General electrical engineering with basic electronics read online. General electrical engineering DjVu
Electric field. Basic Concepts
Every body contains a large number of elementary particles of matter with electrical charges1, for example: protons - positive charges, electrons - negative. Some of the elementary charged particles are part of the atoms and molecules of matter, others are in a free state. In a charged body, positive or negative charges predominate; in an electrically neutral body, the number of both charges is the same.
The electromagnetic field consists of two mutually connected sides - components: a magnetic field and an electric field, identified by the force action on charged elementary particles or bodies.
Oppositely charged bodies attract each other, similarly charged bodies repel each other. Each charge is inextricably linked with the electric field surrounding it, so that the interaction of charged bodies occurs through the electric field.
1 Electric charge is understood as a property of particles of matter or bodies that characterizes their relationship with their own electromagnetic field and their interaction with an external electromagnetic field. An electric charge contains a certain amount of electricity.
Since the electric field exerts a force on an electrically charged body or particle introduced into it, it is capable of doing work. Therefore, the electric field has energy, which is called electrical energy.
Electrically charged particles of matter and their electric field represent two inextricably linked trusses of matter.
Each point of the electric field is characterized by field strength.
The electric field strength is determined by the ratio of the force F with which the field acts on a point test charge q placed at a given point
A point test charge is a charged body whose linear dimensions are very small and whose charge, due to its smallness, practically does not distort the field under consideration.
When q is equal to unity (one coulomb), % is numerically equal to F, therefore, the electric field strength is numerically equal to the force of the aphid acting on a unit charge, i.e., electric charge, equal to one(one pendant).
The field strength is characterized not only by its magnitude, but also by its direction, which coincides with the direction of the field force acting on the positive charge located at a given point in the field. Therefore, field strength is a vector quantity.
In Fig. Figure 1-1 shows the electric field strength vector W between two parallel plates with charges +Q and -Q.
The electric field is graphically represented by electric field strength lines. The tension line is drawn so that at each point its field strength vector is directed along the tangent to it at that point. An electric field line starts at a positive charge and ends at a negative electric charge, so it is not closed.
If through each unit area (for example, 1 cm2), perpendicular to the direction of the line, draw
the number of lines is equal to or proportional to the field strength in this part, then the density of the strength lines can be used to estimate the magnitude of the field strength.
A field is called homogeneous if its intensity vectors are equal to each other at all points. An example is the electric field between parallel plates (Figure 1-1) in a region sufficiently distant from the edges of the plates.
Let us assume that a test positive charge q has moved in a uniform electric field under the influence of the forces of this field from point M to point H over a distance I (Fig. 1-2) in the direction of the field.
M.: Energy, 1972. - 504 p.: ill. The book discusses electrical circuits, electrical machines and transformers, electrical measurements and instruments, electric drive and control equipment, transmission and distribution electrical energy, vacuum tubes, gas-discharge devices, semiconductor devices, photoelectric devices, amplifiers and generators.
The book is intended for students of technical schools with non-electrical specialties. Contents: Electric field
Basic Concepts
Electrical voltage. Potential
Electrical conductivity
Electrical capacity. Capacitors
Connection of capacitors
Electric field energy
Dielectric polarizationElectrical insulating materials
Electrical circuits direct current
Electricity
Electrical value and its elements
Ohm's law
Electrical resistance and conductivity
Dependence of resistance on temperature
Conductor materials
Work and power
Converting electrical energy into heat Electrical load of wires and protecting them from
overload
Loss of voltage in wires
Kirchhoff's first law
Serial connection resistances—energy receivers
Parallel connection resistances - energy receivers
Mixed compound resistance
Two power supply modes
Kirchhoff's second law
Calculation of complex circuits
Chemical power sources
Connection of chemical power supplies
Nonlinear electrical circuits
Laboratory work. Line voltage loss
Electromagnetism
Magnetic field of current. Magnetic induction. Magnetic flux
Electromagnetic force
Interaction of parallel wires by drains
Magnetic permeability
Magnetic field strength. Magnetic voltage
Total current law
Magnetic field of a current coil
Ferromagnets, their magnetization and magnetization reversal
tion
Ferromagnetic materials
Magnetic circuit and its calculation
Electromagnets
Electromagnetic induction
Operating principle of an electric generator
Operating principle of the electric motor
Eddy currents
Inductance. Electromotive force of self-induction
Magnetic field energy
Mutual inductance
Electric machines permanent
Purpose of DC machines
Design of a DC machine
Working principle of DC machine
Armature winding device
Electromotive force of armature winding
Electromagnetic torque on the machine shaft
Mechanical power of DC machine
Armature reaction of DC machine
Current switching
Concept of ratings and characteristics
electric machines
Independently excited generator
Generator with parallel excitation
Mixed excitation generator
DC motors
Electric motor with parallel excitation Electric motor with independent excitation Electric motors with series and mixed
excitement
Losses and efficiency
Laboratory work. Electric motor with parallel excitation
Laboratory work. Generator with parallel excitation
Basic concepts related to alternating currents
Alternating current
Obtaining sinusoidal e. d.s
Phase shift
Effective values current and voltage
Vector diagram
Chains alternating current
Features of AC circuits
Circuit with resistance
Circuit with inductance
Circuit with active resistance and inductance Unbranched circuit with active resistances
and inductances
Branched circuit with active resistances and
inductances
Chain with capacity
Oscillatory circuit
Voltage resonance
Current resonance
Power factor
Active and reactive energy
Laboratory work. AC circuit with active resistance, inductance and capacitance Laboratory work. Parallel connection of coil and capacitor
Three-phase circuits
Three-phase systems
Star connection of generator windings
Connection of generator windings with a triangle
Connecting energy receivers with a star
Connecting energy receivers with a triangle. Laboratory work. Three-phase circuits
Electrical measurements and instruments
Basic Concepts
Classification of electrical measuring instruments
Measuring mechanisms of devices
Current and voltage measurement
Power measurement
Electrical Energy Measurement
Resistance measurement
Measurement of non-electrical quantities by electrical
methods
Laboratory work. Resistance measurement Laboratory work. Checking the induction meter
Laboratory work. Three-phase power measurement
Transformers
Purpose of transformers
Operating principle and design of a single-phase transformer
Single-phase transformer no-load
Operation of a loaded transformer and diagram
magnetomotive forces (mfs)
Transformer voltage change under load Power loss in the windings of a loaded transformer
Three phase transformer
Transformer voltage regulation
Autotransformers
Transformers for arc welding
Instrument transformers
Transformer efficiency
Heating and cooling of transformers
Laboratory work. Single phase transformer
AC Electrical Machines
Purpose of AC machines. Asynchronous
electric motors
Obtaining a rotating magnetic field
Stator winding of an asynchronous electric motor
Rotor winding of an asynchronous motor
Operating principle of an asynchronous motor
Electromotive forces in the stator and rotor windings
Rotor winding resistance
Currents in the rotor winding
Engine torque
Starting up asynchronous motors
Regulating the rotation speed of an asynchronous motor
Single phase asynchronous motor
Losses and efficiency of an asynchronous motor
Synchronous machines
Universal brushed motor
Laboratory work. Three-phase asynchronous electric motor
Electric drive and control equipment
Electric drive system
Heating and cooling of electrical machines
Selecting engine power for continuous
mode
Selecting engine power in short-term mode
Selecting engine power in intermittent mode
Switches
Batch switches
Rheostats for starting and regulating electric motors
Controllers
Fuses
Automatic air circuit breakers
Contactors
Relay
Control circuit for an asynchronous motor using a reversible magnetic starter
Connection diagram for a two-speed asynchronous motor
Automatic start of an asynchronous motor with rings
Automatic DC Motor Start
with parallel excitation
Laboratory work. Assembly and testing of the operation of a relay-contactor control circuit for a three-phase asynchronous motor with a squirrel-cage rotor
Electrical energy transmission and distribution
Power supply diagrams for industrial enterprises Transformer substations and distribution
devices of industrial enterprises
Electrical networks of industrial enterprises Protective grounding
Part two
Basics of Industrial Electronics
Two-electrode lamps and their use for rectifying alternating current
Classification and application electronic devices
Movement of electrons in an electric field
Movement of electrons in a magnetic field
Electronic emission
Cathodes of electrovacuum devices
Two-electrode vacuum tubes - diodes Application of two-electrode tubes
Three-electrode lamps. Four- and five-electrode lamps. Amplifiers
The design and principle of operation of a triode
Static characteristics of the triode
Triode parameters
The simplest amplification stage
Characteristics and parameters of the simplest cascade
gain
Types of triodes
Four-electrode lamps - tetrodes
Five-electrode lamps - pentodes
Combined and multigrid lamps. Types of lamps
General concepts related to amplifiers
Amplifier operating modes
Multistage tube amplifiers
Feedback in amplifiers
Laboratory work. Removing the anode and anode-grid characteristics of the triode and determining them
static parameters
Laboratory work. Removal frequency characteristics low frequency voltage amplifier
Gas discharge devices and their application
Types of gas discharge and its current-voltage characteristics
Ion devices with non-self-sustaining arc discharge
ELECTRICAL ENGINEERING WITH ELECTRONICS FUNDAMENTALS
for students of food specialties of the correspondence department
Reviewed and approved at a meeting of the cycle commission of teachers of special subjects of specialty 2-36 03 31 “Installation and operation of electrical equipment”
Protocol No. 2008
Chairman of the Commission /D.M. Gorokh/
Guidelines in the discipline "Electrical engineering with fundamentals of electronics"
Explanatory note
The discipline “Electrical engineering with fundamentals of electronics” consists of two parts.
Electrical engineering is a branch of science and technology associated with the use of electrical and magnetic phenomena for energy conversion, production and processing of materials, information transfer, covering issues of obtaining, converting and using electrical energy in practical human activities.
Electronics is the science of the interaction of elementary charged particles with electromagnetic fields and of methods for creating electronic instruments and devices in which this interaction is used to transmit, process and store information. The most typical types of such transformations are the generation, amplification and reception of electromagnetic oscillations in a wide range of frequencies.
Modern energy is the leading sector of the country's national economy in the development of scientific and technological progress and the intensification of social production.
Modern enterprises in the industry are highly mechanized farms equipped with the latest types of power equipment, effective means automation, reliable and economical power supply systems. All industrial enterprises are equipped with a variety of monitoring devices for each type of technological process, which significantly reduce and sometimes completely eliminate the output of low-quality products. Electronics tools and devices literally permeate all technological operations, providing high quality work of the enterprise.
Therefore, at present, a specialist of any profile must perfectly master theoretical and practical knowledge in the field of electrical engineering and electronics, without which he cannot successfully solve the most complex problems of modern production.
The subject “Electrical engineering with fundamentals of electronics” consists of two sections containing 14 topics.
The discipline program provides for the study of direct current electrical circuits, electromagnetism, single-phase and three-phase electrical circuits, and also studies electrical measurements, direct and alternating current machines. All these issues are covered in the first section of the subject.
In the second section of the discipline, electrovacuum and semiconductor devices, rectifier circuits, operating principles of amplifiers, and design are studied. integrated circuits.
This discipline is the theoretical basis for the study of subsequent disciplines of the special cycle; its study is based on the scientific material of physics and mathematics.
As a result of studying the program material the student must know :
At the presentation level:
¨ Electrical phenomena in DC circuits.
¨ The laws to which they obey.
¨ Operating modes of DC circuits.
¨ Issues of converting electrical energy into heat.
¨ Methods of connecting resistors.
¨ Basic magnetic quantities and their dimensions.
¨ Processes occurring during magnetization and remagnetization of ferromagnetic substances.
¨ The phenomenon of electromagnetic induction.
¨ Classification of electrical measuring instruments, their structure and principle of operation.
¨ Features of alternating current circuits.
¨ Features of three-phase alternating current circuits.
¨ Purpose, design and principle of operation of transformers and asynchronous motors.
¨ Introduce the features of DC machines.
¨ The operating principle of semiconductor devices and their areas of application.
At the level of understanding:
¨ Methodology for calculating DC circuits.
¨ Methodology of single- and three-phase alternating current circuits.
¨ Methodology for studying a transformer.
¨ Methodology for calculating power and selecting electric motors.
¨ Methodology for calculating rectifiers and selecting diodes for them.
The student must be able to:
¨ Draw diagrams simple connections electrical circuits and be able to assemble them.
¨ Be able to calculate the equivalent circuit resistance at in various ways resistor connections.
¨ Draw vector diagrams for the simplest circuits containing R, L and C and determine the currents in them.
¨ Create rectifier circuits
The student must be able to use reference and technical literature.
The material studied from the textbook must be noted down in a notebook. Basic definitions should be emphasized and formulas highlighted. Electrical circuits must be drawn in symbols that comply with current GOST standards.
After studying a topic, it is necessary to derive proofs of laws and formulas without the help of a textbook. Nothing should be left ununderstood when studying a subject; If you cannot overcome the difficulty yourself, then you need to seek advice from a teacher.
Serious attention should be paid to tasks and questions for self-test, as well as analysis of solutions to typical examples given in the textbook and in these recommendations.
Students must work systematically with textbooks; Long breaks disrupt the completion of the curriculum and reduce the quality of student work.
To consolidate theoretical knowledge and acquire practical skills and abilities, the subject program provides for 6 laboratory works.
To test students' knowledge, the program provides for completing one homework test work, which is performed after studying the entire theoretical course. Recommendations for completing the test in the correspondence department are given below.
Literature
1. Danilov I.A., Ivanov P.M. General electrical engineering with basics of electronics: Textbook for non-electrical engineering students. special secondary education establishments. 4th ed., trans. – M.: Higher. school, 2000. – 752 pp.: ill.
2. Uss L.V., Krasko A.S., Krimovich G.S. General electrical engineering with fundamentals of electronics Mn.: Vysh. school, 1990
3. Uss L.V. Laboratory workshop on general electrical engineering with the basics of electronics Mn.: Vysh. school, 1993
4. Evdokimov F.E. General electrical engineering: Textbook for students. non-electrical specialist. technical schools - 2nd ed. - M.: Higher school, 1990
5. Galkin V.I., Pelevin E.V. Industrial electronics and microelectronics. Educational-Mn.: Belarus, 2000
Approximate thematic plan
| No. | Name of sections and topics | Number of teaching hours | |||||
| For daytime | For correspondence | ||||||
| Total | Including | Total | Including | ||||
| Practical work | Laboratory works | Practical work | Laboratory works | ||||
| Introduction | - | - | - | - | - | ||
| 1. 1.1. 1.2. 1.3. 1.4. 1.5. 1.6. 1.7. | Fundamentals of Electrical Engineering DC Electrical Circuits Electromagnetism Single-Phase AC Circuits Three-Phase AC Electrical Measurements AC Machines DC Machines | - - - - - - - | - - - | - - - | - - - - - - - | - - - - - | |
| Total for the section: | - | - | |||||
| 2. 2.1. 2.2. 2.3. 2.4. 2.5. 2.6. | Fundamentals of electronics Electrovacuum and gas-discharge devices Semiconductor devices Photoelectronic devices Rectifiers Electronic amplifiers and generators Integrated circuits | - - - - - - | - - - - - - | - - - - - | - - - - - - | - - - - - - | |
| Total for the section | - | - | - | - | |||
| Total by discipline | - | - |
Introduction
Electrical energy, its properties, features and applications. The main stages of development of domestic electrical engineering. The role of electrification in development advanced technologies, automation technological processes. Brief summary of the subject. The importance of electrical engineering training for mid-level specialists for mastering new technologies of modern production.
Guidelines
Electrical energy is used in almost all areas of activity of modern society.
Energy is a general quantitative measure of various forms of motion of matter.
Electrical energy is obtained by converting other types of energy (mechanical, thermal, chemical, atomic) and has valuable properties: there are a large number of natural sources for its production; transmitted with low losses to long distance; easily crushed into arbitrarily small parts; easily converted to the right type energy.
Largest part Electricity for the needs of the national economy is generated at thermal power plants (TPP).
Thermal power plants are the main source of air pollution with sulfur dioxide emitted along with flue gases, which significantly worsens the environment.
Considering the rapid depletion of fossil fuel reserves and the adverse impact of thermal power plants on the environment, their share in the volume of electricity production is gradually decreasing.
In our country, hydroelectric power plants (HPPs) are in second place in terms of electricity production.
Nuclear power plants (NPPs) play a vital role in the energy sector.
To transmit electricity over a distance and distribute it between power receivers, power lines, transformers, control and protection equipment are used.
Electrical energy is widely used in industry, transport, agriculture and everyday life.
Questions for self-control
1. Name the main sources of electrical energy.
2. What non-traditional (renewable) sources of electrical energy do you know?
3. Name the main sectors of the national economy, the work of which involves the widespread use of electrical energy.
4. Explain the methods of producing electrical energy at thermal, nuclear and hydroelectric power plants.
5. Which power plants have the least negative impact on the environment?
Literature
Guidelines
The study of the topic begins with the electrical circuit and its elements.
An electrical circuit is a collection of devices and objects that form a closed path for the flow of electric current, electromagnetic processes in which can be described using the concepts of current, voltage, emf and resistance.
Electric current is the directed movement of charge carriers.
The current strength is determined by the amount of electricity (charge) passing through the cross-section of the conductor per unit time:
I = Q/t
The unit of current is ampere (A):
1A = 1C/1 s
Current Density (A/mm2)
I is the current in the conductor, A S is the cross-sectional area, mm 2.
Ohm's law for a section of a circuit: the current passing through a section of a circuit is directly proportional to the voltage U applied to this section and inversely proportional to its resistance R, i.e.
I=U/R
where U – in volts (V); R – in Ohms (Ohm).
Ohm's law for the entire circuit
I = E / (R+r)
where E is the electromotive force of the electrical energy source, V; R – external circuit resistance, Ohm; r – internal resistance source, Ohm.
Electrical resistance conductor
R=U/I
The reciprocal of the resistance is called conductivity G and is expressed in siemens (Sm), 1 Sm = 1/Ohm:
G= 1/R
Wire resistance
R = ρ l/S
where ρ – resistivity, Ohm mm 2 /m; l- conductor length, m; S is its cross-sectional area, mm 2.
Conductor resistance depends on temperature:
R2 = R1
where R 1 – conductor resistance at temperature t 1, Ohm; R 2 - conductor resistance at temperature t 2, Ohm; α is the temperature coefficient of resistance, numerically equal to the relative increase in resistance when the conductor is heated by 1 0 C.
Joule-Lenz law.
The amount of heat (J) released when a direct current passes through a conductor,
Q= I 2 R t
Q= 0.24 ·I 2 ·R·t
here Q is expressed in calories.
Kirchhoff's first law
The sum of currents directed to a node is equal to the sum of currents directed from the node, or the algebraic sum of currents at a node is zero:
I 1 + I 3 + … + I n = I 2 + I 4 + … + I k
where I 1, I 3, I n are currents directed to the node; I 2, I 4, I k - currents directed from the node.
The currents directed towards the node are recorded with the “+” sign, and the currents directed towards the node are recorded with the “-“ sign.
Kirchhoff's second law
In a closed circuit of an electric circuit, the algebraic sum of emf. equal to the algebraic sum of the voltage drops along the same contour:
∑E= ∑I R
When drawing up equations using this law, the emf. written with a “+” sign if its direction coincides with the selected direction of traversing the contour. Voltage drops are recorded with a “+” sign if the direction of the current through the resistor coincides with the selected direction of bypassing the circuit.
Topic 1.2. Electromagnetism
Magnetic field and its characteristics. Interaction of a magnetic field and a conductor with current. Electromagnetic force. Ferromagnetic substances and their magnetization. Magnetic permeability. Magnetization curves.
Magnetic circuit. Electromagnets and their application. Electromagnetic induction. Rule right hand. Lenz's law. Conversion of electrical energy into mechanical energy. Self-induction. Inductance. Eddy currents and their meaning.
Guidelines
Electromagnetic force.
On a conductor with current length l, located in a magnetic field, a force F acts perpendicular to the direction of the field, expressed in newtons (N):
If the current-carrying conductor is located at an angle α to the magnetic induction vector B, then
The direction of the electromagnetic force is determined by the left-hand rule.
Mechanical work Based on the movement of a conductor with current in a magnetic field at a distance a, it is calculated using the formula
where S is the area described by the conductor as it moves, m2.
Work is expressed in joules (J).
Total current law
Total current is the algebraic sum of currents passing through a surface bounded by a closed loop.
According to the law of total current, the magnetizing force F m (n.s.) along a closed loop is equal to the total current:
1. Strength H, (A/m), of the magnetic field at a point removed at a distance R from a straight conductor:
Magnetic induction
2. Magnetic field strength inside a conductor at a point removed from its axis by a distance a,
If a = R, then the tension on the surface of such a conductor
where R is the radius of the cylindrical conductor, m.
’
where R is the radius of the ring, m.
where R x is the radius from the center of the ring coil to the desired point, m.
Magnetic induction
where I is the current in the coil winding, A; w is the number of coil turns; l- length of the average magnetic line of the coil, m.
Magnetic induction
Magnetic flux
,
where S is the cross-sectional area of the coil, m2.
Electromagnetic induction
In a wire moving in a magnetic field and at the same time crossing magnetic lines, the electromotive force of electromagnetic induction is excited. This phenomenon is called electromagnetic induction:
where E is the emf. electromagnetic induction, V; B – magnetic induction, T; l- active conductor length, m; v- speed of conductor movement, m/s.
When a conductor moves in a plane located at an angle α to the magnetic induction vector,
Direction of the induced emf. determined by the right hand rule.
The instantaneous value of the electromotive force induced in the circuit is
where dФ/dt is the rate of change of magnetic flux.
E.m.f. induced in a coil with the number of turns w
where ψ – flux linkage, Wb; ψ=Ф w.
Inductance
The proportionality coefficient between the self-inductance flux linkage ψ L and the coil current I or circuit with a constant magnetic permeability of the medium is called inductance L and is expressed in henry (H):
The phenomenon of emf occurrence in a circuit caused by a change in current I in the same circuit is called self-induction, and the induced emf. – e.m.f. self-induction
Magnetic field energy
For a ring coil, the magnetic field energy W, expressed in joules (J)
Questions for self-control
1. What is magnetic flux? Magnetic induction?
2. What is MDS? Magnetic voltage? How are they directed?
3. How is the law of total current formulated?
4. What is the difference between diamagnetic, paramagnetic and ferromagnetic substances?
5. How does magnetization of ferromagnets occur? What properties do they have?
6. What is the difference between hard and soft magnetic materials?
7. Write a formula relating magnetic induction, tension and magnetic permeability.
8. How does an electromagnet work?
9. How is the work of electromagnetic forces calculated?
10. Formulate the principle of electromagnetic induction.
11. Formulate Lenz’s principle as applied to a contour.
12. What is self-inductance?
13. What are eddy currents? Where are they used?
Literature
§3.1-3.5, §3.7-3.17
Guidelines
Voltage resonance.
In an unbranched RLC circuit, when the reactive resistances are equal X L = X C, voltage resonance occurs:
ω·L= 1/(ω·C),
where does the angular resonant frequency come from?
resonant frequency
Impedance circuit at voltage resonance is equal to the active resistance and acquires a minimum value:
The current in the circuit, at a constant effective value of the input voltage U, has the greatest value and is in phase with the voltage, i.e. φ=0 and power factor cos φ=1.
At voltage resonance, the voltage drops U L and U C are in antiphase, equal to each other U L = U C and acquire a maximum value.
Questions for self-control
1. What values of alternating current do you know?
2. What is phase, initial phase, phase shift?
3. How to determine the phase lagging value?
4. What is a vector diagram called?
5. Which circuit elements have active resistance and which have reactive resistance?
6. What factors does it depend on? reactance?
7. Define active and reactive power. What is their difference?
8. What is voltage resonance? What are its characteristics?
Literature
Laboratory work No. 3 "Series connection of an inductor and a capacitor"
Literature: p.44-51
Guidelines
Guidelines
Measurement is finding the value of a physical quantity experimentally using special technical means.
To make a measurement, i.e. To compare the measured quantity with a unit of measurement, you must have this unit - a measure. A measure is a means of measurement designed to reproduce a physical quantity of a given size.
When making measurements, not only measures are used, but also measuring instruments, with the help of which the process of comparing the measured value with the unit of measurement is performed.
A measuring device is a measuring instrument designed to generate a signal of measuring information in a form accessible to direct perception by an observer.
Electrical measuring instruments are divided into two groups: direct evaluation devices and comparison devices.
Direct assessment devices (ammeters, voltmeters, ohmmeters, wattmeters, etc.) allow you to determine numeric value measured value using a reading device.
A comparison device (bridges, compensators) is used to compare the measured value with the measure. They are used to make more accurate measurements.
According to the principle of operation, all electrical measuring instruments are divided into devices of magnetoelectric, electromagnetic, electrodynamic, induction and other systems.
The instrument reading is the value of the measured quantity, determined by the reading made and the conversion factor (for example, the division price).
A count is a number read from the reading device of a measuring device (on a scale, digital display).
Measurement errors. Absolute error is the difference between the measured and actual value of the measured quantity:
where A meas – measured value; A is the actual value.
The absolute error is expressed in units of the measured value. The absolute error taken with the opposite sign is called the correction.
The relative error β is equal to the ratio of the absolute error ΔA to the actual value of the measured value and is expressed as a percentage:
The reduced error of a measuring device is the ratio of the absolute error to the nominal value. The nominal value for a device with a one-sided scale is equal to the upper limit of measurement, for a device with a double-sided scale (with a zero in the middle) - the arithmetic sum of the upper limits of measurement.
Highest value the reduced error in the operating range of the scale of the measuring device is called the main reduced error, expressed as a percentage and indicated on the scale of this device. Devices are divided according to the value of the main reduced error (accuracy class) into eight classes: 0.05; 0.1; 0.2; 0.5; 1.0; 1.5; 2.5 and 4.0.
Measurement of voltages and currents. Voltage measurements are made using a voltmeter connected in parallel to the section of the circuit on which the measurement is made.
To expand the measurement limits of a voltmeter on direct current, additional resistances are used; on alternating current, additional resistances and measuring voltage transformers are used.
The additional resistance is connected in series with the voltmeter:
where r d – additional resistance, Ohm; r V - voltmeter resistance, Ohm; m is a number showing how many times it is necessary to increase the measurement limit of the voltmeter.
Currents in branches are measured using ammeters connected in series to them.
To measure current greater than the rated value of the ammeter, shunts are used in DC circuits, and measuring current transformers are used in AC circuits.
A shunt is a resistance connected in series to the circuit being measured, and an ammeter is connected in parallel to it.
Shunt resistance:
where r a is the resistance of the ammeter, Ohm; n is the shunt coefficient, showing how many times the measurement limit of the ammeter with the shunt turned on increases.
Questions for self-control
1. What is measurement? What measurement methods do you know?
2. What are absolute and relative measurement errors?
3. What is the accuracy class of the device?
4. What is the operating principle of magnetoelectric system devices? Electromagnetic?
5. What is the operating principle of a wattmeter?
6. Explain the principle of operation of an induction meter.
7. How are power and energy measured?
8. What converters are called parametric?
Literature: §11.1-11.8, 11.11,11.14
Guidelines
Transformers. A transformer is a static electromagnetic device designed to convert alternating current of one voltage into alternating current of another voltage. The operating principle of the transformer is based on the phenomenon of electromagnetic induction.
The simplest transformer consists of a magnetic core (core) made of ferromagnetic material and two windings located on the cores of the magnetic core.
Effective values electromotive forces induced in the primary and secondary windings are determined by the formulas:
where E 1 and E 2 are the EMF of the primary and secondary windings, V; f – alternating current frequency, Hz; Ф m – amplitude value magnetic flux, Wb; ω 1 and ω 2 - the number of turns of the primary and secondary windings.
The ratio of the EMF of the windings, equal to the ratio of the number of turns of the windings, is called the transformation ratio:
The efficiency of a transformer at rated load is determined by the ratio of active powers at the output and input of the transformer:
where P 2 is the active power consumed by the transformer load, W; P 1 - active power supplied to the winding from the network, W; R k and R x – power losses at short circuit and idle, W; R e1 and R e2 - electrical losses in the primary and secondary windings, W.
The efficiency of a transformer at any load is determined by the formula:
where β=I 2 /I 2nom – load factor, defined as the ratio of the current in the secondary winding to the rated current of the secondary winding; S nom = U 1nom I 1nom – total power consumed by the transformer at rated load, VA; cosφ 2 – power factor of the secondary winding.
Asynchronous electric motors. Their work is based on the formation of a rotating magnetic field when a three-phase current flows through the windings of the stationary part of the machine - the stator. Magnetic field rotation frequency n 1, min -1
where f is the frequency of alternating current in the network, Hz; p – number of pole pairs in the winding.
The rotor of an asynchronous motor rotates with a frequency n 2, min -1, which in real conditions cannot reach the rotation frequency of the stator magnetic field.
Slip s is the ratio of the difference between the rotation frequency of the stator magnetic field and the rotation frequency of the rotor of an AC machine to the rotation frequency of the magnetic field:
Active power consumed by the motor from the network:
where U 1ph – phase voltage value, V; I 1ph – Phase current value, A; U 1 – linear voltage value, V; I 1 – linear current value, A; cosφ – phase angle between current and voltage (power factor).
Net power at the engine shaft:
where P 1e – electrical losses in the stator, W; P 2e - electrical losses of the rotor, W; Р 1м - losses in stator steel, W; Р 2м - magnetic losses of the rotor, W; Р mх – mechanical losses, W; R d - additional losses, W.
An important question The topic is the torque of the asynchronous motor M, Nm, which determines the ability of the motor to rotate the working machine:
Questions for self-control
- What is a transformer? What is its purpose?
- device and principle of operation of the transformer.
- What is the purpose of a transformer magnetic circuit?
- What determines the electrical and magnetic losses of a transformer?
- How can you increase the efficiency of a transformer?
- What is the transformation ratio?
- Explain the principle of operation of an induction motor.
- What determines the torque of an asynchronous motor?
- Draw the operating characteristics of an induction motor.
- What is sliding?
- How to change the direction of rotation of a three-phase asynchronous motor?
- Why starting current of an asynchronous motor significantly exceeds its rated current?
- What methods of starting asynchronous motors do you know?
- What is the purpose of magnetic starters?
References: §7.1 – 7.7, 8.1 – 8.11
Laboratory work No. 5 "Testing a single-phase transformer"
Literature: p.79-85
Laboratory work No. 6 " Testing a three-phase asynchronous motor with a squirrel-cage rotor"
Literature: p.96-101
Guidelines
DC machines are divided into generators and motors. The generator converts mechanical energy into electrical energy; The engine converts electrical energy into mechanical energy. Considering the principle of reversibility of electric machines, the same machine can be used both as a generator and as a motor.
DC electric motors can develop a large starting torque and allow smooth adjustment of the rotation speed over a wide range. Therefore, they are used as traction motors in all types of electric transport, in lifting devices, and in automated drives of complex units. In automation, DC machines are used as actuators, signal converters, and speed meters.
The design of a DC machine is basically the same as other electric machines. It has a stationary part - a stator (inductor), which consists of a frame, magnetic poles, bearing shields and bearings. Inside the stator there is a rotor (armature), consisting of an armature core, a commutator, a rotor shaft and a fan. The rotor is supported by bearings mounted in the side shields. The bed is the supporting part of the machine on which all other parts are placed. The main poles are attached to the frame from the inside. The pole consists of a core, a pole piece and an excitation winding. When direct current flows through the field winding, the main magnetic flux of the machine is created. The most important part DC machines are a collector assembled on a mandrel made of copper plates, insulated from each other with micanite. In the generator, the collector serves to rectify the alternating current induced in the armature winding during its rotation; in a DC motor, with the help of a collector, a current of a certain direction from the network enters that part of the armature winding that is in this moment is located under the pole, thereby ensuring continuous rotation of the armature.
For the generator to operate, a magnetic flux exciting the EMF is required. It can be created either by permanent magnets or electromagnetically.
Generators excited by permanent magnets (whose poles are permanent magnets) are called magnetoelectric.
In generators with electromagnetic excitation, the magnetic flux is created by the excitation current flowing through the field winding. There are generators with independent excitation, in which the excitation winding receives power from an external source of direct current energy, and self-excited generators, in which the excitation winding is powered from the generator itself.
Self-excited generators, in turn, are divided into: 1) parallel excitation generators (shunt), in which the excitation winding is connected parallel to the armature winding; 2) series excitation generators (serial), in which the excitation winding is connected in series with the armature winding; 3) mixed excitation generators (compound), having two excitation windings: one connected in parallel to the armature winding, and the other in series.
In practice, DC motors of both parallel and series excitation have become widespread.
When a DC motor is directly connected to the network at the rated voltage, its starting current turns out to be 10-15 times higher than the rated one, since the armature resistance is relatively small.
Due to large starting currents that can damage the armature winding, commutator and brushes, starting a DC motor by direct connection to the network is only permissible for low-power motors (less than 500 W), which have more significant armature resistances that limit the starting current. For P
6th ed. - M.: 2005.- 752 p.
The basics of calculating electrical circuits of direct and alternating current are outlined, a description of electrical machines, electronic devices, computers, etc. is given. New materials on integrated circuits, microprocessors and microcomputers are presented. For students of non-electrical specialties of secondary specialties educational institutions.
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TABLE OF CONTENTS
Preface 3
Introduction 5
Chapter I. Electric field 8
§ 1.1. Definition and representation of the electric field 8
§ 1.2. Coulomb's law. Electric field strength. 10
§ 1.3. Potential. Electrical voltage 13
§ 1.4. Conductors in an electric field. Electrostatic induction 16
§ 1.5. Dielectrics in an electric field. Dielectric polarization 18
§ 1.6. Electrical insulating materials 20
§ 1.7. Electrical capacity. Flat capacitor 23
§ 1.8. Connection of capacitors. Electric field energy 25
Chapter 2. DC electrical circuits 28
§ 2.1. Electric circuit 28
§ 2.2. Electric current 29
§ 2.3. EMF and voltage 32
§ 2.4. Ohm's Law 34
§ 2.5. Electrical resistance and conductivity 37
§ 2.6. Basic conductor materials and conductor products 39
§ 2.7. Dependence of resistance on temperature 41
§ 2.8. Methods of connecting resistances 42
§ 2.9. Electrical work and power. Conversion of electrical energy into heat 50
§ 2.10. Current load of wires and their protection from overloads 52
§ 2.11. Voltage losses in wires 55
§ 2.12. Two power supply modes 57
§ 2.13. Calculation of complex electrical circuits. 60
§ 2.14. Nonlinear electrical circuits 66
Chapter 3. Electromagnetism 69
§ 3.1. Characteristics of magnetic field 69
§ 3.2. Total current law 73
| 3.3. Magnetic field of rectilinear current 75
§ 3.4. Magnetic field of ring and cylindrical coils 78
§ 3.5. Magnetization of ferromagnetic materials.... 81
§ 3.6. Cyclic magnetization reversal 83
§ 3.7. Magnetic circuit calculation 86
§ 3.8. Electron in magnetic field 90
§ 3.9. Conductor with current in a magnetic field. Interaction of parallel conductors with current 93
§ 3.10. Law of electromagnetic induction 96
§ 3.11. Induction EMF in circuit 98
§ 3.12. Lenz Principle 101
§3.13. Conversion of mechanical energy into electrical energy 104
§3.14. Conversion of electrical energy into mechanical energy 106
§ 3.15 Flux linkage and inductance of the coil 108
§ 3.16. Self-induced emf. Magnetic field energy... 111
§ 3.17. EMF of mutual induction. Eddy currents 113
Chapter 4: Basic AC Concepts 116
§ 4.1. Defining, obtaining and depicting alternating current 116
§ 4.2. AC parameters 118
§ 4.3. AC phase. Phase shift 122
§ 4.4. Representing sinusoidal quantities using vectors.... 124
§ 4.5. Addition and subtraction of sinusoidal quantities. . 126
§ 4.6. Surface effect. Active resistance. 129
Chapter 5. Single-phase electrical circuits 131
§ 5.1. Features of electrical circuits 131
§ 5.2. Circuit with active resistance 132
§ 5.3. Circuit with inductance 134
§ 5.4. Circuit with active resistance and inductance. 138
§ 5.5. Chain with capacity 141
§ 5.6. Circuit with active resistance and capacitance 144
§ 5.7. Circuit with active resistance, inductance and capacitance 147
§ 5.8. Resonant mode of operation of the circuit 150
§ 5.9. Voltage resonance 150
§ 5.10. Branched chain. Conductivity method 154
§ 5.11. Current resonance 158
§ 5.12. Power factor 162
Chapter 6. Three-phase electrical circuits 164
§ 6.1. The principle of obtaining three-phase EMF. Basic connection diagrams for three-phase circuits 164
§ 6.2. Star connection of a three-phase circuit. Four- and three-wire circuits 169
§,6.3. Relationships between phase and linear voltages and currents with a symmetrical load in a three-phase circuit connected by a star 171
§ 6.4. Purpose of the neutral wire in a four-wire circuit 174
§ 6.5. Triangle load connection. Vector diagrams, relationships between phase and linear currents and voltages 176
§ 6.6. Active, reactive and apparent power of a three-phase circuit. Power factor 178
§ 6.7. Selecting connection diagrams for lighting and power loads when connecting them to a three-phase network 180
Chapter 7. Transformers 182
§7.1. Purpose of transformers and their application 182
§ 7.2. Transformer device 183
§ 7.3. Transformer EMF formula 187
§ 7.4. The operating principle of a single-phase transformer. Transformation ratio 188
§ 7.5. Three-phase transformers 191
* 7.6. Autotransformers and instrument transformers 193
§ 7.7. Welding transformers 196
Chapter 8. AC electrical machines 199
§ 8.1. Rotating magnetic field 199
§ 8.2. The device of an asynchronous motor 206
§ 8.3. Operating principle of an asynchronous motor. Physical processes occurring when the rotor spins. 209
§ 8.4. Slip and rotor speed 211
§ 8.5. The influence of slip on the EMF in the rotor winding... 213
§ 8.6. Dependence of current value and phase on slip and rotor EMF 215
§ 8.7. Torque of an asynchronous motor. 217
§ 8.8. Influence active resistance rotor windings on the shape of the dependence of torque on slip 220
§ 8.9. Starting an asynchronous motor 222
§ 8.10. Regulating the rotation speed of an asynchronous motor 225
§ 8.11. Efficiency and power factor of an asynchronous motor 227
§ 8.12. Single phase induction motor 230
§ 8.13. Synchronous generator 233
§ 8.14. Synchronous motor 236
Chapter 9. DC Electrical Machines 239
§ 9.1. Construction of DC electrical machines. Reversibility of the machine 239
§ 9.2. Operating principle of a DC machine 243
§ 9.3. The concept of armature winding. Collector and its purpose 248
§ 9.4. EMF induced in the armature winding 251
§ 9.5. Armature reaction 253
§ 9.6. Switching and ways to improve it. Additional poles, 256
§ 9.7. Independent excitation DC generators t 260
§ 9.8. Self-excited generators 264
§ 9.9. DC motors of independent and parallel excitation. Torque 269
§ 9.10. Mechanical and performance characteristics of DC motors of independent and parallel excitation 272
§ 9.11. Regulating the rotation speed of DC motors of independent and parallel excitation 275
§ 9.12. DC motors of series and mixed excitation 277
Chapter 10. Electrical and magnetic elements of automatic machines. 281
§ 10.1. Machines and automation 281
§ 10.2. Structure of the automatic control system. 283
§ 10.3. Devices for measuring signals in automatic systems 287
§ 10.4. Relay 292
§ 10.5. Magnetic amplifiers, their purpose and classification 295
§ 10.6. Operating principle of a magnetic choke amplifier. . 297
§ 10.7. Operating principle of transformer magnetic amplifier 301
§ 10.8. Effect of feedback and gain of magnetic amplifier 303
§ 10.9. Differential magnetic amplifier with bias windings 307
§ 10.10. Differential Magnetic Feedback Amplifier 310
§ 10.11. Magnetic amplifier assembled using a 312 bridge circuit
§ 10.12. Ferromagnetic voltage stabilizers. 315
Chapter 11 Electrical measurements and instruments 318
§ 11.1. Essence and meaning electrical measurements. . . 318
§ 11.2. Basic units of electrical and magnetic quantities in the International System of Units 320
§ 11.3. Derivatives and multiples 323
§ 11.4. Basic methods of electrical measurements. Errors of measuring instruments 324
§ 11.5. Classification of electrical measuring instruments. Symbols on the 327 scale
§ 11.6. Electrical measuring instruments for direct assessment 330
§ 11.7. Magnetoelectric system devices 333
§ 11.8. Electromagnetic system devices 336
§ 11.9. Electrodynamic system devices 338
§ 11.10. Digital devices 340
§ 11.11. Measurement of voltages, currents and power.... 342
§ 11.12. Expanding the measurement limits of direct assessment devices 345
§ 11.13. Power measurement in three-phase circuits 348
§ 11 14. Induction meter of electrical energy. Energy metering in single-phase and three-phase circuits.... 350
§ II 15. Resistance measurement. . 354
§ 11.16. Resistance measurement using a DC bridge. 357
§ 11.17. Magnetoelectric oscilloscope 359
Chapter 12. Transmission and distribution of electrical energy 362
§ 12.1. Purpose and classification electrical networks, their structure and graphic representation 362
§ 12.2. Wires, cables, electrical insulating materials in networks with voltages up to 1000 V 365
§ 12.3. Power supply for industrial enterprises. . . 368
§ 12.4. Voltage drop and loss in power supply lines 371
§ 12.5. Calculation of wires based on permissible voltage loss in direct, single-phase and three-phase current lines. ... 373
§ 12.6. Two-wire comparison single phase system energy transmission with three-phase systems according to the consumption of non-ferrous metal, . 376
§ 12.7. Calculation of wires based on permissible heating 379
5 12.8. Fuses.... 381
§ 12.9. Selection of fuse links 384
§ 12.10. Selecting the cross-sectional area of the wires depending on the installed fuses 386
§ 12.11. The effect of electric current on the human body. The concept of touch tension. Valid values touch voltage 387
§ 12.12. Protective grounding of three-wire three-phase current circuits. 390
§* 12.13. Protective grounding of four-wire three-phase current circuits 392
§ 12.14. Design and simple calculation of grounding conductors. . . 396
Chapter 13. Electric drive basics 398
§ 13.1. Concept of electric drive 398
§ 13.2. Heating and cooling of electric motors.... 400
§ 13.3. Operating modes of electric motors. Power selection 402
§ 13.4. Relay contactor control of electric motors 407
Chapter 14. Vacuum tubes 414
§ 14.1. General information 414
§ 14.2. Electronic emission 414
§ 14.3. Vacuum tube cathodes 417
§ 14.4. Movement of electrons in electric and magnetic fields 419
§ 14.5. Diodes 422
§ 14.6. Triodes. . . . , . 427
§ 14.7. Tetrodes 436
§ 14.8. Pentodes. Beam tetrodes 439
§ 14.9. Multi-electrode and combination lamps 441
Chapter 15. Gas-discharge devices 442
§ 15.1. The main types of electrical discharges in gas 442
§ 15.2. Gazotron... 446
§ 15.3. Thyratron 448
§ 15.4. Zener diode 451
§ 15.5. Gas-light signal lamps and indicators.... 453
§ 15.6. Symbols and markings of gas-discharge devices 455
Chapter 16. Semiconductor devices 457
§ 16.1. Atoms. - 457
§ 16.2. Energy levels and zones 463
§ 16.3. Conductors, insulators and semiconductors 465
§ 16.4. Electrical conductivity of semiconductors 469
§ 16.5. Electron-hole transition 477
§ 16.6. Semiconductor diodes 482
§ 16.7. Bipolar transistor 489
§ 16.8. Field effect transistors 499
§ 16.9. Thyristors 503
§ 16.10. Application areas of transistors and thyristors 508
Chapter 17. Photovoltaic devices 510
§ 17.1. Basic concepts and definitions 510
§ 17.2. Electronic photocells with external photoeffect 512
§ 17.3. Photomultiplier tubes 514
§ 17.4. Photoresistors 517
§ 17.5. Photodiodes 520
§ 17.6. Phototransistors. 523
Chapter 18. Electronic rectifiers 525
§ 18.1. 525 Rectifier Basics
§ 18.2. Half wave rectifier 526
§ 18.3. 529 Full Wave Rectifier
§ 18.4. Three-phase rectifier 531
§ 18.5. Thyristor rectifier. Voltage stabilizer 534
§ 18.6. Anti-aliasing filters. Rectification with voltage multiplication. 537
Chapter 19. Electronic amplifiers. . 541
§ 19.1. General information 541
§ 19.2. Preliminary stage ULF 545
§ 19.3. ULF output stage. 548
§ 19.4. Feedback in 551 amplifiers
§ 19.5. Interstage communications. DC Amplifiers 554
§ 19.6. Switching and selective amplifiers 558
Chapter 20. Electronic generators and measuring instruments 560
§ 20.1. General information 560
§ 20.2. Transistor oscillator type LC 561
§ 20.3. Transistor oscillator type RC 563
§ 20.4. Generator ramp voltage 565
§ 20.5. Multivibrator 569
§ 20.6. Cathode ray tubes 571
§ 20.7. Electronic oscilloscope 575
§ 20.8. Analog electronic voltmeter 578
§ 20.9. Digital electronic voltmeter 581
Chapter 21. Integrated circuits microelectronics 584
§ 21.1. General information 584
§ 21.2. Hybrid integrated circuits 586
§ 21.3. Thick film chips 589
§ 21.4. Thin film chips 591
§ 21.5. Photolithography 595
§ 21.6. Semiconductor integrated circuits. . . 597
§ 21.7. Planar-epitaxial technology for manufacturing IC 599
§ 21.8. Elements of semiconductor microcircuits and their connection 604
§ 21.9. Applications of 607 ICs
Chapter 22. Digital electronic computers. Microprocessors and microcomputers 610
§ 22.1. Number systems 610
§ 22.2. Converting numbers from one system to another 612
§ 22.3. Arithmetic operations with binary numbers 614
§ 22.4. Block diagram of digital electronic computer... 616
§ 22.5. Operating principle of the CEVM 619
§ 22.6. Triggers 621
§ 22.7. Logic elements 625
§ 22.8. Pulse counters. 628
§ 22.9. Registers. 631
§ 22.10. Adder 633
§ 22.11. Arithmetic unit 636
§ 22.12. Random Access Memory 641
§ 22.13. External storage devices 644
§ 22.14. Control unit 647
§ 22.15. Input devices 651
§ 22.16. Information output and display devices 654
§ 22.17. Concept of programming 657
§ 22.18. Specifications and application of the 660 computer
§ 22.19. Microprocessors 662
§ 22.20. Microcalculators 666
§ 22.21. Microcomputer 669
§ 22.22. Robotics 671
Consultations 674
Literature, 745
The structure of the proposed book meets the requirements for organizing training in automated classes equipped with technical means of self-control with a choice of answers. This book can be used for self-study even in the absence of technical means, which is important for correspondence educational institutions. In the latter case, the numbers indicated in brackets next to the number of each self-control card help to verify the correctness of the selected answers or detect an error.