How to make 1 phase out of 3 phase. What is the difference between three-phase voltage and single-phase voltage. What is important to know
In this scheme, as in any other, there may be errors. If you find them, please write to us. Subscribe to the news to be aware of corrections and material updates.
Attention! Assembly of the device requires skills in the field of power electronics, is associated with contact with high voltage, which can be life-threatening for both the engineer himself and the users of the device. Make sure you have the required qualifications.
D5- An operational amplifier designed for operation with a single supply of 12V, with a high input impedance and with the ability to connect to the output of a load of 2 kΩ or less. Well suited K544UD1, KR544UD1.
D6- integrated voltage stabilizer (KREN) for 12V.
VT5- Low power high voltage transistor 600 volts. It only works when the circuit is turned on. So no power is dissipated during operation.
VD9- Zener diode 15V.
C11- 1000uF 25V.
R25- 300kOhm 0.5W
D1- Integrated pulse-width modulating (PWM) controllers. This is 1156EU3 or its imported analogue UC3823.
Addition from 02/27/2013 The foreign manufacturer of controllers Texas Instruments gave us a surprisingly pleasant surprise. UC3823A and UC3823B chips appeared. These controllers have slightly different pin functions than the UC3823. They will not work in UC3823 circuits. Pin 11 has now acquired completely different functions. In order to use controllers with letter indices A and B in the described circuit, you need to double the resistors R22, exclude resistors R17 and R18, hang (do not connect anywhere) legs 16 and 11 of all three microcircuits. As for Russian analogues, readers write to us that the wiring is different in different batches of microcircuits (which is especially nice), although we have not yet seen a new wiring.
D3- Half bridge drivers. IR2184
R7, R6- 10 kOhm resistors. C3, C4- 100nF capacitors.
R10, R11- Resistors of 20 kOhm. C5, C6- Electrolytic capacitors of 30 microfarads, 25 volts.
R8- 20kOhm, R9- trimmer resistor 15 kOhm
R1, R2- 10 kOhm trimmers
R3- 10 kOhm
C2, R5- a resistor and a capacitor that set the frequency of the PWM controllers. We choose them so that the frequency is about 50 kHz. The selection should start with a 1 nF capacitor and a 100 kΩ resistor.
R4- These resistors in different arms are different. The fact is that to obtain a sinusoidal voltage with a phase shift of 120 gr. a phase shifter is used. In addition to shifting, it also weakens the signal. Each link attenuates the signal by 2.7 times. So we select a resistor in the lower arm in the range from 10 kOhm to 100 kOhm so that the PWM controller at minimum value sinusoidal voltage (from the output of the operational amplifier) was closed, with a slight increase it began to produce short pulses, when it reached the maximum, it was practically open. The middle arm resistor will be 9 times larger, the upper arm resistor will be 81 times larger.
After selecting these resistors more accurately, the gain can be adjusted by tuning resistors R1.
R17- 300 kOhm, R18- 30 kOhm
C8- 100nF. These may be low voltage capacitors. On them high voltage does not happen, although they are in the high-voltage part.
R22- 0.23 ohm. 5W.
VD11- Schottky diodes. Schottky diodes are selected to ensure the minimum voltage drop across the diode in the on-state.
R23, R24- 20 Ohm. 1W.
L1- choke 10mH (1E-02 H), for current 5A, C12- 1uF, 400 V.
L2 - several turns of thin wire over the L1 inductor. If in the inductor L1 - X turns, then in the coil L2 should be [ X] / [60 ]
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In a private house, in an apartment, in a country house, that is, in living conditions, most often there is a standard single-phase voltage of 220 volts, which is obtained by connecting the consumer to one phase and a neutral conductor. This voltage is called phase voltage, its generator is mainly power transformer 6 kV/380 V mounted on distribution substation supplying this consumer. Sometimes, especially in a private house, it becomes necessary to start and operate an asynchronous three-phase motor rated at 380 volts. There are schemes that make it possible to connect this motor to a single-phase 220 V network, but the power of the electric asynchronous machine is greatly lost. Accordingly, the question arises of how to get 380 Volts out of 220 at home, for effective work electric motor.
What is important to know
In a three-phase network, all three phases have a shift equal to 120 degrees. If it were necessary to convert a three-phase 220 Volt to 380V, or a single-phase 220 to the same, but with a voltage of 380 V, then this is done very simply by using a conventional step-up transformer. In this problem, it is necessary not just to increase the voltage value, but to obtain a full-fledged three-phase network from a single-phase one.
There are three main ways in which you can do this manipulation:
- using an electronic converter (inverter);
- by connecting two additional phases;
- due to the use of a three-phase transformer, but the power is still reduced.
Before converting the mains voltage, you need to consider whether it is possible to connect the motor to a standard single-phase network without losing power. First you need to look at the plate on the engine itself, some of them are designed for both of these voltages, as shown in the first photo. You just need a capacitor to start.
The second plate shows that the machine is designed exclusively for connecting the windings with a star and a voltage of 380 volts, respectively:
You can, of course, disassemble the engine and find the ends of the windings, but this is already problematic. Let us dwell in more detail on the creation of a high-quality three-phase network 380 V out of 220.
Methods for obtaining 380 V from 220
Voltage transformer
This device is more commonly known as an inverter, and it consists of several blocks. To begin with, the device rectifies this single-phase voltage, and then inverts it into a variable of a given frequency. In this case, there can be as many phases with a shift by a certain degree, but it is optimal for the operation of generally accepted standard electrical equipment to be three and, accordingly, their shift is 120 degrees. It is very problematic to make such a complex device at home, so it is recommended to just buy it, besides, the market for these products is very developed.
Here is the circuit diagram of the inverter:
And this is how it looks in the factory case:
Often, these devices have not only the conversion of single-phase to three-phase voltage, but also protect electric motors from overloads, short circuits and overheating.
Three phase method
This method must be agreed with Energonadzor or the supplier company electrical energy, since this requires the connection of two additional phases from the shield, which are on each floor apartment buildings.
Here, the question is more not how to remake a single-phase voltage, but how to connect it, and for this, just a three-phase extension cord is enough, and if everything is legal, then a meter.
Three phase transformer
To make from 220 Volts 380 Volts is needed three-phase transformer the required power for the voltage of one of the windings is 220, and the other is 380 V. Most often they already have windings connected in a star or triangle. After that, the voltage from the network is connected to the two phases of the winding from the lower side directly, and to the third output through the capacitor. Capacitor capacitance is calculated from the ratio of 7 microfarads for every 100 watts of power. The rated voltage of the capacitor must be at least 400 volts. Without load, such a device cannot be connected. In this case, there will still be a decrease in both engine power and its efficiency. If the converter is performed using an electric motor, and not a transformer, then the output will be a three-phase voltage, but its value will be the same as in the network, namely 220 V.
So, why do some switchboards get 380 V, and some - 220? Why do some consumers have a three-phase voltage, while others have a single-phase voltage? There was a time when I asked these questions and looked for answers to them. Now I’ll tell you in a popular way, without the formulas and diagrams that textbooks abound in.
In other words. If one phase approaches the consumer, then the consumer is called single-phase, and its supply voltage will be 220 V (phase). If we talk about three-phase voltage, then we are always talking about a voltage of 380 V (linear). Who cares? Further - in more detail.
How are three phases different from one?
In both types of power, there is a working neutral conductor (ZERO). Pro protective earth I, this is a broad topic. In relation to zero in all three phases - the voltage is 220 volts. But in relation to these three phases to each other - they have 380 volts.
Voltages in a three-phase system
It turns out this way, because the voltages (with an active load, and current) on three phase wires differ by a third of the cycle, i.e. 120°.
More details can be found in the textbook of electrical engineering - about voltage and current in a three-phase network, as well as see vector diagrams.
It turns out that if we have a three-phase voltage, then we have three phase voltages of 220 V each. And single-phase consumers (and there are almost 100% of them in our homes) can be connected to any phase and zero. It is only necessary to do this in such a way that the consumption for each phase is approximately the same, otherwise phase imbalance is possible.
In addition, it will be difficult and insulting for the overly loaded phase that others are “resting”)
Advantages and disadvantages
Both power systems have their pros and cons, which change places or become insignificant when the power passes through the 10 kW threshold. I'll try to list.
Single-phase network 220 V, pluses
- Simplicity
- Cheapness
- Below dangerous voltage
Single-phase network 220 V, minuses
- Limited consumer power
Three-phase network 380 V, pluses
- Power is limited only by the cross section of the wires
- Savings with three-phase consumption
- Power supply for industrial equipment
- Ability to switch a single-phase load to a “good” phase in case of deterioration in quality or power failure
Three-phase network 380 V, minuses
- More expensive equipment
- More dangerous voltage
- Limited maximum power single-phase loads
When is 380 and when is 220?
So why is the voltage in our apartments 220 V, and not 380? The fact is that, as a rule, one phase is connected to consumers with a power of less than 10 kW. And this means that one phase and a neutral (zero) conductor are introduced into the house. In 99% of apartments and houses, this is exactly what happens.
Single-phase electrical panel in the house. The right automaton is introductory, then - through the rooms. Who will find errors in the photo? Although, this shield is one big mistake ...
However, if you plan to consume more than 10 kW of power, then a three-phase input is better. And if there is equipment with a three-phase power supply (containing), then I strongly recommend bringing a three-phase input with a linear voltage of 380 V into the house. This will save on wire cross-section, on safety, and on electricity.
Despite the fact that there are ways to include a three-phase load in a single-phase network, such alterations drastically reduce Engine efficiency, and sometimes, other things being equal, you can pay 2 times more for 220 V than for 380.
Single-phase voltage is used in the private sector, where the power consumption, as a rule, does not exceed 10 kW. At the same time, a cable with wires with a cross section of 4-6 mm² is used at the input. The consumed current is limited by the introductory circuit breaker, the rated protection current of which is not more than 40 A.
About the choice of a circuit breaker, I already. And about the choice of wire section -. There are also heated discussions.
But if the consumer's power is 15 kW and above, then it is imperative to use a three-phase power supply. Even if there are no three-phase consumers in this building, for example, electric motors. In this case, the power is divided into phases, and the electrical equipment ( input cable, switching) does not bear the same load as if the same power was taken from one phase.
For example, 15 kW is about 70A for one phase, you need copper wire with a cross section of at least 10 mm². The cost of a cable with such cores will be significant. And I have not seen automatic machines for one phase (single-pole) for a current of more than 63 A on a DIN rail.
Therefore, in offices, shops, and even more so in enterprises, only three-phase power is used. And, accordingly, three-phase meters, which are of direct connection and transformer connection (with current transformers).
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And on the input (in front of the counter) there are approximately such “boxes”:
Three-phase input. Introductory machine in front of the counter.
A significant minus of a three-phase input and (marked it above) - the power limit of single-phase loads. For example, the allocated power of a three-phase voltage is 15 kW. This means that for each phase - a maximum of 5 kW. And this means that the maximum current for each phase is no more than 22 A (practically - 25). And you have to spin, distributing the load.
I hope now it is clear what is a three-phase voltage of 380 V and a single-phase voltage of 220 V?
Star and Delta schemes in a three-phase network
Exist various variations inclusion of loading with an operating voltage of 220 and 380 Volts in a three-phase network. These schemes are called "Star" and "Triangle".
When the load is designed for a voltage of 220V, it is connected to a three-phase network according to the “Star” scheme, that is, to the phase voltage. In this case, all load groups are distributed so that the phase powers are approximately the same. The zeros of all groups are connected together and connected to the neutral wire of the three-phase input.
All our apartments and houses with single-phase input are connected to Zvezda, another example is the connection of heating elements in powerful and.
When the load voltage is 380V, it is switched on according to the “Triangle” scheme, that is, to the linear voltage. This phase distribution is most typical for electric motors and other loads, where all three parts of the load belong to a single device.
Power distribution system
Initially, the voltage is always three-phase. By “original” I mean a generator at a power plant (thermal, gas, nuclear), from which a voltage of many thousands of volts is supplied to step-down transformers, which form several voltage steps. The last transformer lowers the voltage to a level of 0.4 kV and supplies it to end consumers - to us, to apartment buildings and to the private residential sector.
Further, the voltage is supplied to the transformer TP2 of the second stage, at the output of which the voltage of the end consumer is 0.4 kV (380V). Power transformers TP2 - from hundreds to thousands of kW. From TP2, voltage is supplied to us - to several apartment buildings, to private sector, etc.
The scheme is simplified, there may be several steps, voltages and powers may be different, but the essence of this does not change. Only the final voltage of consumers is one - 380 V.
A photo
Finally - a few more photos with comments.
Electrical panel with three-phase input, but all consumers are single-phase.
Friends, that's all for today, good luck to everyone!
I look forward to your feedback and questions in the comments!
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Three-phase electric motors in everyday life and amateur practice actuate a variety of mechanisms - circular saw, electric planer, fan, drilling machine, pump. The most commonly used are three-phase asynchronous motors with a squirrel-cage rotor. Unfortunately, three-phase network in everyday life - an extremely rare phenomenon, therefore, for their nutrition from ordinary electrical network amateurs use:
♦ phase-shifting capacitor, which does not allow in full realize the power and starting characteristics of the engine;
♦ trinistor "phase-shifting" devices, which further reduce the power on the motor shaft;
♦ various other capacitive or inductive-capacitive phase-shifting circuits.
But the best thing is to get a three-phase voltage from a single-phase one using an electric motor that acts as a generator. Consider circuits that allow, having a single-phase alternating voltage, to obtain two missing phases.
Note.
Any electric machine reversible: the generator can serve as an engine, and vice versa.
Rotor conventional asynchronous motor after an accidental disconnection of one of the windings, it continues to rotate, and there is an EMF between the terminals of the disconnected winding. This phenomenon makes it possible to use a three-phase asynchronous electric motor to convert a single-phase voltage into a three-phase one.
Scheme No. 1. For example, a conventional three-phase asynchronous electric motor with a squirrel-cage rotor was used for this by S. Gurov (village of Ilyinka, Rostov region). This engine, like the generator, has: a rotor; three stator windings, shifted in space by an angle of 120°.
We apply single-phase voltage to one of the windings. The motor rotor will not be able to start rotating on its own. He needs some way to give the initial impetus. Further, it will rotate due to the interaction with the magnetic field of one stator winding.
Conclusion.
The magnetic flux of the rotating rotor will induce the induction EMF in the other two stator windings, i.e. the missing phases will be restored.
The rotor can be made to rotate, for example, using a device with a starting capacitor. By the way, its capacitance does not have to be large, since the rotor of an asynchronous converter is set in motion without a mechanical load on the shaft.
One of the disadvantages of such a converter is unequal phase voltages, which leads to a decrease in the efficiency of the converter itself and the motor-load.
If you supplement the device with an autotransformer of the appropriate power, turning it on, as shown in Fig. 1, it is possible to achieve an approximate equality of the phase voltages by switching the taps. The stator of a defective electric motor with a power of 17 kW was used as the magnetic circuit of the autotransformer. Winding - 400 turns of enameled wire with a cross section of 4-6 mm 2 with taps after every 40 turns.
Rice. one. circuit diagram converter
It is better to use "low-speed" motors (up to 1000 rpm) as converter motors.
They are very easy to start, the ratio of starting current to operating current is much less than that of motors with a speed of 3000 rpm, and therefore, the load on the network is “softer”.
Rule.
The power of the motor used as a converter must be greater than that of the electric drive connected to it. Always start the converter first, and then connect the three-phase current consumers to it. Turn off the unit in reverse order.
For example, if the converter is a 4 kW motor, the load power should not exceed 3 kW. The 4 kW converter discussed above and manufactured by S. Gurov , has been used in his personal household for several years. A sawmill, a grain mill, a grinder work from it.
Schemes No. 2-4. Under the influence magnetic field stator in the short-circuited winding of the rotor of an asynchronous motor, currents flow, turning the rotor into an electromagnet with pronounced poles, inducing a sinusoidal voltage in the stator windings, including those not connected to the network.
The phase shift between sinusoids in different windings depends only on the location of the latter on the stator and in three-phase motor is exactly 120°.
Note.
The main condition for the transformation of an asynchronous electric motor into a phase number converter is a rotating rotor.
Therefore, it should be untwisted beforehand, for example, using a conventional phase-shifting capacitor.
The capacitance of the capacitor is calculated by the formula:
C=k*I f /U network
where k \u003d 2800 if the motor windings are connected by a star; k \u003d 4800 if the motor windings are connected in a triangle; I f - rated phase current of the electric motor, A; U ce ti - voltage of a single-phase network, V.
You can use capacitors MBGO, MBGP, MBGT K42-4 for an operating voltage of at least 600 V or MBGCH K42-19 for a voltage of at least 250 V.
Note.
The capacitor is needed only to start the motor-generator, then its circuit is broken, and the rotor continues to rotate, so the capacitance of the phase-shifting capacitor does not affect the quality of the generated three-phase voltage.
A three-phase load can be connected to the stator windings. If it is not there, the energy of the supply network is spent only on overcoming friction in the rotor bearings (not counting the usual losses in copper and iron), so the efficiency of the converter is quite high.
As a converter of the number of phases, the author of the schemes V. Kleimenov tested several different electric motors. Those of them, the windings of which are connected by a star, with an output from a common point (neutral) were connected according to the circuit shown in Fig. 2. In the case of connecting the windings with a star without a neutral or a triangle, the circuits shown, respectively, in fig. 3 and fig. 4.
Rice. 2. Scheme of the converter, the motor windings in which are connected by a star, with a conclusion from a common point (neutral)
Rice. 3. Converter circuitmotor windings in which are connected by a star without a neutral
Rice. 4. Converter circuit; motor windings in which are connected by a triangle
In all cases, the engine, launched by pressing the button SB 1 and holding it for 15 C,until the rotor speed reaches the rated speed. Then close the switchSA1, and the button was released.
Schemes No. 5. Usually, the ends of the windings of an asynchronous three-phase electric motor are brought out to a three- or six-terminal block. If the block is three-terminal, then the phase stator windings are connected by a star or a triangle. If it is six-terminal, the phase windings are not connected to each other (Ya. Shatalov, Irba, Krasnoyarsk Territory).
In the latter case, it is important to connect them correctly. When turned on by a star, the winding terminals of the same name (beginning or end) should be combined into a zero point. In order to connect the windings with a triangle, you must:
♦ connect the end of the first winding with the beginning of the second one;
♦ the end of the second - with the beginning of the third;
♦ the end of the third - with the beginning of the first.
But what if the terminals of the motor windings are not marked?
Then proceed as follows. Three windings are determined with an ohmmeter, conventionally designating them I, II and III. To find the beginning and end of each of them, any two are connected in series and an alternating voltage of 6-36 V is applied to them. A voltmeter is connected to the third winding alternating current(Fig. 5).
Rice. 5. Wiring diagram of a voltmeter to determine the windings
The presence of an alternating voltage indicates that the windings I and II are connected in accordance, and the absence of voltage is opposite. In the latter case, the conclusions of one of the windings should be reversed. After that, the beginning and end of the windings I and II are marked (the outputs of the windings I and II of the same name in Fig. 5 are marked with dots). To determine the beginning and end of the winding III, the windings are interchanged, for example, II and III, and the measurements are repeated according to the method described above.