Current power constant and alternating current. Alternating current

Types of current

Among the types of electric current distinguish:

D.C:

Designation (-) or DC (Direct Current \u003d Permanent Current).

Alternating current:

Designation (

) or AC (Alternating Current \u003d Alternating Current).

In the case of direct current (-), the current flows in one direction. Permanent current supply, for example, dry batteries, solar panels and batteries for devices with low power consumption. For aluminum electrolysis, with arc electric welding and during the operation of electrified railways, a constant current of great strength is required. It is created by straightening alternating current or using DC generators.

As the technical direction of the current, it is customary that it flows from contact with the "+" sign to contact with the "-" sign.

In the case of alternating current (

) Different single-phase alternating current, three-phase alternating current and high-frequency current.

With alternating current, the current constantly changes its magnitude and its direction. In the Western European power plant, the current per second changes its direction 50 times. The frequency of changes in oscillations per second is called the current frequency. Frequency unit - Hertz (Hz). Single-phase alternating current requires a conductor conducting voltage and reverse conductor.

The alternating current is used on the construction site and in the industry for the operation of electrical machines, such as hand-held grinding devices, electric drills and circular saws, as well as to illuminate construction sites and construction equipment.

Three-phase alternators generators are produced on each of its three windings A variable voltage with a frequency of 50 Hz. This voltage can be equipped with three separate networks and at the same time use only six wires for direct and reverse conductors. If you combine reverse conductions, you can only be limited to four wires.

The total reverse wire will be a neutral conductor (N). As a rule, it is grounded. Three other conductor (external conductors) have a brief designation Li, L2, L3. In the Unified Energy System of Germany, the voltage between the external conductor and the neutral conductor, or the ground, is 230 V. The voltage between two external conductors, for example, between L1 and L2, is 400 V.

The high-frequency current is said when the frequency of oscillations significantly exceeds 50 Hz (from 15 kHz to 250 MHz). With the help of high frequency current, you can heat the conductive materials and even melted them, for example metals and some synthetic materials.

Converters a variable constant Current. Device.

Vasily Sonykin

If people will stand along the entire Garden Ring, will take hands, and at the same time will walk in one direction, then many people will pass through each intersection. This is a permanent current. If they will make a couple of steps to the right, then to the left, through each intersection there will be many people, but it will be the same people. This is alternating current.

Current is the movement of electrons in a specific direction. It is necessary that electrons move in our devices too. Where does the current be taken in the outlet?

The power plant converts the kinetic energy of electrons into electrical. That is, the hydroelectric power station uses flow water to rotate the turbine. The propeller of the turbine rotates the copper of copper between the two magnets. Magnets make electrons in copper move, due to this, the electrons are started in the wires that are attached to the Copper Talk - the current is obtained.

The generator is like a water pump, and the wire is like a hose. The pump generator shakes electrons-water through wires-hoses.

AC current is the current that we have in the outlet. It is called variables, because the direction of movement of electrons is constantly changing. Alternating current from outlets is different frequency and electrical voltage. What does it mean? In Russian sockets, the frequency is 50 hertz and a voltage of 220 volts. It turns out that in a second the flow of electrons 50 times changes the direction of movement of electrons and charge with positive to negative. Replacing directions can be seen in fluorescent lamps when you turn on. While the electrons accelerate, it flashes several times - this is the change of directions of movement. And 220 volts are the maximum possible "pressure" with which the electrons move in this network.

In alternating current, the charge is constantly changing. This means that the voltage is 100%, then 0%, then again 100%. If the voltage was 100% constantly, it would take a wire of a huge diameter, and with a changing charge of the wires could be thinner. It's comfortable. According to a small wire, the power plant can send millions of volts, then the transformer for a separate house takes, for example, 10,000 volts, and in each rosette produces 220.

Permanent current is a current that you have in a telephone battery or batteries. It is called constant, because the direction of movement of electrons does not change. Chargers transform alternating current from the network to constant, and in this form it turns out to be in batteries.

What is alternating current and what it differs from the current

Alternating current. Unlike the current constant. Continuously changes both in magnitude and in the direction, and these changes occur periodically periodically, that is, they are precisely repeated at equal intervals.

To cause such a current in the circuit, the sources of AC are used, creating an EDC variable, periodically vary in magnitude and direction. Such sources are called alternating current generators.

In fig. 1 shows a diagram of the device (model) of the simplest alternator.

The rectangular frame made of copper wire is reinforced on the axis and with the help of the belt transmission rotates in the field of the magnet. The ends of the frame are soldered to the copper contact rings, which, rotating along with the frame, slide along the contact plates (brushes).

Figure 1. Scheme of the simplest alternator

Make sure that such a device is really the source of the EDC variable.

Suppose that the magnet creates a uniform magnetic field between its poles. i.e. such in which the density of magnetic power lines in any part of the field is the same. Rotating, the frame crosses the power lines of the magnetic field, and in each of its parties A and B are induced by EMF.

The sides of the same in the frame - non-working, since when the framework is rotated, they do not cross the power lines of the magnetic field and, therefore, do not participate in the creation of EMF.

At any time, the EMF, arising from the side A, is opposite to the direction of EMF, arising from the side B, but in the framework of both EMFs act according to and in the amount they constitute the total EMF, that is, the entire framework is induced.

This is not difficult to make sure if used to determine the direction of EDS known to us the rule of the right hand.

To do this, you need to put my hand to the right hand so that it is facing the north pole of the magnet, and the big bent finger coincided with the direction of the movement of the side of the framework in which we want to determine the direction of EMF. Then the direction of EDC in it will indicate the elongated fingers.

For whatever the position of the frame, we determined the direction of the EMF in the sides A and B, they always develop and form a common EMF in the framework. At the same time, with each turnover of the frame, the direction of the general EMF varies in it to the opposite, since each of the working parties of the frame for one turnover passes under different poles of the magnet.

The value of the EDC induced in the frame is also varies, as the speed is changed from which the side of the frame crosses the power lines of the magnetic field. Indeed, at the time when the frame comes up to its vertical position and passes it, the speed of intersection of the power lines by the sides of the frame is the greatest, and the largest EDC is induced in the frame. In those moments of time when the frame takes place its horizontal position, it will be sliding along the magnetic power lines along the magnetic power lines, without crossing them, and the EMF is not induce.

Thus, with even rotation of the frame, it will be induced by EMF, periodically changing both in magnitude and in the direction.

EMF, which occurs in the frame, can be measured by the device and use to create a current in the outer chain.

Using the phenomenon of electromagnetic induction. You can get an EDC variable and, therefore, alternating current.

AC for industrial purposes and for lighting is produced by powerful generators, driven by steam or water turbines and internal combustion engines.

Graphic image of constant and alternating currents

The graphic method makes it possible to visually present the process of changing a variable variable depending on the time.

The construction of graphs of variables varying over time begin with the construction of two mutually perpendicular lines, called the schedule axes. Then, on a horizontal axis, a period of time is laid on a certain scale, and on a vertical, also on some scale, the values \u200b\u200bof the magnitude, whose graph is collected (EMF, voltage or current).

In fig. 2 graphically depicts constant and alternating currents. In this case, we depose current values, and up the vertical points from the point of intersection of the axes about the current values \u200b\u200bof the same direction, which is called positive, and down from this point is the opposite direction, which is called negative.

Figure 2. Graphic image of constant and alternating current

The point itself is simultaneously the beginning of the countdown of current values \u200b\u200b(vertically down and up) and time (horizontally to the right). In other words, this point corresponds to the zero value of the current and the initial moment of the time from which we intend to trace how the current will be changed.

Cleister in the correctness of the built in Fig. 2, and DC graphics of 50 mA.

Since this current is permanent, i.e., which does not change over the time of its magnitude and direction, then the same currents of the current will correspond to the same time, that is, 50 mA. Consequently, at the time of time equal to zero, i.e., at the initial moment of our current monitoring, it will be 50 mA. Putting on the vertical axis up the segment, equal to the current value of 50 mA, we get the first point of our graph.

We have to do the same for the next time corresponding to point 1 on the time axis, i.e., to postpone from this point vertically up the segment, also equal to 50 mA. The end of the segment will determine the second point of the graph.

Having done a similar construction for the next few times, we get a number of points, the connection of which will give a direct line, which is a graphical image of a DC value of 50 mA.

Building a graph of a variable EMF

We now turn to the study of the graph of the EDC variable. In fig. 3 In the upper part, the frame rotating in the magnetic field is shown, and the graphic image of the emerging variable of EDC is given at the bottom.

Figure 3. Building a variable EDC graphics

Let's start evenly rotate the frame clockwise and follow the progress of the change in it. EMF, having accepted the horizontal position of the frame for the initial moment.

At this initial moment, the EMF will be zero, since the side of the frame does not cross the magnetic power lines. On the graph, this zero value of the EMF, corresponding to the moment T \u003d 0, is shown in point 1.

With a further rotation of the frame, the EMC will begin to appear and will increase in magnitude until the frame will reach its vertical position. On the chart, this increase in EMF is depicted by a smooth rising curve, which reaches its vertex (point 2).

As the frame approaches the horizontal position of the EMF in it will decrease and falls to zero. On the chart, it is depicted by a falling smooth curve.

Therefore, in the time corresponding to half the turnover of the frame, the EMF has managed to increase in it from zero to the greatest value and again decrease to zero (point 3).

With the further rotation of the frame, it will again arise the EMC again and will gradually increase in magnitude, but its direction will already change to the opposite, which can be seen by applying the rule of the right hand.

The schedule takes into account the change in the direction of the EMF in the way that the curve depicting the EMF crosses the time axis and is now below this axis. EMF increases again until the frame takes a vertical position. The EMF will begin, and it will become equal to zero, when the frame returns to its original position, performing one full turn. On the chart, this will be expressed by the fact that the EMC curve, reaching in the opposite direction of its vertex (point 4), will then meet with the axis of time (point 5).

This ends with one cycle of EMF change, but if you continue the rotation of the frame, the second cycle immediately begins, the repetitive first, which, in turn, will follow the third, and then the fourth, and so until we stop the rotation framework.

Thus, for each turnover of the EMF frame, arising in it, makes a full cycle of its change.

If the frame will be closed on any outer chain, then the chain will flow alternating current, the graph of which will be the same as the EMF schedule.

The resulting wave curve is called a sinusoid. And the current, emf or voltage varying for such a law is called sinusoidal.

The curve itself is called sinusoid because it is a graphic image of a variable trigonometric value, called sinus.

The sinusoidal nature of the current change is the most common in electrical engineering, therefore, speaking of alternating current, in most cases they mean the sinusoidal current.

To compare various variable currents (EMF and stress), there are values \u200b\u200bcharacterizing one or another current. They are called alternating current parameters.

Period, amplitude and frequency - AC Parameters

AC is characterized by two parameters - a period and amplitude of th, knowing which we can judge, what is the alternating current, and build a current schedule.

Figure 4. Sinusoidal Current Curve

The period of time, during which a complete cycle of current change is performed, is called a period. The period is indicated by the letter T and is measured in seconds.

The period of time, during which half the total current cycle is performed, is called half aode. Consequently, the period of change of current (EMF or voltage) consists of two half-periods. It is obvious that all periods of the same alternating current are equal to each other.

As can be seen from the graph, during one period of its change, the current reaches twice the maximum value.

The maximum variable value of the AC (EMF or voltage) is called its amplitude or amplitude current.

IM, EM and UM are generally accepted indications of current amplitudes, EMF and voltage.

We first drew attention to the amplitude current. However, as can be seen from the schedule, there are countless intermediates of its values \u200b\u200bsmaller than amplitude.

The AC value (EMF, voltage) corresponding to any selected point of time is called an instantaneous value.

i. E and U - generally accepted notation of instantaneous current values, EMF and voltage.

Instant current, as well as an amplitude value, is easy to determine using the graph. For this, from any point on the horizontal axis corresponding to the time of interest to us, we will spend the vertical line to the intersection point from the current curve, the resulting segment of the vertical direct will determine the current value at the moment, i.e. the instantaneous value.

It is obvious that the instantaneous current value after the time of time T / 2 from the starting point of the schedule will be zero, and after the time expires, the T / 4 of its amplitude value. The current also reaches its amplitude, but already in the opposite on the board, after the time of time equal to 3/4 T.

So, the graph shows how the current in the chain changes over time, and that every moment of time corresponds to only one specified value of both the values \u200b\u200band current direction. At the same time, the current value at the moment of time at one point of the chain will be exactly the same at any other point of this chain.

The number of total periods performed by the current in 1 second is called the frequency of alternating current and is indicated by the Latin letter F.

To determine the frequency of alternating current, i.e., to find out how many periods of its change has made for 1 second. It is necessary to divide 1 second at a time of one period f \u003d 1 / t. Knowing the frequency of alternating current, it is possible to determine the period: T \u003d 1 / F

The frequency of alternating current is measured by a unit called Hertz.

If we have alternating current. The frequency of which is equal to 1 hertz, then the period of this current will be equal to 1 second. And, on the contrary, if the current change period is 1 second, the frequency of this current is equal to 1 hertz.

So, we defined the parameters of the AC - a period, amplitude and frequency. - which allow you to distinguish from each other different variables, EMF and voltage and build when necessary, their graphs.

When determining the resistance of different circuits, the variable current use another auxiliary value characterizing the alternating current, the so-called angular or circular frequency.

Circular frequency is indicated by the letter # 969 and is associated with the frequency F by the ratio # 969 \u003d 2 # 960 F

Let us explain this dependence. When building the graphics of the EDS variable, we saw that during one full turnover of the frame there is a full cycle of EMF change. In other words, in order for the frame to make one turnover, that is, turning 360 °, it is necessary to take time equal to one period, that is, for seconds. Then in 1 second the frame makes 360 ° / t turnover. Therefore, 360 ° / T is an angle to which the ICA is rotated at 1 second, and expresses the rod of rod of rotation of the frame, which is customized to call an angular or circular speed.

But since the period T is associated with the frequency f by the ratio f \u003d 1 / t, then the circular speed can be expressed through the frequency and will be # 969 \u003d 360 ° F.

So, we came to the conclusion that # 969 \u003d 360 ° F. However, for the convenience of using a circular frequency with all sorts of calculations, an angle of 360 ° corresponding to one turnover is replaced by its radial expression equal to 2 # 960 radians, where # 960 \u003d 3.14. Thus, we finally get # 969 \u003d 2 # 960 F. Therefore, to determine the circular frequency of alternating current (EMF or voltage), it is necessary to multiply the frequency in Hertz to a constant number of 6.28.

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In this, we will tell you what is an alternating electric current and three-phase variable alternating current.

The concept of an alternating electric current is given in the textbook of physics of a general educational institution - schools. - Current hazardized by a harmonic sinusoidal signal, the main characteristics of which are the active voltage and frequency, changes in the direction and magnitude.

Frequency - This is the number of complete changes in the polarity of the variable electrical current in one second. This means that the current, in the usual household rosette with a frequency of 50 Hertz in one second changes its direction from a positive value to the negative and back exactly fifty times. One complete change in the direction (polarity) of the electric current with a positive value to the negative and again on a positive one - electric current fluctuations . During period T. A variable electric current changes its direction twice.

For visual observation sinusoidal alternating current Usually used. To eliminate electric shock and protect the oscilloscope from network voltage in the input, separation transformers are used. To measure the period, there is no difference for which equivalent (equivalent) to measure it. It is possible at the maximum positive, or negative vertices, and it is possible to zero. This is explained in the figure.

From the textbook of physics, we know that the alternating electric current is produced using an electrical machine - generator. The simplest generator model is a magnetic frame rotating in a magnetic field of a permanent magnet.

Imagine a rectangular wire frame with several turns, evenly rotating in a homogeneous magnetic field. Arising in this frame of EDs. Induction varies according to the sinusoidal law. Period of oscillation T. A variable electric current is one full turn of the magnetic frame around its axis.

One of the important characteristics of the electric current are two values \u200b\u200bof the variable electrical current - the maximum value and the average value.

Maximum voltage value of electric current Umax - This is the magnitude of the voltage corresponding to the maximum value of sinusoids.

The average voltage voltage USR - This is the magnitude of the voltage equal to the value of 0.636 from the maximum. Mathematically it looks like this:

U cp \u003d 2 * u max / π \u003d 0,636 u max

The maximum voltage sinusoid can be monitored on the oscilloscope screen. Understand what is the average value of the electrical voltage You can conduct an experiment in the figure and description below.

Using the oscilloscope, connect the sinusoidal voltage to its input. The vertical shift knob to move the "zero" of the wind to the lowest line of the oscilloscope screen scale. Stretch and shift the horizontal spread so that one half-wave of the sinusoidal voltage can fit at ten (five) cells of the oscilloscope screen. The knob of the vertical expansion (amplification) stretches the spread so that the maximum amplitude of the half-wave placed exactly at ten (five) cells of the oscilloscope screen. Determine the amplitude of sinusoids on ten sites. Summarize all ten values \u200b\u200band divide ten - find it "middle score." As a result, you will receive a voltage value approximately equal to 6.36 of its maximum value - 10.

Measuring instruments - Voltmeters, Castle, Multimeters for measuring alternating voltage have a rectifier and smoothing capacitor in their scheme. This chain "rounds" the multiplier of the maximum and measured voltage to the number of 0.7. Therefore, if you observe the voltage sumplicity of 10 volts on the oscilloscope screen, the Voltmeter (Castle, Multimeter) will show not 10, and about 7 volts. Do you think that in your home outlet - 220 volts? So there is, but not quite so! 220 Volt is the average value of the consumer socket voltage, averaged by the measuring instrument - voltmeter. The maximum voltage follows from the formula:

U max \u003d uim / 0.7 \u003d 220 / 0.7 \u003d 314.3 volts

That is why when you "gets" current from 220 volts with a 220 volt electrical socket, know that this is your illusion. In fact, you are shaking a voltage of about 315 volts.

Three phase current

Along with a simple sinusoidal alternating current, the so-called technique is widely used. three-phase alternating current. Moreover, three-phase electric current is the main type of energy used throughout the world. Three-phase current has gained popularity due to the less costly energy transmission over long distances. If there are two wires for the usual (single-phase) electrical current, then for three-phase current, which has three times more energy, only three wires are required. Physical meaning you will learn in this article later.

Imagine if not one, but three of the same frame rotate around the total axis, the planes of which are rotated relative to a friend of 120 degrees. Then the sinusoidal ED arising in them. Also will be shifted in phase by 120 degrees (see Fig).

Such three coordinated current variables are called three-phase current. The simplified location of the wire windings in the three-phase current generator is illustrated in the figure.

Connecting the three-way windings of three independent lines is shown in Figure below.

Such a connection with six wires is quite cumbersome. Since only potential differences are important for phenomena in electrical circuits, one conductor can be used immediately for two phases, without reducing the load capacity for each of the phases. In other words, in the case of the connection of the generator windings according to the "Star" scheme using "zero", the transmission of energy from three sources is made in four wires (see Fig.), In which one is common - zero wire.

For three wires, energy can be transmitted immediately from three (actually independent) sources of electrical current by the "triangle".

In industrial generators and transformers, the "triangle" is usually connected by the interfacial voltage of 220 volts. In this case, the "zero" wire is absent.

"Star" is used to transmit network voltage using "zero". At the same time, the phase relative to the "zero" acts a voltage of 220 volts. The interfacial voltage is equal to 380 volts.

In frequent phenomenon in the time of "brazening democracy" was the combustion of household equipment in the apartments of good-order citizens, when, due to weak wiring, the total "zero" burned, then depending on how the number of household appliances is included in the apartments, TVs were burned and refrigerators who included them in the least. It is caused by this phenomenon of "skew phases", which occurred when the zero is broken. In an outlet of respectable citizens instead of 220 volts, the interfacial voltage of 380 volts rushed. To date, in many communals and structures resembling housing of our Russian cities and weighs, this phenomenon was not fully eradicated.

And. Before detailing these terms, it should be recalled that the concept of electric current consists in an ordered movement of particles having electrical charges. If electrons are constantly moving in one direction, the current is called permanent. But when the electrons are moving in one direction at one point in one direction, and at another point moves in another direction, this is an ordered movement of charged particles moving without stopping. This current is called variable. The significant difference between them is that the constant value "+" and "-" are constantly on one specific place.

What is constant voltage

A regular battery is used as an example of a constant voltage. On the case of any battery there are notation "+" and "-". This suggests that at a constant current, these values \u200b\u200bhave a permanent location. A variable on the contrary, the values \u200b\u200bof "+" and "-" change through certain short intervals. Therefore, the DC designation is used in the form of one straight line, and the designation of the variable is as a single wavy line.

Difference DC from AC

Most devices using permanent current do not allow when connecting the power source to confuse contacts, since in this case the device can simply fail. With a variable, this will not happen. If you insert the plug into the socket by any side, then the device will still work. In addition, there is a concept as an alternating current frequency. It shows how many times a second change in the minus places with a plus. For example, the frequency of 50 hertz means changing the voltage polarity per second 50 times.

On the represented schedules it is seen a change in voltage at various temporal moments. On the schedule on the left, for example, the voltage on the pocket flashlight light bulb contacts. On the length of time from "0" to the point "A" the voltage is generally absent, since the flashlight is turned off. At the point of time "A", voltage U1 occurs, which does not change in the time "A" - "b" when the flashlight is turned on. When the flashlight is turned off at the time of the time "b", the voltage becomes zero again.

On the chart of alternating voltage, it can be clearly seen that the voltage at different points is rising to the maximum, it becomes equal to zero, then it drops to a minimum. This movement occurs evenly, after the same intervals and repeats until the light turns off.

The electric shock is called the transfer of charge or the movement of charged particles between points, with different electrical potentials. To transfer the electrical charge can ions, protons and / or electrons. In everyday life almost everywhere, the movement of electrons by conductors is used. Usually there are two varieties of electricity - variable and permanent. It is important to know than the constant current is different from the variable.

Standing and alternating current

Any phenomenon that cannot be seen or "swelling" is easier to understand with the help of analogy. In the case of electricity, it is possible to consider water in the pipe as the closest example. Water and electricity flow through their conductors - wires and pipes.

• The volume of the flowing water is the current strength.
• Pressure in the pipe - voltage.
• Pipe diameter - conductivity, reverse resistance.
• Pressure volume - power.

Pressure in the pipe is created by the pump - the pump is stronger than the pump, the pressure is higher, the water flows more. The diameter of the pipe is greater - the resistance is less, the water proceeds more. The source gives the voltage more - electricity proceeds more. Wires are thicker - resistance is less, the current is higher.

For example, you can take any chemical source. Power - battery or battery. His terminals include pole designations: plus or minus. If you connect the corresponding light bulb through the wires and switch to the battery, then it will light up. What happens? The minus source terminal eats electrons - elementary particles carrying a negative charge. By wires, through the connector of the switch and the spiral of the lamp, they move to a positive terminal, striving the level of the potential of the terminals. While the chain is closed on the connector of the switch and the battery, the electrons and the light bulb runs along the spirals.

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

For many reasons the use of only constant voltage is inappropriate: To take at least the impossibility of using transformers. Therefore, by now the system of supplying and consumption of alternating supply voltage, under which household appliances are created.

There is a simple answer, what is the difference between constant and alternating current. In this example, with a light bulb on one power supply terminal, the voltage will always be zero. This is a zero wire, but on the other - phase, the voltage changes. And not only in magnitude, but also in the direction - from the plus for minus. The electrons do not flow with slender rows in one direction, on the contrary, move forward-back, the same particles run on the spiral of incandescent there and produce all the work. Changing the direction of electricity And the concept of "variable" gives itself.

Additional network settings

In addition to the voltage, strength, power and resistance / conductivity, two new features describing processes appear. These parameters are mandatory, as well as the first four. When changing any of them, the properties of the entire chain are changed.

• The form.
• Frequency.

The type of voltage change graphics is played. Ideally, it has a kind of sinusoids with smooth transitions from the value to the value. Deviations from the sinusoidal form can lead to a decrease in energy quality.

Frequency is the number of transitions from one extreme state to another during a certain time. The European standard in 50 Hz (Hertz) means that the voltage changes plus for minus 50 times per second, and the electrons change hundred times the direction of movement. For reference: increased frequency twice leads to a four-time reduction in device dimensions.

If in the outlet of the alternating current of 50 Hz and 220 V (volt), then this means that the maximum supply voltage in the network reaches 380 V. Where is it from? In a permanent network, the voltage value is consistently, and with a change it it falls, it grows. These are these 220 V and are the value of the active sinusoidal current voltage with an amplitude of 380 V. Because the form of changes in the values \u200b\u200bis so important, which, with a strong difference from the sinusoids, the active voltage will change.

The practical value of differences

Here is such a, variable and permanent current. What is the difference, it's not so difficult to figure out. The difference is and very large. DC source will not allow welding, and any other transformer. When calculating isolation or capacitors, not active, but the maximum voltage value is taken. After all, it may be thought of: "Why on the network 220 volts capacitors for 400?". That's the answer, in the network 220 to the voltage comes up to 380 V at normal operation, and with a small failure and 400 not the limit.

Another "paradox". The capacitor has infinite resistance in the DC network, and conductivity in the variable network, the higher the frequency, the smaller the resistance of the condenser. With the coils otherwise, the increase in frequency causes an increase in inductive resistance. This property is used in the oscillatory contour - the basis of the whole communication.

Although we use electrical appliances every day in everyday life, not everyone can answer, what is the difference current from constant, despite the fact that it is described in the framework of the school program. Therefore, it makes sense to remind the main dogmas.

Generalized definitions

The physical process, in which the charged particles move ordered (directionally), is called electric stroke. It is accepted to divide into variable and permanent. The first direction and the quantity remain unchanged, and in the second, these characteristics change according to a certain pattern.

The determinations are greatly simplified, although they explain the difference between permanent and variable electrotox. For a better understanding, what is this difference, it is necessary to bring the graphic image of each of them, and also explain how the variable electromotive force is formed in the source. To do this, turn to electrical engineering, or rather its theoretical basics.

Sources of EMS.

Sources of electric flow of any kind are of two types:

• primary, with their help, the generation of electricity is occurring by turning mechanical, solar, thermal, chemical or other energy into electrical;
• secondary, they do not generate electricity, but convert it, for example, from a variable permanent or vice versa.

The only primary source of the variables is the generator, the simplified diagram of such a device is shown in the figure.

Designations:

• 1 - direction of rotation;
• 2 - magnet with poles S and N;
• 3 - magnetic field;
• 4 - wire frame;
• 5 - EDC;
• 6 - ring contacts;
• 7 - current collectors.

Principle of operation

Mechanical energy is converted by the generator shown in the figure in the figure as follows:

due to such a phenomenon as electromagnetic induction, when the "4" frame is rotated, placed in the magnetic field "3" (arising between the various poles of the magnet "2"), it is formed by EMF "5". The network voltage is fed through the current collectors "7" from the ring contacts "6" to which the "4" frame is connected.

Video: Permanent and alternating current - differences

As for the value of EDC, it depends on the rate of intersection of the power lines "3" by the framework of "4". Due to the characteristics of the electromagnetic field, the minimum intersection rate, which means the lowest value of the electromotive force will be at the moment when the frame is in a vertical position, respectively, the maximum - in horizontal.

Considering the above, in the process of uniform rotation, an emf is induced, the characteristics of the size and direction of which are changed with a certain period.

Graphic images

Thanks to the application of the graphic method, you can get a visual representation of dynamic changes of different quantities. Below is a graph of voltage change over time for a galvanic element 3336l (4.5 V).

As you can see, the graph is a straight line, that is, the source voltage remains unchanged.

Now we will give a schedule for the dynamics of voltage change during one cycle (full turnover of the frame) of the operation of the generator.

For clarity, show the initial position of the frame in the generator, corresponding to the starting point of the report on the chart (0 °)

Designations:

• 1 - pole magnet S and n;
• 2 - frame;
• 3 - direction of rotation of the frame;
• 4 - magnetic field.

Now let's see how EDC will change in the process of one frame rotation cycle. In the initial position of the EMF will be zero. In the process of rotation, this value will begin to grow smoothly, reaching a maximum at the time when the frame will be at an angle of 90 °. Further rotation of the frame will lead to a decrease in EMF, reaching a minimum at the time of rotation 180 °.

Continuing the process, you can see how the electromotive force changes the direction. The nature of the changes has changed the direction of EDC will be the same. That is, it will start smoothly increasing, reaching a peak at a point corresponding to a turn of 270 °, after which it will decrease until the frame will complete the full rotation cycle (360 °).

If the schedule continue to several rotation cycles, we will see a sinusoid characteristic of alternating electrotock. Its period will correspond to one turnover of the frame, and the amplitude is the maximum value of the EMF (direct and reverse).

We now move on to another important characteristic of the variable electrotock - frequency. For its designation, the Latin letter "F" was adopted, and the unit of its measurement - Hertz (Hz). This parameter displays the number of complete cycles (periods) of the EMF change for one second.

The frequency is determined by the formula :. The "T" parameter displays the time of one full cycle (period), is measured in seconds. Accordingly, knowing the frequency, it is easy to determine the period of the period. For example, electrotes with a frequency of 50 Hz are used in everyday life, therefore, its period of its period will be two hundredths of a second (1/50 \u003d 0.02).

Three phase generators

Note that the most cost-effective way to produce an alternating power will be the use of a three-phase generator. The simplified scheme of its design is shown in the figure.

As we can see, the generator uses three coils placed with a 120 ° offset, interconnected by a triangle (in practice, such a connection of the generator windings is not used in the mind of the low efficiency). When passing one of the magnet poles past the coil, it is induce in it.

Than justified the variety of electrotocks

Many people may have a reasonable question - why use such a variety of electrotocks if you can choose one and make it standard? The fact is that not every type of electric flow is suitable for solving a task.

As an example, we give the conditions under which the constant voltage will not only be profitable, nor and sometimes impossible:

• the problem of transmitting the voltage at distances is simply implemented for alternating voltage;
• transform constant electrical shots for heterogeneous electrical caps that have an indefinite level of consumption, almost impossible;
• maintain the required level of voltage in constant electrical circuits is much more complicated and more expensive than variable;
• engines for alternating voltage are constructively simpler and cheaper than for permanent. In this paragraph, it should be noted that such engines (asynchronous) have a high level of starting current, which does not allow them to be used to solve certain tasks.

Now we give examples of tasks where it is more appropriate to use a constant voltage:

• to change the speed of rotation of asynchronous engines required, change the frequency of the power supply, which requires complex equipment. For engines operating from permanent electrotock, it suffices to change the supply voltage. That is why they are installed in electric transport;
• the power of electronic circuits, electroplating equipment and many other devices is also carried out by constant electric stroke;
• the constant voltage is much safer for a person than the variable.

Based on the examples listed above, there is a need to use various types of voltage.