There is another way to reduce the voltage across the load, but only for DC circuits. See about it here.
Instead of an additional resistor, a chain of diodes connected in series in the forward direction is used.
The whole point is that when current flows through the diode, a “forward voltage” drops across it, equal to, depending on the type of diode, power and current flowing through it, from 0.5 to 1.2 Volts.
On a germanium diode the voltage drops 0.5 - 0.7 V, on a silicon diode from 0.6 to 1.2 Volts. Based on how many volts you need to reduce the voltage at the load, turn on the appropriate number of diodes.
To lower the voltage by 6 V, you need to approximately turn on: 6 V: 1.0 = 6 pieces of silicon diodes, 6 V: 0.6 = 10 pieces of germanium diodes. The most popular and accessible are silicon diodes.
The above circuit with diodes is more cumbersome to implement than with a simple resistor. But the output voltage in a circuit with diodes is more stable and weakly dependent on the load. What is the difference between these two methods of reducing the output voltage?
In Fig. 1 - additional resistance - resistor (wire resistance), Fig. 2 - additional resistance - diode.
A resistor (wire resistance) has a linear relationship between the current passing through it and the voltage drop across it. By how many times the current increases, the voltage drop across the resistor will increase by the same amount.
From example 1: if we connect another one in parallel to a light bulb, the current in the circuit will increase, taking into account the total resistance of the two light bulbs to 0.66 A. The voltage drop across the additional resistor will be: 12 Ohm * 0.66 A = 7.92 V The light bulbs will remain: 12 V - 7.92 V = 4.08 V. They will burn at half incandescence.
A completely different picture will be if instead of a resistor there is a chain of diodes.
The relationship between the current flowing through the diode and the voltage dropped across it is nonlinear. The current can increase several times, the voltage drop across the diode will increase by only a few tenths of a volt.
Those. The greater the diode current, the less (compared to a resistor) its resistance increases. The voltage drop across the diodes depends little on the current in the circuit.
Diodes in such a circuit act as a voltage stabilizer. Diodes must be selected according to the maximum current in the circuit. The maximum permissible current of the diodes must be greater than the current in the circuit being calculated.
The voltage drops on some diodes at a current of 0.5 A are given in the table. 
In AC circuits, a capacitor, inductance, dynistor or thyristor (with the addition of a control circuit) can be used as additional resistance.
Instructions
Connect several loads in parallel to one power supply so that their total current consumption is about 80% of the maximum. You cannot increase it any further - the unit will overheat. Please note that if one of the loads fails in such a way that it stops drawing current, the output voltage will increase, which may damage other devices connected to the unit.
If there are no additional loads, connect a resistor in series with the powered device. Select its resistance experimentally until the voltage across the load is close to the nominal one. Start with high resistance and then gradually lower it. Choose a resistor power greater than that which is dissipated by it.
By connecting a diode in series with the load, you can reduce the voltage across it by 0.25 to 0.5 V (the exact value depends on the type of diode). The voltage drop across a diode is less dependent on current than with a resistor, so this option is better suited for loads that draw varying current.
To make the supply voltage of a device connected to a power supply almost constant, use a stabilizer. They are divided into parametric and compensatory, the latter having a higher efficiency. If the power supply itself is not switching, you can install a ferroresonant stabilizer in front of it, but today such a solution is rarely used. You cannot use the power transformer of the power supply itself as a transformer for a ferroresonant stabilizer - it is not designed for this.
Switching stabilizers are noticeably more effective not only than parametric ones, but also compensation ones. You can also build an output voltage feedback loop directly into a switching power supply. Please note that if the feedback circuit is accidentally broken, the output voltage may increase sharply. Also, do not use switching power supplies and stabilizers in conjunction with devices that are sensitive to interference with frequencies ranging from tens of kilohertz to several megahertz.
If you are about to meet and have a conversation with a stranger, you must understand that in the first minutes of communication, tension in the conversation is inevitable. You are unfamiliar and do not know the interaction style of your interlocutor, his psychotype, his manner of conducting dialogue - all this is alarming. Strangers unconsciously create psychological protective barriers for themselves, so your task is to control yourself and not put up such a barrier, and, in addition, to reduce, if possible, the tension that arises during communication.
Instructions
After exchanging greetings, if the initiative for the meeting came from you, switch to a neutral topic. It may concern the weather, the latest political, social or sports news. Here you must express your opinion on what happened, with which your interlocutor will probably agree. In turn, you will confirm your agreement with the judgments expressed by him. By doing this, you will eliminate the moments that cause and begin to destroy the psychological ones.
During a conversation, look into the eyes of your interlocutor, or select a point with your gaze and look at it, periodically reacting to your counterpart’s speech with a nod or a short phrase, making it clear that you are listening to him with concentration and attention.
Start the conversation with phrases that suggest his participation in the conversation and emphasize the importance of his opinion for you: “I’m interested in what you think about...”, “What do you think...”. Replace the pronoun “I” with the pronoun “you”, say not “I want...”, but “If you want...”.
In a conversation, be emotional, smile, react to the words of your interlocutor with facial expressions or gestures, but do not overdo it, everything should be in moderation. Show trust in the person by adopting a slightly relaxed, comfortable posture that demonstrates a desire to listen and communicate.
If in a further conversation your partner began to supplement and explain his statements, respond faster to your questions and immediately express his response judgments, which become more and more extensive, then your goal has been achieved and the tension has been reduced, a constructive dialogue has begun.
Video on the topic
Need to lower voltage industrial power line or power supply for household equipment occurs quite often for one reason or another. This can be successfully done by using transformer or transformerless methods of reducing voltage.
You will need
Instructions
Transformer-based devices are usually used in alternating current. If voltage surges occur, it is recommended to use stabilizing devices (ferroresonance stabilizers). The predicted voltage increase can be compensated by a conventional autotransformer. This device will also provide a reduction in voltage within a specified range. All these devices are based on different types of transformers.
Voltage and current are two basic quantities in electricity. In addition to them, a number of other quantities are also distinguished: charge, magnetic field strength, electric field strength, magnetic induction and others. In everyday work, a practicing electrician or electronics engineer most often has to operate with voltage and current - Volts and Amperes. In this article we will talk specifically about tension, what it is and how to work with it.
Determination of a physical quantity
Voltage is the potential difference between two points and characterizes the work done by the electric field to transfer charge from the first point to the second. Voltage is measured in Volts. This means that tension can only be present between two points in space. Therefore, it is impossible to measure voltage at one point.
Potential is denoted by the letter "F", and voltage by the letter "U". If expressed in terms of potential difference, the voltage is equal to:
If expressed in terms of work, then:
where A is work, q is charge.
Voltage measurement
Voltage is measured using a voltmeter. The voltmeter probes are connected to two voltage points between which we are interested, or to the terminals of a part whose voltage drop we want to measure. Moreover, any connection to the circuit can affect its operation. This means that when you add a load in parallel to an element, the current in the circuit changes and the voltage on the element changes according to Ohm’s law.
Conclusion:
The voltmeter must have the highest possible input resistance so that when it is connected, the final resistance in the measured area remains practically unchanged. The resistance of the voltmeter should tend to infinity, and the higher it is, the greater the reliability of the readings.
The measurement accuracy (accuracy class) is influenced by a number of parameters. For pointer instruments, this includes the accuracy of calibration of the measuring scale, the design features of the pointer suspension, the quality and integrity of the electromagnetic coil, the condition of the return springs, the accuracy of shunt selection, etc.
For digital devices - mainly the accuracy of the selection of resistors in the measuring voltage divider, the ADC capacity (the larger, the more accurate), the quality of the measuring probes.
To measure DC voltage using a digital device (for example,), as a rule, it does not matter whether the probes are connected correctly to the circuit being measured. If you connect a positive probe to a point with a more negative potential than the point to which the negative probe is connected, a “-” sign will appear on the display in front of the measurement result.
But if you measure with a pointer instrument, you need to be careful. If the probes are connected incorrectly, the arrow will begin to deviate towards zero and will hit the limiter. When measuring voltages close to the measurement limit or more, it may jam or bend, after which there is no need to talk about the accuracy and further operation of this device.
For most measurements in everyday life and in electronics at the amateur level, a voltmeter built into multimeters such as DT-830 and the like is sufficient.
The larger the measured values, the lower the accuracy requirements, because if you measure fractions of a volt and have an error of 0.1V, this will significantly distort the picture, and if you measure hundreds or thousands of volts, then an error of 5 volts will not play a significant role.
What to do if the voltage is not suitable for powering the load
To power each specific device or apparatus, you need to supply a voltage of a certain value, but it happens that the power source you have is not suitable and produces a low or too high voltage. This problem is solved in different ways, depending on the required power, voltage and current.
How to reduce voltage with resistance?
The resistance limits the current and as it flows, the voltage across the resistance (current-limiting resistor) drops. This method allows you to lower the voltage to power low-power devices with consumption currents of tens, maximum hundreds of milliamps.
An example of such power supply is the inclusion of an LED in a DC network 12 (for example, the on-board network of a car up to 14.7 Volts). Then, if the LED is designed to be powered from 3.3 V, with a current of 20 mA, you need a resistor R:
R=(14.7-3.3)/0.02)= 570 Ohm
But resistors differ in maximum power dissipation:
P=(14.7-3.3)*0.02=0.228 W
The closest higher value is a 0.25 W resistor.
It is the dissipated power that imposes a limitation on this method of power supply; it usually does not exceed 5-10 W. It turns out that if you need to extinguish a large voltage or power a more powerful load in this way, you will have to install several resistors because The power of one is not enough and it can be distributed among several.
The method of reducing voltage with a resistor works in both DC and AC circuits.
The disadvantage is that the output voltage is not stabilized in any way and as the current increases and decreases, it changes in proportion to the resistor value.
How to reduce AC voltage with a choke or capacitor?
If we are talking only about alternating current, then reactance can be used. Reactance exists only in alternating current circuits; this is due to the peculiarities of energy storage in capacitors and inductors and the laws of switching.
The inductor and capacitor in alternating current can be used as a ballast resistor.
The reactance of the inductor (and any inductive element) depends on the frequency of the alternating current (for a household electrical network 50 Hz) and inductance, it is calculated by the formula:
where ω is the angular frequency in rad/s, L is the inductance, 2pi is necessary to convert the angular frequency to normal, f is the voltage frequency in Hz.
The reactance of a capacitor depends on its capacitance (the lower C, the greater the resistance) and the frequency of the current in the circuit (the higher the frequency, the lower the resistance). It can be calculated like this:
An example of the use of inductive reactance is the power supply of fluorescent lighting lamps, DRL lamps and HPS. The choke limits the current through the lamp; in LL and HPS lamps it is used in conjunction with a starter or a pulse ignition device (starting relay) to form a high voltage surge that turns on the lamp. This is due to the nature and operating principle of such lamps.
A capacitor is used to power low-power devices; it is installed in series with the powered circuit. Such a power supply is called a “transformerless power supply with a ballast (quenching) capacitor.”
It is very often found as a current limiter for charging batteries (for example, lead batteries) in portable flashlights and low-power radios. The disadvantages of such a scheme are obvious - there is no control of the battery charge level, they boil over, undercharge, and voltage instability.
How to lower and stabilize DC voltage
To achieve a stable output voltage, you can use parametric and linear stabilizers. They are often made on domestic microcircuits such as KREN or foreign ones such as L78xx, L79xx.
The LM317 linear converter allows you to stabilize any voltage value, it is adjustable up to 37V, you can make a simple adjustable power supply based on it.
If you need to slightly reduce the voltage and stabilize it, the described ICs will not be suitable. For them to work there must be a difference of about 2V or more. LDO (low dropout) stabilizers were created for this purpose. Their difference lies in the fact that in order to stabilize the output voltage, it is necessary that the input voltage exceed it by an amount of 1V. An example of such a stabilizer is the AMS1117, available in versions from 1.2 to 5V, the 5 and 3.3V versions are most often used, for example, and much more.
The design of all the above-described series-type linear step-down stabilizers has a significant drawback - low efficiency. The greater the difference between the input and output voltage, the lower it is. It simply “burns” excess voltage, converting it into heat, and the energy loss is equal to:
Ploss = (Uin-Uout)*I
The AMTECH company produces PWM analogues of L78xx type converters; they operate on the principle of pulse width modulation and their efficiency is always more than 90%.
They simply turn the voltage on and off with a frequency of up to 300 kHz (ripple is minimal). And the current voltage is stabilized at the required level. And the connection circuit is similar to linear analogues.
How to increase constant voltage?
To increase the voltage, pulse voltage converters are produced. They can be switched on using either a boost or buck scheme or a buck-boost scheme. Let's look at a few representatives:
2. Board based on LM2577, works to increase and decrease the output voltage.
3. Converter board based on FP6291, suitable for assembling a 5 V power source, such as a powerbank. By adjusting the resistor values, it can be adjusted to other voltages, like any other similar converter - you need to adjust the feedback circuits.
Here everything is labeled on the board - pads for soldering the input - IN and output - OUT voltages. The boards can have output voltage regulation, and in some cases, current limiting, which allows you to make a simple and effective laboratory power supply. Most converters, both linear and pulsed, have short-circuit protection.
How to increase AC voltage?
To adjust AC voltage, two main methods are used:
1. Autotransformer;
2. Transformer.
Autotransformer- This is a choke with one winding. The winding has a tap from a certain number of turns, so by connecting between one of the ends of the winding and the tap, at the ends of the winding you get an increased voltage as many times as the total number of turns and the number of turns before the tap.
The industry produces LATRs - laboratory autotransformers, special electromechanical devices for voltage regulation. They are widely used in the development of electronic devices and repair of power supplies. Adjustment is achieved through a sliding brush contact to which the powered device is connected.
The disadvantage of such devices is the lack of galvanic isolation. This means that high voltage can easily be present at the output terminals, hence the risk of electric shock.
Transformer- This is a classic way to change the voltage value. There is galvanic isolation from the network, which increases the safety of such installations. The voltage on the secondary winding depends on the voltage on the primary winding and the transformation ratio.
Uvt=Ufirst*Ktr
A separate species is . They operate at high frequencies of tens and hundreds of kHz. Used in the vast majority of switching power supplies, for example:
Charger for your smartphone;
Laptop power supply;
Computer power supply.
Due to operation at high frequencies, the weight and size indicators are reduced, they are several times less than that of network (50/60 Hz) transformers, the number of turns on the windings and, as a result, the price. The transition to switching power supplies has made it possible to reduce the size and weight of all modern electronics and reduce their consumption by increasing efficiency (70-98% in switching circuits).
Electronic transformers are often found in stores; a 220V mains voltage is supplied to their input, and at the output, for example, 12 V high-frequency alternating voltage; for use in a load that is powered by direct current, it is necessary to additionally install high-speed diodes at the output.
Inside there is a pulse transformer, transistor switches, a driver, or a self-oscillator circuit, as shown below.
Advantages: simplicity of the circuit, galvanic isolation and small size.
Disadvantages - most models that are on sale have current feedback, which means that without a load with a minimum power (specified in the specifications of a particular device), it simply will not turn on. Some copies are already equipped with OS voltage and operate at idle without problems.
They are most often used to power 12V halogen lamps, for example suspended ceiling spotlights.
Conclusion
We covered the basics of voltage, its measurement, and adjustments. A modern element base and a range of ready-made units and converters make it possible to implement any power sources with the required output characteristics. You can write a separate article about each of the methods in more detail; within this article, I tried to fit the basic information necessary to quickly select a solution that is convenient for you.
Hello colleagues!
For example, I’ll take the trance from the Chinese b/w TV “Jinlipu”.
So, first we need to define the primary and secondary windings. To do this, you need a regular ohmmeter. We measure the resistance at the terminals of the transformer. On the primary winding, the resistance is greater than on the secondary and is usually at least 85 ohms. Once we have identified these windings, we can begin to disassemble the transformer. It is necessary to separate the W-shaped plates from each other. To do this, we will need some tools, namely: round nose pliers, pliers, a small screwdriver for “picking up” the plates, wire cutters, and a knife.
To pull out the very first record, you will have to work hard, but then the rest will go like clockwork. You need to work very carefully, as you can easily cut yourself on the plates. Specifically on this transformer, we know that its output is 32 V. In the case when we do not know this, we must measure the voltage before analysis, so that in the future we can calculate how many turns go to 1 V.
Then we find a contact on the secondary winding that is accessible for unwinding and use wire cutters to “bite it off” from the soldering point. Next, we begin to unwind the winding, and be sure to count the number of turns. To keep the wire out of the way, you can wrap it around a ruler or something similar. Since this transformer has 3 terminals on the secondary winding (two extreme and one middle), it is logical to assume that the voltage at the middle terminal is 16V, exactly half of 32V. We unwind the winding to the middle contact, i.e. to half, and count the number of turns that we unwound. (If the transformer has two terminals on the secondary winding, then unwind it “by eye” to half, count the turns while doing so, then cut off the unwound wire, strip its end, solder it back to the contact and assemble the transformer, doing everything the same as when disassembling, only in the reverse order. After this, we need to again measure the voltage that we got after reducing the turns and calculate how many turns are per 1 V. We calculate it like this: let’s say you had a transformer with a voltage of 35 V. After you have unwinded about half and assembled the transformer back, your voltage has become 18 V. The number of turns that you unwinded is 105. This means that 105 turns are per 17 V (35 V-18 V = 17 V). It follows that there are approximately 6.1 turns per 1 V (105/17 = 6.176 Now, in order for us to reduce the voltage by another 6V (18V-12V=6V), you need to unwind approximately 36.6 turns (6.1*6=36.6). You can round this figure to 37. To do this you need disassemble the transformer again and do this “procedure.”). In our case, having reached half of the winding, we got 106 turns. This means that these 106 turns are at 16V. We calculate how many turns there are per 1V (106/16=6.625) and unwind about 26.5 more turns (16V-12V=4V; 4V*6.625 turns=26.5 turns). Then we “bite off” the unwound wire, strip the varnish from its end, tin it and solder it to the contact on the transformer from which it was “bitten off”.
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How to reduce the voltage on a transformer.
In this article I will tell you how to make a transformer with a 12 V output from a transformer with a 32 V output. In other words, reduce the voltage of the transformer.
I think a lot of people have met him or similar.
So, first we need to define the primary and secondary windings. To do this, you need a regular ohmmeter. We measure the resistance at the terminals of the transformer. The resistance on the primary winding is greater than on the secondary winding and is usually at least 85 Ohms. Once we have identified these windings, we can begin disassembling the transformer. It is necessary to separate the W-shaped plates from each other. To do this, we will need some tools, namely: round nose pliers, pliers, a small screwdriver for “picking up” the plates, wire cutters, and a knife.
To pull out the very first record, you will have to work hard, but then the rest will go like clockwork. You need to work very carefully, as you can easily cut yourself on the plates. On this particular transformer, we know that its output is 32 V. In the case where we don’t know this, we must measure the voltage before disassembling it. so that in the future we can calculate how many turns go to 1 V.
So, let's start the analysis. Use a knife to peel off the plates from each other and, using wire cutters and pliers, pull them out of the transformer. This is what it looks like:
After the plates have been removed, you need to remove the plastic case from the windings. We do this boldly, since this will not affect the operation of the transformer in any way.
Then we find a contact on the secondary winding that is accessible for unwinding and use wire cutters to “bite it off” from the soldering point. Next, we begin to unwind the winding, and be sure to count the number of turns. To keep the wire out of the way, you can wrap it around a ruler or something similar. Since this transformer has 3 terminals on the secondary winding (two extreme and one middle), it is logical to assume that the voltage at the middle terminal is 16V, exactly half of 32V. We unwind the winding to the middle contact, i.e. to half, and count the number of turns that we unwound. (If the transformer has two terminals on the secondary winding, then unwind it “by eye” to half, count the turns while doing so, then cut off the unwound wire, strip its end, solder it back to the contact and assemble the transformer. Doing the same as when disassembling, only in the reverse order. After this, we need to again measure the voltage that we got after reducing the turns and calculate how many turns are per 1 V. We calculate it like this: let’s say you had a transformer with a voltage of 35 V. After you have unwinded about half and assembled the transformer back, your voltage has become 18 V. The number of turns that you unwinded is 105. This means that 105 turns are per 17 V (35 V-18 V = 17 V). It follows that there are approximately 6.1 turns per 1 V (105/17 = 6.176 Now, in order for us to reduce the voltage by another 6V (18V-12V=6V), you need to unwind approximately 36.6 turns (6.1*6=36.6). You can round this figure to 37. To do this you need disassemble the transformer again and do this “procedure.”). In our case, having reached half of the winding, we got 106 turns. This means that these 106 turns are at 16V. We calculate how many turns there are per 1V (106/16=6.625) and unwind about 26.5 more turns (16V-12V=4V; 4V*6.625 turns=26.5 turns). Then we “bite off” the unwound wire, strip the varnish from its end, tin it and solder it to the contact on the transformer from which it was “bitten off”.
Now we assemble the transformer in the same way as we disassembled it, only in the reverse order. Don’t worry if you have one or two plates left, the main thing is that they fit very tightly. Here’s what you should get:
It remains to measure the voltage that we got:
Congratulations, colleagues, everything turned out great!
If something doesn't work out the first time, don't get discouraged or give up. Only by showing persistence and patience can you learn something. If you have any questions, leave them in the comments and I will definitely answer.
In the next article I will tell you how to make a 12V DC power supply from this transformer.
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Greetings, reader of my website ceshka.ru!
In this article I want to tell you how the voltage of a 110/10 kV power transformer is regulated under load.
For those who are not at all in the subject, I’ll explain what we’re talking about.
Electricity from a power plant (nuclear power plant, thermal power plant, state district power plant, etc.) is transmitted through overhead line supports many hundreds of kilometers to a substation (I will talk about a 110,000 Volt substation), where step-down transformers are installed - very large and very powerful.
These transformers lower the voltage (in my example to 10,000 Volts) and transmit electricity further, but over a shorter distance - within 10-40 km to the next step-down transformer, which converts the already high voltage of 10 kV into a low three-phase voltage of 400 Volts, which and goes along the wires to our houses.
So, a 110/10 kV transformer installed at a substation is connected to a lot of load - it can be an entire rural area or part of a big city.
The workload changes throughout the day and throughout the seasons and changes greatly.
For example, in winter, many rural residents are heated by electric boilers, so the current consumed is much greater than in summer.
Or there are morning and evening hours of maximum load when people wake up or, on the contrary, come from work, turn on electrical appliances - electricity consumption increases greatly. During the day, the load decreases and sometimes even several times less than in the morning or evening.
But nothing happens to him))) As he lowered the voltage, he continues to lower it - that’s how he’s designed.
110,000 Volts are supplied to the primary winding (high voltage winding), and 10,000 Volts are removed from the secondary (low voltage winding).
This is an ideal option when the voltage on the primary winding is stable and does not change, and the load on the secondary winding is either very small or nonexistent (the transformer operates in no-load mode).
In fact, this is not true at all.
In reality, the high voltage at the primary load is constantly changing within small limits - 110-117 kV
And since the transformation ratio of the transformer is constant, it turns out that on the 10 kV secondary winding the voltage also fluctuates, so to speak, “in step” with the primary voltage.
And after this, voltage fluctuations are transmitted to the next step-down transformers 10/0.4 kV...
And so these fluctuations will reach our apartments and the voltage would fluctuate in proportion to the high voltage of 110 kV.
And our sockets would have either 180 Volts or 250 Volts, and it would constantly change throughout the day. I think that no one will like it when the light in the house constantly changes brightness, as in that joke - it either goes out, then goes out, or doesn’t come on at all)))
And the voltage changes depending on the load, on how much power is connected to the transformer.
Anyone who is familiar with physics knows that the greater the power, the greater the current. In turn, an increase in the value of the electric current leads to an increase in the voltage drop in the electric current conductors.
These are transformer windings, overhead power line wires, power cables, etc. - the main voltage drop occurs on them.
To put it simply and to make it clearer, this is energy (and active!) released in the form of heat.
Let me give you an example. For each wire cross-section there is a maximum allowable current. If to a copper wire with a cross-section of 2.5 sq. mm connect a single-phase electric body with a power of 9 kW with a current consumption of 9000:220 = 41 amperes, then the wire will get very hot.
The material from which the wire is made, copper, actively resists electric current.
According to Ohm's law, the electric current is directly proportional to changes in voltage, therefore, when an electric boiler is connected to this section of the wire, the voltage also increases and the wire heats up.
Unclear? Let's go into more detail. Let's assume a wire resistance of 1 ohm. The current, as already determined, is 41 amperes.
Then the voltage on the wire will be U=R*I= 41 Volts
This is the voltage drop across the wire. In this case, power will be released in the form of heat P=U*I=41*41=1681 Watt
And this is a whole electric heater with a power of 1.7 kW!!!
Of course, such power dissipation in the wire leads to overheating and melting of the insulation. That is why the current is limited for each section.
In this case, for 2.5 sq. mm, the permissible current is 25-27 amperes.
From all of the above it follows:
As the load increases, the current increases and the voltage drop and energy loss in the wires increases
In other words, some of the voltage and energy simply does not reach our sockets, but is released into the air in the form of heat...
And now the most important thing!
To compensate for such inevitable energy losses, the voltage is increased on the secondary winding of the power transformer.
That is, they increase the voltage above 10,000 Volts - up to 11, or even more kilovolts. Then, even if some of the energy is “lost” in the wires, in our apartments and houses the voltage is within normal limits - about 220 Volts.
How can you change the secondary voltage on a step-down transformer? You can change the voltage supplied to the primary winding - then on the secondary it will change in direct proportion.
But this option is not suitable, since transformers connected to the 110 kV network have different loads - some may have 100% load, others may have 20-50% load, etc.
And with this method, the output voltage will change simultaneously for everyone - both where it is necessary and where it is not necessary...
And there are not just a lot of transformers connected, but a lot!
Therefore, another method is used.
The voltage is regulated by changing the transformation ratio of the transformer itself
The number of turns of the primary winding of the transformer changes.
And why in the primary?
In principle, it would be possible to change the coefficient on the secondary winding without any difference; it will still change, since the ratio of turns of the primary to secondary windings will change.
However, it is on the high side that they change - where the voltage is higher. Why?
Everything is very simple. Where the voltage is higher, the electric current is lower.
And since the voltage regulation occurs under load - that is, the transformer is not turned off, then when the turns of the winding change - during switching - an electric arc appears at the point where the contacts switch.
And the higher the current, the larger the arc, and this arc must be extinguished...
By the way, the current values between the primary and secondary windings differ very significantly. For example, on a secondary load, a current of 300 amperes is quite acceptable, and for a primary load the maximum current is 25-30 amperes.
I think there is no need to explain that switching contacts at a current of 300 amperes is much more difficult than at 30, agree)))
Where are these contacts located? In the transformer tank, taps are made from the primary winding to change the transformation ratio and are brought out into a separate compartment, where switching occurs using a special mechanism.
The drive of this mechanism is attached to the outside of the transformer tank, it is called
OLTC stands for Regulation Under Load. The drive contains an electric motor and automatic elements of on-load tap-changer (OLTC) starters, limit switches, a circuit breaker, a terminal block with control cables, etc.
You need to know how to reduce the voltage in a circuit so as not to damage electrical appliances. Everyone knows that two wires come to houses - zero and phase. This is called single-phase and is extremely rarely used in the private sector and apartment buildings. There is simply no need for it, since all household appliances are powered from a single-phase alternating current network. But in the technology itself it is necessary to make transformations - lower the alternating voltage, convert it to constant, change the amplitude and other characteristics. These are the points that need to be considered.
The easiest way is to use a reduced voltage transformer that does the conversion. The primary winding contains more turns than the secondary winding. If there is a need to reduce the voltage by half or three times, the secondary winding may not be used. The primary winding of the transformer is used as an inductive divider (if there are taps from it). In household appliances, transformers are used, from the secondary windings of which voltage of 5, 12 or 24 Volts is removed.
These are the most commonly used values in modern home appliances. 20-30 years ago, most equipment was powered by a voltage of 9 Volts. And tube TVs and amplifiers required a constant voltage of 150-250 V and an alternating voltage of 6.3 for filaments (some lamps were powered by 12.6 V). Therefore, the secondary winding of the transformers contained the same number of turns as the primary. In modern technology, inverter power supplies are increasingly used (as in computer power supplies); their design includes a step-up transformer, which has very small dimensions.
An inductor is a coil wound with (usually) copper wire on a metal or ferromagnetic core. A transformer is a type of inductance. If you make a tap from the middle of the primary winding, then there will be equal voltage between it and the outer terminals. And it will be equal to half the supply voltage. But this is the case if the transformer itself is designed to work with exactly this supply voltage.
But you can use several coils (for example, you can take two), connect them in series and connect them to the AC network. Knowing the values of inductances, it is easy to calculate the drop on each of them:
In these formulas, L1 and L2 are the inductances of the first and second coils, U1 is the supply voltage in Volts, U(L1) and U(L2) are the voltage drop across the first and second inductances, respectively. The circuit of such a divider is widely used in circuits of measuring devices.
A very popular circuit used to reduce the value of the AC supply network. It cannot be used in DC circuits, since, according to Kirchhoff’s theorem, a capacitor in a DC circuit is a break. In other words, no current will flow through it. But when operating in an alternating current circuit, the capacitor has reactance, which is capable of extinguishing the voltage. The divider circuit is similar to the one described above, but capacitors are used instead of inductors. The calculation is made using the following formulas:
Here C1 and C2 are the capacitances of the capacitors, U is the voltage in the supply network, f is the current frequency.
The circuit is in many ways similar to the previous ones, but fixed resistors are used. The method for calculating such a divisor is slightly different from those given above. The circuit can be used in both AC and DC circuits. We can say that it is universal. With its help you can assemble a step-down voltage converter. The drop across each resistor is calculated using the following formulas:
One nuance should be noted: the value of the load resistance should be 1-2 orders of magnitude less than that of sharing resistors. Otherwise, the accuracy of the calculation will be very rough.
To select a supply transformer, you will need to know several basic data:
S = 1.2 *√P1.
And power P1 = P2 / efficiency. The transformer efficiency will never be more than 0.8 (or 80%). Therefore, when calculating, the maximum value is taken - 0.8.
Power in the secondary winding:
P2 = U2 * I2.
This data is known by default, so the calculation is not difficult. Here's how to step down the voltage to 12 volts using a transformer. But that’s not all: household appliances are powered by direct current, and the output of the secondary winding is alternating current. A few more changes will need to be made.
Next comes the conversion of alternating current to direct current. For this purpose, semiconductor diodes or assemblies are used. The simplest type of rectifier consists of a single diode. It's called half-wave. But the most widespread is the bridge circuit, which allows not only to rectify alternating current, but also to get rid of ripple as much as possible. But such a converter circuit is still incomplete, since semiconductor diodes alone cannot get rid of the variable component. And step-down transformers are capable of converting alternating voltage into the same frequency, but with a lower value.
Electrolytic capacitors are used in power supplies as filters. According to Kirchhoff's theorem, such a capacitor in an alternating current circuit is a conductor, and when working with direct current, it is a discontinuity. Therefore, the constant component will flow unhindered, but the variable will close on itself, and therefore will not pass beyond this filter. Simplicity and reliability are exactly what characterize such filters. Resistances and inductances can also be used to smooth out ripples. Similar designs are used even in car generators.
You have learned how to lower the voltage to the desired level. Now it needs to be stabilized. For this purpose, special devices are used - zener diodes, which are made of semiconductor components. They are installed at the output of the DC power supply. The principle of operation is that a semiconductor is capable of passing a certain voltage, the excess is converted into heat and released through a radiator into the atmosphere. In other words, if the output of the power supply is 15 volts, and a 12 V stabilizer is installed, then it will pass exactly as much as needed. And the difference of 3 V will be used to heat the element (the law of conservation of energy applies).
A completely different design is a step-down voltage stabilizer; it makes several transformations. First, the mains voltage is converted to DC at a high frequency (up to 50,000 Hz). It is stabilized and fed to a pulse transformer. Next, a reverse conversion occurs to the operating voltage (mains voltage or a lower value). Thanks to the use of electronic switches (thyristors), direct voltage is converted into alternating voltage with the required frequency (in the networks of our country - 50 Hz).
