We are going to consider how the three-phase motor is connected to a single-phase network and give recommendations on the control of the unit. More often, people want to vary the rotational speed or direction. How to do it? Described blurry earlier how to connect a three-phase motor for 230 volts, now we will attend to details.
The standard scheme for switching a three-phase motor into a single-phase network
The process of connecting a three-phase motor to a voltage of 230 volts is simple. Usually the branch carries a sine wave, the difference is 120 degrees. A phase shift, uniform, is formed, which ensures a smooth rotation of the electromagnetic field of the stator. The effective value of each wave is 230 volts. This will connect the three-phase motor to the home outlet. Focus circus: get three sinusoids using one. The phase shift is 120 degrees.
In practice, this can be done by enlisting the help of special devices of phase shifters. Not those used by high-frequency paths of waveguides, but special filters formed by passive, less often active elements. Fans of zamorochkam prefer the use of a real capacitor. If the motor windings are connected by a triangle, forming a single ring, we obtain phase shifts of 45 and 90 degrees, at a loss enough for the unsteady operation of the shaft:
A three-phase motor connecting circuit by switching windings with an
- triangle One phase winding the outlet. Wires cling potential difference.
- The second winding is powered by a capacitor. A phase shift of 90 degrees relative to the first is formed.
- At the third, due to the applied voltages, a weakly sine-like oscillation is formed with a shift of another 90 degrees.
Total, the third winding is 180 degrees from the first in phase. Shows practice alignment enough to work normally. Of course, the engine sometimes “sticks”, it is very hot, the power drops, the efficiency is lame. Users reconcile when connecting an asynchronous motor to a three-phase network is excluded.
We add from purely technical nuances: the proper wiring diagram is shown on the instrument case. More often it decorates the inside of the casing hiding the shoe, or is drawn nearby on the nameplate. Guided by the scheme, we understand how to connect an electric motor with 6 wires( one pair for each winding).When the network is three-phase( often referred to as 380 volts), the windings are connected by a star. One common coil is formed a point where the neutral is connected( conditional schematic electric zero).Phases are fed to the other ends. It turns out three - by the number of windings.
How to handle a delta to connect a 230 V three-phase motor is understandable. Additionally, we provide a drawing depicting:
- Wiring electrical connection diagram.
- A working capacitor that serves the purpose of creating the correct phase distribution.
- Starting capacitor, facilitating the promotion of the shaft at the initial speed. Subsequently, it is disconnected from the circuit by a button, discharged by a shunt resistor( for safety and being ready for a new start-up cycle).
Connection of a three-phase 230 volt motor with an
delta The picture shows: winding A is under voltage of 230 volts. C is supplied with a phase shift of 90 degrees. Due to the potential difference, the ends of the winding B form a voltage shifted by 90 degrees. The outlines are far from the familiar sinusoid school physicists. Omitted in order to simplify the starting capacitor, the shunt resistor. We believe the location is obvious from the above. This method will at least make it possible to achieve normal operation from the engine. The start capacitor key closes, making a start, is disconnected from the phase, discharged by a shunt.
It's time to say: the capacitance, indicated by the drawing 100 microfarads, is practically selected, considering:
- Shaft rotational speeds.
- Engine power.
- Loads applied to the rotor.
It is necessary to select a capacitor experimentally. According to our picture, the voltage of the windings B and C will be the same. We remind: the tester shows the actual value. Phase voltage will be different, the shape of the signal winding In non-sinusoidal. The actual value indicates: the same power is given to the shoulders. More stable installation is provided. The motor is less heated, engine efficiency is optimized. Each winding is formed by inductive resistance, which also imposes an imprint on the phase shift between voltage and current. That is why it is important to find the right capacity value. You can achieve ideal engine operating conditions.
Making the engine spin in the opposite direction
Three phases of voltage 380 volts
When connected to three phases, changing the direction of rotation of the shaft is ensured by the correct switching of the signal. Special contactors are used( three pieces).1 for each phase. In our case, only one circuit is subject to switching. And( guided by the statements of the guru) it is enough to swap any two wires. Be it the power, the place where the capacitor is docked. Check the rule before issuing farewell to readers. The results are shown by a second drawing, schematically giving diagrams showing the phase distribution of the specified case.
Making the plots, it was assumed that winding C is connected in series to a capacitor, which gives the voltage a positive phase increment. According to the vector diagram, in order to maintain the balance, winding C must have a negative sign with respect to the main voltage. On the other hand, the capacitor, coil B is connected in parallel. One branch provides voltage positive gain( capacitor), the other - the current. Akin to a parallel oscillatory circuit, the currents of the branches flow almost in the opposite direction. Considering the above, the law of changing the sine wave in phase with respect to the winding C was adopted.
The diagrams show: according to the diagram, the maxima bypass the windings counterclockwise. The last review showed a similar context: rotation goes in a different direction. It turns out, really, when the polarity of the supply is changed, the shaft rotates in the opposite direction. We will not draw the distribution of magnetic fields, we consider it unnecessary to repeat.
More precisely, such things will allow you to calculate special computer programs. Explanation given on the fingers. It turned out that the practices are right: by changing the polarity of the supply, the direction of movement of the shaft is reversible. Surely a similar statement is appropriate when the capacitor is turned on by a branch of another winding. For thirsty detailed charts, we recommend exploring specialized software packages like the free Electronics Workbench. In the application, write down the desired number of control points, track the laws of changes in currents, voltages. Fans of mocking their brains will be able to view the spectrum of signals.
Take the trouble to set the inductance of the windings correctly. Of course, the impact is made by the load that impedes the launch. Take into account the loss of such programs is difficult. Practitioners recommend avoiding focusing on the indicated sharpener, selecting capacitor values (empirically) empirically. Thus, the exact wiring diagram of a three-phase motor is determined by the design, the intended purpose. For example, a lathe will differ from a baker with developing loads.
Starting capacitor of a three-phase motor
More often, the connection of a three-phase motor to a single-phase network must be carried out with the participation of a starting capacitor. Especially the aspect concerns powerful models, motors under considerable load at the start. In this case, its own reactance increases, which will have to be compensated with tanks. Easier to pick up again experimentally. It is necessary to assemble a stand on which it is possible to “turn on the hot”, to exclude from the chain individual containers.
Avoid helping the engine to start by hand, as demonstrated by "experienced" masters. Just find the value of the battery at which the shaft rotates briskly, as you spin, start excluding the capacitors one by one from the circuit. As long as there is a set below which the engine does not rotate. The selected elements form the starting capacity. And the correctness of his choice must be controlled with a tester: the voltage in the shoulders of the windings with phase shifted( in our case C and B) must be the same. This means that approximately equal power is given.
Three-phase motor with starting capacitor
As for the estimates and estimates, the battery capacity increases with increasing power and speed. And if we talk about the load, it has a great influence at the start. When the shaft is unwound, in most cases small obstacles are overcome due to inertia. The more massive the shaft, the higher the chance that the engine will not "notice" the arisen difficulty.
Please note that the connection of an asynchronous motor is usually done through a protective circuit breaker. A device that will stop the rotation when the current exceeds a certain value. This not only saves the local network plugs from burning out, but also saves the motor windings when the shaft is jammed. In this case, the current will increase dramatically, and the device will stop working. The automatic machine of protection is also useful for the selection of the required capacity rating. Eyewitnesses claim that if a 3-phase motor is connected to a single-phase network through capacitors that are too weak, the load will increase dramatically. In the case of a powerful motor, this is very important, because even in normal mode, consumption exceeds the nominal 3-4 times.
And a few words on how to estimate in advance the starting current. Let's say you need to connect an asynchronous motor at 230 with a power of 4 kW.But this is for the three phases. In the case of the standard wiring current for each of them flows separately. All this will develop in our country. Therefore, we boldly divide the power by the mains voltage and we get 18 A. It is clear that without a load, such a current is unlikely to be spent, but for the stable operation of the engine to its fullest, an automatic circuit breaker of amazing power is needed. As for a simple test run, the amp device will fit quite well at 16. And there is even a chance that the launch will take place without incident.
We hope readers now know how to connect a three-phase motor to a 230 volt home network. It remains to add to this that the possibilities of a standard apartment do not exceed, in terms of power output to the consumer, values of the order of 5 kW.This means that the engine described above at home is simply dangerous to turn on. Please note that even grinders are rarely more powerful than 2 kW.At the same time the engine is optimized for operation in a single-phase network of 220 volts. Simply put, too powerful devices will not only cause the light to blink, but will most likely provoke other abnormal situations. At best, knock out traffic jams, at worst - the wiring will ignite.
We say goodbye to this and want to note: knowledge of the theory is sometimes useful for practitioners. Especially when it comes to powerful technology that can cause considerable harm.
