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June 12, 2020
What is the difference between a single-phase motor and a three-phase motor
Everyone knows that there are two kinds of electricity, DC and AC, so the motor can be divided into two kinds of DC motor and AC motor. Among them, AC motors are divided into three-phase motors and single-phase motors. Three-phase motors and single-phase motors are commonly used motors in people's daily work. Do you know the difference between this three-phase motor and single-phase motor?
What is a single-phase motor
Single-phase motors generally refer to low-power single-phase asynchronous motors powered by single-phase AC power (AC220V). This type of motor usually has two-phase windings on the stator, and the rotor is a common squirrel-cage type. The distribution of the two-phase windings on the stator and the different power supply conditions can produce different starting characteristics and operating characteristics.
When a single-phase sinusoidal current passes through the stator windings, the motor generates an alternating magnetic field. The strength and direction of this magnetic field change sinusoidally with time, but it is fixed in space, so this magnetic field is also called alternating Pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with the same speed and opposite rotation directions. When the rotor is stationary, these two rotating magnetic fields produce two torques of equal magnitude and opposite directions in the rotor, making the synthesis The torque is zero, so the motor cannot rotate.
When we use external force to rotate the motor in a certain direction (such as clockwise rotation), then the movement of the cutting magnetic field between the rotor and the rotating magnetic field in the clockwise rotation direction becomes smaller; the rotation between the rotor and the rotating magnetic field in the counterclockwise rotation direction The movement of the cutting magnetic field becomes larger. In this way, the balance is broken, the total electromagnetic torque generated by the rotor will no longer be zero, and the rotor will rotate in the pushing direction. To enable the single-phase motor to rotate automatically, we can add a starting winding to the stator. The starting winding and the main winding are 90 degrees apart in space. The starting winding should be connected with a suitable capacitor in series, so that the current with the main winding is The phase difference is approximately 90 degrees, the so-called phase separation principle.
What is a three-phase motor?
Three-phase motor refers to a three-phase stator winding (120 degrees electrical angle difference between the phases) of the motor, when three-phase alternating current is applied, a rotating magnetic field is generated, which cuts the rotor winding, thereby generating an induced current in the rotor winding (The rotor winding is a closed path).
Working principle of three-phase motor:
The current-carrying rotor conductor will generate electromagnetic force under the action of the stator rotating magnetic field, thereby forming an electromagnetic torque on the rotating shaft of the motor, driving the motor to rotate, and the motor rotating direction is the same as the rotating magnetic field direction. The electric motor is also called (commonly known as the motor), and is represented by the letter "M" ("D" in the old standard) in the circuit. Its main function is to generate driving torque. As a power source for electrical appliances or various machines, the motor is fully enclosed, external fan cooled, and squirrel cage structure.
Single phase is 220 volts. The voltage between the phase and the neutral. The two-phase is the phase line A and B or C, the phase voltage between is 380, the common electrical appliance is 380 welding machine. The three-phase is the 380V phase-to-phase voltage between A.B.C. The consumer is the three-phase 380V motor or equipment. The rectifier converts alternating current into direct current.
Two-phase electricity only exists in single-phase motors. It is split from a single phase in two windings. For example, one winding does not have a capacitor, and the other winding has a capacitor. The phase difference between the currents of the two windings is about 90 °, a rotating magnetic field will be generated to make the motor work. The same single-phase power is supplied to the motor, with only one live wire and no two live wires. Three-phase electricity is mainly used as the power source of the motor, that is, the load that needs to be rotated. Because the three phase differences of three-phase electricity are all 120 degrees. The rotor will not get stuck.
The above is the difference between a three-phase motor and a single-phase motor. Single-phase motors are mainly used in household appliances such as hair dryers, refrigerators, washing machines, etc. in life. The three-phase motor is mainly used in production work. Of course, the single-phase motor is also used in production work, but most of the power is too small. In addition to these differences, single-phase electricity can also be used when there are three-phase motors but no three-phase electricity, but some modifications and adjustments are required