why do the motors of household appliances mostly choose shaded pole motors? what are the advantages?
publisher: administrator date：2020-10-13
the shaded pole motor is a simple self-starting ac single-phase induction motor. it is a small squirrel cage motor. one of the auxiliary windings is surrounded by a copper ring. the copper ring is also called a shaded pole ring or a shaded pole ring. the copper ring is used as the secondary winding of the motor. the salient feature of the shaded pole motor is that the structure is very simple, there is no centrifugal switch, the power loss of the shaded pole motor is very large, the motor power factor is low, and the starting torque is also very low. they are designed to maintain a small size and have a low power rating. the speed of the motor is as accurate as the frequency of the power source applied to the motor, and these motors are often used to drive clocks. the shaded pole motor only rotates in a specific direction, and the motor cannot rotate in the opposite direction. the loss generated by the shaded pole coil, the motor efficiency is low, and its structure is simple. these motors are widely used in household fans and other small-capacity electrical appliances.
shaded pole motor working principle
a shaded pole motor is an ac single-phase induction motor. the auxiliary winding is composed of a copper ring, called a shaded pole coil. the current in the coil delays the phase of the magnetic flux at the magnetic pole to provide a rotating magnetic field. the direction of rotation is from the non-shaded pole to the shaded pole ring.
the design of the shaded pole coil (ring) makes the axis of the magnetic pole deviate from the axis of the main pole magnetic pole. the magnetic field coil and the additional shaded pole coil generate a weak rotating magnetic field. when the stator is energized, the magnetic flux of the magnetic pole body generates a voltage in the shaded pole coil. the shaded pole coil acts as the secondary winding of the transformer. the current in the secondary winding of the transformer is not synchronized with the current in the primary winding, and the shaded pole magnetic flux is not synchronized with the main pole magnetic flux.
in a shaded pole motor, the rotor is placed in a simple c-shaped core, and half of each magnetic pole is covered by a shaded pole coil. when an alternating current passes through the power supply coil, a pulsating magnetic flux is generated. when the magnetic flux passing through the shading coil changes, voltage and current are induced in the shaded pole coil, which correspond to the change in the magnetic flux from the power coil. therefore, the magnetic flux under the shaded pole coil lags behind the magnetic flux of the rest of the coil. the rotor produces a small rotation in the magnetic flux, so that the rotor rotates. the following figure shows the magnetic flux lines obtained by finite element analysis.
shaded pole motor structure
the rotor and its related reduction gear system are wrapped in an aluminum, copper or plastic shell. the enclosed rotor is driven by magnetic force through the shell. this gear motor usually has a final output shaft or gear that rotates from 600 rpm to 1 hour per hour. /168 turns (1 turn per week). since there is usually no clear starting mechanism, the rotor of a motor powered by a constant frequency power supply must be very light in order to reach the operating speed within one cycle of the power supply frequency. the rotor can be equipped with a squirrel cage to make the motor start like an induction motor. pulled to synchronize with its magnet, there is no induced current in the squirrel cage, so it no longer functions in operation. the use of frequency conversion control enables the shaded pole motor to start slowly and transmit more torque.
shaded pole motor speed
the speed of the shaded pole motor depends on the design of the motor. the synchronous speed (the speed at which the stator magnetic field rotates) is determined by the frequency of the input ac power and the number of poles in the stator. the more the number of poles of the coil, the slower the synchronization speed, the higher the frequency of the applied voltage, the higher the synchronization speed, the frequency and the number of poles are not variables, the common synchronization speed of 60hz motor is 3600, 1800, 1200 and 900 rpm, this it depends on the number of poles in the original design.
since the starting torque is very low and cannot produce enough torque to turn large equipment, shaded pole motors can only be manufactured in smaller sizes, less than 50 watts, low cost and simple, suitable for small fans, air circulation and other low torque applications. through series reactance to limit the current and torque, or by switching the number of motor coil turns, the motor speed can be reduced.