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

What is the purpose of segment registers in 8086, What is the purpose of se...

What is the purpose of segment registers in 8086? There are 4 segment registers present in 8086. They are 1. Code Segment (CS ) register 2. Data Segment (DS ) register

Compare dispersion effects single mode and multimode fibre, Compare dispers...

Compare dispersion effects in single mode and multimode fibres? The optical fibres were categorized within two according to the number of modes it passes as: • Single mode fibre

Determine the duration of the frame, Four voicemessages, each with 3-kHz ba...

Four voicemessages, each with 3-kHz bandwidth, are to be sampled at Nyquist rate, and time- multiplexed with samples taken at twice the Nyquist rate from six analog monitoring sign

Evaluate the four parameters of the hybrid model, Q. Show that any amplifie...

Q. Show that any amplifier represented by the model of Figure of the text can also be represented by themore general hybridmodel of Figure. Evaluate the four parameters of the hybr

A transistor has how many p-n junction, A transistor has (A) One p-n j...

A transistor has (A) One p-n junction.  (B) Two p-n junction. (C) Four p-n junction. (D) Five p-n junction. Ans: A transistor has two p-n junctions.

Describe about absolute poverty, Q. Describe about Absolute Poverty? Po...

Q. Describe about Absolute Poverty? Poverty defined with respect to an absolute material standard of living. A person is absolutely poor if their income does not allow them to

Literature review on co2 positive displacement pump, Ask question introduc...

Ask question introduction of co2 single stroke positive displacement pump using cam and follow system to transfer co2 into small cylinders

Define the objectives of load flow analysis, Define the Objectives of Load ...

Define the Objectives of Load Flow Analysis The objectives of load flow analysis are: (i) To analyse an existing power system, future expansion or a new power system plan.

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