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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
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.
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
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
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 circuits may be categorized into three configurations based on which terminal is common to both of the input and output of circuit. Th
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 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
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 also requires the use of a phase-coherent reference. Figure shows the general configuration to demodulate the SSBsignal.Asmall carrier component, which
HOW ARE FLIP-FLOPS USED IN BINARY COUNTERS
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.
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