::.Low-voltage synchronous motor< |< Low-voltage synchronous motor
:.Low-voltage synchronous motor can operate at a leading power factor by adjusting the excitation current, which is beneficial to improving the power factor of the power grid. Therefore, large equipment, such as Blower, water pump, ball mill, compressor, rolling mill, etc. are commonly driven by synchronous motors. This advantage is particularly prominent when synchronous motors are used in large, low-speed equipment. In addition, the speed of the synchronous motor is completely determined by the power frequency. When the frequency is constant, the speed of the motor is also constant, and it does not change with the load. This feature is of great significance in certain transmission systems, especially multi-machine synchronous transmission systems and precision speed regulation and steady speed systems. The operating stability of synchronous motors is also relatively high. Synchronous motors generally operate in an over-excitation state, and their overload capacity is larger than that of corresponding synchronous motors. The torque of a synchronous motor is proportional to the square of the voltage, and the torque of a synchronous motor is determined by the product of the voltage and the internal electromotive force generated by the motor's excitation current, which is only proportional to the first power of the voltage. When the grid voltage suddenly drops to about < < of the rated value, the synchronous motor torque often drops to about < < and stops running because it cannot carry the load. However, the torque of the synchronous motor does not drop much. It can also be used by forced excitation. To ensure the stable operation of the motor.
:.< There are roughly two types of synchronous motors in structure:
:.?< The rotor is excited by direct current
:. Its rotor is made of a manifest pole type and is installed on the magnetic pole. The magnetic field coils on the core are connected in series with each other and have alternating opposite polarities, and two leads are connected to two slip rings mounted on the shaft. The field coil is excited by a small DC generator or battery. In most synchronous motors, the DC generator is mounted on the motor shaft to supply the excitation current to the rotor pole coil.
: Since this kind of synchronous motor cannot start automatically, a squirrel-cage winding is installed on the rotor for starting the motor. The squirrel cage windings are placed around the rotor, and the structure is similar to that of a synchronous motor.
:. When a three-phase AC power supply is connected to the stator winding, a rotating magnetic field is generated in the motor. The squirrel cage winding cuts the magnetic lines of force to generate an induced current, thereby causing the motor to rotate. After the motor rotates, its speed slowly increases to a speed slightly lower than the rotating magnetic field. At this time, the rotor magnetic field coil is excited by direct current, causing certain magnetic poles to be formed on the rotor. These magnetic poles attempt to track the rotating magnetic poles on the stator, thus increasing The speed of the motor rotor until it rotates synchronously with the rotating magnetic field.
:.?< Synchronous motors whose rotors do not require excitation
:. Synchronous motors whose rotors do not require excitation can be used on single-phase power supplies or on multi-phase power supplies. One of these motors has a stator winding similar to that of a split-phase or polyphase motor, but also has a squirrel-cage rotor with the surface of the rotor cut into planes. Therefore, it is a manifest-pole rotor. The rotor magnetic poles are made of a kind of magnetized steel and can maintain magnetism at all times. The squirrel cage winding is used to generate starting torque. When the motor rotates to a certain speed, the rotor's dominant pole synchronizes with the current frequency of the stator coil. The polarity of the dominant pole is induced by the stator, so its number should be equal to the number of poles on the stator. When the motor turns to its proper speed, the squirrel cage winding loses its function. Maintaining rotation depends on the rotor and the The magnetic poles follow the stator magnetic poles to synchronize them.
Low voltage synchronous motor | Low voltage synchronous motor