1 electrical technology eet 103/4 define and explain sine wave, frequency, amplitude, phase angle,...

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ELECTRICAL TECHNOLOGY EET 103/4

Define and explain sine wave, frequency, amplitude, phase angle, complex number

Define, analyze and calculate impedance, inductance, phase shifting

Explain and calculate active power, reactive power, power factor

Define, explain, and analyze Ohm’s law, KCL, KVL, Source Transformation, Thevenin theorem.

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(CHAPTER 13)

SINUSOIDAL ALTERNATINGSINUSOIDAL ALTERNATINGWAVEFORMSWAVEFORMS

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13.1 Introduction

Alternating waveformsThe term alternating indicates only that the

waveform alternates between two prescribed levels in a set time sequence.

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13.2 Sinusoidal ac Voltage Characteristics and Definitions

GenerationAn ac generator (or alternator) powered by

water power, gas, or nuclear fusion is the primary component in the energy-conversion process.

The energy source turns a rotor (constructed of alternating magnetic poles) inside a set of windings housed in the stator (the stationary part of the dynamo) and will induce voltage across the windings of the stator.

dt

dNe

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Generation Wind power and solar power energy are receiving

increased interest from various districts of the world.The turning propellers of the wind-power station are

connected directly to the shaft of an ac generator.

Light energy in the form of photons can be absorbed by solar cells. Solar cells produce dc, which can be electronically converted to ac with an inverter.

A function generator, as used in the lab, can generate and control alternating waveforms.

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Definitions Waveform: The path traced by a quantity, such

as voltage, plotted as a function of some variable such as time, position, degree, radius, temperature and so on.

Instantaneous value: The magnitude of a waveform at any instant of time; denoted by the lowercase letters (e1, e2).

Peak amplitude: The maximum value of the waveform as measured from its average (or mean) value, denoted by the uppercase letters Em (source of voltage) and Vm (voltage drop across a load).

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DefinitionsPeak value: The maximum instantaneous value

of a function as measured from zero-volt level. Peak-to-peak value: Denoted by Ep-p or Vp-p, the

full voltage between positive and negative peaks of the waveform, that is, the sum of the magnitude of the positive and negative peaks.

Periodic waveform: A waveform that continually repeats itself after the same time interval.

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DefinitionsPeriod (T): The time interval between

successive repetitions of a periodic waveform (the period T1 = T2 = T3), as long as successive similar points of the periodic waveform are used in determining T

Cycle: The portion of a waveform contained in one period of time

Frequency: (Hertz) the number of cycles that occur in 1 s

Hz hertz,1

Tf

10

Heinrich Rudolph Hertz.

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Example 13.1 Determine:(a) peak value(b) instantaneous value at 0.3 s and 0.6 s(c) peak-to-peak value(d) period(e) how many cycles are shown(f) frequency

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Example 13.1 – solution

(a) 8 V; (b) -8 V at 3 s and 0 V at 0.6 s; (c) 16 V;(d) 0.4 s; (e) 3.5 cycles; (f) 2.5 Hz

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Example 13.2Find the period of periodic waveform with frequency of;

(a) 60 Hz (b) 1000 Hz

Solution

(a) ms 67.1660

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fT

(b) ms 11000

11

fT

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Example 13.3

Determine the frequency of the following waveform

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ms 20T

From the waveform;

Hz 501020

113

Tf

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Defined Polarities and Direction

The polarity and current direction will be for an instant in time in the positive portion of the sinusoidal waveform.

In the figure, a lowercase letter is employed for polarity and current direction to indicate that the quantity is time dependent; that is, its magnitude will change with time.

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Defined Polarities and Direction

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13.4 The Sinusoidal Waveform

The sinusoidal waveform is the only alternating waveform whose shape is unaffected by the response characteristics of R, L, and C elements.

The voltage across (or current through) a resistor, coil, or capacitor is sinusoidal in nature.

The unit of measurement for the horizontal axis is the degree. A second unit of measurement frequently used is the radian (rad).

57.357.296 rad 1

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13.4 The Sinusoidal Waveform If we define x as the number of intervals of r (the

radius) around the circumference of a circle, then

and we find

Therefore, there are 2 rad around a 360° circle, as shown in the figure.

xrrC 2 2x

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13.4 The Sinusoidal Waveform The quantity is the ratio of the circumference of

a circle to its diameter. For 180° and 360°, the two units of measurement

are related as follows:

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13.4 The Sinusoidal Waveform The sinusoidal wave form can be derived

from the length of the vertical projection of a radius vector rotating in a uniform circular motion about a fixed point.

The velocity with which the radius vector rotates about the center, called the angular velocity, can be determined from the following equation:

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13.4 The Sinusoidal Waveform The angular velocity () is:

Since () is typically provided in radians per second, the angle obtained using = t is usually in radians.

The time required to complete one revolution is equal to the period (T) of the sinusoidal waveform. The radians subtended in this time interval are 2.

t

T

2 or f 2

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13.4 The Sinusoidal WaveformExample 13.6

Given = 200 rad/s, determine how long it will take the sinusoidal waveform to pass through an angle of 90

Solution

t rad 2

90

ms 85.7200

2/

t

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13.4 The Sinusoidal WaveformExample 13.7

Find the angle through which a sinusoidal waveform of 60 Hz will pass in a period of 5 ms.

Solution

rad 885.11056022 3 ftt

108180

885.1

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13.5 General Format for the Sinusoidal Voltage or Current

• The basic mathematical format for the sinusoidal waveform is:

where:Am is the peak value of

the waveform

is the unit of measure for the horizontal axis

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The equation = t states that the angle through which the rotating vector will pass is determined by the angular velocity of the rotating vector and the length of time the vector rotates.

For a particular angular velocity (fixed ), the longer the radius vector is permitted to rotate (that is, the greater the value of t ), the greater will be the number of degrees or radians through which the vector will pass.

The general format of a sine wave can also be as:

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For electrical quantities such as current and voltage, the general format is:

sinsin mm ItIi

sinsin mm EtEe

where: the capital letters with the subscript m represent the amplitude, and the lower case letters i and e represent the instantaneous value of current and voltage, respectively, at any time t.

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Example 13.8

Given e = 5sin, determine e at = 40 and = 0.8.

Solution

For = 40, V 21.340sin5 e

For = 0.8

144180

8.0

V 94.2144sin5 e

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Example 13.9

(a) Determine the angle at which the magnitude of the sinusoidal function v = 10 sin 377t is 4 V.

(b) Determine the time at which the magnitude is attained.

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Example 13.9 - solution

V sin tVv m rad/s 377 V; 10 mV

Hence,

V 377sin10 tv

When v = 4 V,

t377sin104 Or; 4.010

4sin377sin t

58.234.0sin 1

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Example 13.9 – solution (cont’d)

rad 412.058.23377 t

ms 1.09377

412.0t

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13.6 Phase Relationship

tAa m sin

The unshifted sinusoidal waveform is represented by the expression:

t

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where is the angle (in degrees or radians) that the waveform has been shifted.

Sinusoidal waveform which is shifted to the right or left of 0° is represented by the expression:

tAa m sin

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13.6 Phase RelationshipIf the wave form passes through the horizontal

axis with a positive-going (increasing with the time) slope before 0°:

tAa m sin

t

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13.6 Phase RelationshipIf the waveform passes through the horizontal

axis with a positive-going slope after 0°:

tAa m sin

t

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13.6 Phase RelationshipThe terms lead and lag are used to indicate

the relationship between two sinusoidal waveforms of the same frequency plotted on the same set of axes.

• The cosine curve is said to lead the sine curve by 90.

• The sine curve is said to lag the cosine curve by 90.

• 90 is referred to as the phase angle between the two waveforms.

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t

40

13.6 Phase RelationshipIf a sinusoidal expression should appear as

tEe m sin

the negative sign is associated with the sine portion of the expression, not the peak value Em , i.e.

tEetEe mm sinsin

And, since; 180sinsin tt

180sinsin tEtE mm

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13.6 Phase RelationshipIf a sinusoidal expression should appear as

tEe m sin

the negative sign is associated with the sine portion of the expression, not the peak value Em , i.e.

tEetEe mm sinsin

And, since; 180sinsin tt

180sinsin tEtE mm

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Determine the phase relationship between the following waveforms;

70sin5

30sin10 (a)

ti

tv

Example 13.2

20sin10

60sin15 (b)

tv

ti

10sin3

10cos2 (c)

tv

ti

10sin2

30sin (d)

tv

ti

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70sin5

30sin10 (a)

ti

tv


i leads v by 40Or

v lags i by 40

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13.6 Phase RelationshipExample 13.2 – solution (cont’d)

i leads v by 80Or

v lags i by 80

20sin10

60sin15 (b)

tv

ti

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i leads v by 110Or

v lags i by 110

10sin3

10cos2 (c)

tv

ti

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v leads i by 160Or

i lags v by 160

10sin2

30sin (d)

tv

ti

i leads v by 200Or

v lags i by 200

OR

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13.7 Average Value

• Understanding the average value using a sand analogy:– The average height

of the sand is that height obtained if the distance form one end to the other is maintained while the sand is leveled off.

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13.7 Average Value

The algebraic sum of the areas must be determined, since some area contributions will be from below the horizontal axis.

Area above the axis is assigned a positive sign and area below the axis is assigned a negative sign.

The average value of any current or voltage is the value indicated on a dc meter – over a complete cycle the average value is the equivalent dc value.

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13.7 Average Value

tAa m sin

t

Average value

mm AtdtAa 2sin of Area0

mm AAa

a 632.02 of Area

average

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13.7 Effective (rms) Value

T

dttiI

T

0

2

(rms) tIti m sin

tItIti mm cos212

1sin 2222

T

dttII

T

m

0

2

(rms)

cos2121

2(rms)

mII

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13.7 Effective (rms) ValueExample 13.21

The 120 V dc source delivers 3.6 W to the load. Find Em and Im of the ac source, if the same power is to be delivered to the load.

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13.7 Effective (rms) ValueExample 13.21 – solution

W6.3dcdc PIE mA 30120

6.3

dcdc

E

PI

2dcrms

mEEE

V 7.169120414.12 dc EEm

and2

dcrmsmIII

mA 43.4230414.12 dc IIm

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13.7 Effective (rms) ValueExample 13.21 – solution

2dcrms

mIII

2dcrms

mEEE

rms2EEm

V 7.169

120414.1

1 electrical technology eet 103/4 define and explain sine wave, frequency, amplitude, phase angle,...

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periodic waveform

definitions period t

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