The Difference Between Synchronous and Asynchronous Motor are explained considering factors like its type, slip, requirement of additional power source, requirement of slip ring and brushes, their cost, efficiency, power factor, current supply, speed, self starting, effect in torque because of change in voltage, their operational speed and various applications of both Synchronous and Asynchronous motor.
Difference Between Synchronous and Asynchronous Motor are explained below in the tabulated form.
| BASIS | SYNCHRONOUS MOTOR | ASYNCHRONOUS MOTOR |
|---|---|---|
| Definition | Synchronous motor is a machine whose rotor speed and the speed of the stator magnetic field is equal. N= NS = 120f/P | Asynchronous motor is a machine whose rotor rotates at the speed less than the synchronous speed. N < NS |
| Type | Brushless motor, Variable Reluctance Motor, Switched Reluctance Motor and Hysteresis motor are the synchronous motor. | AC Induction Motor is known as the Asynchronous Motor. |
| Slip | Does not have slip. The value of slip is zero. | Have slip therefore the value of slip is not equal to zero. |
| Additional power source | It requires an additional DC power source to initially rotate the rotor near to the synchronous speed. | It does not require any additional starting source. |
| Slip ring and brushes | Slip ring and brushes are required | Slip ring and brushes are not required. |
| Cost | Synchronous motor is costly as compared to Asynchronous motor | Less costly |
| Efficiency | Efficiency is greater than Asynchronous motor. | Less efficient |
| Power factor | By changing excitation the power factor can be adjusted accordingly as lagging, leading or unity. | Asynchronous motor runs only at a lagging power factor. |
| Current supply | Current is given to the rotor of the synchronous motor | The rotor of Asynchronous motor does not require any current. |
| Speed | The Speed of the motor does not depend on the variation in the load. It is constant. | The Speed of the Asynchronous motor decreases with the increasing load. |
| Self starting | Synchronous motor is not self starting | It is self starting |
| Affect in torque | Change in applied voltage does not affect the torque of the synchronous motor | Change in applied voltage does affect the torque of the Asynchronous motor |
| Operational speed | They operate smoothly and relatively good at low speed that is below 300 rpm. | Above 600 rpm speed motor operation is excellent. |
| Applications | Synchronous motors are used in Power stations, manufacturing industries etc. it is also used as voltage controller. | Used in Centrifugal pumps and fans, blowers, paper and textile mills, compressors and lifts. etc |
Synchronous motor is a motor that operates at synchronous speed, i.e. speed of the rotor is equal to the stator speed of the motor. It follows the relation N = NS = 120f/P, where N is the rotor speed and Ns is the synchronous speed.
Asynchronous motor is an AC Induction motor. The rotor of the Asynchronous motor rotates at the speed less than the synchronous speed, i.e. N < NS
Difference Between Synchronous and Asynchronous Motor
- Synchronous motor is a machine whose rotor speed and the speed of the stator magnetic field is equal. Asynchronous motor is a machine whose rotor rotates at the speed less than the synchronous speed.
- Brushless motor, Variable Reluctance Motor, Switched Reluctance Motor and Hysteresis motor are the synchronous motor. AC Induction Motor is known as the Asynchronous Motor.
- Synchronous motor does not have slip. The value of slip is zero. Asynchronous motor has slip therefore the value of slip is not equal to zero.
- Synchronous motor requires an additional DC power source to initially rotate the rotor near to the synchronous speed. Asynchronous motor does not require any additional starting source.
- Slip ring and brushes are required in synchronous motor, whereas Asynchronous motor does not require Slip ring and brushes. Only wound type Induction motor requires both slip ring and brushes.
- Synchronous motor is costly as compared to Asynchronous motor.
- Efficiency of Synchronous motor is greater than Asynchronous motor.
- By changing excitation the power factor of the Synchronous motor can be adjusted accordingly as lagging, leading or unity, whereas Asynchronous motor runs only at a lagging power factor.
- Current is given to the rotor of the synchronous motor. The rotor of Asynchronous motor does not require any current.
- The Speed of the Synchronous motor does not depend on the variation in the load. It is constant. The Speed of the Asynchronous motor decreases with the increasing load.
- Synchronous motor is not self starting, whereas Asynchronous is self starting.
- Change in applied voltage does not affect the torque of the synchronous motor, whereas it affect the torque of the Asynchronous motor.
- Synchronous motor operates smoothly and relatively good at low speed that is below 300 rpm, whereas above 600 rpm speed Asynchronous motor operation is excellent. Asynchronous motors are used in Centrifugal pumps and fans, blowers, paper and textile mills, compressors and lifts. etc
- The various applications of the Synchronous motor are that it is used in Power stations, manufacturing industries etc. It is also used as voltage controller.
Hence in this way, a synchronous motor is differentiated from the asynchronous motor.
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Which motor doesn’t slow down with increased load, and, why doesn’t it slow down with increased load?
synchronous motor speed does not depend on load applied. This is because the rotor is held electromagnetically in rigid synchronism with the rotating voltage in the stator(magnetic locking)
if you increase the load, the motor will draw more current(armature wingdings) so synchronous speed is maintained. It may slow a little while it adjusts but only momentarily.
However under certain conditions(i.e. low excitation voltage), the strength of the field hold can fail and the rotor will slip to the next pole(you may have heard of pole slip).
hope this helps
Differential compound motor
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Is it correct to say that slip ring and squirrel cage induction motors, belong only to asynchronous motor?
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