Table of Contents
What is rotor induced emf?
5.3.3 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 rotor frequency?
The frequency of the rotor current fr = Ns x P/120, so fr = 0 if the slip is zero. If the operating speed is zero, Ns = N and the frequency of the rotor current is the same as the frequency of the stator current . f = source frequency in Hz.
How is emf induced in the rotor of an induction motor?
The conductors of the rotor are stationary. This stationary conductor cut the rotating magnetic field of the stator, and because of the electromagnetic induction, the EMF induces in the rotor. This EMF is known as the rotor induced EMF, and it is because of the electromagnetic induction phenomenon.
What is frequency of rotor EMF?
The frequency of the induced emf in rotor is? Explanation: The induced frequency will be f = P(Ns-Nr)/2. f = 4(1500-1450)/2 = 100 Hz.
What happens when slip is zero?
Zero slip means that rotor speed is equal to synchronous speed. If rotor is rotating at synchronous speed in the direction of rotating magnetic field the, there will be no flux cutting action, no emf in the rotor conductors, no current in rotor bar conductor and hence no development of electromagnetic torque.
What happens if fifth harmonics is given to induction motor?
It will rotates in normal operation. Either short circuit or open circuit occurs. The sinusoidal components having frequency five times of fundamental are known as fifth harmonics. Hence induction motor will rotates in reverse direction because of reverse phase sequence of fifth harmonics.
How is rotor current calculated?
For example: A 3.5-horsepower, three-phase motor nameplate lists the motor voltage as 230 volts and the locked rotor code is “K.” The range given on the table is 8.0 to 8.99 KVA. Dividing by the motor voltage of 230 volts gives the inrush current range as 34.8 amps to 39.1 amps.
What is rotor current?
The rotor circuit is shorted and current flows in the rotor conductors. The action of the rotating flux and the current produces a force that generates a torque to start the motor. Direct current (DC) drives the field current in one direction, and is delivered to the wire coil by a set of brushes and slip rings.
What is slip formula?
If the revolving magnetic flux’s synchronous speed & the speed of rotor are Ns & Nr in the motor, then the speed among them can be equivalent to (Ns – Nr). So, slip can be determined as. S = (Ns – Nr) / Ns.
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 crawling in induction motor?
Sometimes, squirrel cage induction motors exhibits a tendency to run at very slow speeds (as low as one-seventh of their synchronous speed). This phenomenon is called as crawling of an induction motor. This action is due to the fact that, flux wave produced by a stator winding is not purely sine wave.
What is the formula of induced emf?
The induced emf is ε = – d/dt (BA cos θ). The magnitude of the magnetic field can change with time. The area enclosed by the loop can change with time. The angle between the magnetic field and the normal to the loop can change with time.
What is slip at standstill?
At standstill, induction motor slip s is 1, hence the frequency of induced EMF in the rotor of the induction motor is same as that of supply frequency and reduces with increase in speed (due to the reduction in slip).
What is the frequency of induced emf?
The induced emf frequency is slip times the frequency of applied voltage. Since emf in induction motor is induced when stator flux cut the rotor conductor so the emf actually is induced only due to their relative speed i.e Ns-Nr (Ns=synchronous speed of stator flux and Nr=rotor speed in RPM) between them.
What happens in the motor if the rotor frequency is negative?
If the rotor of an induction machine rotates above synchronous speed, slip is negative, as are torque, mechanical output power and air gap power. i.e. the machine is operating as a generator.
What is negative slip?
Negative slip: When the theoretical discharge is less than actual discharge is known as negative slip.
When slip is zero rotor will?
If Slip is equal to zero, rotor current is zero and torque is zero. The zero torque means motor will not rotate at all.
What type of motor has a slip factor of 0 %?
In two-pole single-phase motors, the torque goes to zero at 100% slip (zero speed), so these require alterations to the stator such as shaded-poles to provide starting torque. A single phase induction motor requires separate starting circuitry to provide a rotating field to the motor.
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 slip of induction motor when rotor is blocked?
In block rotor test, the low voltage is applied so that the rotor does not rotate and its speed becomes zero and full load current passes through the stator winding. The slip is unity related to zero speed of rotor hence the load resistance becomes zero.
What is slip in synchronous motor?
Slip is the difference between the synchronous speed of a motor and its actual speed. Mathematically it is determined by. Slip = Synchronous Speed − Actual Speed. Using the example above for synchronous speed of a motor with four poles operating at 60 hertz, the value was calculated to be 1800 RPM.
