Table of Contents
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 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 frequency of rotor current of 50hz?
A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. Rotor frequency is? Explanation: s = 0.04, rotor frequency = s*f = 0.04*50 = 2 Hz.
What is the frequency of the rotor current at full load?
(e)The frequency of rotor-currents at full-load is 1.50 Hz.
What is the rotor current frequency when the rotor is stationary?
i.e., Rotor current frequency = Fractional slip x Supply frequency (i) When the rotor is at standstill or stationary (i.e., s = 1), the frequency of rotor current is the same as that of supply frequency (f’ = sf = 1× f = f).
Why rotor is short-circuited?
To facilitate a closed path in the rotor circuit, both sides of the rotor bars are short-circuited by end rings.
What are the different types of rotors?
The four different rotor types are: Blank & Smooth – Blank and smooth rotors are what you’ll find on most passenger vehicles and feature a smooth, blank metal surface all the way around the rotor. Drilled – Drilled rotors feature drilled holes around the metal surface.
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 formula for rotor turns per phase?
8. What is the formula for rotor turns per phase? Explanation: Firstly, the winding factor for stator is obtained along with the winding factor for stator. Next the ratio of the rotor voltage per phase to the stator voltage per phase.
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 are the two types of rotors?
There are two types of induction motor rotors: Squirrel-cage rotor or simply cage rotor. Phase wound or wound rotors.
Why skewing of rotor is done?
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 a short-circuited rotor?
An asynchronous motor has a passive rotor that is short-circuited permanently (squirrel-cage rotor) or temporarily (see Slip ring rotor). The rotor is a metal cage with axial bars arranged in a symmetric circular pattern and fixed to a short-circuit ring (end ring) at each end.
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 rotor speed?
Rotor spinning Rotor speed depends, in part, on rotor diameter. Rotor speeds typically lie in the 120–210 m/s range, but mostly between 150 and 190 m/s, with a tendency to be higher with a smaller rotor diameter [6].
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 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.
How do I calculate RPM?
How to Calculate Motor RPM. 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 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 is cogging and crawling?
The important characteristics normally shown by a squirrel cage induction motors are crawling and cogging. These characteristics are the result of improper functioning of the motor that means either motor is running at very slow speed or it is not taking the load.
What is a skewed rotor?
In the induction motor rotor, the slots for the placement of conductors are not made exactly in parallel with the rotor shaft. A slight angle is maintained that means the rotor slots are made in some angle with the rotor shaft. This is called Skewing of the rotor or Skewed Rotor.
Is DOL is a full voltage starting method?
Principle of Direct On Line Starter (DOL) To start, the contactor is closed, applying full line voltage to the motor windings. The motor will draw a very high inrush current for a very short time, the magnetic field in the iron, and then the current will be limited to the Locked Rotor Current of the motor.
