» basic principles of general electrical engineering.
Topic: basic principles of general electrical engineering, electrical engineering for a beginner.
Before becoming an electrician, you first need to know the theoretical basis of how electricity works. After all, what is the difference between an electrician and an ordinary person? And the fact is that, due to the theory, which over time has been reinforced by practical experience, a person from an ordinary “know-no” turns into an experienced electrical engineer, fully capable of understanding not only faulty electrical devices, but also who will be able to make a homemade “device”. Such an electrician can be entrusted with any task related to his profession, and he will easily cope with this task without any difficulties.
Electrical engineering for beginners is a cognitive path, gradually passing through which a person gains professional experience. Don’t think that after reading a book on the general theory of electrical engineering you can immediately learn how to do everything. Even knowing “how to do it”, people in most cases are either afraid to start (knowing about the dangers of electricity), or they do it so awkwardly and carelessly that later it is better to redo this work in order to avoid emergency consequences associated with the quality of operation of this device, and potential for poor electrical safety.
The basics of general electrical engineering are the basics, telling the student what and how it generally works. For example, a person can be given ready-made instructions “what and how to do consistently.” A capable person will be able to do certain work according to this plan, and it will be completely correct. But if such a person has to face a case in which there are some previously unknown aspects (some electrical equipment has suddenly broken down and which needs to be promptly repaired), then such a situation will cause a slight stupor, fussy behavior, and many incorrect and erroneous actions (and this loss of time, energy and nerves).
Electrical engineering for beginners, namely the basics of general electrical engineering, should begin with the simplest laws of physics (section of electrical engineering). A beginner must learn what electricity is, what its properties are, what dangers it carries, protective measures and precautions, etc. Knowledge of this already gives a general idea of electricians, as such. By first introducing a person to special subjects that are difficult to understand (for example, automation, signal theory, etc.), the main thing is missed, namely the assimilation of basic concepts in figurative language. A “porridge” of a lot of fragmented knowledge forms in the head, which is very difficult to assemble into a general model of how electricity works, even for a smart person.
An important factor that greatly influences the quality of electrical engineering training for beginners is interest and practice. What do you think is better for beginners to learn, “dry theory”, or step-by-step training, in which some theoretical knowledge is first given in a small dose, followed by practical consolidation (much like in chemistry lessons - they talked about the interaction of substances and showed a clear example of how it works). Even having assembled the simplest electrical circuit, consisting of a power source, a light bulb, a switch, a rheostat, and meters, a person will immediately feel what’s what, rather than simply drawing the same thing on the board and dryly talking about the circuit.
P.S. I would advise you to delve more into the basic principles of how electricity works; knowing and understanding them well, then more complex concepts will be given much easier and clearer. Try to independently understand the principles of operation of the simplest circuits and the operation of electrical components. After all, complex circuits are many smaller, simpler circuits combined together.
Everything that will be given in this lesson, you must not only read and remember some key points, but also memorize some definitions and formulations. It is with this lesson that elementary physical and electrical calculations will begin. Perhaps not everything will be clear, but there is no need to despair, everything will fall into place over time, the main thing is to slowly assimilate and remember the material. Even if not everything is clear at first, try to at least remember the basic rules and those elementary formulas that will be discussed here. Having thoroughly mastered this lesson, you will then be able to perform more complex radio engineering calculations and solve the necessary problems. You can’t do without this in radio electronics. In order to emphasize the importance of this lesson, I will highlight all formulations and definitions that need to be memorized in red italics.
ELECTRIC CURRENT AND ITS ASSESSMENT
Until now, when characterizing the quantitative value of electric current, I have sometimes used terminology such as, for example, small current, large current. At first, such an assessment of the current somehow suited us, but it is completely unsuitable for characterizing the current from the point of view of the work that it can perform. When we talk about the work of current, we mean that its energy is converted into some other type of energy: heat, light, chemical or mechanical energy. The greater the flow of electrons, the greater the current and its work. Sometimes they say amperage or simply current. Thus the word current has two meanings. It denotes the very phenomenon of the movement of electrical charges in a conductor, and also serves as an estimate of the amount of electricity passing through the conductor. Current (or current strength) is estimated by the number of electrons passing through a conductor within 1 s. Its number is huge. About 2000000000000000000 electrons pass through the filament of a burning light bulb in an electric flashlight, for example, every second. It is quite clear that it is inconvenient to characterize the current by the number of electrons, since one would have to deal with very large numbers. The unit of electric current is taken Ampere (abbreviated as A) . So it was named in honor of the French physicist and mathematician A. Ampere (1775 - 1836), who studied the laws of mechanical interaction of conductors with current and other electrical phenomena. A current of 1 A is a current of such a value that 6250000000000000000 electrons pass through the cross section of the conductor in 1 s. In mathematical expressions, current is denoted by the Latin letter I or i (read and). For example, they write: I 2 A or 0.5 A. Along with the ampere, smaller units of current are used: milliampere (written mA), equal to 0.001 A, and microampere (written μA), equal to 0.000001 A, or 0.001 mA. Therefore, 1 A = 1000 mA or 1,000,000 µA. Instruments used to measure currents are called ammeters, milliammeters, and microammeters, respectively. They are included in the electrical circuit in series with the current consumer, i.e. into a break in the external circuit. In the diagrams, these devices are depicted in circles with letters assigned to them inside: A (ammeter), (milliammeter) and mA (microampere) μA., and next to them they write RA, which means current meter. The measuring device is designed for a current not exceeding a certain limit for this device. The device must not be connected to a circuit in which a current exceeding this value flows, otherwise it may be damaged.
You may have a question: how to evaluate alternating current, the direction and magnitude of which is continuously changing? Alternating current is usually rated by its rms value. This is the current value that corresponds to direct current producing the same work. The effective value of the alternating current is approximately 0.7 amplitude, i.e., the maximum value .
ELECTRICAL RESISTANCE
When we talk about conductors, we mean substances, materials and, above all, metals that conduct current relatively well. However, not all substances called conductors conduct electric current equally well, that is, they are said to have unequal conductivity of current. This is explained by the fact that during their movement, free electrons collide with atoms and molecules of a substance, and in some substances, atoms and molecules interfere more strongly with the movement of electrons, and in others - less. In other words, some substances offer greater resistance to electric current, while others have less resistance. Of all the materials widely used in electrical and radio engineering, copper has the least resistance to electric current. That's why electrical wires are most often made of copper. Silver has even less resistance, but it is a rather expensive metal. Iron, aluminum and various metal alloys have greater resistance, i.e., poorer electrical conductivity. The resistance of a conductor depends not only on the properties of its material, but also on the size of the conductor itself. A thick conductor has less resistance than a thin one made of the same material; a short conductor has less resistance, a long one has more resistance, just as a wide and short pipe has less obstacle to the movement of water than a thin and long one. In addition, the resistance of a metal conductor depends on its temperature: the lower the temperature of the conductor, the lower its resistance. The unit of electrical resistance is taken to be the ohm (they write Ohm) - named after the German physicist G. Ohm . A resistance of 1 ohm is a relatively small electrical quantity. Such current resistance is provided, for example, by a piece of copper wire with a diameter of 0.15 mm and a length of 1 m. The resistance of the filament of a flashlight light bulb is about 10 ohms, and the resistance of the heating element of an electric stove is several tens of ohms. In radio engineering, one often has to deal with resistances greater than an ohm or several tens of ohms. The resistance of a high-impedance phone, for example, is more than 2000 Ohms; The resistance of a semiconductor diode connected in a non-current direction is several hundred thousand ohms. Do you know how much resistance your body has to electric current? From 1000 to 20000 Ohm. And the resistance of resistors - special parts, which I will talk about later in this conversation, can be up to several million ohms or more. These parts, as you already know, are indicated in the diagrams in the form of rectangles. In mathematical formulas, resistance is denoted by the Latin letter (R). The same letter is placed next to the graphic designations of resistors on the diagrams. To express higher resistances of resistors, larger units are used: kilo-ohm (abbreviated as kOhm), equal to 1000 Ohms, and mega-ohm (abbreviated as MOhm), equal to 1,000,000 Ohms, or 1,000 kOhm. The resistance of conductors, electrical circuits, resistors or other parts is measured with special devices called ohmmeters. In diagrams, is an ohmmeter indicated by a circle with a Greek letter? (omega) inside .
ELECTRICAL VOLTAGE
The unit of electrical voltage, electromotive force (EMF), is taken to be the volt (in honor of the Italian physicist A. Volta). In formulas, voltage is denoted by the Latin letter U (read “y”), and the unit of voltage itself, the volt, is denoted by the letter V. For example, they write: U = 4.5 V; U = 220 V. The unit volt characterizes the voltage at the ends of a conductor, a section of an electrical circuit, or the poles of a current source. A voltage of 1 V is an electrical quantity that in a conductor with a resistance of 1 Ohm creates a current equal to 1 A. The 3336L battery, designed for a flat pocket electric flashlight, as you already know, consists of three elements connected in series. On the battery label you can read that its voltage is 4.5 V. This means that the voltage of each battery element is 1.5 V. The voltage of the Krona battery is 9 V, and the voltage of the electric lighting network can be 127 or 220 V. Voltage is measured (with a voltmeter) by connecting the device with the same terminals to the poles of the current source or in parallel to a section of the circuit, resistor or other load on which it is necessary to measure the voltage acting on it. In diagrams, a voltmeter is denoted by the Latin letter V .
in a circle, and next to it is PU. To evaluate voltage, a larger unit is used - kilovolt (written kV), corresponding to 1000 V, as well as smaller units - millivolt (written mV), equal to 0.001 V, and microvolt (written µV), equal to 0.001 mV. These voltages are measured accordingly kilo-voltmeters, millivoltmeters And microvoltmeters. Such devices, like voltmeters, are connected in parallel to current sources or sections of circuits on which the voltage must be measured. Let us now find out what is the difference between the concepts of “voltage” and “electromotive force”. Electromotive force is the voltage acting between the poles of a current source until an external load circuit, such as an incandescent light bulb or resistor, is connected to it. As soon as an external circuit is connected and a current arises in it, the voltage between the poles of the current source will become less. So, for example, a new, unused galvanic cell has an EMF of at least 1.5 V. When a load is connected to it, the voltage at its poles becomes approximately 1.3-1.4 V. As the element's energy is consumed to power the external circuit, its voltage gradually decreases. The cell is considered discharged and therefore unfit for further use when the voltage drops to 0.7 V, although if the external circuit is turned off, its emf will be greater than this voltage. How is alternating voltage measured? When we talk about alternating voltage, for example, the voltage of an electric lighting network, we mean its effective value, which is approximately, like the effective value of alternating current, 0.7 of the amplitude voltage value.
OHM'S LAW
In Fig. shows a diagram of a familiar simple electrical circuit. This closed circuit consists of three elements: a voltage source - battery GB, a current consumer - load R, which can be, for example, an electric lamp filament or a resistor, and conductors connecting the voltage source to the load. By the way, if this circuit is supplemented with a switch, you will get a complete circuit for a pocket electric flashlight.
The load R, which has a certain resistance, is a section of the circuit. The value of the current in this section of the circuit depends on the voltage acting on it and its resistance: the higher the voltage and the lower the resistance, the greater the current will flow through the section of the circuit. This dependence of current on voltage and resistance is expressed by the following formula:
I = U/R,
where I is current, expressed in amperes, A; U - voltage in volts, V; R - resistance in ohms, Ohm. This mathematical expression is read as follows: the current in a section of the circuit is directly proportional to the voltage across it and inversely proportional to its resistance. This is the basic law of electrical engineering, called Ohm's law (after the name of G. Ohm), for a section of an electrical circuit
. Using Ohm's law, you can find out the unknown third from two known electrical quantities. Here are some examples of the practical application of Ohm's law.
First example:
A voltage of 25 V is applied to a section of the circuit with a resistance of 5 ohms. It is necessary to find out the value of the current in this section of the circuit.
Solution: I = U/R = 25 / 5 = 5 A.
Second example:
A voltage of 12 V acts on a section of the circuit, creating a current of 20 mA in it. What is the resistance of this section of the circuit? First of all, the current 20 mA must be expressed in amperes. This will be 0.02 A. Then R = 12 / 0.02 = 600 Ohms.
Third example: A current of 20 mA flows through a section of a circuit with a resistance of 10 kOhm. What is the voltage acting on this section of the circuit? Here, as in the previous example, the current should be expressed in amperes (20 mA = 0.02 A), resistance in ohms (10 kOhm = 10000 Ohm). Therefore, U = IR = 0.02 x 10000 = 200 V. The incandescent lamp base of a flat flashlight is stamped with: 0.28 A and 3.5 V. What does this information indicate? The fact that the light bulb will glow normally at a current of 0.28 A, which is determined by a voltage of 3.5 V, Using Ohm's law, it is easy to calculate that the heated filament of the light bulb has a resistance R = 3.5 / 0.28 = 12.5 Ohm . This, I emphasize, is the resistance of the incandescent filament of a light bulb. And the resistance of a cooled thread is much less. Ohm's law is valid not only for a section, but also for the entire electrical circuit. In this case, the total resistance of all elements of the circuit, including the internal resistance of the current source, is substituted into the value of R. However, in the simplest circuit calculations, the resistance of the connecting conductors and the internal resistance of the current source are usually neglected.
In this regard, I will give another example: The voltage of the electric lighting network is 220 V. What current will flow in the circuit if the load resistance is 1000 Ohms? Solution: I = U/R = 220 / 1000 = 0.22 A. An electric soldering iron consumes approximately this current.
All these formulas, which follow from Ohm’s law, can also be used to calculate alternating current circuits, but provided that there are no inductors and capacitors in the circuits.
Ohm's law and the calculation formulas derived from it are quite easy to remember if you use this graphical diagram, the so-called. Ohm's law triangle:
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Using this triangle is easy, just remember clearly that the horizontal line in the triangle means the division sign (similar to the fractional line), and the vertical line in the triangle means the multiplication sign .
Now consider this question: how does a resistor connected in a circuit in series with the load or in parallel to it affect the current? Let's look at this example. We have a light bulb from a round electric flashlight, designed for a voltage of 2.5 V and a current of 0.075 A. Is it possible to power this light bulb from a 3336L battery, the initial voltage of which is 4.5 V? It is easy to calculate that the heated filament of this light bulb has a resistance of slightly more than 30 ohms. If you power it from a fresh 3336L battery, then, according to Ohm’s law, a current will flow through the filament of the light bulb, almost twice the current for which it is designed. The thread will not withstand such an overload; it will overheat and collapse. But this light bulb can still be powered from a 336L battery if an additional 25 Ohm resistor is connected in series with the circuit, as shown in Fig..
In this case, the total resistance of the external circuit will be approximately 55 Ohms, i.e. 30 Ohm - the resistance of the light bulb filament H plus 25 Ohm - the resistance of the additional resistor R. Consequently, a current equal to approximately 0.08 A will flow in the circuit, i.e. almost the same as the filament of a light bulb is designed for. This light bulb can be powered from a battery at a higher voltage, or even from an electric lighting network, if you select a resistor of appropriate resistance. In this example, an additional resistor limits the current in the circuit to the value we need. The greater its resistance, the less will be the current in the circuit. In this case, two resistances were connected in series to the circuit: the resistance of the light bulb filament and the resistance of the resistor. And with a series connection of resistances, the current is the same at all points of the circuit. You can connect the ammeter to any point in the circuit, and it will show the same value everywhere. This phenomenon can be compared to the flow of water in a river. The river bed in different areas can be wide or narrow, deep or shallow. However, over a certain period of time, the same amount of water always passes through the cross section of any section of the river bed.
Additional resistor , connected in series with the load (as, for example, in the figure above), can be considered as a resistor that “quenches” part of the voltage acting in the circuit. The voltage that is extinguished by the additional resistor, or, as they say, drops across it, will be greater, the greater the resistance of this resistor. Knowing the current and resistance of the additional resistor, the voltage drop across it can be easily calculated using the same familiar formula U = IR. Here U is the voltage drop, V; I - current in the circuit, A; R - resistance of the additional resistor, Ohm. In our example, resistor R (in the figure) extinguished the excess voltage: U = IR = 0.08 x 25 = 2 V. The remaining battery voltage, approximately 2.5 V, fell on the light bulb filaments. The required resistor resistance can be found using another formula familiar to you: R = U/I, where R is the desired resistance of the additional resistor, Ohm; U-voltage that needs to be extinguished, V; I is the current in the circuit, A. For our example, the resistance of the additional resistor is: R = U/I = 2/0.075, 27 Ohm. By changing the resistance, you can reduce or increase the voltage that drops across the additional resistor, and thus regulate the current in the circuit. But the additional resistor R in such a circuit can be variable, i.e. a resistor whose resistance can be changed (see figure below).
In this case, using the resistor slider, you can smoothly change the voltage supplied to the load H, and therefore smoothly regulate the current flowing through this load. A variable resistor connected in this way is called a rheostat. Rheostats are used to regulate currents in the circuits of receivers, televisions and amplifiers. In many cinemas, rheostats were used to smoothly dim the light in the auditorium. There is, however, another way to connect the load to a current source with excess voltage - also using a variable resistor, but turned on by a potentiometer, i.e. voltage divider, as shown in Fig..
Here R1 is a resistor connected by a potentiometer, and R2 is a load, which can be the same incandescent light bulb or some other device. A voltage drop occurs across resistor R1 of the current source, which can be partially or completely supplied to load R2. When the resistor slider is in its lowest position, no voltage is supplied to the load at all (if it is a light bulb, it will not light up). As the resistor slider moves up, we will apply more and more voltage to the load R2 (if it is a light bulb, its filament will glow). When the slider of resistor R1 is in its uppermost position, the entire voltage of the current source will be applied to the load R2 (if R2 is a flashlight bulb, and the voltage of the current source is high, the light bulb filament will burn out). You can experimentally find the position of the variable resistor motor at which the voltage it needs will be supplied to the load. Variable resistors activated by potentiometers are widely used to control volume in receivers and amplifiers. The resistor can be directly connected in parallel with the load. In this case, the current in this section of the circuit branches and goes in two parallel paths: through the additional resistor and the main load. The greatest current will be in the branch with the least resistance. The sum of the currents of both branches will be equal to the current spent on powering the external circuit. A parallel connection is resorted to in those cases when it is necessary to limit the current not in the entire circuit, as when connecting an additional resistor in series, but only in a certain section. Additional resistors are connected, for example, in parallel with milliammeters, so that they can measure large currents. Such resistors are called shunting or shunts . The word shunt means branch .
INDUCTIVE RESISTANCE
In an alternating current circuit, the value of the current is affected not only by the resistance of the conductor connected to the circuit, but also by its inductance. Therefore, in alternating current circuits, a distinction is made between the so-called ohmic or active resistance, determined by the properties of the conductor material, and inductive resistance, determined by the inductance of the conductor. A straight conductor has a relatively small inductance. But if this conductor is rolled into a coil, its inductance will increase. At the same time, the resistance it provides to alternating current will increase, and the current in the circuit will decrease. As the frequency of the current increases, the inductive reactance of the coil also increases. Remember: the resistance of an inductor to alternating current increases with its inductance and the frequency of the current passing through it. This property of the coil is used in various receiver circuits when it is necessary to limit high-frequency current or isolate high-frequency oscillations, in alternating current rectifiers, and in many other cases that you will constantly encounter in practice. The unit of inductance is henry (H). An inductance of 1 H is possessed by a coil in which, when the current in it changes by 1 A for 1 s, a self-inductive emf equal to 1 V develops. This unit is used to determine the inductance of coils that are included in audio frequency current circuits. The inductance of coils used in oscillating circuits is measured in thousandths of a henry, called millihenry (mH), or another thousand times smaller unit - microhenry (μH). .
POWER AND CURRENT OPERATION
Heating the filament of an electric or electronic lamp, electric soldering iron, electric stove or other device requires a certain amount of electricity. This energy given by the current source (or received from it by the load) for 1 s is called current power. The unit of current power is taken watt (W) . A watt is the power that a direct current of 1A develops at a voltage of 1V. In formulas, current power is denoted by the Latin letter P (read “pe”). Electrical power in watts is obtained by multiplying the voltage in volts by the current in amperes, i.e. P = UI. If, for example, a 4.5 V DC source creates a current of 0.1 A in the circuit, then the current power will be: p = 4.5 x 0.1 = 0.45 W. Using this formula, you can, for example, calculate the power consumed by a flashlight bulb if 3.5 V is multiplied by 0.28 A. We get about 1 W. By changing this formula as follows: I = P/U, you can find out the current flowing through an electrical device if the power it consumes and the voltage supplied to it are known. What, for example, is the current flowing through an electric soldering iron if it is known that at a voltage of 220 V it consumes 40 W of power? I = P/I = 40/220 = 0.18 A. If the current and resistance of the circuit are known, but the voltage is unknown, the power can be calculated using the following formula: P = I2R. When the voltage acting in the circuit and the resistance of this circuit are known, the following formula is used to calculate the power: P = U2/R. But a watt is a relatively small unit of power. When we have to deal with electrical devices, instruments or machines that consume currents of tens or hundreds of amperes, we use a unit of power, kilowatt (written kW), equal to 1000 W. The power of electric motors of factory machines, for example, can range from several units to tens of kilowatts. Quantitative energy consumption is estimated by watt - second, which characterizes the unit of energy - joule. Electricity consumption is determined by multiplying the power consumed by the device by its operating time in seconds. If, for example, the light bulb of an electric flashlight (its power, as we already know, is about 1 W) burned for 25 seconds, then the energy consumption was 25 watt-seconds. However, a watt-second is a very small value. Therefore, in practice, larger units of electricity consumption are used: watt-hour, hectowatt-hour and kilowatt-hour. In order for energy consumption to be expressed in watt-hours or kilowatt-hours, the power in watts or kilowatts must be multiplied by the time in hours, respectively. If, for example, the device consumes 0.5 kW of power for 2 hours, then the energy consumption will be 0.5 X 2 = 1 kWh; 1 kWh of energy will also be consumed if the circuit consumes (or uses) 2 kW of power for half an hour, 4 kW for a quarter of an hour, etc. The electric meter installed in the house or apartment where you live takes into account electricity consumption in kilowatt hours. By multiplying the meter readings by the cost of 1 kWh (amount in kopecks), you will find out how much energy was consumed per week or month. When working with galvanic cells or batteries, we talk about their electrical capacity in ampere hours, which is expressed by multiplying the value of the discharge current and the duration of operation in hours. The initial battery capacity is 3336L, for example 0.5 Ah. Calculate: how long will the battery work continuously if you discharge it with a current of 0.28 A (the current of a flashlight bulb)? About one and three quarters of an hour. If this battery is discharged more intensively, for example, with a current of 0.5 A, it will work for less than 1 hour. Thus, knowing the capacity of the galvanic cell or battery and the currents consumed by their loads, you can calculate the approximate time during which these will work chemical current sources. The initial capacity, as well as the recommended discharge current or external circuit resistance that determines the discharge current of the cell or battery, are sometimes indicated on their labels or in reference literature.
In this lesson, I tried to systematize and lay out the maximum information necessary for a beginning radio amateur on the basics of electrical engineering, without which there is no point in continuing to study anything. The lesson turned out to be perhaps the longest, but also the most important. I advise you to take this lesson more seriously, be sure to memorize the highlighted definitions, if something is not clear, re-read it several times to understand the essence of what was said. For practical work, you can experiment with the circuits shown in the pictures, i.e., with batteries, light bulbs and a variable resistor. This will do you good. In general, in this lesson, of course, the entire emphasis should be placed not on practice, but on mastering theory.
Electricity is used in many areas and surrounds us almost everywhere. Electricity makes it possible to obtain safe lighting at home and at work, boil water, cook food, and work on computers and machines. At the same time, you must know how to handle electricity, otherwise you can not only get injured, but also cause damage to property. How to properly lay wiring and organize the supply of electricity to objects is studied by such a science as electrical engineering.
Electricity concept
All substances are made up of molecules, which in turn are made up of atoms. An atom has a nucleus and positively and negatively charged particles (protons and electrons) moving around it. When two materials are located next to each other, a potential difference arises between them (the atoms of one substance always have fewer electrons than the other), which leads to the appearance of an electric charge - electrons begin to move from one material to another. This is how electricity is created. In other words, electricity is the energy resulting from the movement of negatively charged particles from one substance to another.
The speed of movement may vary. To ensure movement is in the right direction and at the right speed, conductors are used. If the movement of electrons through a conductor is carried out in only one direction, such a current is called constant. If the direction of movement changes with a certain frequency, then the current will be alternating. The most famous and simple source of direct current is a battery or car battery. Alternating current is actively used in households and industry. Almost all devices and equipment work on it.
What does electrical engineering study?
This science knows almost everything about electricity. It is necessary for anyone who wants to obtain a diploma or qualification as an electrician to study it. In most educational institutions, the course in which everything related to electricity is studied is called “Theoretical Foundations of Electrical Engineering” or, abbreviated as TOE.
This science was developed in the 19th century, when a direct current source was invented, and it became possible to build electrical circuits. Electrical engineering received further development in the process of new discoveries in the field of physics of electromagnetic radiation. In order to master science without problems at the present time, it is necessary to have knowledge not only in the field of physics, but also chemistry and mathematics.
First of all, in the TOE course the basics of electricity are studied, the definition of current is given, its properties, characteristics and areas of application are explored. Next, electromagnetic fields and the possibilities of their practical use are studied. The course usually ends with the study of devices that use electrical energy.
To understand electricity, you don’t have to go to a higher or secondary educational institution; it’s enough to use a self-instruction manual or take video lessons “for dummies.” The knowledge gained is quite enough to deal with wiring, replace a light bulb or hang a chandelier at home. But, if you plan to work professionally with electricity (for example, as an electrician or power engineer), then appropriate education will be mandatory. It allows you to obtain a special permit to work with instruments and devices operating from a current source.
Basic concepts of electrical engineering
When learning electricity for beginners, the main thing is– understand three basic terms:
- Current strength;
- Voltage;
- Resistance.
Current strength refers to the amount of electric charge flowing through a conductor with a certain cross-section per unit of time. In other words, the number of electrons that have moved from one end of a conductor to the other over time. The current strength is the most dangerous for human life and health. If you grab a bare wire (and a person is also a conductor), then electrons will pass through it. The more of them that pass, the greater the damage will be, since as they move they generate heat and trigger various chemical reactions.
However, for current to flow through conductors, there must be a voltage or potential difference between one end of the conductor and the other. Moreover, it must be constant so that the movement of electrons does not stop. To do this, the electrical circuit must be closed, and at one end of the circuit a current source must be placed, which ensures the constant movement of electrons in the circuit.
Resistance is a physical characteristic of a conductor, its ability to conduct electrons. The lower the resistance of the conductor, the more electrons will pass through it per unit time, the higher the current. High resistance, on the contrary, reduces the current, but causes the conductor to heat up (if the voltage is high enough), which can lead to a fire.
Selection of optimal relationships between voltage, resistance and current in an electrical circuit is one of the main tasks of electrical engineering.
Electrical engineering and electromechanics
Electromechanics is a branch of electrical engineering. She studies the principles of operation of devices and equipment that operate from a source of electrical current. By studying the basics of electromechanics, you can learn how to repair various equipment or even design it.
As part of lessons in electromechanics, as a rule, the rules for converting electrical energy into mechanical energy are studied (how an electric motor functions, the principles of operation of any machine, and so on). Reverse processes are also studied, in particular, the principles of operation of transformers and current generators.
Thus, without understanding how electrical circuits are composed, the principles of their functioning and other issues that electrical engineering studies, it is impossible to master electromechanics. On the other hand, electromechanics is a more complex discipline and is of an applied nature, since the results of its study are directly used in the design and repair of machines, equipment and various electrical devices.
Safety and Practice
When mastering an electrical engineering course for beginners, it is necessary to pay special attention to safety issues, since failure to comply with certain rules can lead to tragic consequences.
The first rule to follow is to read the instructions. All electrical appliances always have a section in their instruction manual that deals with safety issues.
The second rule is to monitor the condition of the conductor insulation. All wires must be covered with special materials that do not conduct electricity (dielectrics). If the insulating layer is damaged, first of all it should be restored, otherwise harm to health may occur. In addition, for safety reasons, work with wires and electrical equipment should only be done in special clothing that does not conduct electricity (rubber gloves and dielectric boots).
The third rule is to use only special devices to diagnose electrical network parameters. Under no circumstances should you do this with your bare hands or try it on your tongue.
Note! Neglect of these basic rules is the main cause of injuries and accidents in the work of electricians and electricians.
To get an initial understanding of electricity and the principles of operation of devices using it, it is recommended to take a special course or study the manual “Electrical Engineering for Beginners”. Such materials are designed specifically for those who are trying to master this science from scratch and gain the necessary skills for working with electrical equipment at home.
The manual and video lessons explain in detail how an electrical circuit is structured, what a phase is and what a zero is, how resistance differs from voltage and current, and so on. Special attention is paid to safety precautions to avoid injuries when working with electrical appliances.
Of course, studying courses or reading manuals will not allow you to become a professional electrician or electrician, but you will be quite capable of solving most everyday issues based on the results of mastering the material. For professional work, you already need to obtain a special permit and have a specialized education. Without this, various instructions prohibit you from performing your job duties. If an enterprise allows a person without the necessary education to work with electrical equipment and he gets injured, the manager will suffer serious punishment, even criminal.
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Everything a self-taught electrician needs to know. Self-instruction manual. Features of the household lighting electrical network. Self-training in electrical installation. (10+)
Electrician's tutorial - Basic knowledge and skills for performing electrical and electrical work
I'm sure I missed something. There may be various private electrical issues that I have not covered. Be sure to write questions in the article discussion. I will answer them if I can.
Safety precautions
If you have never carried out electrical installation work yourself, then you should not think that after reading this material, you will be able to do everything correctly, safely for yourself and future users. The article will help you understand how a household lighting network is structured and understand the basic principles of its installation. The first time electrical installation work should be carried out under the supervision of an experienced specialist. In any case, regardless of whether you have official clearance, you take responsibility for the life, health and safety of yourself and others.
Never work with high voltage alone. There should always be a person nearby who, in a critical situation, can turn off the power to the system, call emergency services and provide first aid.
Do not perform work under voltage. This is fun for seasoned professionals. Turn off the power to the network you will be working with, making sure that no one can accidentally turn on the electricity while you are doing the installation.
Do not rely on the fact that the wiring was done correctly before you. Get a phase sensor (indicator). This is a device similar to a screwdriver or an awl. He has a dipstick. If the probe touches a live wire, the indicator lights up. Make sure you know how to use this sensor correctly. There are subtleties. Some sensors only work correctly if you press a special contact on the handle with your finger. Before starting work, use the phase indicator to make sure that the wiring is de-energized. I have more than once encountered erroneously executed wiring options, when the machine at the input breaks only one wire, without ensuring complete de-energization of the network. This error is very dangerous, because by turning off the machine, you assume that the network is de-energized, but this is not the case. The phase sensor will immediately warn you of danger.
Main electrical faults
Experts say that there are only two types of faults in electrical engineering. There is no necessary reliable contact and there is an unnecessary one. Indeed, in electrical installation there are no cases when two network points must be connected by a certain resistance. They either must be connected or not connected.
Electrical connection diagrams
The diagram shows typical double-circuit wiring. To the object through the machine ( A2), RCD ( A3) and electric meter ( A4) the mains voltage of the lighting network is turned on ( O1). Next, this voltage is divided into two circuits - lighting and power. Both circuits have separate machines ( A4- lighting circuit, A5- power) to protect them from overloads and separate shutdown during repair work. The lighting circuit breaker is usually selected for a lower current strength than the power circuit breaker. Lamps are connected to the lighting circuit ( L1 - LN) and two sockets ( S1, S2) for connecting low-power loads, such as a computer or TV. These sockets are used during repair work on the power circuit to connect power tools. The power circuit is routed to power sockets ( S3 - SN).
In the diagrams, the connection point of the conductors is indicated by a dot. If the conductors cross each other, but there is no point, then this means that the conductors are not connected, they intersect without connection.
Parallel and serial connections
Electrical circuits can be connected in parallel and in series.
At sequential connection, the electric current coming from one circuit enters the other. Thus, the same current flows through all circuits connected in series.
At parallel connection, the electric current branches out into all circuits connected in parallel. Thus, the total current is equal to the sum of the currents in each circuit. But the same voltage is applied to circuits connected in parallel.
In the diagram shown, the input circuit breaker, RCD, counter and the rest of the circuit are connected in series. As a result, the machine can limit the current in the entire circuit, and the meter can measure the energy consumed. Both circuits and the loads in them are connected in parallel, which allows each load to be supplied with the mains voltage for which it is designed, regardless of other loads.
Here is a schematic electrical diagram. There are also wiring diagrams. They indicate on the site plan where the wiring should go, where to install the panel, where to put sockets, switches and lighting fixtures. There are completely different designations. I am not an expert in these schemes. Look for information about them in other sources.
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If something is unclear, be sure to ask!
We offer a small material on the topic: “Electricity for beginners.” It will give an initial understanding of the terms and phenomena associated with the movement of electrons in metals.
Features of the term
Electricity is the energy of small charged particles moving in conductors in a specific direction.
With constant current, there is no change in its magnitude, as well as in the direction of movement over a certain period of time. If a galvanic cell (battery) is chosen as the current source, then the charge moves in an orderly manner: from the negative pole to the positive end. The process continues until it completely disappears.
Alternating current periodically changes magnitude as well as direction of movement.
AC transmission circuit
Let's try to understand what a phase is in a word everyone has heard, but not everyone understands its true meaning. We will not go into details and details; we will select only the material that the home craftsman needs. A three-phase network is a method of transmitting electric current, in which current flows through three different wires, and one returns it. For example, there are two wires in an electrical circuit.
Current flows through the first wire to the consumer, for example, to a kettle. The second wire is used to return it. When such a circuit is opened, there will be no passage of electric charge inside the conductor. This diagram describes a single-phase circuit. in electricity? A phase is considered to be a wire through which electric current flows. Zero is the wire through which the return is carried out. In a three-phase circuit there are three phase wires at once.
An electrical panel in the apartment is necessary for current in all rooms. are considered economically feasible, since they do not require two. When approaching the consumer, the current is divided into three phases, each with a zero. The ground electrode, which is used in a single-phase network, does not carry a working load. He is a fuse.
For example, if a short circuit occurs, there is a threat of electric shock or fire. To prevent such a situation, the current value should not exceed a safe level; the excess goes into the ground.
The manual “School for Electricians” will help novice craftsmen cope with some breakdowns of household appliances. For example, if there are problems with the functioning of the electric motor of the washing machine, current will flow to the outer metal casing.
If there is no grounding, the charge will be distributed throughout the machine. When you touch it with your hands, a person will act as a grounding conductor and receive an electric shock. If there is a ground wire, this situation will not arise.
Features of electrical engineering
The textbook “Electricity for Dummies” is popular among those who are far from physics, but plan to use this science for practical purposes.
The date of appearance of electrical engineering is considered to be the beginning of the nineteenth century. It was at this time that the first current source was created. The discoveries made in the field of magnetism and electricity managed to enrich science with new concepts and facts of important practical significance.
The “School for Electrician” manual assumes familiarity with the basic terms related to electricity.
Many physics books contain complex electrical diagrams and a variety of confusing terms. In order for beginners to understand all the intricacies of this section of physics, a special manual “Electricity for Dummies” was developed. An excursion into the world of the electron must begin with a consideration of theoretical laws and concepts. Illustrative examples and historical facts used in the book “Electricity for Dummies” will help novice electricians acquire knowledge. To check your progress, you can use assignments, tests, and exercises related to electricity.
If you understand that you do not have enough theoretical knowledge to independently cope with connecting electrical wiring, refer to reference books for “dummies”.
Safety and Practice
First you need to carefully study the section regarding safety precautions. In this case, during work related to electricity, there will be no emergency situations hazardous to health.
In order to put into practice the theoretical knowledge gained after self-studying the basics of electrical engineering, you can start with old household appliances. Before starting repairs, be sure to read the instructions included with the device. Don't forget that you shouldn't joke with electricity.
Electric current is associated with the movement of electrons in conductors. If a substance is not capable of conducting current, it is called a dielectric (insulator).
For free electrons to move from one pole to another, there must be a certain potential difference between them.
The intensity of the current passing through a conductor is related to the number of electrons passing through the cross section of the conductor.
The speed of current flow is affected by the material, length, and cross-sectional area of the conductor. As the length of the wire increases, its resistance increases.
Conclusion
Electricity is an important and complex branch of physics. The manual "Electricity for Dummies" examines the main quantities characterizing the efficiency of electric motors. The units of voltage are volts, current is measured in amperes.
Everyone has a certain power. It refers to the amount of electricity generated by a device over a certain period of time. Energy consumers (refrigerators, washing machines, kettles, irons) also have power, consuming electricity during operation. If you wish, you can carry out mathematical calculations and determine the approximate price for each household appliance.
