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Single phase motor capacitance:
(1) Withstand voltage greater than 220v*1.41 ＝ 310V, 400V
(2) Electrodeless capacitor shall be selected for polarity
(3) Capacitor capacity / rated power ＝ 10nf/100w
If your motor power is 370w*10nf/100w=37nf
Three phase asynchronous motor is a kind of motor powered by 380V three-phase AC power supply (phase difference of 120 °). Because the rotor and stator rotating magnetic field of three-phase asynchronous motor rotate in the same direction and at different speeds, there is slip, so it is called three-phase asynchronous motor.
working principle
There are many forms of motor, but its working principle is based on the law of electromagnetic induction and the law of electromagnetic force. Therefore, the general principle of its structure is to use appropriate magnetic and conductive materials to form a magnetic circuit and circuit for mutual electromagnetic induction, so as to generate electromagnetic power and achieve the purpose of energy conversion.
The three-phase asynchronous motor is an induction motor. After the stator is supplied with current, part of the magnetic flux passes through the short-circuit ring and generates induced current. The current in the short-circuit ring hinders the change of magnetic flux, resulting in a phase difference between the magnetic flux generated by the part with and without the short-circuit ring, thus forming a rotating magnetic field. After power on and start-up, the rotor winding induces electromotive force and current due to the relative movement between the rotor winding and the magnetic field, that is, the rotating magnetic field has a relative speed with the rotor, and interacts with the magnetic field to generate electromagnetic torque, which makes the rotor rotate and realizes energy conversion.
Motor classification
1. classification by working power supply
According to the different working power supply of the motor, it can be divided into DC motor and AC motor. AC motor is also divided into single-phase motor and three-phase motor.
2. classification according to structure and working principle
According to the different structure and working principle of the motor, it can be divided into DC motor, asynchronous motor and synchronous motor.
Synchronous motor can also be divided into permanent magnet synchronous motor, reluctance synchronous motor and hysteresis synchronous motor.
Asynchronous motor can be divided into induction motor and AC commutator motor. Induction motor is divided into three-phase asynchronous motor, single-phase asynchronous motor and shaded pole asynchronous motor. AC commutator motor is divided into single-phase series excitation motor, AC / DC dual-purpose motor and repulsion motor.
According to the structure and working principle, DC motor can be divided into brushless DC motor and brush DC motor. Brush DC motor can be divided into permanent magnet DC motor and electromagnetic DC motor. Electromagnetic DC motor is divided into series excited DC motor, parallel excited DC motor, separately excited DC motor and compound excited DC motor. Permanent magnet DC motor is divided into rare earth permanent magnet DC motor, ferrite permanent magnet DC motor and aluminum nickel cobalt permanent magnet DC motor.
3. classification by startup and operation mode
According to the different starting and operating modes of the motor, it can be divided into capacitor starting single-phase asynchronous motor, capacitor operating single-phase asynchronous motor, capacitor starting operating single-phase asynchronous motor and split phase single-phase asynchronous motor.
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4. classification by use
It can be divided into drive motor and control motor.
Motors for driving are divided into motors for electric tools (including drilling, polishing, polishing, slotting, cutting, reaming and other tools) Motors for household appliances (including washing machines, electric fans, refrigerators, air conditioners, tape recorders, video recorders, DVD players, vacuum cleaners, cameras, hair dryers, electric shavers, etc.) and motors for other general small mechanical equipment (including various small machine tools, small machinery, medical appliances, electronic instruments, etc.).
Control motor is divided into stepping motor and servo motor.
5. classification according to rotor structure
According to the structure of the rotor, the motor can be divided into cage induction motor (called squirrel cage induction motor in the old standard) and wound rotor induction motor (called wound rotor induction motor in the old standard).
6. classification by running speed
According to the running speed of the motor, it can be divided into high-speed motor, low-speed motor, constant speed motor and speed regulating motor.
Low speed motors are divided into gear reduction motors, electromagnetic reduction motors, torque motors and claw pole synchronous motors.
In addition to the stepwise constant speed motor, stepless constant speed motor, stepwise variable speed motor and stepless variable speed motor, the variable speed motor can also be divided into electromagnetic variable speed motor, DC variable speed motor, PWM Variable frequency variable speed motor and switched reluctance variable speed motor.
The rotor speed of asynchronous motor is always slightly lower than the synchronous speed of rotating magnetic field.
The rotor speed of a synchronous motor is always kept at the synchronous speed regardless of the load.
Basic working process:
(1) When the three-phase asynchronous motor is connected to the three-phase AC power supply (each with a difference of 120 degrees), the three-phase stator winding flows through the three-phase magnetomotive force (stator rotating magnetomotive force) generated by the three-phase symmetrical current and generates a rotating magnetic field, which rotates clockwise along the inner circular space of the stator and rotor at the synchronous speed N0.
(2) The rotating magnetic field has relative cutting motion with the rotor conductor. According to the principle of electromagnetic induction, the rotor conductor (the rotor winding is a closed path) generates induced electromotive force and induced current (the direction of induced electromotive force is determined by the right-hand rule).
(3) According to the law of electromagnetic force, under the action of the induced electromotive force, the rotor conductor will produce an induced current basically consistent with the direction of the induced electromotive force. The current carrying rotor conductor is affected by the electromagnetic force in the magnetic field generated by the stator (the direction of the force is determined by the left-hand rule). The electromagnetic force forms an electromagnetic torque on the motor rotor shaft, driving the motor rotor to rotate along the direction of the rotating magnetic field. When the motor shaft is loaded with mechanical load, it will output mechanical energy outward. Since the magnetic flux of the part without short-circuit ring is ahead of that of the part with short-circuit ring, the rotation direction of the motor is the same as that of the rotating magnetic field.
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Why asynchronous motor
Because the induced current in the rotor coil of three-phase asynchronous motor is generated due to the relative movement between the rotor conductor and the magnetic field. The rotor speed of the three-phase asynchronous motor will not be synchronized with the rotating magnetic field, nor will it exceed the speed of the rotating magnetic field. If the rotating speed of the rotor of the three-phase asynchronous motor is equal to the rotating speed of the rotating magnetic field, there will be no relative movement between the magnetic field and the rotor, and the conductor cannot cut the magnetic line of force, so the induced electromotive force and current will not be generated in the rotor coil, and the rotor conductor of the three-phase asynchronous motor will not be affected by the electromagnetic force in the magnetic field to make the rotor rotate. Therefore, the rotor rotation speed of three-phase asynchronous motor cannot be the same as that of the rotating magnetic field, and is always less than the synchronous speed of the rotating magnetic field. However, under special operation mode (such as power generation braking), the rotor speed of three-phase asynchronous motor can be greater than the synchronous speed.
Three phase asynchronous motor torque
Symmetrical 3-phase winding is connected with symmetrical 3-phase current to generate rotating magnetic field. The magnetic field wire cuts the rotor winding. According to the principle of electromagnetic induction, e and I are generated in the rotor winding. The rotor winding is affected by electromagnetic force in the magnetic field, that is, electromagnetic torque is generated to make the rotor rotate. The rotor outputs mechanical energy and drives the mechanical load to rotate.
In AC motor, when the stator winding passes through AC current, the armature magnetomotive force is established, which has a great impact on the energy conversion and operation performance of the motor. Therefore, three-phase AC winding is connected with three-phase AC to generate pulsating magnetomotive force, which can be decomposed into two rotating magnetomotive forces with equal amplitude and opposite speed, so as to establish forward and reverse magnetic fields in the air gap. These two rotating magnetic fields cut the rotor conductor and generate induced electromotive force and induced current in the rotor conductor respectively.
The current interacts with the magnetic field to produce positive and negative electromagnetic torque. The forward electromagnetic torque attempts to make the rotor rotate forward; The reverse electromagnetic torque attempts to reverse the rotor. The superposition of these two torques is the synthetic torque that drives the motor to rotate.
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Three phase asynchronous motor speed
Three alternating currents are connected to the stator of the motor to generate a rotating magnetic field at a speed of N0. Different pole pairs P, under the action of AC with the same frequency f=50hz, will produce different synchronous speeds N0, n0=60f/p.
The speed of the motor rotor is less than that of the rotating magnetic field, which is basically the same as that of the induction motor. s=(ns-n)/ns。 S is the slip rate,
NS is the magnetic field speed and N is the rotor speed.
Type of three-phase asynchronous motor
According to different rotor structures, three-phase asynchronous motors can be divided into cage type and wound type.
Cage rotor asynchronous motor has been widely used because of its simple structure, reliable operation, light weight and low price. Its main disadvantage is the difficulty of speed regulation.
The rotor and stator of wound three-phase asynchronous motor are also equipped with three-phase windings and connected with external rheostat through slip ring and brush. Adjusting the rheostat resistance can improve the starting performance of the motor and adjust the speed of the motor.
Three phase asynchronous motor features:
Advantages: compared with single-phase asynchronous motor, three-phase asynchronous motor has the advantages of simple structure, convenient manufacture, good operation performance, saving various materials and low price.
Disadvantages: lagging power factor, low light load power factor and poor speed regulation performance.
Use of three-phase asynchronous motor
The power of three-phase asynchronous motor is large, and it is mainly made into large motor. It is generally used in large industrial equipment with triple phase power. First of all, the three-phase asynchronous motor is only used as a motor, rarely as a generator, and all synchronous motors are used for power generation.
For the small power three-phase asynchronous motor below 1kW, it can not only operate three-phase, but also operate single-phase.
Classification of DC motors
The excitation mode of DC motor refers to the problem of how to supply power to the excitation winding and generate excitation magnetic flux to establish the main magnetic field. According to different excitation modes, DC motors can be divided into the following types.
Excitation mode of DC motor
1. separately excited DC motor
The excitation winding is not connected with the armature winding, but the DC motor supplied by other DC power supplies to the excitation winding is called separately excited DC motor, and the wiring is shown in figure (a). In the figure, M represents the motor, and if it is a generator, G represents it. Permanent magnet DC motor can also be regarded as separately excited DC motor.
2. Shunt DC motor
The excitation winding and armature winding of Shunt DC motor are connected in parallel, and the wiring is shown in figure (b). As a shunt excitation generator, the terminal voltage from the motor itself supplies power to the excitation winding; As a shunt motor, the excitation winding and armature share the same power supply, which is the same as that of the separately excited DC motor in terms of performance.
3. series excited DC motor
The excitation winding of the series excited DC motor is connected in series with the armature winding, and then connected to the DC power supply. The wiring is shown in figure (c). The excitation current of this DC motor is the armature current.
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4. compound DC motor
The compound excitation DC motor has two excitation windings, parallel excitation and series excitation, and the wiring is shown in figure (d). If the magnetic flux generated by the series excitation winding and the parallel excitation winding have the same direction, it is called cumulative compound excitation. If two magnetic fluxes have opposite directions, it is called differential compound excitation.
DC motors with different excitation modes have different characteristics. Generally, the main excitation modes of DC motor are parallel excitation, series excitation and compound excitation. The main excitation modes of DC generator are separate excitation, parallel excitation and compound excitation.
Characteristics of DC motor
（1） Good speed regulation performance. The so-called "speed regulation performance" refers to that the speed of the motor is artificially changed according to the needs under certain load conditions. DC motor can realize even and smooth stepless speed regulation under heavy load, and the speed regulation range is wide.
（2） Large starting torque. Speed regulation can be realized uniformly and economically. Therefore, all machinery that starts under heavy load or requires uniform speed adjustment, such as large reversible steel rolling mill, winch, electric locomotive, tram, etc., are driven by DC motor.
Working principle of DC motor
Working principle of DC motor
The principle of "the force acting on the energized conductor in the magnetic field" is roughly applied. The two end wires of the excitation coil have the same current in the opposite direction, which makes the whole coil produce the torsion around the shaft and make the coil rotate.
To make the armature receive an electromagnetic torque with the same direction, the key lies in how to change the direction of the current flowing through the coil in time when the coil side is under the magnetic poles of different polarity, that is, the so-called "commutation". Therefore, a device called commutator must be added. The commutator and brush can ensure that the current in the coil side under each pole is always in the same direction, so that the motor can rotate continuously. This is the working principle of DC motor.
