How to connect a three-phase electric motor to a 220V network: tips

Often there is a need for a household or repair work to connect a three-phase electric motor to a 220-volt network. These devices operate on a voltage of 380 V. But, as is known, in most houses the power supply network has only 220V. How to connect a three-phase electric motor to a 220V network? We learn about this from our article.

How to connect a three-phase motor to a single-phase network

Consider an example with a sewing machine. Of course, there will be no problems in the factory with the connection. But to work in a single-phase network you need to slightly tweak the motor. For example, change the scheme for connecting windings from the shape of a star to a triangle. Of course, you need to stick to the polarity. Due to such alteration, it will be possible to connect a three-phase electric motor to the 220V network.

The motor of the sewing machine is 0.4 kW. If you can purchase starting metal paper capacitors, MBTT, MBGO or MBGO with 50 or 100 uF capacity and operating voltage from 450 to 600, then there will be no problems with start-up. However, they can cost too much. Therefore, it is better to look for alternative "cheap" solutions to the problem.

This can be a short-term connection of an additional electrolytic capacitor. It should work only two or three seconds, no more. After all, his work is only necessary to start the electric motor. Then the latter will function in a two-phase mode and lose up to half the power. A stock of it, however, can be envisaged. By the way, the same loss of power will also be observed when working with a phase-shift capacitor.

The lack of method and the solution of the problem

Many people know that in an alternating current network, the electrolytic capacitor heats up very quickly. The electrolyte in it boils and explodes. Practice has shown that this can happen over a period of ten to fifteen seconds. But if this capacitor is turned on only for one and a half seconds, using a small resistance, then the device will not be damaged, since it will not have time to warm up.

In washing machines for short-term use the button PNVS. It is three-contact. Two of them have a fixation, and one does without it. Due to the last contact, the capacitor turns on and ceases to function after stopping the pressing.

Voltage on electrolytic capacitors should be not less than 450V. Therefore, the capacitance can be collected from several capacitors placed in a protective box. This connection scheme in practice proved its viability. True, the experiments were carried out only with electric motors, the power of which was less than one kW. For more powerful motors, you will most likely want to include a small resistor with a current limitation and the necessary dissipation power with the capacitor.

The second way

Let's consider, how the three-phase electric motor in a single-phase network is connected asynchronous with a short-circuited rotor.

In practice, even with the best choice of capacitance of the phase-shifting capacitor, the torque will not exceed thirty-five percent of the nominal capacitance. This is due to the fact that the current flowing through one winding is shifted in phase with respect to the other windings. Therefore, in the magnetic field of the stator, another component is created, in addition to the one that rotates the rotor in the required direction.

The formed component rotates in the opposite direction and brakes the rotor, reducing the torque on the shaft and wasting energy, heating the conventional and magnetic motor wires. But if you turn off the winding, the torque will increase to forty one percent. And if you change the direction of the current in it and reconnect it, it will increase even more and can reach up to fifty eight percent.

How to improve the process

Such optimization of the process is possible not only due to a change in the direction of rotation of the component. It turns out also compensation of fields of other windings which coincide in a direction and do not participate in rotary rotation. The start of the engine will improve even when using two phase-shift capacitors.

Their capacities should be the same. Such indicators are calculated by a special formula. They are checked by measuring the voltage on the windings and should show approximately the same results.

Equal stresses can be connected in parallel with a dashed line.

How to connect a three-phase motor to a 220 volt network

Radio amateurs often have to use the motors in question. Therefore, it is extremely necessary to know how to connect a three-phase electric motor to a 220V network. It is already known that for this it is absolutely not necessary to have a three-phase network. It is better to connect the third winding through a phase-shift capacitor.

For normal operation of the engine, the capacity of the capacitor is changed, given the number of revolutions. In practice, this condition is very difficult to fulfill. From the position they come out in a two-step way: the engine is switched on with starting capacity and is left at the same time a working one. In manual mode, it switches to the work mode.

The capacitor is used only as a paper type, and its operating voltage should be 1.5 times higher than the mains voltage. The scheme of reversing the engine with capacitor start is quite simple. When the switch is activated, the motor changes the direction of rotation. But you need to know the features of the operation of such engines. If the device works idle on the winding, the current will flow from twenty to forty percent more than the rated current. Therefore, when operating with a load, the working capacity should be reduced. If the motor overloads, it will turn off, and for a new start, it will be necessary to turn on the start capacitor again.

You can connect any electric motor to the 220V network, even a three-phase one. However, some of them may work poorly. An example is the double cell of a short-circuited MA rotor. But if the circuit is correctly implemented and the necessary parameters of the capacitors are correctly selected, the workflow will be excellent. For example, asynchronous motors A, AO2, APS, AO, AOA and UAD are successful variants.

The disadvantages of the three ways to connect

The disadvantages of the above described ways is the following:

• Half of the nominal power is lost;
• Not all models of electric motors are started when feeding from a single-phase network;
• The working and launching tanks must be used;
• When idling the current flows more than twenty to forty percent of the nominal;
• For the automated process of shutting down the start capacitor and replacing the paper elements with electrolytic ones, additional revolutions are used.

The fourth way

You can eliminate these shortcomings using the following method. How to connect a three-phase electric motor to a 220V network?

In three-phase voltage, each curve is shifted by one third compared to the other.

Since the network frequency is fifty hertz, the period will be equal to twenty microseconds. Then its third is 6.666 ... microseconds. Let us take a sinusoidal single-phase voltage of 220V and 50 Hertz. If you pass it through the delay circuit for a third of the period, you get a shifted voltage, which will be equal in amplitude and frequency to the original one. If you also pass it through the same delay circuit, you will get the shifted voltage for another third of the period.

Do you know how to connect a three-phase motor to a single-phase network? The scheme should be studied by you in as much detail as possible. And it looks like this.

The mechanism includes a BP and a positive-polarity pulse generator on the transformer. The power supply consists of the second winding of the transformer, the rectifier bridge and the stabilizer. The generator is assembled in the third winding of the transformer, the resistor and the rectifier on the diodes. The zener barrier protects the inputs of the part from accidental increase above the permissible voltage, that is, more than twelve volts. In the detail there is a shaper of rectangular pulses. At the output, rectangular pulses of fifty Hertz plus polarity are applied.

When three-phase current is transformed, three single-phase or special three-phase transformers with a core in the form of rods can be used. The individual elements must be connected according to the star-star scheme.

Conclusion

Thus, the solution of the question of how to connect a three-phase electric motor to a 220V network is possible in several ways. Some of them are more difficult to implement, but the process will be better. Other methods are simpler, but they are not devoid of shortcomings.