220V single-phase electric motors are widely used in a variety of industrial and household equipment: pumps, washing machines, refrigerators, drills and machine tools.
Varieties
There are two most popular varieties of these devices:
- Collector.
- Asynchronous.
The latter are simpler in design, but they have a number of disadvantages, among which are difficulties in changing the frequency and direction of rotation of the rotor.
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 at the ends.
As a rule, a single-phase asynchronous 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. Your namethe single-phase asynchronous electric motor received only because it has only one working winding.
Working principle
The alternating current flowing through the main winding creates a magnetic field that changes periodically. 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 that generates it. If the rotor is in a stationary position, the moments of the forces acting on it are the same, as a result, it remains stationary.
When the rotor rotates, the equality of the moments of forces will be violated, since the sliding of its turns in relation to the rotating magnetic fields will become different. Thus, the Ampère force acting on the rotor turns from the direct magnetic field will be significantly greater than from the side of the reverse field.
In the turns of the rotor, the induction current can only occur as a result of their intersection of the magnetic field lines of force. Their rotation should be carried out at a speed slightly less than the frequency of rotation of the field. Actually, this is where the name asynchronous single-phase electric motor came from.
Due to the increase in mechanical load, the rotation speed decreases, the induction current in the rotor turns increases. It also increases the mechanical power of the motor and the AC power it consumes.
Connection and launch diagram
Of course, manuallyit is inconvenient to spin the rotor every time you start the electric motor. Therefore, a starting winding is used to provide the initial starting torque. Since it forms a right angle with the working winding, in order to form a rotating magnetic field, the current must be shifted in phase relative to the current in the working winding by 90 °.
This can be achieved by including a phase-shifting element in the circuit. A choke or resistor cannot provide a phase shift of 90 °, therefore it is more expedient 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 be structurally represented:
- With run capacitor.
- With start capacitor.
- With run and start capacitor.
The second option is the most common. 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 the circuit when the start button is pressed.
Such a scheme for connecting a single-phase electric motor is characterized by a rather low starting current. However, in 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 permanently connected working capacitor inIn nominal mode, it works better, while the starting characteristics are mediocre. The option with a working and starting capacitor, compared to the previous two, is intermediate.
Collector motor
Consider a single-phase collector-type electric motor. This versatile equipment can be powered by DC or AC power. It is often used in electric tools, washing and sewing machines, meat grinders - where reverse is required, its rotation at a frequency of over 3000 rpm or frequency adjustment.
The rotor and stator windings 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 fit.
The reverse is carried out by changing the polarity of the connection of the rotor or stator to the electrical network, and the rotation speed is regulated by changing the current in the windings.
Flaws
The collector single-phase electric motor has the following disadvantages:
- Radio interference, difficult to operate, significant noise level.
- The complexity of the equipment, it is almost impossible to repair it yourself.
- High cost.
Connection
In order for a motor in a single-phase network to be connected properly, certain requirements must be met. As already mentioned, there are a number of engines capable ofoperate from a single-phase network.
Before connecting, it is important to make sure that the mains frequency and voltage indicated on the case correspond to the main parameters of the electrical network. All connection work must be carried out only with a de-energized circuit. Charged capacitors should also be avoided.
How to connect a single-phase motor
To connect the motor, it is necessary to connect the stator and armature (rotor) in series. Terminals 2 and 3 are connected, and the other two need to be connected to the 220V circuit.
Due to the fact that single-phase 220V electric motors operate in an alternating current circuit, a magnetic alternating flux occurs 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.
Connection without a control unit with electronics can lead to the fact that at the time of starting a significant inrush current is generated, and sparking occurs in the collector. Reversing the direction of rotation of the armature is performed by changing the connection sequence when the armature or rotor leads are reversed. The main disadvantage of these motors is the presence of brushes, which should be replaced after each long operation of the equipment.
Such problems do not exist in asynchronous motors, since they do not have 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
Let's consider how you can connect a single-phase electric motor through a magnetic starter.
1. So, first of all, it is necessary to choose a magnetic current starter in such a way 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 greater the 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 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 advisable to stop at the last option.
4. Next, the magnetic starter circuit is assembled, and the power section is connected. 220V is input 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 of the power contacts of the starter. For example, the phase is connected to the “Stop” button of the closed contact, then from it it goes 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. "Zero" is connected to the second output of the starter. To fix the on position of the magnetic starter, it is necessary to shunt the start button of the closed contact to the blockcontacts of the starter that supplies power from the "Stop" button to the coil.
