Table of Contents
An induction motor cannot run at synchronous speed. Torque developed by induction motor is proportional to the slip. At synchronous speed, slip is zero and hence torque developed by the motor is zero.
Why does an induction motor run at less than synchronous speed?
An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux current in the rotor with flux current in the stator, the rotor will never reach . May 21, 2018
At what speed will the induction motor run?
When operated at 120 Hz, the motor will rotate at a synchronous RPM (3600 RPM). There is no RPM slip associated with the PMM since the rotor magnetic field is supplied by the permanent magnets on the rotor.
Why the speed of synchronous motor is constant?
The rotor of a synchronous motor moves at the same speed as the changing, rotating field in its stator. The rotor’s magnetic field is “synchronized” with the stator’s field. Their speed is dependent on the number of poles and the supply frequency. They have a constant speed at a given supply frequency.
Why can an AC induction motor not operate at 0% slip?
In motors the number of rotor slots and stator slots are different and thus cogging (magnetic locking) can’t happen. And thus The slip motor can’t run at rated speed. Torque developed by induction motor is proportional to the slip. At synchronous speed,slip is zero and hence torque developed by the motor is zero.
What is the maximum speed of induction motor?
The maximum number of poles in the induction motor is 2. The synchronous speed of the motor is 3000 RPM, Considering 3% slip, the speed of the rotor is 2910 RPM.
Can a generator be used as a motor?
In principle, any electrical generator can also serve as an electric motor, or vice versa. In hybrid vehicles and other lightweight power systems, a “motor–generator” is a single electric machine that can be used as an electric motor or a generator, converting between electrical power and mechanical power.
What is 120 in motor speed formula?
The equation for synchronous speed – the speed of the magnetic field inside the motor stator is 120 x F / P where F is the applied frequency in Hz, and P is the number of poles (always a multiple of 2) in the motor winding. 120 is a constant that gives your answer in revolutions per minute.
What is the difference between synchronous speed and rotor speed?
Induction motor with squirrel cage rotor has two different speeds. The synchronous speed refers to the stator rotating magnetic field, which depends on the number of poles and frequency. The other speed is the rotor’s. The rotor speed will be always slower than the stator speed, we call it slip.
Can a VFD increase motor speed?
Speed adjustments can easily be made by using a variable frequency drive (VFD) with an AC motor, and are the most common reason for using them. VFDs allow the minimum and maximum speeds an application is running at to be adjusted, soft starts and stops to be implemented, and compensate for speed variation due to slip.
What is the maximum speed of motor?
Two pole AC motors operating at 60 Hz will always run at approximately 3600 rpm, and four pole AC motors will have speeds around 1800 rpm.
What is rotor induced emf?
3 Rotor induced e.m.f. and current. The rate at which the rotor conductors are cut by the flux, and hence their induced e.m.f., is directly proportional to the slip, with no induced e.m.f. at synchronous speed (s = 0) and maximum induced e.m.f. when the rotor is stationary (s = 1).
What is synchronous speed?
: a definite speed for an alternating-current machine that is dependent on the frequency of the supply circuit because the rotating member passes one pair of poles for each alternation of the alternating current.
What is normal slip of an induction motor?
Because of this speed difference, the motor rotates at a speed slightly slower than the synchronous speed. Slip is normally expressed in percentage. Slip of a power induction motor is 2 to 3% when the motor is operated under the rated load.
What happens if the slip of induction motor is one?
This is the reason; slip is never zero in an induction motor. Slip = 1, means that rotor is stationary. Negative value of slip in induction motor can be achieved when the rotor speed is more than the synchronously rotating magnetic flux.
What happens if the slip of induction motor is 1?
When the Value of Slip is >1 If the slip value of the motor is greater than one then the rotor will turn in the opposite direction to the revolution of magnetic flux. So if the magnetic flux is revolving in the direction of clockwise, then the rotor will turn rotating in the anti-clockwise direction.
Why does synchronous motor is not self starting?
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator. Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.
What happen when induction motor run at synchronous speed?
Due to this difference in flux, the rotor will experience a torque and will start to rotate at speed less than synchronous speed due to lagging. So, theoretically, the Induction motor can never run at synchronous speed. This will result in no torque on the rotor, and it will stop moving due to this.
What is cogging in 3 phase induction?
The phenomenon of Magnetic Locking between the stator and the rotor teeth is called Cogging or Teeth Locking. Even after applying full voltage to the stator winding, the rotor of a 3 phase induction motor fails to start. Thus, a locking is created between the stator and rotor teeth.
Can synchronous motor rotate at any speed other than the synchronous speed?
At any speed other than synchronous speed, its rotor would experience an oscillating torque of zero average value as the rotating magnetic field repeatedly passes the slower moving rotor. Normally, a short-circuited winding similar to that of an induction machine is added to the rotor to provide starting torque.
How do you control the speed of a synchronous motor?
Speed of synchronous motors can be controlled using two methods called open loop and close loop control. Open loop contol is the simplest scalar control method where motor speed is controlled by independent frequency control of the converter.
