Table of Contents
Rotor Current Frequency Hence, when the rotor is stationary, the frequency (fr) of the rotor current is the same as that of the supply frequency (f). When the rotor picks up speed, the relative speed between the rotating magnetic field and the rotor decreases.
What is the formula of 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.
What is the 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 is the rotor frequency when an induction motor is switched on?
Application: When a 3-phase induction motor is switched on, then rotor speed is equal to zero. Hence, at starting or When a 3 phase induction motor is switched on, the rotor frequency is equal to supply frequency.
What does frequency of rotor slip of IM mean?
Slip: We know that rotor rapidly accelerates in the direction of rotating field. This difference in speed depends upon load on the motor. The difference between the synchronous speed Ns of the rotating stator field and the actual rotor speed N is called slip.
What is rotor 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 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.
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.
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 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.
How do you calculate motor rotor speed?
The synchronous speed of the rotor in RPM N = 120f/P where f is the frequency of the stator current and P is the number of poles. The operating speed No = N – Ns where Ns is the slip speed.
Why rotor slots are skewed?
The rotor or stator slot of the induction motor skewed through some angle so that the bars lie under alternate harmonic poles of the same polarity or other words, bars must be skewed through two pitches. The main purpose of skewing is to reduce the magnetic logging between the starter and the rotor.
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 the slip frequency?
Slip frequency can be measured by determining the phase angle traversed in a defined period. For example, with a slip setting of 2 seconds (0.055 Hz) and slip frequency of 0.04 Hz, an angle of approx 29° (elec) is traversed before synchronising is permitted, as shown in Fig 12.15.
What will be the frequency of rotor current at full load?
(e)The frequency of rotor-currents at full-load is 1.50 Hz.
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.
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.
What is the slip?
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 should be done to keep the rotor voltage to an acceptable level?
4. What should be done to keep the rotor voltage to an acceptable level? Explanation: The effective ratio of stator to rotor turns should be adjusted to keep the rotor voltage to an acceptable level. The choice of this turns ratio is arbitrary and is controllable by the designer.
What is full load slip?
The slip corresponding to full load speed of th motor is called full load slip. Example 1 : A 4 pole, 3 phase induction motor is supplied from Hz supply. Determine its synchronous speed. On full load, its speed is observed to be 1410 r.p.m. calculate its full load slip.
What is slip speed?
The speed at which the induction motor work is known as the slip speed. The difference between the synchronous speed and the actual speed of the rotor is known as the slip speed. In other words, the slip speed shows the relative speed of the rotor concerning the speed of the field.
How do you calculate slip frequency?
The frequency of a voltage or current induced due to the relative speed between a vending and a magnetic field is given by the general formula; Frequency = PN /120 Where N = Relative speed between magnetic field and the winding P = Number of poles For a rotor speed N, the relative speed between the rotating flux and.
