According to the formal definition, the slip (s) of an induction motor is: For small values of motor slip, the slip (s) is proportional to the rotor resistance, stator voltage frequency, and load torque — and is in inverse proportion to the second power of supply voltage.
How is slip measured on an induction motor?
It is common to express the slip as the ratio between the shaft rotation speed and the synchronous magnetic field speed. When the rotor is not turning the slip is 100 %.Number of poles, frequencies and synchronous induction motor speed. No. of Magnetic Poles Frequency (Hz) 50 60 6 1000 1200 8 750 900 10 600 720.
What causes slip in an induction motor?
“Slip” in an AC induction motor is defined as: As the speed of the rotor drops below the stator speed, or synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the rotor’s windings and creating more torque.
What is the 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.
How does speed slip occur in an induction motor?
The interaction of currents flowing in the rotor bars and the stators’ rotating magnetic field generate torque. 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.
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.
Why is the efficiency of an induction motor so poor at high slips?
So (1—s)P2 is converted to mechanical power, to which you can subtract mechanical losses to get shaft output. From this it is clear that for a given input the shaft output decreases as slip increases and hence the efficiency decreases at higher slip in the stable operating region.
What is the range of slip when induction motor is running at full load?
The value of slip at full load varies from 6% in the case of a small motor and 2% in a large motor. The induction motor never runs at synchronous speed. The speed of the rotor is always less than that of the synchronous speed.
What is the importance of slip in 3 phase induction motor?
Slip creates a relative speed between the RMF and rotor. That keeps a torque continuously acting on it when the motor is running. So what would happen if slip becomes zero? Bcoz there will be no relative speed between RMF and rotor, and which will stop inducing rotor current.
What is the slip of a 3 phase induction motor?
This speed difference is called slip. Therefore, the difference between the synchronous speed Ns of the rotating stator field and the actual rotor speed N is called slip. The slip increase with load and is necessary for torque production. Slip speed is equal to the difference between rotor speed and synchronous speed.
How is slip in motor calculated?
What is Slip in an Induction Motor? Definition: In Induction Motor, a slip is a speed among the rotary magnetic flux as well as rotor expressed in terms of for every unit synchronous speed. It can be measured in dimensionless & the value of this motor cannot be zero. S = (Ns – Nr) / Ns. Slip = (Ns-Nr/Ns)*100.
Is 3-phase induction motor is self-starting?
Three-phase induction motor is self-starting, because winding displacement is 120 degrees for each phase and supply also has 120 phase shift for 3-phase. It results in a unidirectional rotating magnetic field is developed in air gap which causes 3-phase induction motor to self-start.
What is the difference between induction motor and transformer?
A transformer transfers electrical power from one circuit to another without changing the supply frequency, i.e. it only step-up or step-down the level of voltage and current, whereas induction motor converts electrical power into mechanical power.
Which Induction motor has maximum speed?
Synchronous and full load speed of amplitude current (AC) induction motors Speed (rpm) Number of Poles Frequency (Hz, cycles/sec) Synchronous Full Load 2 3600 2900 4 1800 1450.
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.
Which type of Induction motor is best for EMF?
10. Which type of Induction motor is best for e.m.f injection method? Explanation: E.M.F injection method is used to control the speed of Induction motor. It is only applicable for WRIM because WRIM rotor consists of copper windings connected in star connection.
What is slip torque?
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.
Why must slip be present for motor Action?
Slip of induction motor plays an important role in the operation of the induction motor. The torque produced by the induction motor is directly proportional to induction motor slip. At no-load induction motor requires small torque to meet with the frictional, iron and other losses, therefore slip is small.
What is the difference between rotor speed and synchronous 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.
What are the three types of induction motors?
The types of induction motor depend upon the input supply. There are single phase induction motors and three phase induction motors. Single phase induction motors arenot a self-starting motor, and three phase induction motor are a self-starting motor.
What is the most common induction motor?
Three-phase AC induction motors are widely used in industrial and commercial applications. These are of two types, squirrel cage, and slip ring motors. Squirrel cage motors are widely used due to their rugged construction and simple design. Slip ring motors require external resistors to have high starting torque.
Which types of following motors are most efficient?
BLDC motors are typically 85–90% efficient or more. Efficiency for a BLDC motor of up to 96.5% have been reported, whereas DC motors with brushgear are typically 75–80% efficient.