The working principle of induction motor (induction motor) is to generate induced current in the rotor through the rotating magnetic field of the stator to generate electromagnetic torque, and the rotor does not directly generate magnetic field. Therefore, the rotor speed must be less than the synchronous speed (without this difference Value, that is, slip, there is no rotor induced current), also called induction motor.
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The synchronous motor rotor itself generates a fixed direction of the magnetic field (with permanent magnets or DC current generated), the stator rotating magnetic field “dragged” rotor magnetic field (rotor) rotation, so the rotor speed equal to the synchronous speed, and therefore called synchronous motor. Motor, most of the asynchronous machine; generators are synchronous machine.
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Difference between synchronous motor and asynchronous motor
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When the three-phase alternating current passes through the winding of a certain structure, a rotating magnetic field is generated. Under the action of a rotating magnetic field, the rotor rotates with a rotating magnetic field. If the rotating speed of the rotor is exactly the same as the rotating magnetic field, the synchronous motor is the rotating speed of the rotor Speed, that is to say, the two are asynchronous, are asynchronous motors. Asynchronous motors have a simple structure and are widely used. Synchronous motors require fixed poles (permanent magnets or electromagnetic) of the rotor, such as alternators and synchronous AC motors.
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Motor speed (stator speed) is less than the rotating magnetic field speed, which is called an asynchronous motor. It is basically the same as induction motor. s = (ns-n) / ns. s is the slip,
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Ns is the magnetic field speed, n is the rotor speed.
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Fundamentals: (1) When a three-phase asynchronous motor is connected to a three-phase AC power supply, a three-phase magnetomotive force (stator rotational magnetomotive force) generated by a three-phase stator winding flows through three-phase stator windings and generates a rotating magnetic field.
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(2) The rotating magnetic field has relative cutting motion with the rotor conductor. According to the principle of electromagnetic induction, the rotor conductor generates induced electromotive force and generates induced current.
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(3) According to the law of electromagnetic force, the current-carrying rotor conductor is subjected to electromagnetic force in the magnetic field to form electromagnetic torque to drive the rotor to rotate. When the motor shaft is loaded with mechanical load, the mechanical energy is output to the outside.
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Features:
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Advantages: simple structure, easy manufacture, low price and convenient operation.
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Disadvantages: power factor lag, light load power factor is low, speed performance somewhat less.
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The main motor to do, generally do not do the generator!
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Induction motor is an AC motor, the load speed and the frequency of the grid connected to the frequency ratio is not constant. Induction motors include induction motors, doubly-fed induction motors, and commutator motors. The most widely used induction motor, without causing misunderstanding or confusion, the general can be referred to as induction motor induction motor.
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Ordinary asynchronous motor stator windings AC grid, rotor windings do not need to connect with other power supply. Therefore, it has the advantages of simple structure, convenient manufacture, use and maintenance, reliable operation, low quality and low cost. Asynchronous motors have higher operating efficiency and better operating characteristics, running from no-load to full load at a constant speed and can meet the transmission requirements of most industrial and agricultural machinery. Induction motors are also easy to derive a variety of types of protection to meet the needs of different environmental conditions. Asynchronous motor operation, must be drawn from the grid reactive excitation power, the power factor of the grid worse. Therefore, the drive ball mill, compressors and other high-power, low-speed machinery and equipment, often using synchronous motor. As the asynchronous motor speed and rotating magnetic field speed has a certain slip relationship, the speed performance is poor (except commutator motor). On the broader requirements and smooth speed range of transportation machinery, rolling mills, large machine tools, printing and dyeing and paper machinery, the use of DC motor is more economical and convenient. However, with the development of high-power electronic devices and AC speed regulation systems, the speed control performance and economy of asynchronous motors with wide speed control are comparable with those of DC motors.
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Synchronous motors, like induction motors, are commonly used AC motors. Characteristics are: steady-state operation, the rotor speed and grid frequency constant relationship between n = ns = 60f / p, ns known as the synchronous speed. If the frequency of the grid is constant, the speed of the synchronous motor is constant at steady state regardless of the size of the load.
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Synchronous motor is divided into synchronous generator and synchronous motor. The exchange machine in modern power plants mainly uses synchronous motors.
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working principle
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◆ The establishment of the main magnetic field: Excitation winding through the DC excitation current, the establishment of the excitation phase magnetic field, that is to establish the main magnetic field.
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◆ current-carrying conductor: three-phase symmetrical armature windings act as power windings and become the carrier of induced potential or induced current.
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◆ Cutting movement: The prime mover drags the rotor (the mechanical energy is input to the motor), and the polar magnetic field rotates with the shaft and sequentially cuts the stator windings (corresponding to the reverse magnetic field of the windings).
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◆ Alternating Potential Generation: Due to the relative cutting motion between the armature windings and the main magnetic field, the three-phase symmetrical alternating potential of the armature winding will be induced to periodically change in magnitude and direction. Through the lead-out, you can provide AC power.
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◆ Exchangeability and symmetry: due to the rotating magnetic field polarity phase, making the polarity of the induced potential alternating; due to the symmetry of the armature windings to ensure the three-phase symmetry of the induced potential.
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Operation mode
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There are three main modes of operation of a synchronous motor, that is, as a generator, motor and compensator. As the generator operation is the most important operation of synchronous motor, as the motor operation is another important synchronous motor operation. Synchronous motor power factor can be adjusted in the case does not require speed control, the application of large synchronous motor can improve operating efficiency. In recent years, small synchronous motors in the frequency control system began to get more applications. Synchronous motor can also be connected to the grid as a synchronous compensation machine. In this case, the motor does not have any mechanical load, and the excitation current in the rotor sends out the desired inductive or capacitive reactive power to the power grid to achieve the purpose of improving the power factor of the power grid or regulating the power grid voltage.
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Like other types of rotating electrical machines, synchronous generators consist of two parts, a fixed stator and a rotatable rotor. Generally divided into transitional synchronous motor and rotary synchronous motor.
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The commonest synchronous generator is the commonest. The inner circle of the stator core is evenly distributed with the stator slots, and the three-phase symmetrical windings arranged regularly are embedded in the slots. This synchronous motor stator also known as the armature, stator core and windings, also known as the armature core and armature windings.
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The rotor core is equipped with a pair of magnetic poles formed into a certain shape, and the magnetic poles are wound with excitation windings. When a direct current is passed, a distributed magnetic field with polar phases will be formed in the air gap of the motor and is called an excitation magnetic field Magnetic field, rotor field).
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The prime mover drags the rotor (the mechanical energy is input to the motor), and the polar magnetic field rotates along with the shaft and sequentially cuts each phase winding of the stator (corresponding to the reverse magnetic field of the winding of the conductor).