Low voltage devices general information. Electrical apparatus - purpose, classification, application. Electrical network protection devices

CHAPTER 2

Job 2

STUDY OF THE DESIGN AND PROTECTIVE CHARACTERISTICS OF FUSES

purpose of work

To study the design, marking of the main types of fuses with a fuse-link used to protect electrical circuits and installations in agricultural production.

Learn the methodology for calculating and selecting fuses.

Task to work

1. According to the methodological instructions and the set of fuses, study the design and marking of the fuses.

2. On the instructions of the teacher, calculate the fuse-link and select the type of fuse for the electrical installation or distribution network.

General information

Fuses are electrical switching products used to protect the electrical network from overcurrents and short-circuit currents. The principle of operation of fuses is based on the destruction of live parts specially designed for this (fuse-links) inside the device itself when a current flows through them, the value of which exceeds a certain value.

Fuse links are the basic element of any fuse. After burnout (power outage), they must be replaced. Inside the fuse-link there is a fusible element (it is he who burns out), as well as an arc extinguishing device. The fusible link is most often made of a porcelain or fiber housing and is attached to special conductive parts of the fuse. If the fuse is designed for low currents, then the fuse link for it may not have a case, i.e. be frameless. The main characteristics of fuse fuse rates include: rated current, rated voltage, breaking capacity.

Also, fuse elements include:

- fuse-link holder - a removable element, the main purpose of which is to hold the fuse-link;

- fuse-link contacts - part of the fuse that provides electrical connection between conductors and fuse-link contacts;

- fuse striker - a special element, the task of which, when a fuse is triggered, affects other devices and contacts of the fuse itself.

All fuses are divided into several dozen types:

- according to the design of the fuse-links, the fuses are collapsible and non-collapsible. With collapsible fuses, the fuse can be replaced after it burns out; with non-collapsible fuses, this will not work;

- by the presence of filler. There are fuses with and without filler;

- by the construction of the manufacture of fusible links. There are fuses with knife, bolt and flange contacts;

- according to the body of the fuse-link, the fuses are divided into tubular and prismatic. In the first type of fuses, the fuse has a cylindrical shape, in the second type, it is in the shape of a rectangular parallelepiped;

- by the type of fuse-links, depending on the range of breaking currents. There are fuses with breaking capacity in the full range of breaking currents - g and with breaking capacity in part of the range of breaking currents - a;

- by speed. There are non-high-speed fuses (used in most cases in transformers, cables, electrical machines) and high-speed (used in semiconductor devices);

- according to the design of the base, the fuses can be with a calibration base (in such fuses it will not be possible to install a fuse designed to work with a rated current greater than the fuse itself) and with an uncalibrated base (in such fuses, you can install a fuse, the rated current of which is higher rated current of the fuse itself);

- by voltage, fuses are divided into low-voltage and high-voltage;

- by the number of poles. There are one-, two-, three-pole fuses;

- by the presence and absence of free contacts. There are fuses with and without free contacts;

- by the presence of a striker and an operation indicator, there are fuses - without a striker and without a pointer, with an indicator without a striker, with a striker without an indicator, with a pointer and a striker;

- according to the method of fastening the conductors, the fuses are divided into - with front connection, with rear, with universal (both rear and front);

- according to the method of installation. There are fuses on their own base and without it.

Historically, the mechanical design of fuse cases and their overall and connection dimensions are different in different countries. There are four main national standards for fuse connection sizes: North American, German, British and French. There are also a number of fuse boxes that are the same for different countries and not related to national standards. Most often, such cases refer to the standards of the manufacturer, which developed a specific type of device, which turned out to be successful and entrenched in the market. In recent decades, as part of the globalization of the economy, manufacturers have gradually joined the international system of fuse box standards to facilitate the interchangeability of devices. When choosing, you should try to use fuses of international standards: IEC 60127, IEC 60269, IEC 60282, IEC 60470, IEC60549, IEC 60644.

It should be noted that according to the type of fuse-links, depending on the range of breaking currents and speed of action, the fuses are divided into classes of use. In this case, the first letter indicates the functional class, and the second indicates the object to be protected:

1st letter:

a - protection with breaking capacity in part of the range (accompanied fuses): fuse-links of fuses capable of at least for a long time passing currents not exceeding the rated current indicated for them, and disconnecting currents of a certain multiplicity relative to the rated current up to the rated breaking capacity;

g - full range breaking capacity (general purpose fuses): fuse-links capable of at least continuously passing currents not exceeding their rated current and breaking currents from the minimum melting current to the rated breaking capacity.

2nd letter:

G - protection of cables and wires;

M - protection of switching devices / motors;

R - protection of semiconductors / thyristors;

L - protection of cables and wires (in accordance with the old, no longer valid DIN VDE standard);

Tr - transformer protection.

A general view of the time-current characteristics of fuses of the main categories of use is shown in Fig. 2.1.

Fuse links with the following classes of use provide:

gG (DIN VDE / IEC) - protection of cables and wires in the entire range;

aM (DIN VDE / IEC) - protection of switching devices in a part of the range;

aR (DIN VDE / IEC) - protection of semiconductors in a part of the range;

gR (DIN VDE / IEC) - protection of semiconductors in the entire range;

gS (DIN VDE / IEC) - protection of semiconductors, as well as cables and lines in the entire range.

Fuses with breaking capacity in the entire range (gG, gR, gS) are reliably disconnected both at short-circuit currents and at overloads.

Part-range fuses (aM, aR) are used exclusively for short-circuit protection.

To protect installations for voltages up to 1000 V, electrical, tubular and open (plate) fuses are used.

The electrical fuse consists of a porcelain body and a fused plug. The supply line is connected to the fuse contact, the outgoing line to the screw thread. In the event of a short circuit or overload, the fusible link burns out, and the current in the circuit stops. The following types of electrical fuses are used: Ts-14 for a current up to 10 A and a voltage of 250 V with a rectangular base; Ts-27 for a current up to 20 A and a voltage of 500 V with a rectangular or square base and Ts-33 for a current up to 60 A and a voltage of 500 V with a rectangular or square base.

For example: electric fuses of the PRS series are designed to protect against overloads and short circuits of electrical equipment and networks. The rated voltage of the fuses is 380 V AC with a frequency of 50 or 60 Hz. Structurally, the PRS fuses (Fig. 2.2) consist of a body, a HPP fusible link, a head, a base, a cover, and a central contact.

PRS fuses are produced for the rated currents of the fuse-link from 6 to 100 A. The fuse designation indicates which connection it is: PRS-6-P - 6 A fuse, front wire connection; PRS-6-Z - 6A fuse, rear connection of wires.

Cylindrical fuses PTsU-6 and PTsU-20 with a threaded base Ts-27 and fuse-links for currents of 1, 2, 4, 6, 10, 15, 20 amperes are produced in a plastic case. PD fuses have a porcelain base, and PDS has a base material - steatite. In domestic conditions, automatic plug fuses are used, where the protected circuit is restored by a button.

Tubular fuses are of the following types: PR-2, NPN and PN-2. PR-2 fuses (collapsible fuse) are intended for installation in networks with voltage up to 500 V and for currents of 15, 60, 100, 200, 400, 600 and 1000 A.

In the PR-2 fuse holder (Fig. 2.3), the fusible insert 5, attached with screws 6 to the contact blades 1, is placed in a fiber tube 4, on which threaded bushings 3 are mounted. Brass caps 2 are screwed onto them, securing the contact blades, which enter into fixed spring contacts installed on the insulating plate.

Under the influence of the electric arc that occurs when the fuse blows, the inner surface of the fiber tube decomposes and gases are formed, which contribute to the rapid extinguishing of the arc.

Closed fuses with fine-grained filler include NPN, NPR, PN2, PN-R, KP fuses. The fuses of the NPN type (the filled fuse is non-separable) has a glass tube. The rest have porcelain pipes. NPN fuses have a cylindrical shape, PN - rectangular.

The NPN fuse kit consists of: a fusible link - 1 piece; contact bases - 2 pcs.

NPN fuses are manufactured for voltages up to 500V and currents from 15 to 60 A, PN2 fuses (bulk collapsible fuse) - for voltages up to 500 V and currents from 10 to 600 A. In bulk fuses, fuses made of several parallel copper or silver-plated wires , placed in a closed porcelain cartridge filled with quartz sand. Quartz sand promotes intensive cooling and deionization of gases generated during arc burning. Since the tubes are closed, splashes of molten metal of the fuse-links and ionized gases are not emitted outside. This reduces the fire hazard and increases the safety of fuse maintenance. Fuses with filling, as well as type PR fuses, are current-limiting ones.

Lamellar open fuses consist of copper or brass plates - lugs, into which copper calibrated wires are soldered. The terminals are bolted to the contacts on the insulators.

NPR fuses - closed collapsible cartridge (porcelain) filled with quartz sand for rated currents up to 400 A.

PD (PDS) fuses - 1, 2, 3, 4, 5 - with filler for installation directly on busbars for currents from 10 to 600 A.

To protect the power valves of semiconductor converters of medium and high power in case of external and internal short circuits, fast-acting fuses are widely used, which are the cheapest means of protection. They consist of contact knives and a silver foil fusible insert, housed in a sealed porcelain holder.

The fusible link of such fuses has narrow calibrated isthmuses, which are equipped with heat sinks made of ceramic material that conducts heat well, by means of which heat is transferred to the fuse body. These radiators also serve as arcing chambers with a narrow slot, which significantly improves the extinguishing of the arc arising in the isthmus region. A signal cartridge is installed in parallel with the fusible link, the blinker of which signals the melting of the fusible link and, acting on the microswitch, closes the signal contacts.

For a long time, the industry produced two types of fast-acting fuses designed to protect against short-circuit currents of converters with power semiconductor valves:

1) fuses of PNB-5 type (Fig. 2.4, a) for operation in circuits with a rated voltage of up to 660 V DC and AC for rated currents of 40, 63, 100, 160, 250, 315, 400, 500 and 630 A;

2) fuses of type PBV for operation in alternating current circuits with a frequency of 50 Hz with a rated voltage of 380 V for rated currents from 63 to 630 A.

electroplated coating (high conductivity and durability).

The fuse body is made of high-strength ultra-porcelain. The fuse design allows the use of additional devices - operation indicator, free contact.

The structure of the symbolic designation of PNB7-400 / 100-X1-X2 fuses:

PNB-7 - series designation;

400 - rated voltage, V;

100 - rated current;

X1 - conventional designation of the type of installation and the type of connection of conductors to the terminals: 2 - on its own insulating base with base contacts; 5 - on the bases of complete devices with base contacts; 8 - without base, without contacts (fusible link);

X2 - symbolic designation of the presence of the operation indicator: 0 - without signaling; 1 - with striker and free contact; 2 - with an indicator of operation; 3 - with a striker.

Industrial fuses of the PP series are designed to protect electrical equipment of industrial installations and electrical circuits from overloads and short circuits.

Fuses of this series of the following main types are produced: PP17, PP32, PP57, PP60S. Fuses are made with a trip indicator, with a trip indicator and a free contact or without signaling. Depending on the type, the fuses are designed for voltages up to 690 V and rated currents from 20 A to 1000 A. Design features allow you to install free make or break contacts, as well as the installation method - on its own base, on the basis of complete devices, on the conductors of complete devices ...

Designation structure of fuses type PP17 and PP32 - X1X2 - X3 - X4 - XXXX:

1) Х1Х2 - conventional designation of dimensions (rated current, A): 31 –100A; 35 - 250A; 37 - 400A; 39 - 630A.

( the fuse-link in some dimensions is unified with the PN2-100 and PN2-250 fuses).

3) X4 - symbolic designation of the presence of an actuation indicator, striker, free contact: 0 - without signaling, 1 - with striker and free contact, 2 - with actuation indicator, 3 - with striker.

4) XXXX - climatic version: UHL, T and placement category 2, 3.

Currently, semiconductor converters are equipped with PP57 series fuses (Fig. 2.5, a) and PP60S (Fig. 2.5, b).

The first ones are designed to protect the converter units in case of internal short circuits of alternating and direct currents at voltages of 220 - 2000 V for currents of 100, 250, 400, 630 and 800 A. The second - for internal short circuits of alternating current at voltages of 690 V for currents of 400, 630 , 800 and 1000 A.

Designation structure of type PP57 - ABCD - EF fuses:

The letters PP - fuse;

Two-digit number 57 - conditional number of the series;

A - two-digit number - symbol of the rated current of the fuse;

B - figure - symbol of the rated voltage of the fuse;

C - number - a conventional designation according to the method of installation and the type of connection of conductors to the terminals of the fuse (for example, 7 - on the conductors of the converter device - bolted with angle terminals);

D - number - a symbol for the presence of an operation indicator and an auxiliary circuit contact: 0 - without an operation indicator, without an auxiliary circuit contact; 1 - with a trip indicator, with an auxiliary circuit contact; 2 - with operation indicator, without auxiliary circuit contact;

E - letter - conventional designation of climatic version;

An example of a fuse symbol: PP57-37971-UZ.

Fuse fuses PPN are designed to protect cable lines and industrial electrical installations from overload and short circuit currents. Fuses are used in alternating current electrical networks with a frequency of 50 Hz with a voltage of up to 660 V and are installed in low-voltage complete devices, for example, in distribution panels ShchO-70, input-distribution devices VRU1, power distribution cabinets ShRS1, etc.

Advantages of PPN fuses: 1) the body of the fuse and the base of the holder are made of ceramics; 2) fuse and holder contacts are made of electrical copper; 3) the fuse box is covered with finely dispersed quartz sand; 4) overall dimensions of fuses are ~ 15% less than PN-2 fuses; 5) power losses are ~ 40% less than that of PN-2 fuses; 6) the presence of a response indicator; 7) fuses are mounted and dismantled using a universal puller.

The design features of the PPN series fuses are shown in Fig. 2.6.

Fuse fuses of the PPNI series (Fig. 2.7) of general use are designed to protect industrial electrical installations and cable lines against overload and short circuit and are produced for rated currents from 2 to 630 A.

They are used in single-phase and three-phase networks with voltage up to 660 V and frequency of 50 Hz. Fields of application of PPNI fuses: input-distribution devices (ASU); distribution cabinets and points (ShRS, ShR, PR); equipment of transformer substations (KSO, SCHO); low voltage cabinets (SHR-NN); cabinets and control boxes.

Due to the use of high-quality modern materials and a new design, power losses in PPNI fuses are reduced compared to PN-2 fuses. The data presented in table. 2.1, show the efficiency of PPNI fuses in comparison with PN-2.

Table 2.1

Example of fuse selection

For a rectifier valve group in a six-pulse bridge circuit, whose rated direct current is I d = 850 A, it is necessary to select the fuse-links for the fuse in the branches. The fuse selection is based on the above four typical loads.

Rectifier valve group parameters:

- supply voltage

U N = 3 АС 50 Hz 400 V,

- recovery voltage

U W = 360 V = U N · 0.9 (in case of inverter rollover,

- thyristor T 508N (by Eupec)

integral of ultimate load ∫I²dt = 320 103 A2s (10 ms, cold),

- safety inserts with natural cooling, ambient temperature tu = + 35 ° С

- cross-section of connection for fuse links, copper: 160 mm 2,

- the effective value of the branch current (operating current of the fuse) I La = I d · 0.58.

Direct current I d = 850 A

I eff = I La = I d 0.58 = 493 A

Full joule integral

∫I² · tА = 360 · 103 · 0.53 = 191 · 103 А2s

In accordance with the nomograms given in, it is necessary to apply the following correction factors:

k u = 1.02 (tu = + 35 ° С),

Required rated current I P of the fuse

I Р = I La · (1 / k u · k q · k l · k i · k WL) = 493 · (1 / 1.02 · 0.91 · 1.0 · 1.0 · 1.0) = 531 A

Check: 560 A> 531 A

Unknown variable load with known maximum current I MAX

I eff = I MAX = 435 A

Full joule integral

∫I² · tА = 260 · 103 · · 0.53 = 138 · 103 А2s

Control cross section: 400 mm 2

k u = 1.02 (tu = + 35 ° С),

k q = 0.91 (cross-section of the connection on both sides 40% of the reference cross-section),

k l = 1.0 (current cutoff angle l = 120 °),

k i = 1.0 (no intensive air cooling)

Required rated current IР of the fuse

I Р = ILa · (1 / k u · k q · k l · k i · k WL) = 435 · (1 / 1.02 · 0.91 · 1.0 · 1.0 · 1.0) = 469 A

Check: 560 A> 469 A

Variable load with known load cycle.

D.C:

I d1 = 1200 A, t 1 = 20 s (Fig.2.14),

I d2 = 500 A, t 2 = 240 s,

I d3 = 1000 A, t 3 = 10 s,

I d4 = 0 A, t4 = 60 s.

Current flowing through the fuse:

I La1 = 1200 0.58 = 696 A (Fig.2.14),

I La2 = 500 0.58 = 290 A,

I La3 = 1000 0.58 = 580 A,

I La4 = 0 0.58 = 0 A.

Effective operating current

Full joule integral

∫I² · tА = 175 · 103 · 0.53 = 93 · 103 А2s

Control cross section: 320 mm 2

We apply the following correction factors:

k u = 1.02 (tu = + 35 ° С),

k q = 0.94 (cross-section of the connection on both sides 50% of the reference cross-section),

k l = 1.0 (current cutoff angle l = 120 °),

k i = 1.0 (no intensive air cooling)

I Р = I eff · (1 / k u · k q · k l · k i · k WL) = 317 · (1 / 1.02 · 0.94 · 1.0 · 1.0 · 1.0) = 331 A

Check: 450 A> 331 A

I Р / = k u · k q · k l · k i · k WL · I Р = 1.02 · 0.94 · 1.0 · 1.0 · 1.0 · 450 = 431 A

2. Checking the permissible duration of the overload by current blocks that exceed the permissible operating current of the fuse I P /.

V = I eff / I P / = 317/431 = 0.74

From the curve k RW1 = f (V) (Fig. 11) we determine the value of k RW1 for V = 0.74, we have k RW1 = 0.2

We determine the shortened duration of the permissible load t SC for the corresponding block of current by the expression:

t SC = k RW1 t S, (2.15)

where t S is the melting time of the insert for currents I La1 and I La3 flowing through the fuse (from the time-current characteristic for 3NE3 333).

We have: t S1 = 230 s, t S3 = 1200 s.

Then t S1С = k RW1 t S1 = 0.2 230 = 46 s,

t S3С = k RW1 t S3 = 0.2 1200 = 240 s

Check: t S1С = 46 s> t 1 = 20 s

t S3С = 240 s> t 3 = 10 s

Random shock load from preload with unknown shock pulse sequence

I eff = I vor, (2.16)

where I vor - preload current (Fig.2.15),

I Stoss - overload current,

t Stoss - overload duration (t Stoss = 8 s).

Direct current: Current flowing through the fuse:

I dvor = 700 A I vor = I dvor 0.58 = 406 A

I dStoss = 1750 A I Stoss = I dStoss 0.58 = 1015 A

The frequency and duration of shock load impulses must satisfy the following conditions - t pausa ³ 3 · t Stoss and t pausa ³ 5 min.

Full joule integral

∫I² · tА = 360 · 103 · 0.53 = 191 · 103 А2s

Control cross section: 400 mm 2

We apply the following correction factors:

k u = 1.02 (t u = + 35 ° С),

k q = 0.91 (cross-section of the connection on both sides 40% of the reference cross-section),

k l = 1.0 (current cutoff angle l = 120 °),

k i = 1.0 (no intensive air cooling)

1. Required rated current I P of the fuse

I Р = I vor · (1 / k u · k q · k l · k i · k WL) = 406 · (1 / 1.02 · 0.91 · 1.0 · 1.0 · 1.0) = 437 A

Check: 450 A> 437 A

Permissible operating current I P / of the selected fuse insert:

I Р / = k u · k q · k l · k i · k WL · I Р = 1.02 · 0.91 · 1.0 · 1.0 · 1.0 · 560 = 520 А

2. Checking the permissible duration of the overload with the peak current I Stoss.

Preliminary load factor:

V = I vor / I P / = 406/520 = 0.78

From the curve k RW1 = f (V) (Fig. 2.11) we determine the value of k RW1 for V = 0.78, we have k RW1 = 0.18

We determine the shortened duration of the permissible load t SC for the surge current by the expression:

t SC = k RW1 t S, (2.17)

where t S is the melting time of the insert for the shock current I Stoss = 1015 A flowing through the fuse (from the time-current characteristic for 3NE3 333).

We have: t S = 110 s.

Then t SC = k RW1 tS = 0.18 110 = 19.8 s

Check: t SC = 19.8 s> t Stoss = 8 s

1. The name and purpose of the work.

2. The main types of fuses used to protect electrical installations and electrical circuits.

3. Calculation and selection of a fuse on an individual request.

4. Answers to security questions.

Control questions

1. By what design features do fuses differ?

2. Give an explanation of the designation of the fuses.

3. Describe the design of the PR-2 fuse.

4. Describe the design of the NPR fuse.

5. Describe the design of the PNB fuse.

6. What is the difference between PN fuses and PNB-7?

7. Scope of fuses PP57 and PP60S.

8. Scope of PPNI fuses.

9. What is the difference between PPNI fuses and PN-2?

10. How is the current of the fuse-link calculated for different loads?

11. What is the selectivity of protection?

12. What is the time-current characteristic of a fuse?

13. What are the advantages of PPNI fuses over other types of fuses?

14. How to ensure the selectivity of series-connected fuse-links?

15. How is the contact of the fuse blades with the jaws of the posts checked?

Bibliographic list

1. Rules for electrical installations [Text]: All current sections PUE-6 and PUE-7. Novosibirsk: Normatika, 2013 .-- 464 p., Ill.

2. Installation of electrical equipment and automation equipment: a textbook for universities / I.R. Vladykin, A.P. Kolomiets, N.P. Kondratyev, S.I. Juran. - M .: Publishing house "KolosS", 2007.

3. Sibikin Yu.D. Installation, operation and repair of electrical equipment of industrial enterprises and installations: Textbook. manual for prof. study. institutions / Yu.D. Sibikin, M. Yu. Sibikin. - M .: Higher. shk., 2003.

4. Akimova N.A. Installation, maintenance and repair of electrical and electromechanical equipment: textbook. allowance / N.A. Akimova, N.F. Kotelenets, N.I. Sentiurikhin; ed. N.F. Kotelents. - 3rd ed., Stereotype. - M .: Academy, 2005

5. Kostenko E.M. Installation, maintenance and repair of industrial and household electrical equipment: practical. manual for an electrician / E.M. Kostenko. - M .: Publishing house NTs ENAS, 2005.

6. EKF electrotechnica [Official site] Url: http://ekfgroup.com/produktsiya (accessed September 01, 2014).

7. KEAZ - Kursk Electrical Apparatus Plant [Official site] Url: http://keaz.ru (date of treatment September 01, 2014).

8. IEK - Inter electro kit [Official site] Url: http://www.iek.ru (date of treatment September 01, 2014).

9. Siemens - Electrical products [Official site] Url: http://electrosiemens.ru (date of treatment September 01, 2014).

CHAPTER 2

LOW VOLTAGE ELECTRIC APPARATUS

Electrical apparatus are called electrical devices for managing energy and information flows, operating modes, monitoring and protecting technical systems and their components. Electric devices, depending on the element base and the principle of operation, are divided into electromechanical and static.

TO electromechanical apparatus refers to technical devices in which electrical energy is converted into mechanical or mechanical energy into electrical energy.

Electromechanical devices are used in almost all automated systems. Some systems are entirely based on electromechanical devices. For example, automation circuits for starting, reversing and braking in an unregulated electric drive consist mainly of electromechanical devices such as relays and contactors. Electromechanical devices are used as sensors, amplifiers, relays, actuators, etc. The input and output values ​​of these devices can be both mechanical and electrical. However, they must necessarily carry out the mutual transformation of mechanical energy into electrical energy and vice versa.

Static devices are made on the basis of electronic components (diodes, thyristors, transistors, etc.), as well as controlled electromagnetic devices, in which the input and output are connected through a magnetic field in a ferromagnetic core. Examples of such devices include a conventional electrical steel transformer and a magnetic amplifier.

The basis of the functioning of most types of electrical devices (circuit breakers, contactors, relays, control buttons, toggle switches, switches, fuses, etc.) are the processes of switching (turning on and off) electrical circuits.

Another numerous group of electrical devices designed to control operating modes and protect electromechanical systems and components are regulators and stabilizers of electrical energy parameters (current, voltage, power, frequency, etc.). Electrical devices of this group operate on the basis of a continuous or impulse change in the conductivity of electrical circuits.

Let's consider some types of electrical devices.

Contactor Is an electrical device designed for switching power electrical circuits both at rated currents and at overload currents.

Magnetic switch Is an electrical device designed for starting, stopping, reversing and protecting electric motors. Its only difference from the contactor is the presence of a protection device (usually a thermal relay) against thermal overloads.

The uninterrupted operation of induction motors is highly dependent on the reliability of the starters. Therefore, high requirements are imposed on them in terms of durability, switching capacity, accuracy of operation, reliability of motor overload protection, and minimum power consumption.

In crane mechanisms, controllers are widely used that control small and medium power motors, and controllers (high power motors).

Controller is an apparatus with the help of which the necessary switching in the circuits of AC and DC motors is carried out. Switching is carried out manually by turning the handwheel.

Command controller in principle of operation does not differ from the controller, but has a lighter contact system designed for switching in control circuits.

Relay such an electrical apparatus is called, in which, with a smooth change in the control (input) value, an abrupt change in the controlled (output) value occurs.

Electromagnetic relays are widely used in various automated electric drive systems. They are used as current and voltage sensors, time sensors, for transmitting commands and multiplying signals in electrical circuits. They are used as actuators in sensors of technological parameters of various machines and mechanisms.

Magnetically operated contact (reed switch) Is a contact that changes the state of an electrical circuit by mechanically closing or opening it when a control magnetic field is applied to its elements. Reed switches have an increased speed, as well as, due to their design features, reliability of operation, therefore they are widely used in automatic systems. On their basis, relays for various purposes, sensors, buttons, etc. are created.

Executive device- this is a device that moves the executive body or force action on this body in accordance with the specified functions and when the appropriate signals are applied to the control windings. Most often, electromechanical actuators are used to convert an electrical signal into movement of the moving part of the device. Examples are solenoid valves, electromagnetic clutches, electromagnetic latches, latches, etc.

All elements of the apparatus have established graphic images and names, some of which are given in table.

Symbols of device elements

Name	Designation
Push-button switch: with NO contact
with break contact
Single pole switch
Switching device contact: NO
unlocking
switching
Contact for switching a high-current circuit: closing
unlocking
closing arcing
breaking arcing
Closing contact with retarder acting when triggered
Electrical relay with make, break and changeover contact

The position of the contacts of the devices shown on the control diagrams, in the absence of external influence, corresponds to their normal state. The contacts of the devices are subdivided into closing, opening and switching. In electric drive control circuits, power or main circuits are distinguished through which electric current is supplied to electric motors, as well as auxiliary circuits, which include control, protection and signaling circuits.

Electric drives of pumps,

Fans, compressors

In modern technology, a large class is made up of machines designed for the supply of liquids and gases, which are divided into pumps, fans and compressors. The main parameters characterizing the operation of such machines are the supply (productivity), pressure and head created by them, as well as the energy imparted to the flow by their working bodies.

Typically, these drive systems are divided into several groups:

1) Pumps, fans, compressors of a centrifugal type, the static power on the shaft of which varies in proportion to the cube of the speed, if the losses of idling can be neglected and there is no back pressure, that is, these are mechanisms with the so-called fan characteristic. This is the most common group;

2) Various piston-type pumps and compressors, the shaft power of which changes sinusoidally depending on the crank angle. For single-acting piston pumps, the supply is carried out only when the piston moves forward; during the reverse stroke, there is no supply;

3) Various piston type double acting pumps and compressors. The feed is carried out with a piston stroke in both directions.

Adjustable electric drive of mechanisms with fan torque

In installations requiring smooth and automatic flow control, the electric drive is performed regulated.

The characteristics of the centrifugal type mechanisms create favorable conditions for the operation of the variable electric drive both with respect to static loads and the required speed control range. Indeed, with decreasing speed, at least quadratically, the moment of resistance on the motor shaft also decreases. This facilitates the thermal behavior of the engine when running at reduced speed. It follows from the laws of proportionality that the required range of speed control, provided there is no static head does not exceed the specified range of feed change

If the static head is not zero, then to change the flow from zero to the nominal value speed regulation range required

where is the head developed by the mechanism at.

On average, for variable speed centrifugal mechanisms, the required speed control range usually does not exceed 2: 1. The noted features of these mechanisms and low requirements in relation to the rigidity of mechanical characteristics make it possible to successfully use simple circuits of a controlled asynchronous electric drive for them.

For installations of low power (7 ... 10 kW), the problem is solved with the help of a voltage regulator system - an asynchronous motor with a squirrel-cage rotor. Thyristor switches are most often used as voltage regulators. Such systems have found application in complexes of ventilator equipment designed to provide the required air exchange and create the necessary temperature conditions in livestock and poultry buildings in accordance with veterinary standards.

In installations where, according to the operating conditions, it is permissible to use an induction motor with a wound rotor, the possibilities of a controlled electric drive are expanded. The mechanical characteristics of this drive ensure stable operation in a sufficiently wide range of speeds with an open-loop drive system.

In a number of cases, the speed control of mechanisms with a drive by their asynchronous or synchronous motors is used. At the same time, a fluid coupling or asynchronous slip clutch is installed between the motors and the production mechanism, which allows you to change the speed of the production mechanism without changing the speed of the engine.

For example, consider electrical circuit for automation of the fan unit.

Squirrel cage induction motor control circuit M a fan located in the machine room and designed for independent ventilation of large electrical machines is shown in Fig. 4.13. The fan is controlled from the panel using the control key K1 with four contacts and a self-resetting handle. Key K2 serves to allow or prohibit turning on the fan at the installation site when there is no need for its operation.

The scheme works as follows. Key K2 is set to position R (allowed). The machine turns on IN 2 control circuits and machine IN 1 main circuits (its contact in the self-locking circuit of the starter is closed). The green lamp lights up P3 (engine off). To start the engine M key K1 is transferred from zero position 0 to starting NS ... this turns on the magnetic starter TO, put on self-supply and with the main contacts turns on the motors into the network. Green lamp LZ goes out, red lamp OK lights up - the engine is on.

Key handle K1 released, and the key returns to the zero position, at which the contact 2 the key is closed, and the contact 1 remains closed.

The scheme provides for testing the fan at the installation site using the button KNO . Interlocking is also provided (by means of a closing auxiliary contact TO ), which does not allow the ventilated machine to be turned on before the fan starts. Protection against short circuits or motor overload M carried out automatically IN 1 with combined release. And zero protection - by a starter TO (a new start of the engine is not possible until the key handle is K1 will not be put into start position NS) ... When the fan is switched off as a result of the protection action, a warning signal is triggered, since the contacts 3 and 4 key K1 at the same time are closed. When manually turning off the fan by moving and then releasing the key handle K1 pregnant WITH the warning signal is not given because the contact is open 4 .

Electricity basics

Electricity supplycalled the generation, transmission and distribution of electrical energy between consumers.

Electricity generation is created by power plants. Almost all industrial power plants have a three-phase sinusoidal voltage synchronous generator as a final element. With an increase in the unit power of a generator, its efficiency increases; therefore, modern stations have generators of very high power.

Power plants can be classified as follows:

thermal, hydraulic, nuclear, wind power plants, solar power plants, geothermal, tidal, etc. more common than others thermal power plants that burn coal, peat, gas, oil, etc., these stations generate electrical energy with an efficiency of about 40%. Thermal plants pollute the air due to incomplete combustion of fuel and insufficient filtration of exhaust gases.

Hydraulic stations use the energy of the water flow. At such stations, much cheaper electrical energy is generated. A high-power hydroelectric power plant has an efficiency approaching 90%. Hydraulic stations disturb the water balance of rivers and also degrade the environment.

Nuclear power plants convert the fission energy of an atomic nucleus into electrical energy. The efficiency of the reactor of a nuclear power plant is 25 ... 35%. In the event of an accident at a nuclear power plant, there is a threat of radiation pollution of the environment.

The operation of any source of electrical energy can cause environmental damage. Therefore, in developed countries, much attention is paid to the technology of generating electricity. Using modern technology, some countries safely generate over 60% of their electricity from nuclear power plants.

The use of wind and solar power plants begins. Small capacity electricity is provided by geothermal (in Kamchatka) and tidal (on the Kola Peninsula) stations.

Synchronous generators of power plants induce a three-phase sinusoidal EMF of 18 kV. To reduce losses in power lines at step-up substations, the voltage is transformed to 110 and 330 kV and fed into the Unified Energy System. Losses in transmission lines are proportional to the square of the current, so electricity is transported at higher voltage and lower current.

Power lines there are air and cable. Overhead power lines (PTL) are much cheaper than cable (underground) ones and therefore are more widely used. Power lines are connected to transformers with special high-voltage switching devices.

Usually, industrial enterprises consume electric energy with a voltage of 380 V. Therefore, distribution points and transformer substations are installed in front of the consumer, lowering the voltage to 6 ... 10 kV and 380 ... 220 V.

There are three main power supply schemes for consumers: radial, main, mixed.

Radial power supply diagram provides for the use of a transformer substation for each consumer. This is a very reliable power supply scheme, but requires a large number of substations.

Trunk diagram provides only a few substations that are included in the power line. Many consumers are connected to each substation.

Mixed scheme provides for sections with radial and main connection. Consumers are connected in a differentiated manner. This scheme is used more often.

The power supply scheme of an autonomous energy unit can be quite original. Features of power supply depend on the functional tasks of the actuators, operating conditions, special requirements regarding weight, dimensions, efficiency of electrical devices, etc.

Power supply for industrial enterprises... About two thirds of all electricity is consumed by industry. The power supply scheme for industrial enterprises is built on a stepwise principle, the number of steps depends on the capacity of the enterprise and the layout of individual electricity consumers. At the first stage, the voltage of the power system is supplied to the main substation, where it is reduced from 110-220 kV to 10 -6 kV. The second-stage networks supply this voltage to the workshop transformer substations, where it is reduced to the voltage of the consumers. The third stage is made up of networks that distribute the voltage of the workshop substation between individual consumers.

At large enterprises with a large consumption of electricity, consumers can be powered at a voltage of 660 V. Most enterprises use three-phase networks of 380/220 V. In rooms with increased danger, the permissible supply voltage of consumers should not exceed 36 V. ) - 12 V.

According to the required reliability of power supply, consumers of electrical energy are divided into three categories. The first category includes such consumers, the interruption in the supply of electricity to which is associated with a danger to people or entails large material damage (blast furnace shops, industrial steam boiler houses, hoisting and ventilation installations of mines, emergency lighting, etc.), they must work continuously. For consumers of the second category (the most numerous), food breaks for a limited time are allowed. Consumers of the third category include auxiliary shops and other facilities for which a power outage of up to one day is allowed.

To increase the reliability of power supply, it is planned to supply consumers from two independent networks and an automatically switched on backup power source. Distinguish between "hot" and "cold" backup sources. The "hot" standby source provides immediate emergency power and is used for trouble-free shutdown of the consumer.

Further improvement of the power supply systems of industrial enterprises is associated with an increase in the supply voltage (from 220 to 380 V, from 6 to 10 kV, etc.) with the maximum possible approach of high voltage to consumers (deep input) and a decrease in the number of transformation stages.

Wires and cables... For laying overhead lines, various types of bare wires are used. Steel single-wire wires are made with a diameter of not more than 5 mm. The most widespread are stranded wires, which have high strength and flexibility. They are made from identical wires, the number of which can reach 37. The diameter of the wires and their number are selected in such a way as to ensure the highest packing density of the wires in the wire. Usually 6, 11, 18 wires are placed around one central one and twisted slightly. Stranded wires are steel, aluminum, steel-aluminum and bimetallic wires. In steel-aluminum wires, some of the wires are steel, some are aluminum. This provides mechanical strength with increased electrical conductivity. Bimetallic wires are made electrolytically: the steel core is covered with a layer of copper or aluminum.

For indoor wiring, insulated copper or aluminum wires are usually used. Insulated single-wire wires have a high rigidity and a cross-sectional area not exceeding 10 mm 2.

Stranded wires are made from tinned copper or aluminum conductors. They are convenient for installation and operation.

For the laying of hidden unsupported lines, as well as for the sewerage of electricity supplied to moving objects, electric cables are used. In the cable, the wires of two or three-phase lines are enclosed in a strong sealed multilayer sheath, which increases the reliability of power lines. Cables can be laid underground and under water. Underground cables are the main means of sewerage electricity in large cities. The disadvantage of cable lines is their high cost.

Basics of electrical safety

Electric apparatus Is a device that controls electrical consumers and power supplies, and also uses electrical energy to control non-electrical processes.

Electrical devices for general industrial purposes, electrical household devices and devices are produced with voltage up to 1 kV, high-voltage - over 1 kV. Up to 1 kV are divided into manual and remote control devices, protection devices and sensors.

Electrical devices are classified according to a number of characteristics:

1.As intended, i.e. the main function performed by the device,

2.on the principle of action,

3.by the nature of the work

4.kind of current

5.amount of current

6.voltage value (up to 1 kV and above)

7.execution

8.degrees of protection (IP)

9. by design

Features and areas of application of electrical devices

Classification of electrical devices depending on the purpose:

1. Control devices, designed for starting, reversing, braking,speed regulationrotation, voltage, current of electrical machines, machine tools, mechanisms or for starting and regulating the parameters of other electricity consumers in power supply systems. The main function of these devices is to control electric drives andother consumers of electrical energy. Features: frequent switching on, switching off up to 3600 times per hour i.e. 1 time per second.

These include electrical manual control devices-, controllers and commanders, rheostats, etc., and electrical remote control devices-, contactors, etc.

2. Protection devices are used for switching electrical circuits, protecting electrical equipment and electrical networks from overcurrents, ie, overload currents, peak currents, short-circuit currents.

These include, etc.

3. Control devices, are designed to control specified electrical or non-electrical parameters. This group includes sensors. These devices convert electrical or non-electrical quantities into electrical ones and provide information in the form of electrical signals. The main function of these devices is to control the specified electrical and non-electrical parameters.

These include current, pressure, temperature, position, level sensors, photosensors, as well as relays that implement sensor functions, for example, voltage, current.

Classification of electrical devices according to the principle of operation

According to the principle of operation, electrical devices are divided depending on the nature of the impulse acting on them. Based on the physical phenomena on which the operation of the devices is based, the following categories are the most common:

1. Electrical switching devices for closing and opening electrical circuits using contacts connected to each other to ensure the passage of current from one contact to another or remote from each other to break an electrical circuit (switches, switches, ...)

2. Electromagnetic electrical apparatus, the action of which depends on the electromagnetic forces arising during the operation of the device (contactors, relays, ...).

3. Electrical induction apparatus, the action of which is based on the interaction of current and magnetic field ().

4. Inductors(reactors, saturation chokes).

Classification of electrical devices by the nature of work

By the nature of the operation, electrical devices are distinguished depending on the mode of the circuit in which they are installed:

1. Devices that work for a long time

2.intended for short-term operation,

3. working under conditions of intermittent load.

Classification of electrical devices by the type of current

By the nature of the current: direct and alternating.

Requirements for electrical apparatus

The design varieties of modern devices are especially diverse, in this regard, the requirements for them are also different. However, there are some general requirements, regardless of the purpose, application or design of the apparatus. They depend on the purpose, operating conditions, and the required reliability of the devices.

The insulation of the electrical apparatus must be calculated depending on the conditions of possible overvoltages that may arise during the operation of the electrical installation.

Devices designed for frequent switching on and off of the rated load current must have high mechanical and electrical durability, and the temperature of the current-carrying elements must not exceed the permissible values.

In case of short circuits, the current-carrying part of the apparatus is subjected to significant thermal and dynamic loads, which are caused by a large current. These extreme loads should not interfere with the continued normal operation of the apparatus.

Electrical devices in the circuits of modern electrical devices must have high sensitivity, speed, versatility.

A common requirement for all types of devices is the simplicity of their construction and maintenance, as well as their efficiency (small size, the lowest weight of the device, the minimum amount of expensive materials for the manufacture of individual parts).

Operating modes of electrical devices

The nominal operating mode is a mode when an element of the electrical circuit operates at the values ​​of current, voltage, power indicated in the technical passport, which corresponds to the most favorable operating conditions in terms of efficiency and reliability (durability).

Normal operation- mode when the device is operated with mode parameters slightly different from the nominal.

Emergency operation- this is a mode when the parameters of current, voltage, power exceed the nominal two or more times. In this case, the object must be disabled. Emergency modes include the passage of short-circuit currents, overload currents, lowering the voltage in the network.

Reliability - trouble-free operation of the device for the entire period of its operation.

The property of an electrical apparatus to perform specified functions, keeping in time the values ​​of the established operational indicators within the specified limits, corresponding to the specified modes and conditions of use, maintenance and repairs, storage and transportation.

Execution of electrical devices according to the degree of protection

Determined by GOST 14254-80. In accordance with GOST, 7 degrees are established from 0 to 6 from the ingress of solids and from 0 to 8 from the penetration of liquid.

Designation of degrees of protection	Protection against the penetration of solid bodies and the contact of personnel with live and rotating parts.	Protection against water ingress.
	There is no special protection.
	Large areas of the human body such as hands and solids larger than 50 mm.	Drops falling vertically.
	Fingers or objects not exceeding 80 mm in length and solids exceeding 12 mm in length.	Drops when the shell is tilted up to 15 0 in any direction relative to the normal position.
	Tools, wires and solids over 2.5 mm in diameter.	Rain falling on the shell at an angle of 60 ° from the vertical.
	Wire, solids larger than 1 mm.	Splashes falling on the shell in any direction.
	Insufficient amount of dust to interfere with the operation of the product.	Jets ejected in any direction.
	Complete dust protection (dustproof).	Waves (water should not get inside during excitement).
		When immersed in water for a short time.
		With prolonged immersion in water.

The abbreviation "IP" is used to indicate the degree of protection. For example: IP54.

With regard to electrical devices, there are the following types of execution:

1. Protected IP21, IP22 (not lower).

2. Splash-proof, drip-proof IP23, IP24

3. Waterproof IP55, IP56

4. Dustproof IP65, IP66

5. Closed IP44 - IP54, these devices have an internal space isolated from the external environment

6. Sealed IP67, IP68. These devices are made with particularly tight insulation from the environment.

Climatic performanceelectrical apparatus determined by GOST 15150-69. In accordance with climatic conditions, it is designated by the following letters: У (N) - temperate climate, CL (NF) - cold climate, TB (TH) - tropical humid climate, ТС (TA) - tropical dry climate, О (U) - all climatic regions, on land, rivers and lakes, M - temperate maritime climate, OM - all areas of the sea, B - all macroclimatic regions on land and at sea.

1. Outdoors,

2. Rooms where fluctuations in temperature and humidity do not differ significantly from fluctuations in the open air,

3. Closed rooms with natural ventilation without artificial regulation of climatic conditions. No exposure to sand and dust, sun and water (rain),

4. Premises with artificial regulation of climatic conditions. No exposure to sand and dust, sun and water (rain), outside air,

5. Premises with high humidity (prolonged presence of water or condensed moisture)

Selection of electrical devices

The choice of electrical devices is a problem, in the solution of which the following should be taken into account:

• currents, voltages and powers switched by an electric apparatus;
• parameters and nature of the load - active, inductive, capacitive, low or high resistance, etc.;
• the number of switched circuits;
• voltages and currents of control circuits;
• coil voltage of the electrical apparatus;
• operating mode of the apparatus - short-term, long-term, repeated-short-term;
• operating conditions of the device - temperature, humidity, pressure, vibration, etc .;
• methods of fixing the device;
• economic and weight and size indicators;
• ease of pairing and electromagnetic compatibility with other devices and devices;
• resistance to electrical, mechanical and thermal overload;
• climatic modification and category of placement;
• IP protection degree,
• safety requirements;
• height above sea level;

terms of Use.

Section 2. Low voltage electrical apparatus

Topic 2.1 Electrical manual control devices

1.Crushers-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

Choice of circuit breakers, batch switches

Question 1: chippers

Switch- the simplest manual control device, which is used for switching electrical circuits at voltages up to 660 V AC and 440 V DC and currents from 25 to 10000 A.

Circuit breaker symbol on electrical diagrams: - single pole

Three-pole

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

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

Arc extinguishing 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 influence of the electrodynamic forces of the current circuit (parts of the switch, etc.).

When installing switches in distribution boxes or closed switchgears of small volume, limiting the size of the arc becomes very relevant. It is necessary that the ionized gases remaining after the arc extinction do not cause an overlap on the case or between live parts. In such cases, circuit breakers are equipped with various types of arc chutes.

Fig. 2.1 Two-pole changeover breaker

Structural designation of the circuit breaker:

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

Question 2. Command devices

Pushbutton switches (buttons)–Electric devices for manual control, designed for the operator to give 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, pushbuttons, NO and NC contacts. Several buttons installed on a common panel or in a common body is called a button post.

STOP button, START button

Example symbolic designation of a 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- the number of contact elements: 1-1 or 2; 2 - 3 or 4;

XXX- climatic version in accordance with GOST 15150-69: U, HL, T - for switches of the Kamenets-Podolsk Electromechanical Plant; У, В - for switches of the Rheostat control equipment plant;

The device of push-buttons (Fig. 2.3.)

Fig. 2.3. Design and designation of pushbutton switches

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

a- button with normally open contacts ( "start");
b- button with break contacts ( "stop").

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

Package switches and switches(Figure 2.4) - electrical devices for manual control, designed for switching control and signaling circuits in the circuits for starting the reverse of electric motors, as well as electrical circuits of alternating current with a voltage of 380 V and direct current of 220 V of low power under load.

Figure 2.4 General view of a packet switch

Conventional designation of any switch:

Basically, the switches are of the following design: on one shaft, switching packets (contacts) of identical design are assembled, 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 movable contacts of the MK and PMO series and cam UP5300, PKU.

Standard universal switches are produced in the UP5300 series; waterproof - UP5400 series; explosion-proof - series UP5800. 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.

Figure 2.5 General view of universal switches

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

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

The letters I, K, L, M, H, S, F, X indicate that the switch is latched in positions after 45 °. The letter I indicates that the handle can be rotated to the right one position, K - left one position, L - right or left two positions, M - right or left three positions, H - right eight positions, C - right or to the 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 be oval or revolving. Usually, switches with up to 6 sections inclusive with circular rotation (eight positions) have an oval handle.

The designation of each switch contains the abbreviated name, the conventional number of the given design, the number indicating the number of sections, the type of retainer and the number of the switch diagram according to the catalog. For example, the designation UP5314-N20 is deciphered as follows: U - - universal, P - switch, 5 - unregulated command device, 3 - railless design, 14 - number of sections, H - type of retainer, 20 - diagram number by catalog.

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

Small switches designed for installation on switchboards, 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 designed for a rated current of 6 A.

Each switch has its own wiring diagram and contact closure diagram.

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

The switches are composed of 2, 4 and 6 pin packs. Packet cam universal switches PKU are used in electric motor control circuits in manual, semi-automatic and automatic modes. They are rated for 220 VDC and 380 VAC.

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 - execution according to the method of installation and fastening (installation behind the panel of the shield with fastening for the front bracket with a front ring), L - fixing the position after 45 °, 2020 - number of the diagram and diagram from the catalog.

Task 2. b) .Name the position of the packet switch shown in Figure 2.6.

Figure 2.6 Batch Switch

Tumblers designed for manual switching of low-voltage electrical circuits of low power, which do not require frequent switching.

Rice. 2.7 Toggle switch

Assignment 2.c). What are the approximate dimensions of the toggle switch?

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

There are three types of controllers : flat, drum, cam.

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

Drum controllers used to control motors up to 75 kW. Their switching capacity 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 arcing system.

Task 2.d). Name the controller positions in Figure 2.8.

Fig 2.8. Power controller

Figure 2.9. Types of resistors

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

Frame resistors They consist of a steel plate, on the side edges of which porcelain or steatite insulators are fixed, which have recesses in which a wire or resistance tape is laid. The outputs of the steps are made in the form of clamps or soldered copper lugs.

Cast iron resistors and steel stamped 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 image of the rheostat. The dimensions of the rectangle are 8x4.

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

Starting devices for starting electric motors of direct and alternating current;

Controllers for starting and regulating the speed of rotation of the electric motor;

Excitation rheostats - to regulate the excitation current in the excitation windings of electrical machines (Figure 2.10.);

Figure 2.10. Structural diagram of the excitation rheostat

Load or ballast - to absorb electricity.

Task 3.a) Try, looking at Figure 2.11, 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?

Figure 2.11

Task 4. Checking the degree of assimilation of the studied information on questions1,2,3

topics 2.1 "Electrical manual control devices"

a) name the devices shown in Figure 2.12.

Figure 2.12.

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

Table 2.1. Selection of circuit breakers, packet switches

Task 5. Select the main three-phase switch installed in the power panel with an input voltage of 380 V. The power transmitted by the circuit is 20 kW. The calculated value of the maximum short-circuit current. is equal to 11.5 kA. Technical data of three-phase circuit breakers are presented in table 2.2. Decipher the brand of the accepted switch

Solution: 1.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

Circuit breaker type	P-25	RPS-1 (with fuse, lateral offset)	RC-1 (with a 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	three-pole	three-pole	three-pole
Mechanical durability		At least 2500 VO cycles	At least 2500 VO cycles	-

Task 6. Topic "Manual control devices"

Choose the correct answer:

Home 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 supplied through slip rings to the field winding mounted on the driven shaft. This winding creates a magnetic flux F, which is closed through the clutch armature. The resulting electromagnetic force moves the armature to the left and through the friction surfaces 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. Common materials can be used: steel on steel, steel on cast iron, steel on bronze, etc. The most advanced are cermet materials (copper 68%, tin 8%, lead 7%, graphite 6%, silicon 4%, iron 7%). A uniform mixture of these powders is pressed under high pressure and sintered at a temperature of 700-800 C. Low-melting components penetrate into the pores of the mixture and solder the entire composition.

The field winding can be supplied with direct and alternating current. In the case of AC power supply, there are differences in the design of the coupling in terms of the manufacture of the magnetic circuit. The magnetic core 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 drive shaft. If the space between 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-bonds, which will create an adhesion force from 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 adheres to the magnetic materials of the coupling (steel part, ring, ferromagnetic powder, rotor)

For ferro-powder couplings, carbonyl, siliceous, 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 a separator-graphite, zinc oxide, talc, etc. It is designed to protect the powder from sticking, the formation of lumps.

In the couplings, special seals are created so that the powder does not go beyond the air gaps, and magnetic catchers that attract powder particles that have come out of 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 the ferromagnetic cylinder (drum) 3. Inside the cylinder there is an electromagnet 4 connected to the driven shaft 6. The winding 5 of the electromagnet is fed through slip rings (in the figure not shown). 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, organosilicon 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 filler grains 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 rises sharply. 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 filler are completely solidified. The drum and electromagnet become rigidly coupled. The transmitted moment can be considered as the moment from the friction 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 (electromagnet power).

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

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

In hysteresis couplings(Figure 2.2.3) The mechanical forces of adhesion between the driving and driven parts are created by using the phenomenon of remanent magnetization of magnetically hard 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 least 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 operation of an AD, 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 off. They are subdivided 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) Finish 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

The law of electromagnetic induction: crossing a conductor by a magnetic field induces an electromotive force in the conductor.

The law of electromagnetic force: the interaction of the 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 quantities.

The following main characteristics of the relay are distinguished.

1. The magnitude of the relay Xcr actuation- the value of the parameter of the input value at which the relay is switched on. The magnitude of the operation to which the relay is adjusted is called setpoint.

2. Power of actuation Рср of the 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. Controlled power Rupr- the power that is controlled by the switching elements of the relay in the process of switching. In terms of control power, relays are distinguished for low-power circuits (up to 25 W), relays for medium-power circuits (up to 100 W) and relays for high-power circuits (over 100 W), which belong to power relays and are called contactors.

4. Response time tav relay- the time interval from the Xav signal to the relay input to the beginning of the impact on the controlled circuit. According to the response time, there are normal, high-speed, delayed relays and time relays. Usually for normal relays tav = 50 ... 150 ms, for high-speed relays tav 1 s.

Assignment 3: a) Make a relay classification

Fig. 2.2.5

The sensing 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, 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 apparatus that was used to control electric motors. The most widespread all over the world are electromagnetic contactors. They are the main switching devices for circuits with currents exceeding 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;

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

by rated voltage of the main circuit: from 27 to 2000 V DC; from 110 to 1600 VAC with a frequency of 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

Contactors consist of a main contact system, arcing, electromagnetic systems and auxiliary contacts.

Fig. 2.2.9. Diagram of the electromagnetic contactor

2.2.10. Electromagnetic contactor device: a) general view, b) arc extinguishing system and contact system, c) electromagnetic system

On the metal rail 5 with a bracket 17, the core 2 of the magnetic circuit with the coil 4 is fixed. The core 2 has a short-circuited coil 3 and is damped by a spring 18. Through the insulating block 15, three blocks of 1 poles are attached to the rail, which have fixed contact parts 9 and an arc-extinguishing coil 16. Moving system the contactor is mounted on an insulated shaft 7 and rotates in bearings 6. The movable contact piece 11 is fixed in the contact holder 13 and is spring-loaded by a spring 12. The connection with the contact bolt is provided by a flexible connection 14. Each unit has an arc chamber 10. Auxiliary contacts 8 are also installed on the shaft.

Main contacts close and open the power circuit. They must be designed for long-term carrying 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 retractor coil of the contactor is not current 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 - straight-through. Figure 2.2.11 shows sequentially the kinematics of the contactor contact movement when closing.

Fig. 2.2.11.

As a rule, for lever contacts, the pivot points of the contact do not coincide. In addition, the contacts touch before the moving system reaches the end position. As a result, when closing and opening, rolling and sliding of the movable contact along the fixed one occurs. Therefore, the starting point of tangency when closing and it, the end point of tangency and, accordingly, the point where the arc arises when opening is displaced with respect to the point of final contact of the contacts. Due to this, the surfaces that provide long-term conduction of current and that determine the contact resistance are remote from the arc. Well, slipping of the contacts with sufficient contact pressure leads to the erasure of the oxide film and various accumulated dirt from the contact surface, that is, the contacts are self-cleaning. Since the contacts in the switching devices are, perhaps, the weakest parts of the apparatus, we see that in this case, the very design of the power contacts of the contactors allows the contact resistance to remain stable for a long time, which in turn greatly affects the reliability and failure-free operation. the contactor as a whole. But nothing is perfect, so this lever contact has its drawbacks. Slippage with the roughness that the contact surfaces (especially working ones) usually have, cause additional contact bounce when closing, and, consequently, 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 evils.

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

Lever contacts require a flexible connection to connect to a conductor, but flexible connection in some cases is a weak point of the contact system. It is difficult to implement at high currents and its mechanical durability is lower than that of other parts.

Next, let's figure out the purpose and possible constructions. arc extinguishing system contactors. The arc extinguishing system extinguishes the electric arc that occurs when the main contacts are opened. Methods for extinguishing the arc and the design of arc-extinguishing systems are determined by the type of current in the main circuit and the mode of operation of the contactor. Arc extinguishing systems of DC contactors differ from arc extinguishing systems of AC contactors due to the fact that the principles of arc extinguishing for DC and AC are different.

Arc extinguishing chambers of DC contactors are based on the principle of extinguishing an electric arc by a transverse magnetic field in chambers with longitudinal slots. The magnetic field, in the overwhelming majority of structures, is excited by an arc-extinguishing 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 get widespread. 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 chamber volume cannot be achieved with this chamber.

AC contactors are available with deionic interrupters. When arising, the arc moves to the lattice, breaks up into a number of small arcs and extinguishes at the moment the current passes through zero. It is, in principle, easier to extinguish an 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 diagram.

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

Auxiliary contacts... They switch in the contactor control circuits, as well as in the blocking and signaling circuits. They are designed for long-term conduction of current no more than 20 A, and disconnection of current no more than 5 A. Contacts are made both closing and opening, in the overwhelming majority of cases of bridge type.

Task 4.b) Fill in table 1

Table 1

Contactor operating principle... In the initial disconnected position, when the voltage from the coil is removed, 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 (bypass) the contacts of the "Start" button. Contact pressing is carried out by a spring. The anchor has a gasket made of non-magnetic material, which reduces the force of attraction and when the voltage is removed from the coil, the armature immediately moves away 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

→ Basic definitions

1. Basic definitions and classification of electrical devices
1.1. Basic definitions
Electrical devices (EA) are called electrical technical devices for control. flows of energy and information, modes of operation, control and protection of technical systems and their components.
Electrical devices are used for switching, signaling and protection of electrical networks and electrical receivers, as well as control of electrical and technological installations and are extremely widely used in various areas of the national economy: in the electric power industry, in industry and transport, in aerospace systems and defense industries, in telecommunications, in utilities, in household appliances, etc. Moreover, in each of the areas, the range of the used range of devices is very wide. It can be definitely said that there is no area associated with the use of electrical energy, where electrical devices are not used.
The functioning of most types of electrical devices is based on the processes of switching (switching on and off) electrical circuits. The main phenomena accompanying the operation of any electrical apparatus include: the processes of switching electrical circuits, electromagnetic and thermal processes. Electromagnetic processes are understood as electromechanical and induction phenomena, electromagnetic interactions of the elements of the apparatus, etc.
Thermal processes have a direct impact on the operation of the apparatus and depend on the mode of operation of the apparatus. Three types of operating modes are installed for electrical devices:
- long-term (in this mode, with long-term passage of current, the apparatus heats up to a steady-state temperature);
- short-term (in this mode, when the state is off, between individual inclusions, the heating temperature of the apparatus is reduced almost to the ambient temperature);
- intermittent (the heating temperature during the current pause does not have time to drop to the ambient temperature).
The last two modes are characterized by the relative duration of the PV activation,%. Standard values ​​of duty cycle: 15; 25; 40; 60%.
1.2. Classification of electrical apparatus
An exceptionally wide range of fields of application of electrical devices determines the variety of types of their classification.
Electrical devices are classified according to the characteristics:
1) by the value of the operating voltage - low-voltage (up to 1000 V) and high-voltage (more than 1000 V);
2) by the value of the operating or switching current - low-current (control, protection, signaling devices) and high-current used in power circuits;
3) according to the function performed:
- switching devices: switches, disconnectors, contactors, magnetic starters;
- control, protection, signaling: relays of various types, travel and limit switches (contact and non-contact);
- command: control buttons, keys, command controllers and command devices;
- protection devices: arresters, fuses. Electric devices also include ballasts.
On the basis of switching and element base, electrical devices are divided into:
- electromechanical
- static
- hybrid.
Electromechanical devices are distinguished by the presence of moving parts. Electromechanical devices have movable and fixed contact systems that switch electrical circuits.
Static devices are made on the basis of power semiconductor devices: diodes, thyristors, transistors, as well as controlled electromagnetic devices: magnetic amplifiers, saturation chokes, etc. Devices of this type usually belong to power electronic devices, as they are used to control the flow of electrical energy.
Hybrid electrical devices are a combination of electromechanical and static devices.
By functional purpose, they are distinguished:
- control devices for NI and VN;
- low voltage switchgear devices;
automatic devices.
Electrical devices are also classified:
by voltage: LV devices - low (up to 1000 V) And HV devices - high (from units to thousands of kilovolts) voltage;
According to the value of the switched current: low-current devices (up to 5 A) and high-current (from 5 A to hundreds of kilo-amperes);
by the nature of the current: direct and alternating;
by the frequency of the power source: devices with normal (up to 50 Hz) and devices with increased (from 400 Hz to 10 kHz) frequency;
by the nature of the functions performed: switching, regulating, controlling, measuring, limiting current or voltage, stabilizing;
- according to the design of the switching body: contact and non-contact (static), hybrid, synchronous, without arc.
1.3. High voltage apparatus
Functionally, high-voltage devices are divided into the following types:
- switching devices (switches, load break switches, disconnectors);
- measuring devices (current and voltage transformers, voltage dividers);
- limiting devices (fuses, reactors, arresters, nonlinear surge arresters);
- compensating devices (controlled and uncontrolled shunt reactors);
- complete switchgears.
Electrical devices also include various types of sensors with a complete design. The purpose of the majority of sensors related to electrical devices is to convert parameters of physical quantities of different nature into electrical signals of an informational nature. Such sensors are widely used in various automatic control systems.
1.4. Electrical control devices
Electrical control devices are designed to control the operating mode of electrical equipment and are divided into the following types:
- contactors;
- starters;
- controllers;
- electrical control relays;
- command devices;
- knife switches;
- control electromagnets
- electrically controlled couplings.
Contactors are used for multiple switching on and off the electrical circuit at load currents not exceeding the rated one, as well as for rare shutdowns at overload currents (usually 7-10 times the rated one). The type of current determines the design features of the contactors. Therefore, AC and DC contactors are usually not interchangeable. However, there are contactors that combine the possibilities of switching both direct and alternating currents.
Starters are designed to turn on and off motors and differ from contactors mainly by the presence of a built-in system that protects motors from overload currents.
The controller is an electrical device with manual control, designed to change the connection diagram of the electric motor to the power supply system, as well as to switch the transformer windings.
Electric control relays work in automatic control circuits for electric drives. The switched currents do not exceed 10 A, and therefore arcing devices are not used in them.
Control devices are designed for switching in control circuits of power electrical devices (contactors, starters).
The switches are designed for almost the entire range of rated currents. The disconnection of the electrical circuit by a breaker is usually carried out in a de-energized state or at low currents.
Control electromagnets are used in actuators for various industrial purposes, as well as as an independent functional unit.
Electrically operated couplings are designed to transmit the flow of mechanical energy or torque
o the leading part of the coupling to its driven part.
Depending on the type of connection between the master and the slave
parts couplings are divided into three main types:
- electromagnetic clutches with mechanical coupling;
- electromagnetic powder clutches;
- induction couplings.
1.5. Switchgear devices
Low voltage switchgear devices (up to 1000 V) are designed to protect electrical equipment from various emergency modes associated with the occurrence of overload and short circuit currents, unacceptable voltage drop, the appearance of earth leakage currents in case of insulation damage, reverse currents, etc.). These devices are classified into circuit breakers and low voltage fuses.
Circuit breakers (circuit breakers) are switched on and off relatively rarely. Automatic devices for different rated currents are capable of disconnecting large short-circuit currents (up to 150 kA). In this case, the shutdown occurs with a pronounced current-limiting effect. The machines are usually equipped with complex contact-arc extinguishing devices.
Low-voltage fuses are used to protect electrical equipment against high overload currents and short-circuit currents. There are fuses with an open fusible link, closed fuses (the fusible link is located in the cartridge) and fuses with a filler, which is used as quartz sand, chalk, etc.
1.6. Electrical automatic devices
Electrical automatic devices are technical means by which various operations with signals are performed (receiving and collecting, reading, forming, processing, converting, addressing, comparing, storing, multiplying, changing the level, logical operations, etc.), if at least one of the signals (at the input or output of the apparatus) is electrical.
Corresponding operations with non-electrical or electrical signals are performed in the information processing path.
A signal is the information perceived or transmitted by the apparatus about a material or energy parameter. The real parameter is understood as the size, density, color, etc. Under the energy parameter - speed, pressure, temperature, voltage, current, abbreviation, efficiency.
Signals can be periodic and non-periodic, continuous and discrete.
The information processing path includes, as a rule, the following devices:
- primary converters (sensors) that convert the controlled (input, as a rule, non-electrical) quantity into an output electrical signal;
- distributors (switches) that distribute information in the form of electrical signals over various communication channels;
- adders, logic elements, regulating bodies that process information coming through various channels (inputs) in the form of electrical signals and generate a command (signal) for executive devices;
- executive bodies.
The latter type of devices includes the actual electrical relays of automation, electrohydraulic valves, electrohydraulic cranes, electrovalves, magnetic supports and suspensions, latches, etc.
Electrical relays of automation are devices for protecting electrical systems, networks and circuits, as well as other objects from unauthorized operating modes; to generate signals that notify of the approach of emergency situations and their occurrence; to amplify, multiply, process, encode and store incoming information.
The types of electrical relays of automation include reed relays, which are based on sealed magnetically controlled contacts (reed switches), as well as relay devices with mechanical control (input) and electrical output: buttons, keys, keyboards, toggle switches, microswitches.