How to make 2 phases from 3. How to get three phases from one

Hi all! Today I will show you how to get three-phase from a regular single-phase 220 V network, and without special costs. But first, I’ll tell you about my problem that preceded the search for such a solution.
I had a powerful Soviet desktop circular saw(2 kW), which was connected to a three-phase network. My attempts to power it from a single-phase network, as is usually customary, were not possible: there was a strong power drawdown, the starting capacitors got hot, and the engine itself got hot.
Fortunately, at one time I spent due time searching for a solution on the Internet. Where I came across a video where one guy made a kind of splitter using a powerful electric motor. Next, he installed this three-phase network around the perimeter of his garage and connected to it all other devices requiring three-phase voltage. Before starting work, he came to the garage, started the dispensing engine and it worked until he left. In principle, I liked the solution.
I decided to repeat it and make my own splitter. As an engine, I took an old Soviet one with 3.5 kW of power, with star-connected windings.

Scheme

The whole circuit consists of just a few elements: a general power switch, a start button, a 100 uF capacitor and a powerful motor itself.

How does it all work? First, we supply single-phase power to the distributing motor, connect the capacitor with the start button, thereby starting it. Once the motor has spun up to the desired speed, the capacitor can be turned off. Now you can connect a load to the output of the phase splitter, in my case table circular and several more three-phase loads.

The body of the device - the frame is made of L-shaped corners, all equipment is fixed to a piece of OSB sheet. Handles for carrying the entire structure have been redesigned on top, and a three-pin socket is connected to the output.

After connecting the saw through such a device, there was a significant improvement in operation, nothing gets hot, there is enough power, and not only for the saw. Nothing growls or buzzes like it did before.
It is only advisable to take the distributing motor at least 1 kW more powerful than the consumers, then there will not be a noticeable drop in power under sudden load.
No matter who says anything about the sine not being pure or it will give nothing, I advise you not to listen to them. The voltage sine wave is clean and split exactly 120 degrees, as a result the connected equipment receives high-quality voltage, which is why it does not heat up.
The second half of the readers who will speak in the 21st century and the large availability of three-phase voltage frequency converters, I can say that my output is several times cheaper, since old motor quite easy to find. You can even take one that is unsuitable for the load, with weak and almost broken bearings.
My phase splitter in idle mode does not consume so much: 200 - 400 W somewhere, the power of the connected tools increases significantly compared to the usual scheme connections via starting capacitors.
In conclusion, I want to justify my choice this decision: reliability, incredible simplicity, low costs, high power.

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Attention! Assembly of the device requires skills in the field of power electronics and involves contact with high voltage, which can be life-threatening for both the engineer and the users of the device. Make sure you have the required qualifications.

D5- an operational amplifier designed to operate with a single-supply 12V supply, with a high input impedance and the ability to connect a load of 2 kOhm or less to the output. K544UD1, KR544UD1 are well suited.

D6- integrated voltage stabilizer (KREN) for 12V.

VT5- Low-power high-voltage transistor at 600 volts. It only works when the circuit is turned on. So there is no power dissipation 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 Foreign controller manufacturer Texas Instruments gave us a surprisingly pleasant surprise. UC3823A and UC3823B microcircuits appeared. These controllers have slightly different pin functions than the UC3823. They will not work in circuits for UC3823. 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 (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 30 µF, 25 volts.

R8- 20kOhm, R9- tuning resistor 15 kOhm

R1, R2- 10 kOhm trimmers

R3- 10 kOhm

C2, R5- a resistor and a capacitor that set the operating frequency of the PWM controllers. We select them so that the frequency is about 50 kHz. The selection should start with a 1 nF capacitor and a 100 kOhm resistor.

R4- These resistors in different arms are different. The fact is that to obtain a sinusoidal voltage with a phase shift of 120 degrees. a phase-shifting circuit 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 is closed at the minimum value of the sinusoidal voltage (from the output of the operational amplifier), when it increases slightly, it begins to produce short pulses, and when the maximum is reached, it is practically open. The resistor of the middle arm will be 9 times larger, the resistor of the upper arm will be 81 times larger.

After selecting these resistors, the gain can be more accurately adjusted using trimming resistors R1.

R17- 300 kOhm, R18- 30 kOhm

C8- 100nF. These can be low voltage capacitors. There is no high voltage on them, although they are located in the high-voltage part.

R22- 0.23 Ohm. 5W.

VD11- Schottky diodes. Schottky diodes are selected to provide minimal on-state voltage drop across the diode.

R23, R24- 20 Ohm. 1W.

L1- choke 10mH (1E-02 H), for current 5A, C12- 1uF, 400V.

L2 - several turns of thin wire on top of inductor L1. If inductor L1 has X turns, then coil L2 should have [ X] / [60 ]

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In a private house, in an apartment, in a country house, that is, in living conditions, the most common standard single-phase voltage is 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 a 6 kV/380 V power transformer installed on distribution substation, feeding this consumer. Sometimes, especially in a private home, there is a need to launch and operate an asynchronous three-phase motor designed for 380 Volts. There are schemes that make it possible to connect this motor to a single-phase 220 V network, but in this case the power of the electric asynchronous machine is greatly lost. Accordingly, the question arises of how to get 380 Volts from 220 at home, for efficient work electric motor.

What is important to know

In a three-phase network, all three phases have a shift of 120 degrees. If it were necessary to convert three-phase 220 Volts to 380V, or single-phase 220V to the same, but with a voltage of 380V, then this can be done very simply using a conventional step-up transformer. In this problem, it is necessary not just to increase the voltage, but to obtain a full-fledged three-phase network from a single-phase one.

There are three main ways in which this manipulation can be done:

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 loss of 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 for starting.

The second plate shows that the machine is designed exclusively for star connection of windings and a voltage of 380 Volts:

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 of 380 V from 220.

Methods for obtaining 380 V from 220

Voltage converter

This device is more widely 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 an alternating voltage of a given frequency. In this case, there can be any number of phases shifted by a certain degree, but optimally for the operation of generally accepted standard electrical equipment it is three and, accordingly, their shift is 120 degrees. Making such a complex device at home is very problematic, so it is recommended to simply buy it; besides, the market for this product is very developed.

Here circuit diagram inverter:

And this is what it looks like in the factory building:

Often, these devices not only convert single-phase to three-phase voltage, but also protect electric motors from overloads, short circuit and overheating.

Three phase method

This method must be agreed upon with Energonadzor or the supplier company electrical energy, since this requires connecting two additional phases from the panel, which are on each floor apartment buildings.

Here the question is not how to convert single-phase voltage, but how to connect it, and for this you only need a three-phase extension cord, and if everything is done legally, then a meter.

Three-phase transformer

To convert 220 Volts to 380 Volts you need a three-phase transformer required power the voltage of one of the windings is 220 V, and the other 380 V. Most often, they already have windings connected in a star or triangle. After that, the voltage from the network is connected directly to two phases of the winding on the lower side, and to the third terminal through a capacitor. The capacitance of the capacitor is calculated from the ratio of 7 μF for every 100 W of power. The rated voltage of the capacitor must be at least 400 Volts. Such a device cannot be connected without a load. In this case, there will still be a decrease in both engine power and efficiency. If the converter is made using an electric motor rather than a transformer, then the output will have a three-phase voltage, but its value will be the same as in the network, namely 220 V.

So, why do some electrical panels receive a voltage of 380 V, and some - 220? Why do some consumers have three-phase voltage, while others have single-phase? There was a time when I asked myself 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 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 they talk about three-phase voltage, then we are always talking about a voltage of 380 V (linear). Who cares? More details below.

How are three phases different from one?

In both types of power there is a working neutral conductor (ZERO). About protective grounding I, this is a broad topic. Relative to zero at all three phases ah - voltage 220 Volts. But in relation to these three phases to each other, they have 380 Volts.

Voltages in a three-phase system

This happens because the voltages (with an active load, and the current) on the three phase wires differ by a third of the cycle, i.e. at 120°.

You can read more in the electrical engineering textbook - about voltage and current in a three-phase network, and also see vector diagrams.

It turns out that if we have 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. You just need to do this in such a way that the consumption in each phase is approximately the same, otherwise phase imbalance is possible.

In addition, it will be difficult for the overly loaded phase and it will be offensive 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 the 10 kW threshold. I'll try to list.

Single-phase network 220 V, advantages

Simplicity
Cheapness
Below dangerous voltage

Single-phase network 220 V, cons

Limited consumer power

Three-phase network 380 V, advantages

Power is limited only by wire cross-section
Savings with three-phase consumption
Power supply for industrial equipment
Possibility of switching a single-phase load to a “good” phase in case of deterioration in quality or power failure

Three-phase network 380 V, cons

More expensive equipment
More dangerous voltage
Limited maximum power single-phase loads

When is it 380 and when is it 220?

So why do we have a voltage of 220 V in our apartments and not 380? The fact is that, as a rule, consumers with a power of less than 10 kW are connected to one phase. This means that one phase and a neutral (zero) conductor are introduced into the house. This is exactly what happens in 99% of apartments and houses.

Single-phase electrical panel in the house. The right machine is introductory, then through the rooms. Who can find mistakes in the photo? Although, this shield is one big mistake...

However, if you plan to consume power more than 10 kW, then a three-phase input is better. And if you have equipment with three-phase power supply (containing), then I strongly recommend introducing a three-phase input into the house with a linear voltage of 380 V. This will save on wire cross-section, on safety, and on electricity.

Despite the fact that there are ways to connect a three-phase load to a single-phase network, such modifications sharply reduce the efficiency of motors, and sometimes, all 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 power consumption, as a rule, does not exceed 10 kW. In this case, a cable with wires with a cross section of 4-6 mm² is used at the input. The current consumption is limited by the input automatic switch, the rated protection current of which is no more than 40 A.

I’ve already talked about choosing a circuit breaker. And about the choice of wire cross-section -. There are also heated discussions of issues.

But if the consumer’s power is 15 kW or higher, then three-phase power must be used. 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 cross section of at least 10 mm². The cost of a cable with such cores will be significant. But I have never seen single-phase (single-pole) circuit breakers with a current greater than 63 A on a DIN rail.

Therefore, in offices, stores, and especially in enterprises, only three-phase power is used. And, accordingly, three-phase meters, which come in direct connection and transformer connection (with current transformers).

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And at the input (in front of the counter) there are approximately the following “boxes”:

Three-phase input. Introductory machine in front of the counter.

A significant disadvantage of three-phase input and (noted above) – limitation on the power of single-phase loads. For example, the allocated power of three-phase voltage is 15 kW. This means that for each phase - a maximum of 5 kW. This means that the maximum current in each phase is no more than 22 A (practically 25). And you have to spin, distributing the load.

I hope it is now clear what three-phase voltage 380 V and single-phase voltage 220 V are?

Star and Delta circuits in a three-phase network

There are various variations connecting a load with an operating voltage of 220 and 380 Volts to a three-phase network. These patterns 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” circuit, that is, to phase voltage. In this case, all load groups are distributed so that the powers in the phases are approximately equal. 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 has a voltage of 380V, it is switched on according to the “Triangle” circuit, that is, to 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 “initially” 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 stages. The last transformer lowers the voltage to the level of 0.4 kV and supplies it to end consumers - you and me, in apartment buildings and in the private residential sector.

Next, the voltage is supplied to the second stage transformer TP2, at the output of which the end-user voltage is 0.4 kV (380V). The power of transformers TP2 is from hundreds to thousands of kW. From TP2 the voltage comes to us - to several apartment buildings, to private sector, etc.

The circuit is simplified, there may be several steps, the voltage and power may be different, but the essence does not change. There is only one final voltage of consumers - 380 V.