Rotating magnetic fields, Electrical Engineering

Assignment Help:

When a machine has more than two poles, only a single pair of poles needs to be considered because the electric, magnetic, and mechanical conditions associated with every other pole pair are repetitions of those for the pole pair under consideration. The angle subtended by one pair of poles in a P-pole machine (or one cycle of flux distribution) is defined to be 360 electrical degrees,or2π electrical radians. So the relationship between the mechanical angle m and the angle  in electrical units is given by

804_ROTATING MAGNETIC FIELDS.png

because one complete revolution has P/2 complete wavelengths (or cycles). In view of this relationship, for a two-polemachine, electrical degrees (or radians)will be the same asmechanical degrees (or radians).

In this section we set out to show that a rotating field of constant amplitude and sinusoidal space distribution of mmf around a periphery of the stator is produced by a three-phase winding located on the stator and excited by balanced three-phase currents when the respective phase windings are wound 2π/3 electrical radians (or 120 electrical degrees) apart in space. Let us consider the two-pole, three-phase winding arrangement on the stator shown in Figure.

The windings of the individual phases are displaced by 120 electrical degrees from each other in space around the air-gap periphery. The reference directions are given for positive phase currents. The concentrated full-pitch coils, shown here for simplicity and convenience, do in fact represent the actual distributed windings producing sinusoidal mmf waves centered on the magnetic axes of the respective phases. Thus, these three sinusoidal mmf waves are displaced by 120 electrical degrees from each other in space. Let a balanced three-phase excitation be applied with phase sequence a-b-c, ia = I cos ωs t ; ib = I cos(ωs t - 120°); ic = I cos(ωs t - 240°) where I is the maximum value of the current, and the time t = 0 is chosen arbitrarily when the a-phase current is a positive maximum. Each phase current is an ac wave varying in magnitude sinusoidally with time. Hence, the corresponding component mmf waves vary sinusoidally with time. The sum of these components yields the resultant mmf.


Related Discussions:- Rotating magnetic fields

Electricity hazards in the laboratory, ELECTRICITY HAZARDS IN THE LABOR...

ELECTRICITY HAZARDS IN THE LABORATORY : You've probably read about, or heard of, people falling onto high voltage rails or cables and surviving thousands of volts. As a contra

Error in simulink, dear sir, when i am going to simulate my model in matlab...

dear sir, when i am going to simulate my model in matlab i am getting the following error : the derived input for the integrator is inf or nan at time xxxxx. try to reduce the step

Find in wavelengths how long the line, Q. A transmission line with air diel...

Q. A transmission line with air dielectric is 25 m long. Find, in wavelengths, how long the line is at frequencies of 1 kHz, 10 MHz, and 100 MHz.

Asynchronous and synchronous logic design, One of the simplest circuits is ...

One of the simplest circuits is the asynchronous or ' ripple' counter. Below is shown the circuit diagram of a simple 3 stage ripple counter. The operation of this circuit

Find the equation of the circle concentric, 1. Find the slope and the y-int...

1. Find the slope and the y-intercept of the line whose equation is 5x + 6y = 7. 2. Find the equation of the line that is parallel to 2x + 5y = 7 and passes through the midpoint

What is the maximum speedup, Question: (a) Explain the following metric...

Question: (a) Explain the following metrics: (i) Throughput (ii) Latency (iii) IPC (b) Of the three factors in the equation (EXCPU = Number of instructions × CPI × cy

Find the new synchronous speed, Q. A wye-connected, three-phase, 50-Hz, six...

Q. A wye-connected, three-phase, 50-Hz, six-pole synchronous alternator develops a voltage of 1000 V rms between the lines when the rotor dc field current is 3A. If this alternator

C program, write a c program for suggler message decoder

write a c program for suggler message decoder

Simulation in Proteus, Hi, I need help simulating my project in Proteus, ...

Hi, I need help simulating my project in Proteus, problem is, I have never used it before. This is what I have so far. However, feel free to suggest ideas that will make the circ

Ac, power factor improvement

power factor improvement

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd