IP and two numbers, according to GOST. The first digit indicates the degree of protection against the ingress of solid bodies and the contact of personnel with current-carrying parts, and the second digit indicates the degree of protection against the ingress of moisture and liquids.

At all stages of production, transmission, distribution and consumption of electrical energy in almost all sectors of the national economy, electrical devices play an important role.

Electrical devices (contactors, starters, electromagnets) are part of automatic, semi-automatic and manual control systems for electric power plants, electric drives, electric lighting devices, electrotechnological installations, etc. They are used to control start-up, speed control and electric braking of electric motors. With the help of electrical devices, the currents and voltages of generators are regulated. They carry out the functions of monitoring and protecting installations that consume electricity.

Thus, the use of electromechanical devices allows you to control the operation of electrical and non-electrical objects according to a given program, as well as protect these objects from unwanted modes - overloads, overvoltages, unacceptably high currents, etc.

Many electrical devices are designed to perform a single function in a control or protection system, but there are also multifunctional devices.
The operation of electromechanical devices in automation systems is based on a number of physical phenomena: the interaction of ferromagnetic bodies in a magnetic field, the force interaction of a conductor with a current and a magnetic field, the occurrence of EMF in coils and eddy currents in massive bodies made of electrically conductive material when an alternating magnetic field appears, the thermal effect of an electric current, etc.

The main parts of electrical apparatus are

electrical contacts (fixed and movable, main and auxiliary),
mechanical or electromagnetic drive of the contact group (bringing into contact and pressing the movable and fixed contacts),
control handles (buttons) and working windings.
The electrical apparatus is triggered, i.e., it closes and opens contacts or connects the movable and fixed parts of the electromagnetic mechanism, under the influence of:

1) maintenance personnel pressing the control handles (buttons); in this case, the apparatus is called manual or semi-automatic;
2) electrical quantities characterizing the operation of a controlled (managed) object, changing or on working windings; in this case the device is called automatic.

Depending on the functions that the device must provide, various requirements may be imposed on it, but the main requirements are reliability and accuracy of operation: reliability of the connection of contacts, low electrical resistance at the junction of the contacts, accuracy of the dependence of the moment of operation on the value of the control current or voltage.

By appointment, the following electrical devices are distinguished

1) switching (disconnectors, switches, switches);
2) protective, the main purpose of which is to protect electrical circuits from unacceptably high currents, overvoltages, drops, etc. (fuses, protection relays);
3) ballasts designed to control electric drives and other industrial consumers of electricity (contactors, starters, control relays);
4) controlling and regulating, designed to control and maintain the main process parameters (sensors and relays) within a given range;
5) electromagnets (power) used to hold or
moving objects in production or management
process.

This chapter deals with electrical devices (relays, starters, contactors and electromagnets) and some control and regulation circuits using electromechanical devices.

First of all, we will consider the features of the operation of electrical contacts and the operation of the electromagnetic mechanism - the drive of the contact group of electrical devices.

An electric apparatus is a device necessary for carrying out the operations of starting and switching off electric current circuits. This equipment is required to perform the functions of monitoring, protecting and managing various installations used for the transmission, conversion, distribution and consumption of electrical energy.

Electric devices have found their application in everyday life and in various industries. In some cases, such devices play the role of an auxiliary device. A certain category of electrical devices can perform a controlling and corrective function, which allows you to achieve uninterrupted operation of electrical equipment and prevent the occurrence of possible failures and breakdowns of electrical machines.

Classification of electrical apparatus

For the most part, the work of electrical hardware devices is not limited to the performance of any one specific function, but, on the contrary, is associated with the implementation of a whole set of actions. In this regard, there is a certain difficulty in dividing such devices into specific types and groups.

In order to classify electrical devices, it is important to highlight the main functional features of specific types of electrical equipment:

Switching devices. Such equipment is used to open and close electrical circuits. These devices include various switches, switches, disconnectors.
Protection devices. The devices protect the conductive elements of electrical circuits from voltage surges, increased network load and short circuits. The presented protection functions can be implemented in various types of fuses and relays.
Devices that regulate the start of electrical machines. Devices of this kind are designed to ensure smooth start and stop of industrial consumers of electric current. The devices regulate the speed of rotation of the motor armature. Such devices include starters, rheostats, contactors.
Restrictive devices. Such devices are called reactors and arresters, they have the function of limiting short-circuit currents and overvoltages.
Apparatus providing control various parameters of electrical circuits. The most common types of such devices are sensors and relays.
Apparatus for correcting and changing various parameters of electrical equipment. These devices include regulators and stabilizers.
Measuring devices. The function of this equipment is to ensure the isolation of the primary switching line from the circuits of measuring instruments and protection devices.
Devices for carrying out work of a mechanical nature. The main element of such devices is an electromagnet designed to perform specific functions: lifting electromagnet, electromagnetic brake.

Each electrical device is composed of three main elements:

perceiving;
transformative;
executive element.

If we proceed from the principle of operation of the perceiving element of the device, then electrical devices are divided into electromagnetic, induction, semiconductor, magnetic.

Depending on the principle of operation of the actuating element, electrical devices are divided into contact and non-contact devices.

There are a number of fundamental differences related to the peculiarities of the operation of the equipment in question, which allow the division of electrical devices into certain groups. Electrical devices can be designed for high or low voltage. According to the duration of operation, such devices can operate in short-term or long-term operation.

If we take into account the principle of control, then we can distinguish two main types of devices: with automatic and manual control.

Switching electrical apparatus

Switching electrical devices are widely used in various industries. It is difficult to imagine how the various tasks of operating and performing operations related to electrical equipment would be performed without this functional device.

An electrical switching device is used to disconnect and close an electrical circuit using a contact group. Simply put, such a device can be called a switch. The main types of the presented device include: knife switches, switches, contactors, relays. Despite the fact that these devices have almost the same principle of operation, they all have a number of differences from each other.

Consider each type of apparatus separately.

knife switch refers to the simplest switching device. The device is put into action manually by means of the handle. This type of device is designed for large values of current.

switches have different modifications. In industrial applications, oil circuit breakers are among the most common types of such devices. Such switches are designed for voltage up to 220 kV. Oil, in this case, serves to suppress / extinguish the arc of electric current passing through it. Air and electrogas circuit breakers deserve special attention. The extinguishing of the arc, that is, the cessation of the supply of electric current, occurs due to the supply of a jet of compressed air or an electronegative gas.

A radically new method of opening a conductive line is embodied in electromagnetic switches. The principle of operation of such a device is as follows: an electric arc burns under normal conditions at atmospheric pressure - the circuit is on. As soon as it is required to open the circuit, a strong magnetic field is applied towards the arc. Due to the influence of the magnetic field, the arc begins to stretch and eventually splits, thereby opening the conductive line.

Relay designed to open and close the electrical circuit. The main characteristic property of this switching device is a fundamentally new way of operation of the contact pair. An electromagnetic relay, as in a contactor, under the influence of an electric current, sets in motion the core of an electromagnet with contacts installed on it, which leads to a circuit closure. The method of influence on the contact pair of the relay can be not only electrical, but also thermal or acoustic.

Contactors are a type of electromagnetic relay. The main purpose is to turn on and off the conductive line of power electrical circuits. Contactors can be used in both AC and DC circuits. The principle of operation of the contactor is based on the electromagnetic effect. The core of the electromagnet of the contactor, under the influence of electric current, carries along the movable contact, which, due to such movement, is pressed against the fixed contact and the circuit is closed. As soon as the current supply stops, the core returns to its original position and the contacts open.

High voltage electrical apparatus

High voltage electrical apparatus includes various devices that perform the functions of controlling, protecting and monitoring electrical circuits and systems. The list of types of high voltage electrical apparatus is similar to the list of electrical devices discussed above. These types of devices include:

switching devices;
devices for grounding individual sections of the electric current circuit (ground electrodes);
devices for closing the circuit under load (short circuits);
equipment for switching off the electric circuit in case of a short circuit, limiting devices.

Electrical devices up to 1000 volts

Electrical devices up to 1000 volts are commonly called low voltage electric current devices.

Equipment is divided into three categories. The first is devices for controlling and protecting electrical circuits (contactors, relays, starters, fuses, knife switches). The next view is devices with the function of automated adjustment of the parameters of the electric line (stabilizers, regulators). And, finally, automation devices (sensors, relays, amplifiers).

Electrical devices up to 1000 volts perform certain functions of controlling, amplifying and converting an electrical signal.

Electric network protection devices

To ensure an appropriate level of safety of the current-carrying line and to eliminate negative consequences due to a short circuit or network overload, a variety of electrical network protection devices are used. The most common device that provides this protection is a safety device in the form of fuses or circuit breakers. Components of a fuse: body, fusible substance and contact part.

The principle of operation of such a device is based on the release of a large amount of heat by a conductor with a fusible substance, if a large current value passes through it. This effect leads to a break in the conductive element of the fuse and the circuit.

The next type of protective device is the circuit breaker. Such a device consists of a cover, a body, an arc chute and a free trip mechanism. The last element of the device can be electromagnetic or thermal. Circuit breakers, which are equipped with an electromagnetic tripping mechanism, are designed to protect against short circuits. If the device has a thermal release mechanism, then the purpose of such a device is protection against network overloads.

Locomotive electrical apparatus

Electrical devices of a locomotive are divided into the following types: protection devices, control devices and measuring instruments. Depending on the mains voltage, low-voltage and high-voltage devices can be distinguished.

The most common types of electrical devices of a diesel locomotive include control devices:

reversers;
controllers;
switches;
contactors;
relay.

The controllers perform the function of adjusting the power of the diesel engine. The control elements of this device are made in the form of two handles: main and reversible. With the help of the controller, the driver supplies current to the traction motors. The movement of the reversing lever leads to a change in the polarity of the electric motor, and, accordingly, changes the direction of movement of the diesel locomotive.

Switches are used to turn on and off auxiliary devices and lighting devices.

Contactors perform the function of switches, opening and closing power lines.

The control relay allows you to turn on and off the corresponding control lines. The transition relay allows you to switch the power electrical installations of a diesel locomotive in automatic mode.

Another group of electrical equipment for a diesel locomotive is automatic control devices (voltage regulators and amplistats).

Voltage regulators provide constant voltage to the auxiliary generator set.

The amplistat is made in the form of a magnetic amplifier. The main function of this device is to regulate the excitation current of the locomotive traction generator.

The safety electrical devices of the diesel locomotive are a blocking magnet, an oil pressure switch, an earthing switch, a boxing switch, a current limiting switch and a temperature switch.

Modes of operation and heating of electrical apparatus

Any devices, regardless of the scope and nature of the functions they perform, are designed for certain operating modes. Electrical devices can operate in short-term, intermittent, continuous and intermittently continuous modes.

There are two types of heating modes for electrical devices: steady state and transient. The heating process can be considered established if, after one hour of heating, the temperature of the electrical apparatus increases by no more than 1 0 C. In order to calculate the temperature value in the transient mode, it is necessary to use the heat balance equation.

Thermal calculations of current-carrying parts of electrical apparatus

When current passes through the conductor, power P is released, which is calculated by the formula: P=I2R, where R is the active resistance of the conductor with length l and cross section S: R=pl/S.

Resistivity p is directly dependent on temperature T and is calculated by the following formula: p=p 0 (1+aT), where p 0 is the specific resistance of the conductor material at a temperature equal to 0 0 C, aT is the temperature coefficient of expansion.

Consider the concept of the surface effect and the proximity effect. The skin effect is an uneven distribution of the density of an alternating electric current over the entire cross-sectional area of the conductor. The proximity effect is reduced to an uneven distribution of AC density due to the fact that the two conductors are at a close distance from each other. This phenomenon causes significant power losses.

Testing of electrical machines, devices and devices

To confirm full compliance with the stated requirements and standards, electrical machines are subjected to various tests that are carried out at different stages of production and operation of the equipment.

Tests can be:

acceptance- prototypes are subjected to such tests in order to subsequently launch the equipment into a series;
acceptance- carried out with each piece of equipment in order to establish optimal technical and operational parameters;
periodical- are carried out at a certain time and are designed to identify the compliance of the technical characteristics of the equipment with the declared requirements and standards of the enterprise;
typical- necessary when making certain changes to the design of the device;
attestation- aimed at establishing quality standards for products;
operational- carried out during the operation of the equipment. Such tests are aimed at identifying possible malfunctions and failures in the operation of devices.

Thermal and electrodynamic resistance of electrical apparatus

Equipment subjected to excessive thermal loads is at risk of premature failure. The heating of the components and assemblies of electrical devices can proceed so intensely that heat will not be removed from the heated elements in a timely manner.

The thermal resistance of electrical devices is commonly referred to as their ability to overcome excessive thermal loads without damage to equipment components and current-carrying lines. The quantitative characteristic of thermal resistance refers to the thermal resistance current passing through the conductor for a certain period of time. The most unfavorable mode of operation of the device is the short circuit mode, in which the value of the current strength and power of heat sources increases sharply.

Under the electrodynamic resistance of electrical apparatus is meant the ability of this equipment to withstand the electrodynamic effect of short-circuit current, without the occurrence of failures and other detrimental consequences that adversely affect its operation.

The electrodynamic resistance is characterized by the rated current of the electrodynamic resistance, the value of which is established according to the results of type tests, namely: the effective and instantaneous value of the current strength.

When carrying out verification work for electrodynamic resistance, it is necessary to compare the nominal value of the currents with the calculated values.

Electrodynamic forces in electrical apparatus

If the operation of the electrical apparatus proceeds in the optimal mode, the electrodynamic forces are very small and do not create any difficulties for the smooth operation of the equipment. If a short circuit occurs, such forces can cause serious damage to electrical devices.

In order to avoid such situations, it is necessary to calculate the apparatus or its individual components for electrodynamic stability. The need for such a calculation is caused by another reason. The fact is that the implementation of new technical solutions to minimize equipment elements leads to the fact that the conductive lines are in close proximity to each other, which increases the risk of a short circuit.