Direct and alternating electric current. Direct and alternating current

Despite the fact that electricity has firmly entered our lives, the vast majority of users of this benefit of civilization do not even have a superficial understanding of what current is, not to mention how direct current differs from alternating current, what is the difference between them, and what current is in general . The first person to be electrocuted was Alessandro Volta, after which he devoted his whole life to this topic. Let us also pay attention to this topic in order to have general idea about the nature of electricity.

Where does the current come from and why is it different?

We will try to avoid complex physics and will use the method of analogies and simplifications to consider this issue. But before that, let us recall an old joke about an exam, when an honest student pulled out a ticket “What is electricity».

Sorry professor, I was preparing, but I forgot,” answered the honest student. - How could you! The professor reproached him, “You are the only person on Earth who knew this!” (With)

This is of course a joke, but in it great amount truth. Therefore, we will not look for Nobel laurels, but simply figure it out, alternating current and constant, what is the difference, and what is considered to be current sources.

As a basis, we will take the assumption that current is not the movement of particles (although the movement of charged particles also transfers charge, and therefore creates currents), but the movement (transfer) of excess charge in a conductor from a point of high charge (potential) to a point of less charge. An analogy is a reservoir; water always tends to occupy the same level (to equalize the potentials). If you open a hole in the dam, water will begin to flow downhill, creating a direct current. The larger the hole, the more water will flow, the current will increase, as will the power and the amount of work that this current can do. If the process is not controlled, the water will destroy the dam and immediately create a flood zone with the surface at the same level. This short circuit with equalization of potentials, accompanied by great destruction.

Thus, direct current appears in a source (usually due to chemical reactions), in which a potential difference arises at two points. The movement of charge from a higher "+" value to a lower "-" value equalizes the potential while the chemical reaction lasts. The result of fully equalizing the potential, we know - “the battery is dead.” This leads to an understanding of why DC and AC voltage differ significantly in stability characteristics. The battery (accumulator) consumes charge, so the voltage direct current decreases over time. To maintain it at the same level, additional converters are used. Initially, humanity spent a long time deciding the difference between direct current and alternating current for widespread use, the so-called. "War of Currents". It ended with the victory of alternating current, not only because there were fewer losses during transmission over a distance, but also the generation of direct current from alternating current turned out to be easier. Obviously, the direct current obtained in this way (without a consumable source) has much more stable characteristics. In fact, in this case, alternating and direct voltage are strictly connected, and in time they depend only on the generation of energy and the amount of consumption.

Thus, direct current by its nature is the occurrence of an uneven charge in the volume (chemical reaction), which can be redistributed using wires by connecting a point of high and low charge (potential).

Let us dwell on this definition as generally accepted. All other direct currents (not batteries) are derived from the alternating current source. For example, in this picture the blue wavy line is our direct current, as a result of the alternating current conversion.

Pay attention to the comments on the picture, “ a large number of circuits and collector plates." If the converter is different, the picture will be different. The same blue line, the current is almost constant, but pulsating, remember this word. Here, by the way, pure direct current is the red line.

The relationship between magnetism and electricity

Now let's see how alternating current differs from direct current, which depends on the material. The most important - the occurrence of alternating current does not depend on reactions in the material. Working with galvanic (direct current), it was quickly established that conductors are attracted to each other like magnets. The consequence was the discovery that a magnetic field under certain conditions generates an electric current. That is, magnetism and electricity turned out to be an interrelated phenomenon with a reverse transformation. A magnet could give a current to a conductor, and a conductor with a current could be a magnet. This picture shows a simulation of the experiments of Faraday, who, in fact, discovered this phenomenon.

Now the analogy for alternating current. Our magnet will be the force of attraction, and the current generator will be an hourglass with water. On one half of the clock we will write “top”, on the other “bottom”. We turn our clock over and see how the water flows “downwards”, when all the water has flowed over, we turn it over again and the water flows “upwards”. Despite the fact that we have a current, it changes direction twice per full cycle. According to science, it will look like this: the frequency of the current depends on the rotation speed of the generator in the magnetic field. Under certain conditions, we will get a pure sine wave, or simply alternating current with different amplitudes.

Again! This is very important for understanding the difference between direct current and alternating current. In both analogies, water flows “downhill.” But in the case of direct current, the reservoir will be empty sooner or later, and for alternating current, the clock will overflow water for a very long time, it is in a closed volume. But in both cases the water flows downhill. True, in the case of alternating current, half the time it flows downhill, but up. In other words, the direction of movement of alternating current is an algebraic quantity, that is, “+” and “-” continuously change places, while the direction of current movement remains unchanged. Try to think about and understand this difference. It’s so fashionable to say online: “You got it, now you know everything.”

What causes the wide variety of currents

If you understand the difference between direct and alternating currents, a natural question arises - why are there so many of them, currents? We would choose one current as the standard, and everything would be the same.

But, as they say, “not all currents are equally useful,” by the way, let’s think about which current is more dangerous: constant or alternating, if we have roughly imagined not the nature of the current, but rather its features. Man is a collodium that conducts electricity well. Kit different elements in water (we are 70% water, if anyone doesn’t know). If a voltage is applied to such a collodium - an electric shock is applied, then the particles inside us will begin to transfer charge. As it should be, from a point of high potential to a point of low potential. The most dangerous thing is to stand on the ground, which is generally a point with infinite zero potential. In other words, we will transfer all the current, that is, the difference in charges, to the ground. So, with a constant direction of movement of the charge, the process of equalizing the potential in our body occurs smoothly. We are like sand letting water pass through us. And we can safely “absorb” a lot of water. With alternating current, the picture is a little different - all our particles will be “pulled” here and there. The sand will not be able to easily pass water, and it will be all agitated. Therefore, the answer to the question of which current is more dangerous: direct or alternating current, the answer is clear - alternating. For reference, the life-threatening threshold DC current is 300mA. For alternating current, these values depend on frequency and start at 35mA. At a current of 50 hertz 100mA. Agree, a difference of 3-10 times in itself answers the question: which is more dangerous? But this is not the main argument in choosing a current standard. Let's organize everything that is taken into account when choosing the type of current:

Delivery of current to long distances . Almost all direct current will be lost;
Convert to heterogeneous electrical circuits with an uncertain level of consumption. For direct current, the problem is practically unsolvable;
Maintaining a constant voltage for alternating current is two orders of magnitude cheaper than for direct current;
Conversion electrical energy in mechanical power is much cheaper in AC motors and mechanisms. Such motors have their drawbacks and in some areas cannot replace DC motors;
For mass use Thus, direct current has one advantage - it is safer for humans.

Hence the reasonable compromise that humanity has chosen. Not just one current, but the entire set of available transformations from generation, delivery to the consumer, distribution and use. We will not list everything, but we consider the main answer to the question of the article, “how does direct current differ from alternating current,” in one word – characteristics. This is probably the most correct answer for any household purposes. And to understand the standards, we suggest considering the main characteristics of these currents.

Main characteristics of currents used today

If for direct current the characteristics have remained generally unchanged since its discovery, then with alternating currents everything is much more complicated. Look at this picture - a model of current movement in a three-phase system from generation to consumption

From our point of view, very visual model, in which it is clear how to remove one phase, two or three. At the same time, you can see how it gets to the consumer.

As a result, we have a generation chain, alternating and direct voltage (currents) at the consumer stage. Accordingly, the further away from the consumer, the higher the currents and voltages. In fact, in our outlet the simplest and weakest is single-phase alternating current, 220V with a fixed frequency of 50 Hz. Only an increase in frequency can make the current high-frequency at this voltage. The simplest example is in your kitchen. Microwave printing converts simple current into high-frequency current, which actually helps in cooking. By the way, let’s answer the question about microwave power - this is exactly how much “ordinary” current it converts into high-frequency currents.

It is worth remembering that any transformation of currents is not “for nothing”. To get alternating current, you need to rotate the shaft with something. To get a constant current from it, you will have to dissipate part of the energy as heat. Even energy transmission currents will have to be dissipated in the form of heat when delivered to the apartment using a transformer. That is, any change in current parameters is accompanied by losses. And of course, losses accompany the delivery of current to the consumer. This seemingly theoretical knowledge allows us to understand where our overpayments for energy come from, eliminating half of the questions about why there are 100 rubles on the meter, but 115 on the receipt.

Let's return to currents. We seem to have mentioned everything, and we even know how direct current differs from alternating current, so let’s remind you what currents generally exist.

D.C, the source is the physics of chemical reactions with a change in charge, can be obtained by converting alternating current. Variety – impulse current, which changes its parameters, in wide range, but does not change the direction of movement.
Alternating current. Can be single-phase, two-phase or three-phase. Standard or high frequency. This simple classification is quite sufficient.

Conclusion or each current has its own device

The photo shows the current generator at the Sayano-Shushenskaya hydroelectric power station. And this photo shows the place where it was installed.

And this is an ordinary light bulb.

Isn’t it true that the difference in scale is amazing, although the first was created, among other things, for the work of the second? If you think about this article, it becomes clear that the closer the device is to a person, the more often it uses direct current. With the exception of DC motors and industrial applications, this is indeed a standard based precisely on the fact that we have found out which current is more dangerous, direct or alternating current. The characteristics of household currents are based on the same principle, since alternating current 220V 50Hz is a compromise between danger and losses. The price of compromise is protective automation: from the fuse to the RCD. Moving away from the person, we find ourselves in the zone transient characteristics, where both currents and voltages are higher, and where the danger to humans is not taken into account, but attention is paid to safety precautions - the zone of industrial use of current. The furthest thing from humans, even in industry, is energy transmission and generation. There is nothing for a mere mortal to do here - this is a zone of professionals and specialists who know how to manage this power. But even with everyday use of electricity, and of course when working with electrical equipment, understanding the basic nature of currents will never be superfluous.

Electric current is the directional, ordered movement of charged particles.

Direct current has stable properties and the direction of movement of charged particles that do not change over time. It is used in many electrical devices in homes as well as in cars. Operates on DC current modern computers, laptops, TVs and many other devices. To convert alternating current to direct current, special power supplies and voltage transformers are used.

All electrical devices and electrical tools powered by batteries and rechargeable batteries are considered DC consumers, since a battery is a source of DC current that can be converted to AC using inverters.

Difference between AC and DC

Variable is an electric current that can change in the direction of movement of charged particles and in magnitude over time. The most important parameters AC current is considered to be its frequency and voltage. In modern electrical networks at various facilities, alternating current is used, which has a certain voltage and frequency. In Russia, in household electrical networks, the current has a voltage of 220 V and a frequency of 50 Hz. The frequency of electrical alternating current is the number of changes in the direction of movement of charged particles in 1 second, that is, at a frequency of 50 Hz, it changes direction 50 times per second. Thus, the difference between alternating current and direct current is that in alternating current charged particles can change the direction of movement.

AC power sources at sites for various purposes are sockets. We connect various sockets to Appliances receiving the required voltage. Alternating current is used in electrical networks because the voltage can be converted to the required values using transformer equipment with minimal losses. In other words, it is much easier and cheaper to transport from power sources to end consumers.

Transmission of alternating current to consumers

The path of alternating current begins with power plants, where the most powerful electric generators, from which electric current comes out with a voltage of 220-330 kV. Current flows through electrical cables to transformer substations installed in close proximity to electrical consumption objects - houses, apartments, enterprises and other structures.

Substations receive electric current with a voltage of about 10 kV and convert it into a three-phase voltage of 380 V. In some cases, a current with a voltage of 380 V is used to power objects; this is required by powerful household and industrial appliances, but most often at the point where electricity is introduced into a house or apartment , the voltage drops to the usual 220 V.

Converting AC to DC

We have already figured out what is in household sockets electrical systems There is alternating current, but many modern consumers of electricity need constant current. The conversion of alternating current to direct current is carried out using special rectifiers. The entire conversion process includes three stages:

Connection diode bridge with 4 diodes required power. Such a bridge can “cut off” the upper values of alternating current sinusoids or make the movement of charged particles unidirectional.
Connecting an anti-aliasing filter or a special capacitor to the output of the diode bridge. The filter is able to correct the dips between the peaks of AC sinusoids. Connecting a capacitor seriously reduces ripple and can bring it to a minimum.
Connecting voltage stabilizers to reduce ripple.

Current conversion can be carried out in both directions, that is, constant can also be converted into alternating. But this process is much more complicated and is carried out through the use of special inverters, which are expensive.

Thomas Edison had a little refreshment in New York with street lamps and its direct current. The alternating current changes back and forth periodically. In a second, the electricity in our electrical grid moves 50 times! After direct current and alternating current were invented, both inventors guaranteed each other. Not with weapons, but with words. They even have dogs connected to electrical network, to show how dangerous other electricity is.

We need both types of electricity because both have their advantages and disadvantages. It is ideal for charging batteries and batteries. They need a constant current to charge because the current must always alternate in the same direction. This also applies to some household appliances. It's just that everything with batteries and rechargeable batteries requires constant current to charge. For example, a flashlight or a laptop that has batteries. And such devices require direct current, i.e. direct current.

Where does the current come from and why is it different?

Sorry professor, I was preparing, but I forgot,” the honest student answered. - How could you! The professor reproached him, “You are the only person on Earth who knew this!” (With)

But television or radio also need direct current. They cannot run with alternating voltage, which always requires constant current. Again, there are devices that don't matter what you use. Bulbs, for example, are browsing this site. A light bulb is just a wire that gets hot, and the current direction doesn't matter. Alternating current is used with electric motors, that is, with all rotating devices. For example, the blender rotates. Or the stovetop can also work with AC power, which does not turn, however it must be heated, and then it is like a light bulb, there is wire and heat in it.

This is of course a joke, but there is a huge amount of truth in it. Therefore, we will not look for Nobel laurels, but simply figure out alternating current and direct current, what is the difference, and what is considered to be current sources.

As a basis, we will accept the assumption that current is not the movement of particles (although the movement of charged particles also transfers charge, and therefore creates currents), but the movement (transfer) of excess charge in a conductor from a point of high charge (potential) to a point of less charge. An analogy is a reservoir; water always tends to occupy the same level (to equalize the potentials). If you open a hole in the dam, water will begin to flow downhill, creating a direct current. The larger the hole, the more water will flow, the current will increase, as will the power and the amount of work that this current can do. If the process is not controlled, the water will destroy the dam and immediately create a flood zone with the surface at the same level. This is a short circuit with potential equalization, accompanied by great destruction.

But alternating current has a decisive advantage; it can be produced in large quantities in power plants, and it can be transported much better than direct current because the losses over long distances are much lower. So, outside the power plant, change alternating current in large quantities to the land line, then to the distribution boxes. From there, alternating current is distributed to households, and what we used then is solved by this device. The mixer will directly use AC power.

The computer or television first converts alternating current to direct current. This works with a so-called voltage converter without problems. Only thanks to a voltage converter can we connect the TV to conventional power sources. A voltage transformer is already installed for all devices that require DC current.

Thus, direct current appears in a source (usually due to chemical reactions), in which a potential difference arises at two points. The movement of charge from a higher "+" value to a lower "-" value equalizes the potential while the chemical reaction lasts. The result of fully equalizing the potential, we know - “the battery is dead.” This leads to an understanding of why DC and AC voltage differ significantly in stability characteristics. The battery uses up its charge, so the DC voltage decreases over time. To maintain it at the same level, additional converters are used. Initially, humanity spent a long time deciding the difference between direct current and alternating current for widespread use, the so-called. "War of Currents". It ended with the victory of alternating current, not only because there were fewer losses during transmission over a distance, but also the generation of direct current from alternating current turned out to be easier. Obviously, the direct current obtained in this way (without a consumable source) has much more stable characteristics. In fact, in this case, alternating and direct voltage are strictly connected, and in time they depend only on the generation of energy and the amount of consumption.

Electrical resistance is a measure of how much voltage is required to pass a certain current through a conductor. This also means that a certain voltage drops across each resistor in the circuit. In practice, there are three types of resistors.

RTD resistors in AC systems. . On this moment we are only interested in the first one. When we use a resistor as a component, we usually talk about ohmic resistance, i.e. about resistance, which does not depend on temperature, current or voltage. Thus we have constant resistance, and this allows for the following example applications.

If we connected it directly to a voltage source, it would be broken. We have just looked at down regulation of tension and also found a solution. Only this solution has a serious weakness: the current one. If it changes, the voltage that drops through the resistor also changes. But there is a solution for this: a voltage divider. This is what it looks like.

Why do high voltage cables operate at 300 kV?

This is a question that I asked myself every time or had to ask. The answer follows from Ohm's law and the formula for power. Wattage determines how much energy is required over time. This means that our 220V power supply uses current. Now we connect our device with a very long power cable with this connector. We turn it on and this happens: nothing. The aforementioned “internal restoration” is worth mentioning here. The long line connecting to the power supply has such a high resistance, let's say, that due to the voltage drop there is no voltage at the output for the consumer.

Pay attention to the comments on the picture, “a large number of circuits and collector plates.” If the converter is different, the picture will be different. The same blue line, the current is almost constant, but pulsating, remember this word. Here, by the way, pure direct current is the red line.

Since the power does not change due to more high voltage on the connection line, this means that current is flowing there, so this is our voltage drop and therefore the limit. And this is also the reason why high voltage cables also carry 100 kV - 300 kV. Due to the high voltage and associated lower current, the effect of the cables' sometimes very high internal resistances is minimized. General: Definition is a quantity indicating how much work or energy is required to move a charge carrier with a certain electric charge in an electric field.

The relationship between magnetism and electricity

This definition is also easier to imagine. In order for "current" to flow in a closed system, voltage is required as a prerequisite. This electrical voltage means driving force, which allows or causes the movement of a charge. Summary so far: If no current or voltage source is loaded by a load, no current flows and therefore there is no voltage drop. The open circuit voltage can be measured at the terminals of the current source. When a load is connected to a current or voltage source, current flows and the initial open circuit voltage is divided between the load resistance and the internal resistance of the voltage source.

Now the analogy for alternating current. Our magnet will be the force of attraction, and the current generator will be an hourglass with water. On one half of the clock we will write “top”, on the other “bottom”. We turn our clock over and see how the water flows “downwards”, when all the water has flowed over, we turn it over again and the water flows “upwards”. Despite the fact that we have current, it changes direction twice in a full cycle. According to science, it will look like this: the frequency of the current depends on the rotation speed of the generator in the magnetic field. Under certain conditions, we will get a pure sine wave, or simply alternating current with different amplitudes.

This chapter will now cover the terms voltage source and current source. Voltage Source: The terms current source and voltage source should not be confused with each other. In principle, current and voltage sources have opposite properties. A voltage source serves as a source of electrical energy that supplies electrical current depending on the connected load, but cannot be confused with a current source. Important characteristic voltage source is that the voltage is only low, or, in the case of the ideal voltage source model, is independent of the electrical current received.

Because the essential property of a current source is that the current is only low, or in the ideal current source model, the frame current is independent of the electrical voltage. Examples of voltage sources are batteries, Solar cells and generators and, unlike current sources, do not supply direct current, but constant voltage. Typically, current sources are created by using a voltage source and converting it into a current source using a suitable circuit.

Within the term "voltage source" can still be divided into ideal and real voltage source. An ideal voltage source is one that generates a constant voltage independent of current and connected loads. Real voltage sources can be considered as an ideal voltage source that supplies voltage without load and depends on internal resistance, so the voltage profile across the actual voltage source depends on the current that is drawn.

What causes the wide variety of currents

But, as they say, “not all currents are equally useful,” by the way, let’s think about which current is more dangerous: constant or alternating, if we have roughly imagined not the nature of the current, but rather its features. Man is a collodium that conducts electricity well. A set of different elements in water (we are 70% water, if anyone doesn’t know). If voltage is applied to such a collodium - an electric shock is applied, then the particles inside us will begin to transfer charge. As it should be, from a point of high potential to a point of low potential. The most dangerous thing is to stand on the ground, which is generally a point with infinite zero potential. In other words, we will transfer all the current, that is, the difference in charges, to the ground. So, with a constant direction of movement of the charge, the process of equalizing the potential in our body occurs smoothly. We are like sand letting water pass through us. And we can safely “absorb” a lot of water. With alternating current, the picture is a little different - all our particles will be “pulled” here and there. The sand will not be able to easily pass water, and it will be all agitated. Therefore, the answer to the question of which current is more dangerous: constant or alternating current, the answer is clear - alternating. For reference, the life-threatening threshold DC current is 300mA. For alternating current, these values depend on frequency and start at 35mA. At a current of 50 hertz 100mA. Agree, a difference of 3-10 times in itself answers the question: which is more dangerous? But this is not the main argument in choosing a current standard. Let's organize everything that is taken into account when choosing the type of current:

Visualizing the two terms: First, figuring out current and voltage again. The stronger the two sides, the stronger the force that acts between them and the greater the tension. The two current sources and voltage sources can be explained with a light-hearted example. A mountain lake is imagined, representing tension in a transposed sense. The higher the lake, the higher the voltage. Now water from the mountain lake is folded into the valley through pipes. There is a pipeline from the mountain lake to the valley.

Water can be thought of as electrons. If a pipe is open at the top of a mountain lake, water flows down the pipe, which is a current in the transposed sense. This means that the more water there is in the lake, the more water will "flow" down. Of course, there is resistance at the voltage source or current source. This can also be imagined. In the example presented, the diameter of the pipe will be the resistance. The narrower the tube, the less water can flow. The narrow tube ensures resistance to water flow.

Delivery of current over long distances. Almost all direct current will be lost;
Conversion in heterogeneous electrical circuits with an uncertain level of consumption. For direct current, the problem is practically unsolvable;
Maintaining a constant voltage for alternating current is two orders of magnitude cheaper than for direct current;
Converting electrical energy into mechanical force is much cheaper in AC motors and machinery. Such motors have their drawbacks and in some areas cannot replace DC motors;
For mass use, therefore, direct current has one advantage - it is safer for humans.

Hence the reasonable compromise that humanity has chosen. Not just one current, but the entire set of available transformations from generation, delivery to the consumer, distribution and use. We will not list everything, but we consider the main answer to the question of the article, “how does direct current differ from alternating current,” in one word - characteristics. This is probably the most correct answer for any household purposes. And to understand the standards, we suggest considering the main characteristics of these currents.

Mathematically, you can combine the two terms. Mountain lake: pipe thickness = water flow. Direct current, alternating current, constant voltage, alternating voltage - electrical variables are briefly explained. With an oscilloscope. Batteries as direct voltage sources.

Transmission of electrical energy via alternating current lines. Voltage diagram DC voltage. AC Voltage Diagram. Electric current does not last long Electric current moves charge carriers, they can have either a negative charge or a positive charge. In a metal, electrons can move freely. They move because they are excited by an electric field. The measure of current intensity is electric current. It is measured in "Ampere", abbreviated as A.

Main characteristics of currents used today

Electrical voltage is briefly explained. If at some point we have a lot of positive charges, their electric field is attractive to electrons, they want to move to positive charges. The more positive charges, the stronger the force that controls the electrons. A measure has been defined for the amount of electrical charges, this is “electrical voltage”. It simply indicates the difference in electrical charges between two points.

For current to flow, there must be voltage. What is Polarity? Electrical voltage has two poles - a positive positive pole and a negative negative pole. There is an electron deficiency at the positive pole, electrons want to migrate to this positive pole. At the minus pole there is an excess of electrons, the electrons are repelled from the minus pole. Polarity is sometimes used instead of polarity. What is a voltage source? The voltage source is a bipolar component, between the two poles of which there is an electrical voltage.

From our point of view, it is a very clear model, which makes it clear how to remove one, two or three phases. At the same time, you can see how it gets to the consumer.

Let's return to currents. We seem to have mentioned everything, and we even know how direct current differs from alternating current, so let’s remind you what currents generally exist.

D.C, the source is the physics of chemical reactions with a change in charge, can be obtained by converting alternating current. A variety is a pulsed current that changes its parameters in a wide range, but does not change the direction of movement.
Alternating current. Can be single-phase, two-phase or three-phase. Standard or high frequency. This simple classification is quite sufficient.

Conclusion or each current has its own device

The photo shows the current generator at the Sayano-Shushenskaya hydroelectric power station. And this photo shows the place where it was installed.

And this is an ordinary light bulb.

Isn’t it true that the difference in scale is amazing, although the first was created, among other things, for the work of the second? If you think about this article, it becomes clear that the closer the device is to a person, the more often it uses direct current. With the exception of DC motors and industrial applications, this is indeed a standard based precisely on the fact that we have found out which current is more dangerous, direct or alternating current. The characteristics of household currents are based on the same principle, since alternating current 220V 50Hz is a compromise between danger and losses. The price of compromise is protective automation: from the fuse to the RCD. Moving away from humans, we find ourselves in the zone of transient characteristics, where both currents and voltages are higher, and where the danger to humans is not taken into account, but attention is paid to safety - the zone of industrial use of current. The furthest thing from humans, even in industry, is energy transmission and generation. There is nothing for a mere mortal to do here - this is a zone of professionals and specialists who know how to manage this power. But even with everyday use of electricity, and of course when working with electrical equipment, understanding the basic nature of currents will never be superfluous.

D.C (direct current) –This is the ordered movement of charged particles in one direction. In other words
quantities characterizing electric current, such as voltage or current, are constant both in value and direction.

In a direct current source, such as a conventional AA battery, electrons move from minus to plus. But historically, the technical direction of current is considered to be the direction from plus to minus.

For direct current, all the basic laws of electrical engineering, such as Ohm's law and Kirchhoff's laws, apply.

Story

Initially, direct current was called galvanic current, since it was first obtained using a galvanic reaction. Then, at the end of the nineteenth century, Thomas Edison attempted to organize the transmission of direct current through power lines. At the same time, the so-called “war of currents”, in which there was a choice as the main current between alternating and direct. Unfortunately, direct current “lost” this “war” because, unlike alternating current, direct current suffers large power losses when transmitted over distances. Alternating current is easy to transform and thanks to this it can be transmitted over vast distances.

DC power supplies

Sources of direct current can be batteries or other sources in which current appears due to a chemical reaction (for example, a AA battery).

Also, direct current sources can be a direct current generator, in which current is generated due to
the phenomenon of electromagnetic induction, and then rectified using a collector.

Direct current can be obtained by rectifying alternating current. There are various rectifiers and converters for this purpose.

Application

Direct current is widely used in electrical diagrams and devices. For example, at home, most devices such as a modem or Charger for mobile, operate on direct current. The car's generator produces and converts direct current to charge the battery. Any portable device Powered by DC source.

In industry, direct current is used in direct current machines such as motors or generators. In some countries, high-voltage DC power lines exist.

Direct current has also found its application in medicine, for example in electrophoresis, a treatment procedure using electric current.

In railway transport, in addition to alternating current, direct current is also used. This is due to the fact that traction motors, which have more rigid mechanical characteristics than asynchronous motors, are DC motors.

Effect on the human body

Direct current, unlike alternating current, is safer for humans. For example, a fatal current for a person is 300 mA if it is a direct current, and if it is an alternating current with a frequency of 50 Hz, then 50-100 mA.

Initially, people did not know what current was. Was famous static charge, but no one understood or realized the nature of electricity. It took many centuries until Coulomb developed his own theory, and the German priest von Klein discovered that the jar was capable of storing energy. By the time Van de Graaff created the first generator, everyone already knew the difference between direct current and alternating current.

History of alternating and direct electric current

For a long time, for example, people have seen that a tourmaline crystal attracts ashes. By the way, the properties of piezoelectricity were first described using the example of tourmaline.

At the beginning of the 19th century it was shown that a heated crystal acquires electric charge. Due to deformation, two poles were formed:

Southern (analogous).
Northern (antilogical).

Moreover, if the temperature remains constant after heating, the electricity disappears. Then the appearance of the poles is noted during cooling. It turns out that a tourmaline crystal produces electricity when the temperature changes. Further research showed that the size of the potential depends on:

Cross section of the crystal (cut across the poles).
Temperature differences.

Other factors do not influence the amount of charge. This phenomenon is called pyroelectricity. The tourmaline dielectric was slowly charged from the current flowing inside. And the charge remained in place (certain areas of the surface) due to its insulating properties. Until the tourmaline poles are short-circuited with a conductor, the crystal will continue to accumulate charge as the temperature changes. The line connecting the poles was called the pyroelectric axis.

Piezoelectricity was discovered by the famous Curie pair based on tourmaline in 1880. It was realized that when the size of the crystal changes, charges will begin to be generated; all that remained was to come up with a technique for carrying out the experiment. Curie used for this static pressure normal weight. The experiment is carried out on an insulating surface. For example, a mass of 1 kg causes the appearance of an electric charge in a tourmaline crystal within five hundredths of a static unit.

How does electric current appear?

It is curious that a coherent theory on the described phenomenon has not yet been created. It is important to note that in nature there are charges obtained various methods. During a thunderstorm, this occurs due to the frictional forces of air masses, moisture molecules and other phenomena. The earth is negatively charged, current constantly flows upward through the atmosphere. Current is the movement of charge carriers due to certain reasons. For example, potential differences are differences in carrier levels between two points in space.

Let's compare it with water pressure. When the obstruction is removed, the flow will rush in the direction of lower pressure. Now let's take the analogy of a tourmaline crystal. Let's say charges appear at its ends. Next you will need to cause movement, for example, with a copper wire. Let's connect the poles and electric current will flow. The movement of carriers will continue until the potential is equalized. In this case, the crystal is discharged.

It is impossible to say about the variability or constancy of the current during the indicated process. Alternating and direct current are physical ideals, and are used due to the relative ease of obtaining mathematical models and using them to control technological equipment.

Electric current in reality

In practice, the current shape (charge density versus time) is not sinusoidal. By various reasons the graph view is distorted. This, for example, happens when equipment starts and stops due to induced interference of various natures. The shape of alternating and direct current is distorted. Moreover, it has long been established that this harms the equipment. To combat such a scourge, methods were required, and mathematicians came up with spectral analysis.

An oscillation of any shape can be represented as a sum with different specific gravity of the simplest sinusoids different frequencies. It turns out that a mass of components move along the circuit simultaneously, collectively producing current. Moreover, not all components necessarily move at the same time as the main mass. Imagine the elements as a group of ants, each pulling in its own direction, and the resulting effect causes the load to move in only one direction. Let us mention that in addition to the coefficient (amplitude), each component has a phase (direction), and is called a harmonic.

The equipment cascades are designed so that useful frequencies (mainly 50 Hz) pass inside the device, and the rest goes to the ground. A sign is indicated to solve the difficulty mentioned at the beginning. Any oscillation is represented as a set of useful and harmful signals, based on this, the equipment must be designed appropriately. For example, all receivers operate on the described principle: they selectively pass current required frequency. This makes it possible to cut off interference, and the wave is transmitted with minimal distortion over long distances.

Examples of using AC and DC current

The discharge current of a car battery is considered approximately constant. The voltage here gradually drops, and therefore, even with the same load, the effect varies chronometrically. In general, this happens smoothly. The current flows in one direction and exhibits approximately constant density. They work similarly:

Cell phone battery.
Any type of battery.
Laptop battery.

In nature, there are no direct current sources (generators), with the exception of Mother Earth. It is much more convenient for a person to create rotors that, rotating at a specific frequency, create conditions for the formation of alternating electric current in the stator coils. Then the industrial frequency of 50 Hz passes through the wires and is supplied to the consumer through the substation.

Adapters can be considered a DC source. These are devices that convert alternating current into direct current. Let's say cell phones this is +5 V, and mobile radios are characterized by a large spread. A DC device can only operate at the rating for which it is designed. Otherwise, either the performance is impaired, or, with large deviations, complete failure is possible.

This applies to both alternating and direct current. Now the time has come to say that in industry the conversion of direct current to alternating current and vice versa is not practiced. For reasons of economy, the motors operate on three phases. Each is considered an alternating current with a frequency of 50 Hz. We said above that any harmonic has a phase. In the case under consideration, the phase is 120 degrees. A circle is formed by 360 degrees. It turns out that the three phases are equally spaced from each other. In this situation, it is easier for hydroelectric power station generators to produce energy that enters homes unchanged. But the only phase of alternating current enters the apartment.

Therefore, household appliances internal structure very different from industrial ones. AC parameters are considered important. In any state they are standardized and strictly adhered to. AC parameters include:

Effective value voltage - causing a constant of identical rating in an ordinary conductor. The effective value is below the amplitude by the root of two times or close to the specified one. The requirements for the Russian Federation are 220-230 V plus or minus 10% of the nominal value.
The frequency of alternating current is subject to increased stringent requirements. The limit of deviations from 50 Hz is measured in tenths of a percent. That is why so much attention is paid to stabilizing the movement of the shaft at hydroelectric power plants. The parameter depends on the speed of its rotation.
Nonlinear distortions are considered a separate topic. There are many requirements, it’s not easy to decide. The harmonics of the fundamental frequency are especially strictly standardized, for example: 100, 150, 200, 250 Hz.

Similar requirements apply to direct current parameters. Let's say known car batteries in fact, they include in the arsenal not 12, but 14 V. As the discharge progresses, the voltage drops. If a voltage of 11.9 V is registered on the battery, the bank is considered faulty. We suggest you read the instructions carefully. Let's add: in separate laptops There is a charge to conserve battery power. In this case, the level is maintained within two-thirds of the full level. It is believed that then the battery will last longer.

So, the requirements are aimed at maintaining a long and proper functioning equipment. The parameters of direct and alternating current are considered a factor determining the reliability and performance of the system.

Electric current is the transfer of charge or the movement of charged particles between points with different electrical potentials. Electrical charge can be carried by ions, protons and/or electrons. IN Everyday life Almost everywhere, the movement of electrons through conductors is used. There are usually two types of electricity - alternating and direct. It is important to know how direct current differs from alternating current.

Direct and alternating current

Any phenomenon that cannot be seen or “touched” directly is easier to understand using analogies. In the case of electricity, we can consider water in a pipe as the closest example. Water and electricity flow through their conductors - wires and pipes.

The volume of flowing water is the current strength.
The pressure in the pipe is tension.
Pipe diameter is conductivity, the reciprocal of resistance.
Volume per pressure - power.

The pressure in the pipe is created by the pump - the pump pumps harder, the pressure is higher, more water flows. The diameter of the pipe is larger - the resistance is less, more water flows. The source produces more voltage - more electricity flows. Wires are thicker - less resistance, higher current.

For example, you can take any chemical source power - battery or accumulator. Its terminals have pole designations: plus or minus. If you connect a corresponding light bulb to the battery, through the wires and the switch, it will light up. What happens? The negative terminal of the source emits electrons - elementary particles carrying a negative charge. Along the wires, through the switch connectors and the lamp spiral, they move towards the positive terminal, trying to equalize the potential of the terminals. As long as the circuit is closed across the switch connectors and the battery is not dead, electrons flow in a spiral and the light bulb is on.

The direction of movement of charges remains unchanged all the time - from minus to plus. This is direct current, it can be pulsating - weaken or increase.

For many reasons Using only constant voltage is inappropriate: Take, for example, the inability to use transformers. Therefore, by now a system of supply and consumption has developed AC voltage power supply, for which household appliances are created.

There is a simple answer to what is the difference between direct and alternating current. In this light bulb example, the voltage on one terminal of the power supply will always be zero. This is the neutral wire, but on the other - the phase wire - the voltage changes. And not only in size, but also in direction - from plus to minus. Electrons do not flow in orderly rows in one direction, on the contrary, they rush back and forth, the same particles run back and forth along the incandescent spiral and do all the work. Changing the direction of electricity and gives the very concept of “variable”.

Advanced network settings

In addition to voltage, force, power and resistance/conductivity, two new features appear that describe processes. These parameters are required, just like the first four. When any of them changes, the properties of the entire chain change.

Form.
Frequency.

The type of voltage change graph plays a big role. Ideally, it has the form of a sinusoid with smooth transitions from value to value. Deviations from the sinusoidal shape can lead to poor power quality.

Frequency is the number of transitions from one extreme state to another per certain time. European standard at 50 Hz (hertz) means that the voltage changes plus and minus 50 times per second, and the electrons change direction a hundred times. For reference: doubling the frequency leads to a fourfold reduction in device dimensions.

If the socket has an alternating current of 50 Hz and 220 V (volts), then this means that the maximum supply voltage in the network reaches 380 V. Where does this come from? IN permanent network The voltage value is constant, but when there is a change, it either falls or rises. These 220 V are the value of the effective voltage of a sinusoidal current with an amplitude of 380 V. That is why the form of change in values is so important, because if it differs greatly from the sinusoid, the effective voltage will also change greatly.

Practical significance of the differences

This is what it is, alternating and direct current. It's not that difficult to figure out what the difference is. There is a difference and a very big one. A DC source will not allow you to connect a welding, or any other, transformer. When calculating insulation or capacitors, it is not the current that is taken for breakdown, but maximum value voltage. After all, the thought may certainly arise: “why do you need 400-volt capacitors in a 220-volt network?” Here is the answer, in a 220 V network the voltage reaches 380 V at normal operation, and in the event of a minor failure, 400 V is not the limit.

Another "paradox". A capacitor has infinite resistance in a DC network, and conductivity in an AC network; the higher the frequency, the lower the resistance of the capacitor. With coils it’s different - an increase in frequency causes an increase inductive reactance. This property is used in oscillatory circuit- the basis of all communication.