Single-phase electric motors 220V 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 varieties of these devices:
The latter in their design are simpler, but they have a number of disadvantages, among which difficulties with changing the frequency and direction of rotation of the rotor can be noted.
Induction motor device
The power of this engine depends on the design 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, a single-phase asynchronous electric motor is equipped with two windings offset by 90 ° relative to each other. In this case, the main (working) occupies a significant part of the grooves, and the auxiliary (starting) - the rest. A single-phase asynchronous electric motor got its name only because it has only one working winding.
Principle of operation
The alternating current flowing through the main winding creates a periodically changing magnetic field. It consists of two circles of the same amplitude, the rotation of which occurs towards each other.
In accordance with the law of electromagnetic induction, the magnetic flux changing in the closed turns of the rotor forms an induction current that interacts with the field generating 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 the moments of forces is violated, since the slip of its turns with respect to the rotating magnetic fields will become different. Thus, the Ampere force acting on rotor turns from a direct magnetic field will be significantly greater than from the side of the reverse field.
Induction current can occur in the turns of the rotor only as a result of the intersection of the magnetic field lines by them. Their rotation should be carried out at a speed slightly less than the frequency of rotation of the field. Actually from here the name asynchronous single-phase electric motor went.
Due to the increase in mechanical load, the rotation speed decreases, the induction current in the rotor turns increases. And also increases the mechanical power of the engine and the alternating current that it consumes.
Connection and startup diagram
Naturally, it is inconvenient to manually spin the rotor every time you start the electric motor. Therefore, to ensure the initial starting torque, a starting winding is used. Since it makes a right angle with the working winding, for the formation of a rotating magnetic field, the current must be phase-shifted relative to the current in the working winding by 90 °.
This can be achieved by incorporating a phase-shifting element into the circuit. The inductor or resistor cannot provide a phase shift of 90 °, therefore it is more advisable to use a capacitor as a phase-shifting element. This single-phase motor circuit has excellent starting properties.
If a capacitor acts as a phase-shifting element, the electric motor can structurally be represented:
- With a working capacitor.
- With starting capacitor.
- With working and starting capacitor.
The most common is the second option. In this case, a short connection of the starting winding with a capacitor is provided. This only happens during start-up, then they turn off. This option can be implemented using a time relay or by closing a circuit by pressing the start button.
A similar connection scheme for a single-phase electric 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).
A circuit with a continuously connected operating capacitor in the nominal mode works better, while the starting characteristics are mediocre. The option with a working and starting capacitor, in comparison with the two previous ones, is an intermediate one.
Commutator motor
Consider a single-phase collector-type electric motor. This versatile equipment can be powered by direct or alternating current sources. It is often used in electric tools, washing and sewing machines, meat grinders - where reverse is required, its rotation with a frequency of over 3000 rpm or frequency control.
The windings of the rotor and 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 rotor windings are suitable.
The reverse is carried out by changing the polarity of the connection of the rotor or stator to the electric network, and the rotation speed is regulated by changing the current value in the windings.
disadvantages
A single-phase collector motor has the following disadvantages:
- The creation of radio interference, difficult control, significant noise.
- The complexity of the equipment, it is almost impossible to repair it yourself.
- High price.
Connection
In order for the electric motor in the single-phase network to be connected properly, certain requirements must be observed. As already mentioned, there are a number of motors that can operate on a single-phase network.
Before connecting, it is important to make sure that the frequency and voltage indicated on the housing correspond to the main parameters of the electrical network. All connection work must be done only with a de-energized circuit. 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 need to be connected to the 220B circuit.
Due to the fact that single-phase 220V electric motors operate in an alternating current circuit, a magnetic alternating current arises in magnetic systems, which provokes the formation of eddy currents. That is why the magnetic system of the stator and rotor is made of electrical steel sheets.
Connecting without a control unit with electronics can lead to the formation of a significant inrush current at the moment of start-up and sparking in the collector. Changing the direction of rotation of the armature is performed by disrupting the connection sequence when the outputs of the armature or rotor are interchanged. The main drawback of these engines is the presence of brushes, which should be replaced after each long-term operation of the equipment.
Such problems in induction motors do not exist, since they lack a collector. 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, it is necessary to choose a magnetic current starter so that its contact system can withstand the load of an electric motor.
2. Starters, for example, are divided by a value from 1 to 7, and the larger this indicator, the more current the contact system of these devices can withstand.
- 10A - 1.
- 25A - 2.
- 40A - 3.
- 63A - 4.
- 80A - 5.
- 125A - 6.
- 200A - 7.
3. After the starter value has been determined, attention must be paid to the control coil. It can be on 36B, 380B and 220B. It is advisable to dwell on the latter option.
4. Next, the magnetic starter circuit is assembled, and the power part is connected. An input 220B is made to open contacts, an electric motor is connected to the output of the power contacts of the starter.
5. The “Stop - Start” buttons are connected. Their power is supplied from the input power contacts of the starter. For example, the phase is connected to the “Stop” button of the closed contact, then it passes to the start button of the open contact, and from the contact of the “Start” button to one of the contacts of the magnetic starter coil.
6. A “zero” is connected to the second terminal of the starter. To fix the switched on position of the magnetic starter, it is necessary to bypass the start button of the closed contact to the contact block of the starter, which supplies power from the Stop button to the coil.