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

A.c. machines-the single phase alternator, The single phase alternator ...

The single phase alternator   The underlined italicised terms in the following text identifies terms that you should understand and remember. The simple two pole generator

Determine the bit-error probability for the two systems, Let both coherent ...

Let both coherent ASK and coherent PSK systems transmit the same average energy per bit interval and operate on the same channel such that E b /N 0 = 18. Determine the bit-error p

Explain electric flux density, Electric flux density (D): Electric flux...

Electric flux density (D): Electric flux density is a measurement of electric flux that pass through a unit of plate's area with a coincide angle, that is an area of 1 meter 2

Transistor configurations, TRANSISTOR CONFIGURATIONS: Transistor circu...

TRANSISTOR CONFIGURATIONS: Transistor circuits may be categorized into three configurations based on which terminal is common to both of the input and output of circuit. Th

Factors that influence choice of carrier frequency, 1. Why must a modem be ...

1. Why must a modem be used to transmit binary data through a PSTN? (1) Use sketches and additional text to describe the following modulation methods. (a) Amplitude shift key

Explain significance of loss tangent of dielectric material, Explain the si...

Explain the significance of the loss tangent of a dielectric material. The loss tangent contains a very small value for free space. For solid materials there tan δ = 0.003, tha

Interrupt structure of the 8085 microprocessor, List the four instructions ...

List the four instructions which control the interrupt structure of the 8085 microprocessor. DI ( Disable Interrupts ) EI ( Enable Interrupts ) RIM ( Read Interrupt Masks

Demodulation of ssb signals, Demodulation of SSB signals also requires the ...

Demodulation of SSB signals also requires the use of a phase-coherent reference. Figure shows the general configuration to demodulate the SSBsignal.Asmall carrier component, which

FLIP-FLOPS, HOW ARE FLIP-FLOPS USED IN BINARY COUNTERS

HOW ARE FLIP-FLOPS USED IN BINARY COUNTERS

Obtain complete solution for the current for given circuit, For the circuit...

For the circuit of Figure(a), obtain the complete solution for the current i L (t) through the 5-H inductor and the voltage v x (t) across the 6- resistor.

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