(Motor) is a device that converts electric energy into mechanical energy. It is made by using the phenomenon that the electrified coil is forced to rotate in the magnetic field, which is distributed on all users. According to different power sources, motors are divided into DC motors and AC motors. The motors in power system are mostly AC motors, which can be synchronous motors or asynchronous motors (the rotating speed of stator magnetic field is not synchronous with that of rotor). The motor is mainly composed of stator and rotor. The direction of the force of the live wire moving in the magnetic field is related to the direction of the current and the direction of the magnetic induction line (magnetic field direction). The working principle of the motor is that the magnetic field acts on the current to make the motor rotate.
This is a machine that converts electric energy into mechanical energy. Usually, the working part of the motor rotates, which is called rotor motor; There is also linear motion, called linear motor. The motor can provide a wide range of power from milliwatts to ten thousand kilowatts. The motor is very convenient to use and control, and has the ability of self-starting, accelerating, braking, reversing and braking, which can meet various operation requirements. The motor has high working efficiency, no smoke, no smell, no environmental pollution and low noise. Because of its series of advantages, it is widely used in industrial and agricultural production, transportation, national defense, commercial and household appliances, medical electrical equipment and so on.
Among all kinds of motors, AC asynchronous motor (also known as induction motor) is the most widely used. It is easy to use, reliable in operation, low in price and firm in structure, but it has low power factor and difficult in speed regulation. Synchronous motors are often used in large-capacity and low-speed power machinery (see synchronous motors). Synchronous motor not only has high power factor, but also its speed has nothing to do with load and only depends on grid frequency. The work is relatively stable. DC motors are often used in situations where large-scale speed regulation is needed. However, it has a commutator, which is complex in structure, expensive and difficult to maintain, and is not suitable for harsh environment. Since the 1970s, with the development of power electronics technology, AC motor speed regulation technology has gradually matured, and the equipment price has been continuously reduced, which has been applied. The maximum output mechanical power that the motor can withstand under the specified working system (continuous, short-term operation system and intermittent periodic operation system) is called its rated power, and attention should be paid to the provisions on the nameplate when using it. When the motor is running, attention should be paid to matching its load characteristics with those of the motor to avoid overspeed or stall. There are many methods of motor speed regulation, which can meet the requirements of different production machinery speed changes. Generally speaking, the output power of the motor will change with the change of speed when it is adjusted. From the perspective of energy consumption, speed regulation can be roughly divided into two types: ① keeping the input power unchanged. The speed of the motor can be adjusted by changing the energy consumption of the speed regulating device and adjusting the output power. ② Control the input power of the motor to adjust the speed of the motor.