Electric current Lecture plan 1. The concept of conduction current. Current vector and current strength. 2. Differential form of Ohm's law. 3. Serial 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, and charged particles.  If an electric field is created in a conductor, then free electric charges in it will begin to move - a current appears, called conduction current.  If a charged body moves in space, then the current is called convection.

 The direction of current is usually taken to be the direction of movement of positive charges. For the occurrence and existence of current it is necessary: ​​1. the presence of free charged particles; 2.presence of an electric field in the conductor.  The main characteristic of current is the current strength, which is equal to the amount of charge passing through the cross-section of the conductor in 1 second. Where q is the amount of charge; t – charge transit time; Current strength is a scalar quantity. I   q  t I  [  ] A Cl s

The electric current over the surface of a conductor can be distributed unevenly, so 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 change in current; S – change in area.

Current Density

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

We express from this formula R  B   R  U I   A Ohm 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.

Let us express :  SR  l     mOhm 2  m    mOhm   The resistance of the conductor depends on the 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

Let's rearrange the terms of the expression I S U 1   l Where I/S=j – current density; 1/= – specific conductivity of the conductor substance; U/l=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. Serial and parallel connection of conductors Serial 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 a circuit, it is necessary to separate positive and negative charges in the current source; for this, forces of non-electrical origin, called external forces, must act on the 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 through the circuit. Extraneous forces cause the separation of unlike charges and maintain a potential difference at the ends of the conductor. An additional electric field of external forces in a conductor is created by current sources (galvanic cells, batteries, electric generators).

EMF of a current source The physical quantity equal to the work of external forces to move a single 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 section of the chain 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 12 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 – internal resistance.  U ` A q U   1 where is the voltage across the external 2 resistance; A – work on moving charge q inside the current source, i.e. work on internal resistance.

Then since A  U  IUR , then Ir rt we 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 on 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. Kirchhoff's first and second rules The first Kirchhoff rule is the condition for constant current in the circuit. The algebraic sum of the current strength in the branching node is equal to zero n  0 iI where n is the number of conductors; i  1 Ii – currents in conductors. Currents approaching the node are considered positive, and currents leaving the node are considered 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 the point at which at least three conductors converge. The sum of the currents converging at a node is equal to zero - Kirchhoff’s first rule. I 4  0 0 Kirchhoff’s first rule is a consequence of the law of conservation of charge - 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 electrical circuit, the algebraic sum Ii of the resistance 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 create an equation, you need to select the direction of traversal (clockwise or counterclockwise). All currents coinciding in direction with the circuit bypass are considered positive. The EMF of current sources is considered positive if they create a current directed towards bypassing the circuit. So, for example, Kirchhoff’s rule for parts I, II, III. 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, the circuits are calculated.

7. Contact potential difference. Thermoelectric phenomena  Electrons, which have the greatest 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. There is a dynamic equilibrium between the electron gas in the metal and the “electron cloud”.  The work function of an electron is the work that must be done to remove an electron from a metal into airless space.  The surface of the metal is an electrical double layer, like a very thin capacitor.

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

Volta's laws:  1. When two conductors made of different metals are connected, 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 metal conductors connected in series at the same temperature does not depend on the chemical composition of the intermediate conductors. It is equal to the contact potential difference that arises when the outermost conductors are directly connected.

 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 TT contact between two metals. T  (a T b ) b In this case, a thermoelectromotive force appears in the closed circuit, 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 a medium whose temperature T1 needs to be measured, and the second junction is placed in a medium with a constant known temperature.  Thermocouples have a number of advantages over conventional thermometers: they allow you to measure temperatures in a wide range from tens to thousands of degrees of the absolute scale.

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

Gas ionization is the disintegration of a neutral atom into a positive ion and an electron under the influence of an ionizer (external influences - strong heating, ultraviolet and x-rays, radioactive radiation, bombardment of gas atoms (molecules) by fast electrons or ions). electron ion atom neutral

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

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

 1. Non-self-sustaining gas discharge is a discharge that exists only under the influence of external ionizers. Current-voltage characteristics 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=Uк I n Ne  0 saturation current Where e is the elementary charge; N0 is the maximum number of pairs of monovalent ions formed in the volume of gas in 1 s.

2. Self-sustaining gas discharge – a discharge in a gas that persists after the external ionizer stops operating. Maintained and developed due to impact ionization. A non-self-sustaining gas discharge becomes independent at Uз – ignition voltage. The process of such a transition is called electrical breakdown of the gas. There are:

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

Plasma is a special state of aggregation of a substance, characterized by a high degree of ionization of its particles. Plasma is divided 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 and plasma sources electrical energy, magnetodynamic generators.

 In solids, an electron interacts not only with its own atom, but also with other atoms of the crystal lattice, and the energy levels of the atoms are split to form an energy band.  The energy of these electrons can be found within shaded regions called allowed energy bands. Discrete levels are separated by areas of prohibited energy values ​​- forbidden zones (their width is commensurate with the width of the forbidden zones). The differences in the electrical properties of various types of solids are explained by: 1) the width of the energy gaps; 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 is 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 influence 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 a liquid by electrodes (“+” – anode, “–” – cathode). Positive ions (cations) move towards the cathode, negative ions move towards the anode.  The appearance of ions in electrolytes is explained by electrical dissociation - the disintegration of molecules of a soluble substance into positive and negative ions as a result of interaction with the 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  With the thermal movement of ions, the reverse process of reunification of ions, called recombination, also occurs. n 0 n 0

Contents of the lectureFormalities
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
2

Formalities

Lecturer:
Degtyarev Sergey Andreevich
Final examination:
Exam
Classes:
Lectures
Practice (a rating is compiled based on the results)
Reporting during the semester:
The rating is submitted to the dean's office 3 times per semester
(in October, in November, at the end of the semester)
Missing two or more classes in a row - memo to the dean's office
Homework is due at the next practical lesson
3

Formalities (continued)

Types of intermediate control:
Independent work - usually possible
use notes, study guides, etc.
Tests – 3 papers per semester; it is forbidden
use no reference materials;
unwritten tests are taken to the exam
Homework - assigned at each
practical lesson, must be passed
next practical lesson
4

Rating

Main indicators for calculating the rating
Average score
Completion percentage curriculum(percent
completed work – domestic, independent,
control)
Rating = (average score) x (percentage of completion)
Attendance
Rating may influence exam performance
assessment in controversial cases
5

Bibliography

Main literature:
Additional
literature:
6
Fundamentals of theoretical electrical engineering: Tutorial/ Yu. A.
Bychkov, V. M. Zolotnitsky, E. P. Chernyshev, A. N. Belyanin - St. Petersburg:
Publishing house "Lan", 2009.
Collection of problems on the fundamentals of theoretical electrical engineering:
Textbook / Under. ed. Yu. A. Bychkova, V. M. Zolotnitsky,
E. P. Chernysheva, A. N. Belyanina, E. B. Solovyova. – St. Petersburg:
Publishing house "Lan", 2011.
Fundamentals of Circuit Theory: Laboratory Workshop on
theoretical electrical engineering / Ed. Yu. A. Bychkova, E. B.
Solovyova, E. P. Chernysheva. St. Petersburg: Publishing house of St. Petersburg Electrotechnical University "LETI",
2012.
Handbook of Fundamentals of Theoretical Electrical Engineering: Educational
allowance / Under. ed. Yu. A. Bychkova, V. M. Zolotnitsky, E. B.
Solovyova, E. P. Chernysheva. – St. Petersburg: Lan Publishing House, 2012.
Savelyev I.V. Course of general physics. Book 2. Electricity and
magnetism
Beletsky A.F. Theory of linear electrical circuits
K. Tietze, U. Schenk Semiconductor circuit technology
Horowitz P., Hill W. - The Art of Circuit Design
MIT Open Course 6.002 OCW – http://ocw.mit.edu

Course Overview

Main topics of the course on theoretical foundations of electrical engineering (1
semester):
Calculation of resistive electrical circuits (circuit design)
Calculation of linear dynamic circuits (circuit design, theory
management)
Numerical calculation methods (computer processing
signals)
Calculation of linear dynamic circuits with sinusoidal
influences (circuitry, power supply circuits)
Operator method for calculating circuits - Laplace transform
(control theory)
Frequency characteristics (radio equipment, audio equipment, TV)
Calculation of three-phase circuits (power supply circuits)
Inductively coupled circuits (transformer technology,
power supply diagrams)
7

Course Overview

Main topics of the course on theoretical foundations of electrical engineering
(2nd semester):
Spectral methods for calculating circuits (radio engineering,
television, audiovisual equipment)
Active circuits and operational amplifiers
(circuitry, digital technology)
Long lines – circuits with distributed parameters
(microwave devices and antennas)
Discrete systems ( digital processing signals,
computer vision, digital devices and
microprocessors, systems on a chip, medical
technique)
Nonlinear systems (circuitry, audiovisual
technology, radio engineering)
8

Example

Incandescent lamp
Task: to simulate the behavior of an incandescent lamp in
electrical circuit
*image source: http://jeromeabel.net
9

Example (continued)

Connect the lamp to a voltage source
*image sources: http://jeromeabel.net, https://openclipart.org
10

Example (continued)

Target
Construct an object model suitable for
predicting its behavior with sufficient accuracy
Means to achieve the goal:
Consider only properties that are interesting to us and
object parameters (abstraction)
Use the simplest methods, accuracy
which are still enough to solve the problem (simplification
and idealization)
Use known mathematical methods For
building and using the model
11

Example (continued)

How much current will flow through the light bulb?
How long will the light bulb last on one battery?
What cross section should I choose for the wires to connect? Koreneva D. A.

Electrical Engineering (from Electrical... and Engineering)
- branch of science and technology related to
the use of electrical and magnetic
phenomena for energy conversion,
obtaining and changing chemical
composition of substances, production and processing
materials, information transfer,
covering issues of receipt,
conversion and use
electrical energy in practical
human activity.

Historical reference.

The emergence of electricity
preceded by a long period
accumulation of knowledge about electricity. Total
200 years ago the first experiments began on
practical applications of electricity, and
now it’s hard to imagine at least one
industry that is not used
Electric Energy.
We are proud that in development
electrical engineers made invaluable contributions
Russian scientists. Their work has always been
original, closely linked to practice
and had worldwide significance.

Historical reference.
1711-1765
Back in 1753 our
brilliant compatriot academician Mikhail
Vasilievich Lomonosov
in the speech “A Word about Phenomena”
air, originating from electric force,”
spoken in
Petersburg at the act
Academy of Sciences, outlined
my observations on
atmospheric electricity and made a series
theoretical and
practical conclusions.

Historical reference.
In my research
M. V. Lomonosov opened
physical nature of atmospheric electricity, indicated the possibility
protection against damage
lightning using a lightning rod, was the first to express the idea of ​​​​the electromagnetic nature of the northern
radiance, etc.

Historical reference.
1711-1753
Russian academician worked together with M.V. Lomonosov
Georg Wilhelm Richmann. He
began his research in
field of electricity in 1745
d. The credit belongs to him
creation of the first electrical device - the “electrical pointer”, which allowed
produce quantitative
electricity measurements. This
the device was used for
studying
atmospheric
electrical
phenomena.

Historical reference.
Russian scientist academician
F. W. Apinus in 1759
expressed the idea of ​​a connection
electrical and magnetic
phenomena. Among his
inventions include
electrophore (simplest
device for receiving
electricity) and
capacitor.
1724-1802

Historical reference.
1761-1834
Relying on Scientific research M. V. Lomonosova,
G. V. Richman, F. U. Epinus and
other scientists, academician
Vasily Vladimirovich
Petrov made the most important
discoveries in the field of practical applications of electricity. He built one of
largest galvanic batteries of its time and with
with her help a number of
outstanding research.

Historical reference.
In 1802 V.V. Petrov
received for the first time in the world
electric arc.
V.V. Petrov came up with the idea of ​​using
electric arc for
lighting. He wrote,
what with the help
open to them
electric arc
"dark peace is quite
be clearly lit
Maybe".

Historical reference.
V.V. Petrov first in
arc flame melted
metals, welded
pieces of metal. This
widely used
all over the world and in
our days.

Historical reference.
V.V. Petrov for the first time
applied insulation
metal
conductors. He
researched special
the glow of bodies, so
called
luminescence.

Historical reference.
His work on
generating electricity through friction
research
electrical
phenomena in gases
and many others.
In the TOE laboratory

Historical reference.
Contemporary V.V.
Petrova was famous
Russian scientist Pavel
Lvovich Shilling. In 1812
P. L. Schilling applied
electricity to explode
underwater mines Our
Motherland came first
the country in which he became
practically used
electromagnetic telegraph,
invented
P. L. Schilling in 1832
1786-1837

Historical reference.
1804-1865
1801-1874
Of particular note are the Russian academicians Boris
Semenovich Jacobi and Emilia Khristianovich
Lenza. Their discoveries are still widely used today
in various branches of electrical engineering.

Historical reference.
B. S. Jacobi created the first electric
engine. More than 170 years ago (in September 1838)
A boat with 14 passengers passed the Neva against the current. In this
the boat was equipped with an electric motor designed
B. S. Jacobi
together with
E. H. Lentz.

Historical reference.
Electroplating
B. S. Jacobi discovered in 1838
galvanoplasty and galvanostegy - the beginning of practical
whom the use of chemical
action of electric current; created the first direct-printing telegraph
apparatus (1850), proposed
underground insulation method
wires, invented the rheostat and
much
other.

Historical reference.
The widest
are famous
works by E. H. Lenz on
electromagnetism. He
formulated a rule
allowing to determine
direction
induced current in
conductor (Lenz's rule).
E. H. Lenz, regardless of
English physicist Joule
discovered thermal action
current (Joule-Lenz law).

Historical reference.
B. S. Jacobi and E. H. Lenz are considered the founders of the theory of electrical machines. They own
part of such a wonderful discovery as the phenomenon
"reversibility
machines", i.e.
ability
generator
to work in
quality
electric motor,
and vice versa.

Historical reference.
(1847-1894)
Talented inventor
Pavel Nikolaevich
Yablochkov using an arc
Petrova, gave the world the first
electric light - "candle"
Yablochkova." He's the first
understood the benefits
AC, and feel free
put it into practice. P.N.
Yablochkov designed and
practically used
transformers.

Historical reference.
Talented inventor
Pavel Nikolaevich Yablochkov
using Petrov's arc, gave
world's first electric
light - “Yablochkov’s candle”.
He was the first to understand
benefits of variable
current, and boldly introduced him into
practice. P. N. Yablochkov
designed and
practically used
transformers.

Historical reference.
(1847-1923)
The work of P. N. Yablochkov was continued by the inventor-compatriot Alexander Nikolaevich
Lodygin. In 1873 he creates
an electric incandescent lamp with a carbon filament, and in 1890 -
lamp with a metal thread.
A. N. Lodygin “the first
I took the incandescent lamp out of the physical office and onto the street.”

Historical reference.
(1839-1896)
The largest Russian scientist
Alexander Grigorievich
Stoletov in detail
explored magnetic
phenomena and discovered a series
laws used in
calculation of electrical
cars When researching
photovoltaic
created the effect
photocells.

Historical reference.
Almost simultaneously with P.N.
Yablochkov original
transformer design
suggested by Russian self-taught physicist Ivan Filippovich
Usagin. Demonstration
transformers Usagina on
industrial exhibition in 1882
in Moscow caused a “loud and
unanimous approval."
(1855-1919)

Historical reference.
Physicist Nikolay
Alekseevich Umov decided
(in 1874) the most difficult
problem of theory
electricity is a problem
electric movement
energy.
(1846-1915)

Historical reference.
Military electrical engineer Fedor Apollonovich
Pirotsky proposed using water flow to
obtaining electricity,
(1845-1898)
and also produced
numerous experiments on
electrical transmission
energy for large
distances.

Historical reference.
In 1874 he practically carried out
electrical power transmission
about 6 horsepower per distance
up to 1 km. F.A.
Pirotsky
created the first in the world
electric tram and
carried out successful
experience in using
this tram for
movement.
August 22, 1880 at 2 pm on Peski in St. Petersburg.

Historical reference.
Researching issues
transmission of electricity to
worked long distances
Dmitry Aleksandrovich
Lachinov. He also deeply researched the issues of parallel
inclusion of lamps in the circuit of one
generator
D. A. Lachinov invented the device
for power measurement
electric motors, introduced a number
significant changes in
design of floodlights, etc.
(1842-1902)

Historical reference.
(1862-1919).
The creator of the first three-phase gene
rator, motor and transformato
ra was an innovative engineer Mikhail
Osipovich Dolivo-Dobrovolsky. Thanks to inventions
M. O. Dolivo-Dobrovolsky
transfer became possible
electrical energy for large
distances with low losses and,
hence electrification
huge territories. He's the same
created devices such as
wattmeter, phase meter, frequency meter.

Historical reference.
The greatest discovery of modern times was the discovery
Alexander Stepanovich
Popova. This is a discovery
marked the beginning of a new
electrical engineering industries –
radio engineering.
Broadcasting, radio communications,
television, telecontrol,
radar, radio navigation would be
impossible without a brilliant discovery
A. S. Popova.
(1859-1906).

Historical reference.
The greatest discovery of our time
was the discovery of Alexander Stepanovich
Popova. This discovery marked the beginning
new branch of electrical engineering -
radio engineering.
Broadcasting, radio communications,
TV,
telecontrol,
radar,
radio navigation would be
impossible without genius
discoveries of A. S. Popov.

Historical reference.
Russian inventors
Nikolai Nikolaevich Benardos and
Nikolai Gavrilovich Slavyanov
used an electric arc for welding and
cutting metals.
(1842-1905)
(1854-1897)

Historical reference.
The growth of the electrical industry was facilitated by the unprecedented flowering of domestic and foreign science. Instead of lone scientists who carried out their scientific work in semi-makeshift laboratories during tsarism, scientists appeared working
in numerous research
institutes and academies.

Historical reference.
The greatest triumph
national science was launched
in 1954 the first in the world
industrial power plant
.
at the nuclear
.
useful energy
.
power
.
5000 kW.

Electricity is firmly established
into our lives. Not today
such areas of industrial and agriculture,
.
where not used.
would be electric.
energy. We can't
.
we're safe
.
exist without
.
electricity and
.
Houses.

All electrical appliances require
competent handling. Their
repair, maintenance and
operation is not possible
without knowledge of the basics of electrical engineering. Studying
electrical engineering impossible
without such fundamental
sciences like mathematics and
physics. Successful
mastering theoretical
basics of electrical engineering
will make learning easier
special disciplines on
senior courses.

Thank you for your attention

complex systems and networks":
Microprocessors and
microprocessor
systems;
Construction
computer facilities
Teacher-Ivanov Pavel
Vitalievich

Electrical engineering helps to master the disciplines.
For specialty 230101 “Computers,
complex systems and networks":
Peripheral
devices
Teacher - Sizova Olga
Alexandrovna

Electrical engineering helps to master the disciplines.
For specialty 230101 “Computers,
complex systems and networks":
Automatic
design
digital devices;
Design
automated
control systems;
Development
instrumental
funds
Teacher-Fedorov Alexey
Aleksandrovich

equipment":
Contactless
electric
devices
Teacher - Butorin Alexander
Grigorievich

Electrical engineering helps to master the disciplines. For specialty 140613 " Technical operation And
electrical and electromechanical maintenance
equipment":
Electrical
cars;
Electrical
equipment;
Electric
drive unit.
Teacher - Andreeva Leonella
Germanovna

Electrical engineering helps to master the disciplines. For specialty 140613 “Technical operation and
electrical and electromechanical maintenance
equipment":
Electricity supply
Automation
Teacher - Myasnikova Tatyana
Vyacheslavovna

Electrical engineering helps to master the disciplines. For specialty 140613 “Technical operation and
electrical and electromechanical maintenance
equipment":
Technical
exploitation
electrical and
electromechanical equipment;
Trial
reliability,
Adjustment of electrical and electromechanical
equipment;
Teacher - Zakharov Andrey
Mikhailovich

Electrical engineering helps to master the disciplines. For specialty 140613 “Technical operation and
electrical and electromechanical maintenance
equipment":
Structural processing technology
devices;
Control devices
Teacher - Svetlana Grigorieva
Valerievna

Contents Concept of electric current Physical quantities Electricity distribution Ohm's law IP degree IK degree

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

Concept of electric current How to create directed movement of charged particles? To maintain electric current in a conductor, it is necessary external source energy, which would always maintain a 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.

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

Concept of electric current Direct current (DC) Direct current is an electric current that does not change direction over time. Sources of direct current are galvanic cells, batteries and direct current generators. Alternating current (AC) An alternating current is an electric current whose magnitude and direction changes over time. The scope of application of alternating current is much wider than that of direct current. This is because the AC voltage can be easily lowered or raised using a transformer, within almost any range. 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 different points in an electrical circuit, causing the presence of electric current in it. Unit of measurement - Volt (V) 1 V = 1 J/C

Current strength (I) is a value equal to the ratio of the charge q passing through the cross section of the conductor to the time period t during which the current flowed. Unit of measurement: 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 current flowing through it. Unit of measurement - Ohm (Ohm)

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

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

Electricity 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 the Electromotive force of a source or voltage with the current and resistance of a conductor. Experimentally established 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. Formula Ohm's law for a section of a chain: I= U R

A diagram to help you remember Ohm's law. You need to close the desired value, and two other symbols will give the formula for calculating it. Ohm's law

IP and IK IP protection degree, consisting of two letters followed by two numbers. The IP code indicates the degree of protection against contact with live parts, penetration of foreign solids, and liquids. The IK protection level consists of two letters followed by two numbers. The IK code indicates the degree of protection against external mechanical shock.

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

IP degree 1. Protection against vertically falling drops of water (condensation) 2. Protection against drops of water falling at a vertical angle of up to 15° 3. Protection against spraying water at a vertical angle of up to 60° 4. Protection against spraying water from any side 5. Protection against low pressure water jets from all directions 6. Protection against powerful water jets and waves 7. Protection against liquid penetration during temporary immersion 8. Protection against liquid penetration during prolonged 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

Description of the presentation by individual slides:

1 slide

Slide description:

2 slide

Slide description:

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

3 slide

Slide description:

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

4 slide

Slide description:

The second stage of development of electrical engineering. 1820 – The magnetic effect of current was discovered (Hans Christian Ørsted) (Danish) – Danish physicist. 1821 – The law of interaction of electric currents was discovered (Andre-Marie Ampère) (French) – French physicist. 1827 – The fundamental law of the electric circuit was discovered (Georg Simon Ohm) (German) – German physicist. 1831 – The law of electromagnetic induction was discovered (Michael Faraday) (English) – English physicist. 1832 – The phenomenon of self-induction was discovered (Joseph Henry) (American) – American physicist. 1832 - Manufacturing of a direct current electric generator (Hippolyte Pixie) (French) - French instrument maker (commissioned by Andre-Marie Ampère (French) - French physicist.

5 slide

Slide description:

The second stage of development of electrical engineering. 1833 - A rule was formulated that determines the direction of the induction current (Emily Christianovich (Heinrich Friedrich Emil) Lenz) (German) - Russian physicist. 1838 - Invention of the first electric motor suitable for practical purposes (Boris Semenovich (Moritz Hermann von) Jacobi) (German) - Russian physicist. 1841 – 1842 – Determination of the thermal effect of current (James Prescott Joule) (English) – English physicist, (Heinrich Friedrich Emil) Lenz) (German) – Russian physicist. 1845 – Rules for calculating circuits were formulated (Gustav Robert Kirchhoff) (German) – German physicist.

6 slide

Slide description:

The third stage of development of electrical engineering. 1860-1865 - The theory of the electromagnetic field was created (James Clerk (Clark) Maxwell) (English) - English physicist. 1870 - Creation of the first electric generator that received practical application (Zenobe (Zinovy) Theophilus Gramm) (Belgian) - French physicist. 1873 – Invention of the electric incandescent lamp (obtaining a patent) (Alexander Nikolaevich Lodygin) (Russian) – Russian electrical engineer. 1876 ​​- Invention of the telephone (receipt of a patent) (Alexander Graham Bell) (English) - American physicist.

7 slide

Slide description:

The third stage of development of electrical engineering. 1876 ​​– Creation of a transformer for powering lighting sources (obtaining a patent) (Pavel Nikolaevich Yablochkov) (Russian) – Russian electrical engineer. 1881 – Construction of the first power transmission line (Marcel Depres) (French) – French physicist. 1885 – Invention of the radio receiver (Alexander Stepanovich Popov) (Russian) – Russian electrical engineer. 1886 – Invention of the radiotelegraph (Guglielmo Marconi) (Italian) Italian radio engineer. 1897 – The electron was discovered (Sir Joseph John Thomson) (English) – English physicist.

8 slide

Slide description:

The fourth stage of development of electrical engineering. 1904 - Invention of the tube diode (Sir John Ambrose Fleming) (English) - English physicist. 1906 – Invention of the tube triode (Lee de Forest) (English) – American physicist. 1928 – Invention of the field-effect transistor (receipt of a patent) (Julius Edgar Lilienfeld) Austro-Hungarian physicist. 1947 – Invention of the bipolar transistor (William Shockley, John Bardeen and Walter Brattain at Bell Labs) by American physicists. 1958 – Invention of the integrated circuit. (Jack Kilby (Texas Instruments) based on germanium, Robert Noyce (founder of Fairchild Semiconductor) based on silicon) American inventors.

Slide 9

Slide description:

Electrical engineering is the science of practical application electrical and magnetic phenomena. Electron from Greek. electron – resin, amber. All basic definitions related to electrical engineering are described in GOST R 52002-2003. Constant quantities are denoted in capital letters: I, U, E; time-varying quantities are written in lowercase letters: i, u, e. 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, determined for the electron and proton by equal numerical values ​​with opposite signs. Conventionally, a negative sign is assigned to the charge of the electron, and a positive sign to the charge of the proton. (-1.6*10-19 C)

10 slide

Slide description:

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

11 slide

Slide description:

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

12 slide

Slide description:

Direct current is a current at which the same charge is transferred during each equal period of time, i.e.: where I is the electric current, (A); q – charge, (C); t – time (s). Electric current intensity 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. Measured in N/C or V/m. An external force is a force acting on an electrically charged particle, caused by processes that are non-electromagnetic when viewed macroscopically. Examples of such processes are chemical reactions, thermal processes, the influence of mechanical forces, and contact phenomena.

Slide 13

Slide description:

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 of charge q (C) equal to 1 C. where E - (EMF) electromotive force, V; A – work of external forces when moving a charge (J); q – charge, (C). Electric voltage is a scalar quantity equal to the line integral of the electric field strength along the path under consideration. Determined for electric voltage U12 along the considered path from point 1 to point 2. Where ε is the electric field strength, dl is the infinitesimal element of the path, r1 and r2 are the radius vectors of points 1 and 2, i.e. voltage is the work of field forces with intensity ε spent on transferring a unit of charge (1 C) along path l. Potential difference is an electric voltage in an irrotational electric field, characterizing the independence of the choice of integration path.

Slide 14

Slide description:

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

15 slide

Slide description:

An element of an electrical circuit 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).

16 slide

Slide description:

In electrical energy sources different kinds Energy, for example chemical, mechanical, is converted into electrical (electromagnetic). In electrical energy receivers, a reverse conversion occurs - electromagnetic energy is converted into other types of energy, for example chemical (galvanic baths for smelting aluminum or applying a protective coating), mechanical (electric motors), thermal (heating elements), light (fluorescent lamps).

Slide 17

Slide description:

An electrical circuit diagram is a graphical representation of an electrical circuit containing symbols its elements and showing the connection of these elements. To collect circuits, schematic 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 compiled in accordance with GOST, for example: GOST 2.723-68 “ one system design documentation. Conditional graphic designations in schemes. Inductors, chokes, transformers, autotransformers and magnetic amplifiers” GOST 2.728-74 “Unified system of design documentation. Conditional graphic designations in schemes. Resistors, capacitors”

18 slide

Slide description:

Slide 19

Slide description:

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

20 slide

Slide description:

21 slides

Slide description:

22 slide

Slide description:

Slide 23

Slide description:

24 slide

Slide description:

Based on the type of current, circuits are divided into direct, variable and alternating current circuits. Direct current is an electric current that does not change over 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. a) b) c) Fig. 1.3. Types of currents in circuits.

25 slide

Slide description:

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 (volt-ampere characteristic) of sections of the circuit is presented in the form of a straight line (linear dependence) (Fig. 1.3. a). a) b) Fig. 1.3. Volt - ampere characteristics (VAC) of circuits. where U is voltage, (V); I – current strength, (A). The remaining circuits are called nonlinear (Fig. 1.3.b).

26 slide

Slide description:

Electrical resistance to direct current is a scalar quantity equal to the ratio of the direct electrical voltage between the terminals of a passive two-terminal network to the direct electric current in it. where R is the electrical resistance to direct current, (Ohm); ρ - resistivity, (Ohm*m); ℓ - conductor length, (m); S – cross-sectional area, (m2), where R – electrical resistance to direct current, (Ohm); U - voltage, (V); I – current strength, (A). A resistor is an element of an electrical circuit designed to use its electrical resistance. For wires, resistance is found by the formula:

Slide 27

Slide description:

The resistance of wires, resistors and other conductors of electric current depends on the temperature T environment Electrical conductivity (for direct current) is a scalar quantity equal to the ratio of direct electric current through a passive two-terminal network to the constant electric voltage between the terminals of this two-terminal network. Those. the reciprocal value of resistance where R is the electrical resistance to direct current, (Ohm); R20 – electrical resistance to direct current at a temperature of 20ºС, (Ohm); α is the temperature coefficient of resistance, depending on the material; T – ambient temperature, (ºС). where G is electrical conductivity, (Sm) (Siemens) or Ohm-1; U - voltage, (V); I – current strength, (A); R – electrical resistance, (Ohm).

28 slide

Slide description:

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

Slide 29