Single-phase 220V electric motors are widely used in a variety of industrial and household equipment: pumps, washing machines, refrigerators, drills and processing machines.
Varieties
There are two most popular types of these devices:
- Collector.
- Asynchronous.
The latter are simpler in their design, but they have a number of drawbacks, among which one can note difficulties with changing the frequency and direction of rotation of the rotor.
The device of the induction motor
The power of this engine depends on thedesign features and can vary from 5 to 10 kW. Its rotor is a short-circuited winding - aluminum or copper rods, which are closed from the ends.
As a rule, the electric motor is asynchronousSingle-phase is equipped with two windings offset by 90 ° relative to each other. In this case, the main (working) occupies an essential part of the grooves, and the auxiliary (starting) remains. Its name is an asynchronous single-phase electric motor received only because it has only one working winding.
Principle of operation
The alternating current flowing through the main winding creates a magnetic periodically changing field. It consists of two circles of the same amplitude, the rotation of which occurs towards each other.
In accordance with the law of electromagneticInduction, the magnetic flux changing in closed rotor turns forms an induction current, which interacts with the field that generates it. If the rotor is in a stationary position, the moments of forces acting on it are the same, as a result, it remains stationary.
When the rotor rotates, the equality of moments breaks downforces, since the sliding of its turns relative to the rotating magnetic fields will become different. Thus, the Ampere force acting on the rotor coils from the direct magnetic field will be substantially greater than on the side of the inverse field.
In the turns of the rotor, the induction current can occuronly as a result of their crossing of the magnetic field lines. Their rotation should be carried out at a speed slightly less than the rotation frequency of the field. Actually from here also the name asynchronous single-phase electric motor has gone.
Due to the increased mechanical loadthe speed of rotation decreases, the induction current in the rotor turns increases. And also increases the mechanical power of the motor and the alternating current that it consumes.
Connection and start-up scheme
Naturally, manually untwist at eachThe start of the electric motor of the rotor is inconvenient. Therefore, the starting winding is used to provide the initial starting torque. Since it forms a right angle with the working winding, to form a rotating magnetic field on it, the current must be shifted in phase with respect to the current in the working winding by 90 °.
This can be achieved by including in the chainphase-shifting element. A choke or resistor can not provide a phase shift of 90 °, so it is better to use a capacitor as the phase-shifting element. Such a single-phase motor circuit has excellent starting properties.
If a capacitor acts as a phase-shifting element, the motor can be structurally represented:
- With a working capacitor.
- With starting capacitor.
- With a working and starting capacitor.
The most common is the second option.In this case, short-term connection of the starting winding with the capacitor is provided. This happens only for the duration of the start, then they are disconnected. This option can be realized by means of a time relay or by closing the circuit when the start button is pressed.
Such a single-phase connection schemeelectric motor is characterized by a rather low starting current. However, in the nominal mode the parameters are low due to the fact that the stator field is elliptical (it is stronger in the direction of the poles).
Scheme with a permanent workerThe capacitor in the nominal mode works better, and the starting characteristics are mediocre. The variant with the operating and starting capacitor, in comparison with the two previous ones, is intermediate.
Collector motor
Consider a single-phase electric motorcollector type. This universal equipment can be powered from DC or AC power sources. It is often used in electric tools, washing and sewing machines, meat grinders - wherever a reverse is required, its rotation at a frequency above 3000 rpm or frequency adjustment.
The windings of the rotor and the stator of the electric motor are connected in series. The current is supplied by means of brushes in contact with the collector plates, to which the ends of the windings of the rotor are suitable.
The reversal is accomplished by changing the polarity of the rotor or stator connection to the electrical network, and the speed is controlled by changing the current in the windings.
disadvantages
The collector single-phase electric motor has the following drawbacks:
- Creation of radio interference, difficult control, considerable noise level.
- The complexity of the equipment, it is almost impossible to repair it yourself.
- High price.
Connectivity
That the electric motor in a single-phase network wasproperly connected, certain requirements must be met. As already mentioned, there are a number of engines that can function from a single-phase network.
Before connecting, it is important to make sure thatthe frequency and voltage of the network indicated on the housing correspond to the main parameters of the electrical network. All work on the connection must be made only with the circuit de-energized. Charged capacitors should also be avoided.
How to connect a single-phase electric motor
To connect the motor, it is necessary to connect the stator and the armature (rotor) in series. Terminals 2 and 3 are connected, and the other two must be connected to the 220B circuit.
Due to the fact that single-phase electric motors220V function in an alternating current circuit, magnetic magnetic flux generates a magnetic flux, which causes the formation of eddy currents. That is why the magnetic system of the stator and rotor is made of electrical steel sheets.
Connection without control unit withelectronics can lead to the fact that at the time of start-up a considerable inrush current is generated and arcing will occur in the collector. Changing the direction of rotation of the armature is performed by disrupting the connection sequence when the armature or rotor terminals change places. The main drawback of these engines is the presence of brushes, which should be replaced after each long operation of the equipment.
Such problems in asynchronous electric motors do not exist, since there is no collector in them. The magnetic field of the rotor is formed without electrical connections due to the external magnetic field of the stator.
Connection via magnetic starter
Consider how you can connect a single-phase motor through a magnetic starter.
1. So, first of all, you need to choose a magnetic starter with respect to the current in such a way that its contact system can withstand the load of the electric motor.
2. Starters, for example, are divided by a value from 1 to 7, and the higher this index, the greater the current can withstand the contact system of these devices.
- 10A to 1.
- 25A - 2.
- 40A to 3.
- 63A to 4.
- 80A - 5.
- 125A to 6.
- 200A to 7.
3. After the size of the starter has been determined, it is necessary to pay attention to the control coil. It can be on 36B, 380B and 220B. It is desirable to stay on the last option.
4. Next, the magnetic starter circuit is assembled, and the power section is connected. The 220V input is applied to the open contacts, the electric motor is connected to the output of the power contacts of the starter.
5. The "Stop-Start" buttons are connected.Their power is provided by the input of the starter's power contacts. For example, the phase is connected to the button "Stop" of the closed contact, then from it goes to the open button of the open contact, and from the contact of the button "Start" - to one of the contacts of the coil of the magnetic starter.
6. On the second output of the starter is connected "zero".To fix the switched on position of the magnetic starter, it is necessary to shunt the closed contact starter button to the starter contact block, which supplies power from the "Stop" button to the coil.
