An electric motor is a device that converts energy into machinery. It is mainly composed of
A stator winding used to generate a magnetic field, or an electromagnet winding or rotor distributed in a stator group Into.
Using an electric coil to generate a rotating magnetic field, and in the rotor to generate a magnetic electric torque in the action of the current Generate a magnetic field, Turn the motor.
- According to the varieties
Ac motor can be divided into synchronous motor and asynchronous motor. The speed NS of the rotor of a synchronous motor is the same as that of the rotating magnetic field, which is called synchronous speed. There is a strict relationship between NS and the frequency (f) of the connected AC and the logarithm of the magnetic poles (P) of the motor.
ns=60f/P
The name derives from the fact that the rotor speed of an asynchronous motor is always lower or higher than the speed of its rotating magnetic field. The difference between rotor speed and magnetic field speed (called slip) is usually within 10%. Asynchronous motors are simple in structure and widely used. Most factory include Zhejiang Aoer produce the asynchronous motors.
2. According to motor phase number divided the ac motor to single phase motor (such as elecmotor products) and three phase motor. Because of the limited of power resource. Most household appliances (such as mower motor, coofee grinder motor, concrete mixer motor and small inductrial machine use single phase motor (shuch as pump motor, polish machine motor etc.)
3.Single-phase motor is divided into two categories, that is, phase separation and cover pole type. Theoretically, the problem of boot can be solved by making the AC current flowing between the two sets of windings have a certain phase difference, and the magnetic potential or flux in the two Spaces have missed a certain Angle have a certain phase difference.
3.1 Split-phase single-phase motor
Phase separation single-phase motor uses capacitive or resistance series starting windings to shift phase, so that the current phases of starting windings and working windings are staggered
(1) Capacitor split-phase single-phase motor
Figure (a) shows the capacitance single phase motor principle connection line. As the role of capacitor phase shift is more obvious, as long as the capacitor is connected into a similar size (generally 20~ 50μ F), the current difference between the two windings is close to 90°, then the synthetic magnetic field is close to the circular rotating magnetic field, so the capacitor with a larger starting torque starts at the same time. This single-phase motor is widely used and can be retained (i.e. capacitatively operated motors) or excised (i.e. switch motors, performed by centrifugal switches placed within the motor) as required after start-up. If you want to change the motor steering, you only need to adjust the outgoing end of any winding, and the current phase relationship between the two windings is opposite.
(2) Resistance phase separation single-phase motor
The starting winding of this kind of motor has few turns and thin wire, and its reactance is small and resistance is large compared with the running winding. When the resistance phase separation is used for starting, the current of the starting winding is ahead of that of the running winding. The synthetic magnetic field is oval rotating magnetic field with large ellipticity, and the starting torque is small. It is only used for no-load or light-load situations and seldom applied. Generally, the starting winding of the single-phase motor of resistance split-phase is designed for short-time operation. After starting, the starting winding is cut by the centrifugal switch, and the working winding is maintained for operation. Figure (b) shows the principle wiring of the resistance phase separation single-phase motor.
3.2 Hood pole type single phase motor
The covered pole single-phase motor is composed of short-circuit copper ring or short-circuit coil (group) embedded in a part of the stator pole.
When the stator windings are filled with single-phase AC current, most of the pulse vibration magnetic field generated by the stator is directly connected to the rotor through the air gap, and a small part generates induced flux through the cover copper ring, and then enters the rotor magnetic circuit through the air gap after synthesis. According to Lenz’s law, the induced flux always blocks the change of the primary flux, and the induced flux lags behind the phase of the primary flux. Thus, there are two magnetic flux in space stagger a certain Angle, and some phase difference, the resultant magnetic field is a kind of elliptical rotating magnetic field. Cover pole type motor rotation direction by the cover pole part of the cover pole, its power is lower, the starting moment of rotation is small, simple structure, cheap. Cover pole motor is usually used for blower, fan and other small motor
When the single-phase sinusoidal current passes through the stator winding, the motor generates an alternating magnetic field. The intensity and direction of the motor change with the law of sinusoidal in time, but are fixed in space direction, so the magnetic field is also called alternating pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields, which rotate at the same speed and in opposite directions. When the rotor stops, these two rotating magnetic fields create a moment of the same size and opposite direction, making the resultant magnetic field zero, so that the motor cannot rotate. When we use external force to rotate the motor to a certain direction (such as clockwise rotation), then the cutting magnetic line motion between the clockwise rotor and the rotating magnetic field becomes smaller; The motion of the cut magnetic field lines between the rotor and the counterclockwise rotating magnetic field becomes larger. The balance is broken, the rotor’s electromagnetic moment is no longer zero, and the rotor rotates in the direction of propulsion.
difference of 90 degrees approximately, the so-called phase principle. These two differ 90 degrees of electricity flow in time into the two differ 90 degrees of winding on the space, will be produced in the space (two-phase) rotating magnetic field, under the effect of the rotating magnetic field, the rotor can be automatic starting, after starting, to speed up to a certain, with the aid of an installed on the rotor of the centrifugal switch or other automatic control device will start winding disconnect, Only the main winding works during normal operation. Therefore, the starting winding can be made to work in a short time. But there are many times, the starting winding is not disconnected, we call this kind of motor capacitive single-phase motor, to change the steering of this kind of motor, can be realized by changing the position of capacitor series connection.
5.Starting of motor. The capacitive induction motor has two windings, namely the starting winding and the running winding. The two windings differ by 90 degrees in space. A capacitor with a large capacity is connected in series on the starting winding. When the running winding and the starting winding pass a single alternating current, the current in the starting winding is 90 degrees ahead of the current in the running winding due to the action of the capacitor, and reaches the maximum value first. Two identical pulse magnetic fields are formed in time and space, so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, induction current is generated in the rotor of the motor, and the current interacts with the rotating magnetic field to generate electromagnetic field torque, so that the motor rotates.
6.The starting mode of ac single-phase motor can be divided into several kinds:
The first is the split phase starting type, as shown in Figure 1
It is started by the auxiliary starting winding, and the starting torque is not large. The operating rate remains roughly constant. Mainly used in electric fans, air conditioning fan motors, washing machines and other motors.
Second, when the motor is still, the centrifugal switch is connected, and the starting capacitor participates in the starting work. When the rotor speed reaches 70% to 80% of the rated value, the centrifugal switch will automatically jump off, and the starting capacitor completes its task and is disconnected. The starting winding does not participate in the operation, while the motor continues to operate with the operation winding coil, as shown in Figure 2.
Third, when the motor is still, the centrifugal switch is connected, and the starting capacitor participates in the starting work. When the rotor speed reaches 70% to 80% of the rated value, the centrifugal switch will automatically jump off, and the starting capacitor completes its task and is disconnected. The running capacitor is connected to the starting winding in series to participate in the operation. This connection method is generally used in air compressors, cutting machines, woodworking machines and other heavy load and unstable places. As shown in figure 3.
Motor with centrifugal switch, if the motor can not be successfully started in a very short time, then the winding coil will be burned quickly.
Capacitance value: double value capacitor motor, large starting capacitor capacity, small operating capacitor capacity, voltage is generally more than 400V.
Reverse control:
FIG. 4 is the wiring diagram with positive and negative switch. Generally, the resistance values of the starting winding and the running winding of this kind of motor are the same, that is to say, the starting winding and the running winding of the motor are exactly the same in wire diameter and coil number. This kind of motor is commonly used in washing machines. The forward and reverse control method is simple and does not require complex transfer switches.
FIG. 1, FIG. 2, FIG. 3, positive and negative control. The reverse can be completed by switching 1-2 lines or 3-4 lines.
For judging the starting and running windings in Figure 1, Figure 2 and Figure 3, the dc resistance of the starting winding is usually much larger than that of the running winding, which can be measured by a multimeter. The dc resistance of the general running winding is several ohms, while that of the starting winding is more than ten ohms to dozens of ohms.
7.Due to single phase motors use 220~230V or 110~115V, so it is easy to connect to eletric power, and low voltage is more safe than 380V three phase motor. Meanwhile becasue of single phase motor’s structure simple, low cost and needn’t maintain, so they widely used in household and industry field. In household use in Mower, and air condiction, fan, refrigerator, coffee grinder, range hood etc. In industry, can be use to supply the power to machine such as concrete mixer motor, pump motor, wash machine motor, some gear motor or gear reducer motor use to farm to blend milk, some motor use to be circulation fans, cooling, exhaust fans etc. All of the above motors can be made by Zhejian Aoer.
8. the conclusion
The development of household appliances and industrial mass production promote the rapid development of single-phase motor, single-phase motor design cost is low, simple assembly structure disassembly, suitable for mass production. In short, the application of single-phase motor in production and life will be more and more extensive
