If the rotor is spun at synchronous speed there would be zero induction and hence zero torque produced. What you see is slip and that slip creates enough induction which leads to enough torque to overcome residual friction and losses when no proper mechanical load is connected.
Why does an induction motor need slip?
In actual operation, rotor speed always lags the magnetic field’s speed, allowing the rotor bars to cut magnetic lines of force and produce useful torque. This speed difference is called slip speed. Slip also increases with load and it is necessary for producing of torque.
What happens if the slip of induction motor is one?
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.
Under what condition the slip in an induction motor is greater than one?
So if the magnetic flux is revolving in the direction of clockwise, then the rotor will turn rotating in the anti-clockwise direction. So, the speed among them will be like (Ns + Nr). In braking or Plugging of this motor, the slip is greater than ‘1’ is attained to rapidly bring the rotor of the motor at rest.
Can slip of induction motor be negative?
From the above equation it is clear that, for slip to be negative, the rotor speed should be greater than synchronous speed. Hence,Negative slip is a situation when an induction motor becomes an Hence,Negative slip is a situation when an induction motor becomes an induction generator.
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.
Why the slip is never zero in an induction motor?
The slip of an Induction motor can never be zero. This is because 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. If the slip becomes Zero, it will be a synchronous motor and not an Induction motor.
How is motor rating slip calculated?
The multiplication of 100 and speed difference divided by the synchronous speed is known as slip of an induction motor. It’s always represented in percentage, generally it ranges from 0.4% to 6% based on its design factors.
What is slip in DC motor?
Slip is the differentiation between synchronous and asynchronous speed. … The difference between the synchronous speed of the electric motor magnetic field, and the shaft rotating speed is slip – measured in RPM or frequency. Slip increases with increasing load – providing a greater torque.
What is Torque slip?
The torque slip curve for an induction motor gives us the information about the variation of torque with the slip. The slip is defined as the ratio of difference of synchronous speed and actual rotor speed to the synchronous speed of the machine.
What is cogging and crawling in induction motor?
A.Cogging can also be reduced by using skewed rotor. Q.What is Crawling? A: It has been observed that squirrel cage type induction motor has a tendency to run at very low speed compared to its synchronous speed, this phenomenon is known as crawling. The resultant speed is nearly 1/7th of its synchronous speed.
What type of rotor is most commonly used in an induction motor?
What is negative slip?
Slip is defined as the difference between theoretical discharge and actual. discharge. If actual discharge is greater than theoretical discharge negative value is found this negative value is called negative slip.13 Jan 2017.
What is synchronous speed?
Synchronous speed is a significant parameter for the rotating magnetic field-type AC motor. It is determined by the frequency and the number of magnetic poles. Synchronous speed No = [rps, revolutions per second] f = Frequency [Hz]
Can induction motor runs 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 . …21 мая 2018 г.
What will happen if air gap is increased in an induction motor?
If the air gap of an induction motor is increased, the following will happen: The permeability of the magnetic circuit rotor-to-stator will decrease. The magnetizing inductance of he motor thus decreases. The magnetizing current will increase.