Lecture contentFormalities
Course Overview
Introduction to theoretical electrical engineering:
TOE is not difficult!
Basic definitions
Ohm's and Kirchhoff's laws
Classification of electrical circuits
Brief conclusions
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formalities

Formalities (continued)

Rating

Bibliography

Course Overview

Course Overview

Example

Example (continued)

Example (continued)

Example (continued)

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DC circuits

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Electrical engineering is the science of electrical phenomena, the production, transmission, distribution, transformation and use of electrical energy. The rapid development of electrical engineering is explained by the fact that electrical energy has a number of significant advantages compared to other types of energy. 1. Electrical energy is easily converted into other types of energy - thermal, mechanical, chemical (and vice versa). 2. Electrical energy can be easily transmitted through wires over long distances. 3. Electric energy is easy to bring to the consumer and spend in any quantity. 4. The efficiency of electrical installations is much higher than the efficiency of installations powered by other energy sources.

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The purpose of studying the discipline is to provide fundamental knowledge for the development of special disciplines and practical work in the operation of electrical devices in automotive technology. The objectives of the discipline are: the study of the basic laws of electrical engineering, the formation of the trainees' concepts of the theory of electrical circuits; study of the structure of electrical machines and electronic devices; mastering the methods of theoretical analysis and experimental study of electromagnetic processes; formation of ideas about the structure and principles of operation of electrical equipment used in transport and technological machines.

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At present, the basic concepts of electrical engineering are defined by: current terminological standards and recommendations of the International Electrotechnical Commission (IEC), International Electrotechnical Dictionary (IEC, 2nd edition, 1954, French and English); interstate standard GOST 19880 - 74 "Electrical engineering. Basic concepts. Terms and definitions"; Russian standard GOST R 52002 - 2003 “Electrical engineering. Terms and definitions of basic concepts.

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Table 1 - Basic concepts and their designations

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Table 2 - Multipliers and prefixes for the formation of decimal multiples and submultiples

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Table 3 - Some units of mechanical quantities in the SI system

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Table 4 - Some units of electrical quantities in the SI system

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Table 5 - Some units of magnetic quantities in the SI system

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Any electrical circuit contains sources of electrical energy, receivers (electrical loads), switching equipment, connecting lines and measuring instruments.

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The sources of electrical energy are electrical generators, in which mechanical energy is converted into electrical energy or primary cells and batteries, in which chemical, thermal, light and other types of energy are converted into electrical energy. Consumers of electrical energy include electric motors, heating and lighting devices, etc. An electrical circuit is a graphical representation of an electrical circuit. The equivalent circuit of an electric circuit consists of a set of various idealized elements chosen so that it is possible to describe the processes in the circuit with a given or necessary approximation.

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Conditionally - graphic designations in accordance with ESKD

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The circuit equivalent circuit configuration is determined by the following geometric (topological) concepts: branch, node, contour. A circuit branch consists of one or more series-connected elements, each of which has two outputs (beginning and end), and the beginning of the next is attached to the end of each previous element. Three or more branches are connected at a circuit node. A contour is a closed path passing through several branches so that no branch and no node occurs more than once. All consumers of electrical energy are usually characterized by some parameters.

Electric current Lecture plan 1. The concept of conduction current. Current vector and current strength. 2. Differential form of Ohm's law. 3. Series and parallel connection of conductors. 4. The reason for the appearance of an electric field in a conductor, the physical meaning of the concept of external forces. 5. Derivation of Ohm's law for the entire circuit. 6. Kirchhoff's first and second rules. 7. Contact potential difference. Thermoelectric phenomena. 8. Electric current in various environments. 9. Current in liquids. Electrolysis. Faraday's laws.

1. The concept of conduction current. Current vector and current strength Electric current is the ordered movement of electric charges. Current carriers can be electrons, ions, charged particles.  If an electric field is created in a conductor, then free electric charges will move in it - a current arises, called conduction current.  If a charged body moves in space, then the current is called convection.

 It is customary to take the direction of movement of positive charges as the direction of current. For the emergence and existence of current, it is necessary: ​​1. the presence of free charged particles; 2. the presence of an electric field in the conductor.  The main characteristic of the current is the strength of the current, which is equal to the amount of charge that has passed in 1 second through the cross section of the conductor. Where q is the amount of charge; t is the charge passage time; The current strength is a scalar value. I   q  t I  [  ] A Cl s

The electric current over the surface of the conductor can be unevenly distributed, therefore, in some cases, the concept of current density j is used. The average current density is equal to the ratio of the current strength to the cross-sectional area of ​​the conductor.  I  S   I  S dI dS j j  lim  S 0      A m 2     Where j is the current change; S - area change.

current density

2. The differential form of Ohm's law In 1826, the German physicist Ohm experimentally established that the current strength J in the conductor is directly proportional to the voltage U between its ends Where k is the proportionality factor, called electrical conductivity or I  Uk [k] = [Sm] (Siemens). conductivity; conductor size. R  Ohm 1 k is called the electrical resistance of Ohm's law for a section of an electrical circuit that does not I  containing a current source U R

We express from this formula R  V   R  U I   A Ohm The electrical resistance depends on the shape, size and substance of the conductor. The resistance of a conductor is directly proportional to its length l and inversely proportional to the cross-sectional area S R  l S Where  characterizes the material from which the conductor is made and is called the resistivity of the conductor.

We express :  SR  l     mΩ 2  m    mΩ   Conductor resistance depends on temperature. With increasing temperature, the resistance increases Where R0 is the resistance of the conductor at 0С; t – temperature;  – temperature coefficient of resistance RR  1(0 t) (for metal   0.04 deg1). The formula is also valid for resistivity Where 0 is the resistivity of the conductor at 0С.  1(0 t)

At low temperatures (<8К) сопротивление некоторых металлов (алюминий, свинец, цинк и др.) скачкообразно уменьшается до нуля: металл становится абсолютным проводником. Это явление называется сверхпроводимостью. Подставим  US  l I  U l  S

We regroup the terms of the expression I S U 1   l Where I/S=j is the current density; 1/= - specific conductivity of the conductor substance; U / l \u003d E - electric field strength in the conductor. i  E Ohm's law in differential form.

Ohm's law for a homogeneous section of a chain. Differential form of Ohm's law.   1   E  r    E j r j   j dS d  j dS l    I E d  E dS  

3. Series and parallel connection of conductors Series connection of conductors R1 R2 R3 I=const (according to the law of conservation of charge); U=U1+U2 Rtot=R1+R2+R3 Rtot=Ri R=N*R1 (For N identical conductors)

Parallel connection of conductors R1 R2 R3 U=const I=I1+I2+I3 U1=U2=U 1 R  2 1 R 1 R 1 R R 1 N For N identical conductors

4. The reason for the appearance of electric current in the conductor. The physical meaning of the concept of external forces To maintain a constant current in the circuit, it is necessary to separate positive and negative charges in the current source, for this, forces of non-electric origin, called external forces, must act on free charges. Due to the field created by external forces, electric charges move inside the current source against the forces of the electrostatic field.

Due to this, a potential difference is maintained at the ends of the external circuit and a constant electric current flows in the circuit. External forces cause separation of opposite charges and maintain a potential difference at the ends of the conductor. An additional electric field of external forces in the conductor is created by current sources (galvanic cells, batteries, electric generators).

EMF of the current source The physical quantity equal to the work of external forces to move a unit positive charge between the poles of the source is called the electromotive force of the current source (EMF). q   1 E А st q E A st  

Ohm's law for an inhomogeneous chain section A 12 A 12   A A  q  1      q E 12 1  2 2 1   A q   A E I t E q     1   2 2 12 U  A 12 q U      1 2 E

5. Derivation of Ohm's law for a closed electrical circuit Let a closed electrical circuit consist of a current source with , with internal resistance r and an external part with resistance R. R is external resistance; r is the internal resistance.  U ` A q U   1 where is the voltage at the external 2 resistance; A - work on moving the charge q inside the current source, i.e. work on the internal resistance.

Then since A  U  IUR , then Ir rt rewrite the expression for : A `  I 2 IR  Ir q  It ,  IR I 2 rt It Since according to Ohm’s law for a closed electric circuit ( =IR) IR and Ir - voltage drop in the external and internal sections of the circuit,

Then I    rR Ohm's law for a closed electrical circuit In a closed electrical circuit, the electromotive force of the current source is equal to the sum of the voltage drops in all sections of the circuit.

6. The first and second Kirchhoff's rules The first Kirchhoff's rule is the condition of constant current in the circuit. The algebraic sum of the current strengths in the branching node is equal to zero n  0 iI where n is the number of conductors; i  1 Ii – currents in conductors. The currents approaching the node are considered positive, leaving the node - negative. For node A, the first Kirchhoff rule will be written:  I 1 I 2 I  03

Kirchhoff's first rule A node in an electrical circuit is a point at which at least three conductors converge. The sum of the currents converging in the node is equal to zero - the first rule of Kirchhoff. I 4  0 0 Kirchhoff's first rule is a consequence of the law of conservation of charge - an electric charge cannot accumulate in a node. I 1  I 2   I 3  I i N  i 1

Kirchhoff's second rule Kirchhoff's second rule is a consequence of the law of conservation of energy. In any closed circuit of a branched electric circuit, the algebraic sum Ii on the resistances Ri of the corresponding sections of this circuit is equal to the sum of the EMF applied in it i n  i  1  i RI i  i n i  1

Kirchhoff's second rule

To draw up an equation, you must choose the direction of the bypass (clockwise or counterclockwise). All currents coinciding in direction with the loop bypass are considered positive. The EMF of current sources is considered positive if they create a current directed towards the bypass of the circuit. So, for example, the Kirchhoff rule for I, II, III k. I I1r1 + I1R1 + I2r2 + I2R2 = - 1 - 2 II -I2r2 - I2R2 + I3r3 + I3R3 = 2 + 3 III I1r1 + I1R1 + I3r3 + I3R3 = – 1 + 3 Based on these equations, circuits are calculated.

7. Contact potential difference. Thermoelectric phenomena  Electrons with the highest kinetic energy can fly out of the metal into the surrounding space. As a result of the emission of electrons, an “electron cloud” is formed. Between the electron gas in the metal and the "electron cloud" there is a dynamic equilibrium.  The work function of an electron is the work that must be done to remove an electron from a metal into a vacuum.  The surface of the metal is an electrical double layer, similar to a very thin capacitor.

 The potential difference between the plates of the capacitor depends on the work function of the electron. A e Where e is the electron charge;  - contact potential difference between the metal and the environment; A is the work function (electronvolt - EV).  The work function depends on the chemical nature of the metal and the state of its surface (contamination, moisture).

Volta's laws:  1. When connecting two conductors made of different metals, a contact potential difference arises between them, which depends only on the chemical composition and temperature.  2. The potential difference between the ends of a circuit consisting of series-connected metal conductors at the same temperature does not depend on the chemical composition of the intermediate conductors. It is equal to the contact potential difference arising from the direct connection of the extreme conductors.

 Consider a closed circuit consisting of two metal conductors 1 and 2. The EMF applied to this circuit is equal to the algebraic sum of all potential jumps.   (If the temperatures of the layers are equal, then =0.  If the temperatures of the layers are different, for example,   (TTT     1 a 2 b 2 a) 1 b) then a b a  Where  is a constant, characterizing the properties of the TT contact of two metals. T  (a T b ) b In this case, a thermoelectromotive force appears in the closed circuit, which is directly proportional to the temperature difference of both layers.

 Thermoelectric phenomena in metals are widely used to measure temperature. For this, thermoelements or thermocouples are used, which are two wires made of various metals and alloys. The ends of these wires are soldered. One junction is placed in the medium whose temperature T1 is to be measured, and the second junction is placed in the medium with a constant known temperature.  Thermocouples have a number of advantages over conventional thermometers: they allow measuring temperatures in a wide range from tens to thousands of degrees absolute.

Gases under normal conditions are dielectrics R=>∞, they consist of electrically neutral atoms and molecules. When gases are ionized, electric current carriers (positive charges) arise. Electric current in gases is called a gas discharge. To carry out a gas discharge to a tube with ionized gas, there must be an electric or magnetic field.

Gas ionization is the decay of a neutral atom into a positive ion and an electron under the action of an ionizer (external influences - strong heating, ultraviolet and X-rays, radioactive radiation, when atoms (molecules) of gases are bombarded by fast electrons or ions). electron ion atom neutral

 The measure of the ionization process is the intensity of ionization, measured by the number of pairs of oppositely charged particles that appear in a unit volume of gas in a unit period of time.  Impact ionization is the detachment from an atom (molecule) of one or more electrons, caused by a collision with atoms or molecules of a gas of electrons or ions accelerated by an electric field in a discharge.

Recombination is the union of an electron with an ion to form a neutral atom. If the action of the ionizer stops, the gas again becomes a dialectic. electro n ion

 1. A non-self-sustained gas discharge is a discharge that exists only under the action of external ionizers. Current-voltage characteristic of a gas discharge: as U increases, the number of charged particles reaching the electrode increases and the current increases to I=Ik, at which all charged particles reach the electrodes. In this case, U=Uk I n Ne  0 saturation current Where e is the elementary charge; N0 is the maximum number of pairs of univalent ions formed in the gas volume in 1 s.

2. Independent gas discharge - a discharge in a gas that persists after the termination of the external ionizer. It is maintained and developed by impact ionization. The non-self-sustained gas discharge becomes independent at Uz - ignition voltage. The process of such a transition is called electrical breakdown of the gas. Distinguish:

 Corona discharge - occurs at high pressure and in a sharply inhomogeneous field with a large curvature of the surface, is used in the disinfection of crop seeds.  Glow discharge - occurs at low pressures, used in gas-light tubes, gas lasers.  Spark discharge - at P = Ratm and at high electric fields lightning (currents up to several  thousand Amperes, length - several kilometers). E  Arc discharge - occurs between closely shifted electrodes, (T = 3000 ° C - at atmospheric pressure. It is used as a light source in powerful spotlights, in projection equipment.

Plasma is a special aggregate state of matter, characterized by a high degree of ionization of its particles. Plasma is subdivided into: - weakly ionized ( - fractions of a percent - upper layers of the atmosphere, ionosphere); – partially ionized (several %); - fully ionized (sun, hot stars, some interstellar clouds). Artificially created plasma is used in gas-discharge lamps, plasma sources of electrical energy, and magnetodynamic generators.

 In solids, an electron interacts not only with its own atom, but also with other atoms of the crystal lattice, the energy levels of atoms are split with the formation of an energy band.  The energy of these electrons can be within the shaded areas, called allowed energy bands. Discrete levels are separated by areas of forbidden energy values ​​- forbidden zones (their width is commensurate with the width of the forbidden zones). Differences in the electrical properties of various types of solids are explained by: 1) the width of the forbidden energy bands; 2) different filling of allowed energy bands with electrons

Many liquids conduct electricity very poorly (distilled water, glycerin, kerosene, etc.). Aqueous solutions of salts, acids and alkalis conduct electricity well.  Electrolysis - the passage of current through a liquid, causing the release of substances that make up the electrolyte on the electrodes. Electrolytes are substances with ionic conductivity. Ionic conductivity is the ordered movement of ions under the action of an electric field. Ions are atoms or molecules that have lost or gained one or more electrons. Positive ions are cations, negative ions are anions.

 An electric field is created in the liquid by electrodes (“+” – anode, “–” – cathode). Positive ions (cations) move towards the cathode, negative - towards the anode.  The appearance of ions in electrolytes is explained by electrical dissociation - the disintegration of solute molecules into positive and negative ions as a result of interaction with a solvent (Na + Cl; H + Cl; K + I ...).  The degree of dissociation α is the number of molecules n0 dissociated into ions, to the total number of molecules n0  During the thermal motion of ions, the reverse process of ion reunification occurs, called recombination. n 0 n 0

Electrical (electromagnetic) energy is one of the types of energies at the disposal of man. Energy is a measure of various forms of matter movement and the transition of matter movement from one type to another. The advantages of electrical energy include: - relative ease of production, - the possibility of almost instantaneous transmission over great distances, - simple methods for converting into other types of energy (mechanical, chemical), - ease of control of electrical installations, - high efficiency of electrical devices.

To mine 1 ton of coal or ore, it is necessary to spend about 20 kWh of electricity, and to enrich the ore to 1 ton of ferrous concentrate, about 90 kWh is needed, to smelt 1 ton of electric steel, about 2000 kWh. Such a large enterprise of KMA as Lebedinsky GOK consumes about kWh of electricity per month for its work 1960 1970 1980 1990 2000 2005. Totally produced (billion kWh) 30, At TPPs, % .2 At HPPs, %39.91214.2 At NPPs, %00.115.6 Electricity generation at power plants in Russia (RSFSR).

The prehistory of electrical engineering should be considered the period up to the 17th century. During these times, some electrical (attracting dust particles to amber) and magnetic phenomena (compass in navigation) were discovered, but the nature of these phenomena remained unknown. The 17th century should be considered the first stage in the history of electrical engineering, when the first research in the field of electrical and magnetic phenomena appeared. Based on these studies, in 1799 the first source of electric current was created by Alessandro Volt (Alessandro Giuseppe Antonio Anastasio Volta) (Italian) - “voltaic column” This source is now called a galvanic cell in honor of Luigi Galvani (Italian), which is one year did not live to see this discovery, but as a doctor, he did a lot to make this discovery

The second stage in the development of electrical engineering d. – The magnetic action of current was discovered (Hans Christian Oersted) (Dutch) – Danish physicist d. – The law of interaction of electric currents was discovered (Andre-Marie Ampère) (French) – French physicist d. – The fundamental law was discovered electrical circuit (Georg Simon Ohm) (German) - German physicist d. - Discovered the law of electromagnetic induction (Michael Faraday) (English) - English physicist d. - Discovered the phenomenon of self-induction (Joseph Henry) (Amer.) - American physicist d - Manufacture of a DC electric generator (Hippolyte Pixie) (French) - French toolmaker (commissioned by André-Marie Ampère (French) - French physicist.

The second stage in the development of electrical engineering d. - A rule was formulated that determines the direction of the induction current (Emily Khristianovich (Heinrich Friedrich Emil) Lenz) (German) - Russian physicist d. - Invention of the first electric motor suitable for practical purposes (Boris Semenovich (Moritz Hermann von) Jacobi) (German) - Russian physicist - 1842 - Determination of the thermal effect of current (James Prescott Joule) (English) - English physicist, (Heinrich Friedrich Emil) Lenz) (German) - Russian physicist d. - Rules formulated for calculating circuits (Gustav Robert Kirchhoff) (German) - German physicist.

The third stage in the development of electrical engineering d. - The theory of the electromagnetic field was created (James Clerk (Clark) Maxwell) (English) - English physicist d. - The creation of the first electric generator that received practical application (Zenobe (Zinovy) Theophilus Gramm) (Belgian) - French physicist d. - Invention of the electric incandescent lamp (obtaining a patent) (Alexander Nikolaevich Lodygin) (Russian) - Russian electrical engineer d. - Invention of the telephone (obtaining a patent) (Alexander Graham Bell) (English) - American physicist.

The third stage in the development of electrical engineering d. - Creation of a transformer for supplying current to lighting sources (obtaining a patent) (Pavel Nikolaevich Yablochkov) (Russian) - Russian electrical engineer d. - Construction of the first power line (Marcel Despres) (French) - French physicist d. - Invention of the radio receiver (Alexander Stepanovich Popov) (Russian) - Russian electrical engineer d. - Invention of the radiotelegraph (Guglielmo Marconi) (Italian) Italian radio engineer d. - Electron discovered (Sir Joseph John Thomson) (English) - English physicist.

The fourth stage in the development of electrical engineering d. - Invention of the tube diode (Sir John Ambrose Fleming) (English) - English physicist d. - Invention of the tube triode (Lee de Forest) (English) - American physicist d. - Invention of the field-effect transistor (obtaining a patent ) (Juli Edgar Lilienfeld) Austro-Hungarian physicist d. – Invention of the bipolar transistor (William Shockley, John Bardeen and Walter Brattain at Bell Labs) American physicists d. – Invention of the integrated circuit. (Jack Kilby (Texas Instruments) based on germanium, Robert Noyce (founder of Fairchild Semiconductor) based on silicon) American inventors.

Electrical engineering is the science of the practical application of electrical and magnetic phenomena. Electron from Greek. electron - resin, amber. All basic definitions related to electrical engineering are described in GOST R. Constant values ​​are denoted in capital letters: I, U, E, time-varying values ​​​​of quantities are written in lowercase letters: i, u, e. An elementary electric charge is a property of an electron or proton that characterizes their relationship with their own electric field and interaction with an external electric field, which is determined for an electron and a proton by equal numerical values ​​with opposite signs. Conventionally, a negative sign is attributed to the charge of the electron, and a positive sign to the charge of the proton. (-1.6* C)

An electromagnetic field is a type of matter determined at all points by two vector quantities that characterize its two sides, called "electric field" and "magnetic field", which has a force effect on electrically charged particles, depending on their speed and electric charge. The electric field is one of the two sides of the electromagnetic field, characterized by the impact on an electrically charged particle with a force proportional to the charge of this particle and independent of its speed. Magnetic field - one of the two sides of the electromagnetic field, characterized by the impact on a moving electrically charged particle with a force proportional to the charge of this particle and its speed.

A carrier of electric charges is a particle containing an unequal number of elementary electric charges of different signs. Electric current is a phenomenon of directed movement of electric charge carriers and (or) a phenomenon of changes in the electric field over time, accompanied by a magnetic field. In metals, charge carriers are electrons, in electrolytes and plasmas, ions. The value of the electric current through a certain surface S at a given moment of time is equal to the limit of the ratio of the electric charge q transferred by charged particles through the surface during a time interval t to the duration of this interval, when the latter tends to zero, i.e. where i - electric current, (A); q is the charge, (C); t is time (s).

Direct current - a current at which the same charge is transferred during each identical period of time, i.e.: where I - electric current, (A); q is the charge, (C); t is time (s). The electric current strength is a vector quantity that characterizes the electric field and determines the force acting on an electrically charged particle from the electric field. It is equal to the ratio of the force acting on a charged particle to its charge and has the direction of the force acting on a particle with a positive charge. It is measured in N/C or V/m. Extraneous force - a force acting on an electrically charged particle, due to non-electromagnetic processes in macroscopic consideration. Examples of such processes are chemical reactions, thermal processes, the impact of mechanical forces, contact phenomena.

Electromotive force; EMF is a scalar quantity that characterizes the ability of an external field and an induced electric field to cause an electric current. Numerically, the EMF is equal to the work A (J) performed by these fields when transferring a unit charge q (C) equal to 1 C. where E - (EMF) electromotive force, V; A is the work of external forces when moving the charge (J); q is the charge, (C). Electrical voltage is a scalar value equal to the linear integral of the electric field strength along the considered path. It is determined for electric voltage U 12 along the considered path from point 1 to point 2 voltage is the work of field forces with strength ε, spent on the transfer of a unit charge (1 C) along the path l. The potential difference is the electric voltage in an irrotational electric field, which characterizes the independence of the choice of the integration path.

Electric circuit - a set of devices and objects that form a path for electric current, electromagnetic processes in which can be described using the concepts of electromotive force, electric current and electric voltage. The simplest electrical circuit (wiring diagram).

An electrical circuit element is a separate device that is part of an electrical circuit and performs a specific function in it. The main elements of the simplest electrical circuit are sources and receivers of electrical energy. The simplest electrical circuit (wiring diagram).

In sources of electrical energy, various types of energy, such as chemical, mechanical, are converted into electrical (electromagnetic). In receivers of electrical energy, the reverse transformation occurs - electromagnetic energy is converted into other types of energy, for example, chemical (galvanic baths for aluminum smelting or protective coating), mechanical (electric motors), thermal (heating elements), light (fluorescent lamps). Sources of electrical energy Receivers of electrical energy Conductors

Electrical circuit diagram - a graphical representation of an electrical circuit containing the symbols of its elements and showing the connection of these elements. To collect circuits, circuit diagrams are used, where each element corresponds to a conventional graphic and letter designation, and for circuit calculations, equivalent circuits are used, in which real elements are replaced by calculation models, and all auxiliary elements are excluded. Schematic diagrams are drawn up in accordance with GOST, for example: GOST Unified system for design documentation. Conditional graphic designations in schemes. Inductors, chokes, transformers, autotransformers and magnetic amplifiers GOST Unified system for design documentation. Conditional graphic designations in schemes. Resistors, capacitors

Equivalent circuit - a diagram of an electrical circuit that displays the properties of the circuit under certain conditions. An ideal element (of an electric circuit) is an abstract representation of an element of an electric circuit, characterized by one parameter. An electrical circuit outlet is a point in an electrical circuit intended to be connected to another electrical circuit. A two-terminal network is a part of an electrical circuit with two dedicated terminals. Chains are simple and complex. In simple circuits, all elements are connected in series. In complex circuits, there are branches for current.

According to the type of current, the circuits are divided into direct, variable and alternating current circuits. Direct current - an electric current that does not change in time t (Fig. 1.3.a). All other currents are time-varying (Fig. 1.3.b.) or variable (Fig. 1.3.c.). An alternating current circuit is a circuit with a current that varies according to a sinusoidal law. I t I t t I a) b) c) Fig Types of currents in circuits.

Linear circuits include circuits in which the electrical resistance of each section does not depend on the value and direction of current and voltage. Those. the current-voltage characteristic (CVC) of the circuit sections is presented as a straight line (linear dependence) (Fig. a). a) b) Fig. Volt - ampere characteristics (CVC) of circuits. U I U I where U - voltage, (V); I - current strength, (A). The remaining circuits are called non-linear (Fig. 1.3.b).

The electrical resistance to direct current is a scalar value equal to the ratio of the constant electrical voltage between the terminals of a passive two-terminal network to the direct electrical current in it. where R is the electrical resistance to direct current, (Ohm); ρ - specific resistance, (Ohm*m); - conductor length, (m); S is the cross-sectional area, (m 2), where R is the electrical resistance to direct current, (Ohm); U - voltage, (V); I - current strength, (A). Resistor - an element of an electrical circuit designed to use its electrical resistance. For wires, the resistance is found by the formula:

The resistance of wires, resistors and other conductors of electric current depends on the ambient temperature T. Electrical conductivity (for direct current) is a scalar value equal to the ratio of direct electric current through a passive two-terminal network to a constant electrical voltage between the terminals of this two-terminal network. Those. the reciprocal of the resistance where R is the electrical resistance to direct current, (Ohm); R 20 - electrical resistance to direct current at a temperature of 20ºС, (Ohm); α - temperature coefficient of resistance, depending on the material; T is the ambient temperature, (ºС). where G - electrical conductivity, (Cm) (Siemens) or Ohm -1; U - voltage, (V); I - current strength, (A); R - electrical resistance, (Ohm).

Flux linkage is the sum of magnetic fluxes linked to the elements of the circuit of an electric circuit. Flux linkage of self-induction - flux linkage of an element of an electrical circuit, due to electric current in this element. Intrinsic inductance is a scalar value equal to the ratio of the flux linkage of the self-induction of an electrical circuit element to the electric current in it. where Ψ is the flux linkage, (Wb); m is the number of turns; Ф – magnetic flux (Wb). where L - inductance, (H); Ψ – flux linkage, (Wb); I - current strength, (A).

An inductive coil is an element of an electrical circuit designed to use its own inductance and (or) its magnetic field. The voltage at the terminals of the coil is equal to the product of the inductance and the rate of change of current through it. where u L is voltage, (V); L - inductance, (H); i - current strength, (A). The current through the coil is directly proportional to the integral of the voltage and inversely proportional to the inductance of the coil. where i L is the current strength, (A); L - inductance, (H); u - voltage, (V).

The inductance of a single-layer solid wound coil can be determined by the empirical formula: Inductance of a multilayer coil: where L is the inductance, (uH); D is the coil diameter, (cm); ω is the number of coil turns; - winding length, (cm); t is the thickness of the winding, (cm).

The electrical capacitance of a conductor is a scalar quantity that characterizes the ability of a conductor to accumulate an electric charge, equal to the ratio of the electric charge of the conductor to its electric potential, assuming that all other conductors are at infinity and that the electric potential of an infinitely distant point is taken equal to zero. The electrical capacitance between two conductors is a scalar value equal to the absolute value of the ratio of the electric charge of one conductor to the difference in the electric potentials of two conductors, provided that these conductors have the same charge, but opposite in sign, and that all other conductors are at infinity. where C is the capacitance, (F); q - charge, (C); Uc is the voltage between the terminals of the capacitor, (V).

The electric capacitance of a capacitor is the electric capacitance between the electrodes of an electric capacitor. For a flat capacitor with two plates (plates), the capacitance is: where C is the capacitance, (pF); S is the area of ​​the capacitor plates, (cm2); d is the distance between the capacitor plates (dielectric width), (cm); ε is the permittivity of the dielectric (vacuum and air = 1; amber = 2.8; dry pine = 3.5; marble = 8-10; ferroelectric ceramics =). An electrical capacitor is an element of an electrical circuit designed to use its electrical capacitance.

Where u С is voltage, (V); C - capacity, (F); i - current strength, (A). The equivalent current through a capacitor is directly proportional to the capacitance of the capacitor and the rate of change of voltage across its plates. where C - capacity, (F); i C - current strength, (A). u is voltage, (V). The voltage at the terminals of the capacitor will change in direct proportion to the integral over the current and inversely proportional to the capacitance of the capacitor.

A section of an electric circuit is a part of an electric circuit containing a selected set of its elements. A branch of an electrical circuit is a section of an electrical circuit along which the same electric current flows (section a-b, b-d, b-d). Node of the electrical network - the junction of the branches of the electrical circuit (a, b, c, c, d, d). The contour of an electrical circuit is a sequence of branches of an electrical circuit that forms a closed path, in which one of the nodes is both the beginning and end of the path, and the rest meet only once (section a-b-d-c-a). E1E1 R2 R3 E2E2 R4 R5 E4 R7 ab c d R6 c d R1

Each device in the electrical circuit can correspond to several equivalent circuits. The type and parameters of the circuit depend on the features of many factors, for example, on the design of the device, operating mode, frequency of the acting signal, the required accuracy of calculations, the assumptions made

Contents The concept of electric current Physical quantities Distribution of electricity Ohm's law Degree IP Degree IK

The concept of electric current Electric current is the directed movement of electrically charged particles. Is it electric current?

The concept of electric current How to create a directed movement of charged particles? To maintain an electric current in a conductor, an external source of energy is needed, which would constantly maintain the potential difference at the ends of this conductor. Such energy sources are the so-called sources of electric current, which have a certain electromotive force (EMF), which creates and maintains a potential difference at the ends of the conductor for a long time.

The concept of electric current Is it possible for charged particles to move in all substances? Conductor Semiconductor. A dielectric is a body that contains a sufficient amount of free electric charges that can move under the influence of an electric field; this is a body that does not contain free electric charges inside. In insulators, electric current is impossible metals, solutions of salts and acids, moist soil, bodies of people and animals glass, plastic, rubber, cardboard, air is a material that conducts current, only under certain conditions silicon and alloys based on it

The concept of electric current Direct current (DC) Direct current is an electric current that does not change in time in direction. DC sources are galvanic cells, batteries and DC generators. Alternating current (AC) AC is called an electric current, the magnitude and direction of which change over time. The scope of alternating current is much wider than direct current. This is because the AC voltage can be easily stepped up or down with a transformer, almost anywhere. Alternating current is easier to transport over long distances.

Physical quantities Voltage Current Resistance Frequency Active power Reactive power Apparent power

Voltage (U) between two points is the potential difference at various points in an electrical circuit, which determines the presence of an electric current in it. Unit of measure - Volt (V) 1 V \u003d 1 J / C

Current strength (I) - a value equal to the ratio of the charge q passed through the cross section of the conductor to the time interval t during which the current flowed. Unit of measure - Ampere (A)

Resistance (R) is a physical quantity that characterizes the properties of a conductor to prevent the passage of electric current and is equal to the ratio of the voltage at the ends of the conductor to the strength of the current flowing through it. Unit of measure - Ohm (Ohm)

Frequency (f) - determines the number of current oscillations per second. Unit - Hertz (Hz) 50 Hz

Power Electrical power is a physical quantity that characterizes the rate of transmission or conversion of electrical energy. W VAR VA Q = U ∙ I ∙ sin φ P = U ∙ I ∙ cos φ S=U ∙ I

Power distribution Line voltage (U l) is the voltage between two phase wires (380 V) Phase voltage (U f) is the voltage between the neutral wire and one of the phase wires (220 V)

Ohm's Law: A physical law that defines the relationship between a source's Electromotive Force or voltage with current and conductor resistance. Experimentally installed in 1826, and named after its discoverer Georg Ohm. The essence of the law is simple: the current generated by the voltage is inversely proportional to the resistance that it has to overcome, and is directly proportional to the generating voltage. Ohm's law formula for a chain section: I \u003d U R

Diagram to help remember Ohm's law. You need to close the desired value, and the other two characters will give a formula for calculating it. Ohm's law

IP and IK Degree of protection IP consisting of two letters followed by two numbers. The IP code indicates the degree of protection against contact with conductive parts, the ingress of foreign solids, as well as liquids. The degree of protection IK consists of two letters followed by two numbers. The IK code indicates the degree of protection against external mechanical shocks.

IP rating 1. Protection against ingress of solid objects larger than 50 mm (example: accidental contact with the hand) 2. Protection against ingress of solid objects larger than 12 mm (example: contact with fingers) 3. Protection against ingress of solid objects larger than 2, 5 mm (example: contact with tools, wires) 4. Protection against ingress of solid bodies larger than 1 mm (example: contact with small tools, thin wires) 5. Protection against ingress of dust (harmless deposits) 6. Fully dustproof0. No protection

IP rating 1. Protection against vertically falling drops of water (condensation) 2. Protection against drops of water falling at a vertical angle up to 15° 3. Protection against water spray at a vertical angle up to 60° 4. Protection against water spray from any direction 5. Protection against low pressure water jets from all directions 6. Protection against powerful water jets and waves 7. Protection against ingress of liquid during temporary immersion 8. Protection against ingress of liquid during continuous immersion under pressure 0. No protection

Grade IK 01 - Impact energy 0.150 J 02 - Impact energy 0.200 J 03 - Impact energy 0.350 J 04 - Impact energy 0.500 J 05 - Impact energy 0.700 J 06 - Impact energy 1.00 J 07 - Impact energy 2.00 J 08 - Impact energy 5.00 J 09 - Impact energy 10.00 J 10 - Impact energy 20.00 J