Table of Contents
Note – an induction motor will never reach its synchronous speed. If it did – the rotor would appear to be stationary to the rotating stator field since it would rotate with the same speed. With no relative motion between stator and rotor field no voltage will be induced in the motor.
What will happen if the rotor of induction motor reaches synchronous speed?
The rotor is placed in such a way that this magnetic field induces a current in the rotor. This induced current will flow through the rotor winding causing another flux in the rotor. This flux in the rotor will lag stator flux. So, theoretically, the Induction motor can never run at synchronous speed.
What happens when the rotor speed is equal to the synchronous speed?
If the rotor reached synchronous speed, there would be no movement of stator field relative to the rotor conductors, and no induced voltage, current or torque. In order that the no-load losses can be met, the rotor attains a speed less than synchronous.
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 are the starting methods of induction motor?
They are as follows:
- Direct on-line starter. The direct on-line starter method, of an induction motor, is simple and economical.
- Star delta starter. The star delta starter method of starting three-phase induction motors is very common and widely used among all the methods.
- Autotransformer starter.
Which generator can run at synchronous speed?
An induction generator produces electrical power when its rotor is turned faster than the synchronous speed. For a typical four-pole motor (two pairs of poles on stator) operating on a 60 Hz electrical grid, the synchronous speed is 1800 rotations per minute (rpm).
What does N 120 F P mean?
N=120f/P. This expression represents SYNCHRONOUS SPEED* while the speed of Induction motor is slightly less than synchronous speed. The difference between that synchronous and actual speed is known as SLIP of induction motor. S= (synchronous speed) – (actual speed)
How do you know if a motor is synchronous?
TESTING THE SYNCHRONOUS MOTOR The rotor can be tested with an ohmmeter for an open winding or a grounded winding. To test the rotor for an open winding, connect one of the ohmmeter leads to each of the slip rings on the rotor shaft, Figure 17–5.
What is formula of synchronous speed?
The Synchronous speed can be calculated as follows: 120 times the frequency (F), divided by the number of poles (P): The synchronous speed decreases as the number of poles increases. The table below shows the synchronous speed associated with various numbers of poles at supply frequencies of 50Hz and 60Hz: No.
What is the impact of slip on rotor current?
When the rotor is stationary, s = 1. Under these conditions, the per phase rotor e.m.f. E2 has a frequency equal to that of supply frequency f. At any slip s, the relative speed between stator field and the rotor is decreased.
How does a synchronous motor achieve synchronous speed?
The speed of the rotating stator field is called the synchronous speed. The frequency of the power supply and the number of poles of the machine determine the synchronous speed. A synchronous motor is one in which the rotor turns at the same speed as the rotating magnetic field in the stator.
What is the function of synchronous motor?
In higher power industrial sizes, the synchronous motor provides two important functions. First, it is a highly efficient means of converting AC energy to work. Second, it can operate at leading or unity power factor and thereby providing power-factor correction.
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 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.
Why the rotor of an induction motor Cannot run at 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 .
How is motor speed calculated?
To calculate RPM for an AC induction motor, you multiply the frequency in Hertz (Hz) by 60 — for the number of seconds in a minute — by two for the negative and positive pulses in a cycle. You then divide by the number of poles the motor has: (Hz x 60 x 2) / number of poles = no-load RPM.
What are the advantages of synchronous motor?
Advantages of Synchronous Motor
- The advantage of using synchronous motor is the ability to control the power factor.
- Speed remains constant irrespective of the loads in synchronous motors.
- Synchronous motors are built with wider air gaps than induction motors which make them mechanically more stable.
What is standstill rotor EMF?
When rotor is stationary i.e. s = 1, the frequency of rotor e.m.f. is the same as that of the stator supply frequency. The value of e.m.f. induced in the rotor at standstill is maximum because the relative speed between the rotor and the revolving stator flux is maximum.
What is the principle of 3 phase induction motor?
The stator of an induction motor consists of a number of overlapping windings offset by an electrical angle of 120°. When the primary winding or stator is connected to a three phase alternating current supply, it establishes a rotating magnetic field which rotates at a synchronous speed.
