Author: workhouse123
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AVERAGE VALUE OF SINUSOIDAL CURRENT
The alternating current varying sinusoidally, as shown in Figure 6.9, is given by the equation: i = Imsinθ Fig. 6.9 Current varying sinusoidally Consider an elementary strip of thickness dθ in the positive half cycle, i be its mid-ordinate. Then, Area of strip = idθ Area of half cycle = Im[–1(–1–1)] = 2Im Base = 0 to π = π − 0 = π ∴ Average value,
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PEAK VALUE
The maximum value attained by an alternating quantity during one cycle is called ‘peak value’. This is also called ‘maximum value or crest value or amplitude’. A sinusoidal alternating quantity obtains its maximum value at 90° as shown in Figure 6.7. The peak of an alternating voltage and current is represented by Em and Im. The knowledge of…
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VALUES OF ALTERNATING VOLTAGE AND CURRENT
The voltage and current in DC system are constant so that there is no problem of specifying their magnitudes, whereas in AC system, the alternating voltage and current vary from time to time. Hence, it is necessary to explain the ways to express the magnitude of alternating voltage and current. The following three ways are…
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DIFFERENT FORMS OF ALTERNATING VOLTAGE EQUATION
The alternating voltage is given by the following standard equation: e = Em sin θ or e = Em sin ω t or e = Em sin 2 π ft (sin ω = 2π f) = Em sin 2 πt/T (since f = 1/T) Which form of the above equation is to be applied will depend upon the data given? To determine the various values, for example, maximum value, frequency, time period, angular velocity, etc., the given equation is compared…
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IMPORTANT RELATIONS
Some of the terms used in AC terminology have definite relations among themselves as given below:
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EQUATION OF ALTERNATING EMF AND CURREN
Consider a coil having ‘N’ turns rotating in a uniform magnetic field of density B Wb/m2 in the counterclockwise direction at an angular velocity of ω radians per second as shown in Figure 6.6. At the instant, as shown in Figure 6.6(b), maximum flux ɸm is linking with the coil. After t seconds, the coil is rotated through an angle θ = ω t radians. The component of flux…
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GENERATION OF ALTERNATING VOLTAGE AND CURRENT
An alternating voltage can be generated either by rotating a coil in a uniform magnetic field at constant speed as shown in Figure 6.3 or by rotating a uniform magnetic field within a stationary coil at a constant speed as shown in Figure 6.4. Fig. 6.3 Production of ac voltage (rotating coil, field stationary) Fig. 6.4 Production…
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SINUSOIDAL ALTERNATING QUANTITY
n alternating quantity (i.e., voltage or current) that varies according to sine of angle θ (θ = ωt) is known as ‘sinusoidal alternating quantity’. Its wave shape is shown in Figure 6.2(f). For the generation of electric power, sinusoidal voltages and currents are selected all over the world due to the following reasons: Whenever the word ‘alternating voltage or…
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DIFFERENCE BETWEEN AC AND DC
AC DC (1) An alternating current reverses periodically and its magnitude changes. (1) Direct current flows only in one direction and remains unaltered. (2) Amplitude and polarities are varying continuously. (2) Amplitude and polarities are fixed. (3) It has a particular frequency. (3) It is independent of frequency. (4) AC can be generated at higher…
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ALTERNATING VOLTAGE AND CURRENT
A voltage that changes its polarity and magnitude at regular intervals of time is called an ‘alternating voltage’. When an alternating voltage source is connected across a load resistor R as shown in Figure 6.1, the current flows through it in one direction and then in opposite direction when the polarity is reversed. Figure 6.1(c) shows the…