introduction to electrical engineering l 13: single phase...
TRANSCRIPT
![Page 1: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/1.jpg)
ELL 100 - Introduction to Electrical Engineering
LECTURE 13: SINGLE PHASE AC CIRCUITS
1
![Page 2: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/2.jpg)
Introduction
Basics of sinusoid and phasors
Average, RMS value of an AC quantity
Steady state AC response for a pure resistive circuit
Exercise/Numerical Analysis
2
OUTLINE
![Page 3: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/3.jpg)
3
INTRODUCTION
Why alternating current (AC) power system became popular?
While direct current (DC) electricity flows in one direction through a
wire, AC electricity alternates its direction in a back-and-forth motion
AC electricity is created by an AC electric generator, which determines
the frequency
The major advantage of AC electricity is that the voltage can be readily
changed, thus making it more suitable for long-distance transmission
than DC electricity
![Page 4: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/4.jpg)
4
AC can also be employed using capacitors and inductors in electronic
circuitry, allowing for a wide range of applications
INTRODUCTION
Various AC Waveforms
![Page 5: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/5.jpg)
5
Single Phase Transformer
SINGLE PHASE APPLIANCES
![Page 6: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/6.jpg)
6
Single Phase Meter
SINGLE PHASE APPLIANCES
![Page 7: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/7.jpg)
7
Single Phase Power Supply with
Battery
Single Phase Grid Connected System
SINGLE PHASE APPLIANCES
![Page 8: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/8.jpg)
8
Single Phase Fan Induction Motor
SINGLE PHASE APPLIANCES
![Page 9: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/9.jpg)
9
APPLICATIONS
Phase-Shifter Circuits
![Page 10: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/10.jpg)
10
APPLICATIONS
![Page 11: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/11.jpg)
BASICS OF SINUSOID
A sinusoid is a signal that has the form of the sine or cosine function
A sinusoidal current is usually referred to as alternating current (AC)
Such a current reverses at regular time intervals and has alternately
positive and negative values as shown,
11Fig. Sinusoidal Variation
![Page 12: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/12.jpg)
A sinusoidal signal is easy to generate and transmit
It is the dominant form of signal in the communications and electric
power industries
Through Fourier analysis, any practical periodic signal can be
represented by a sum of sinusoids
Circuits driven by sinusoidal current or voltage sources are called
AC circuits
BASICS OF SINUSOID
12
![Page 13: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/13.jpg)
We experience sinusoidal variation in,
Fig. Motion of a pendulum Fig. Vibration of a string
BASICS OF SINUSOID
13
![Page 14: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/14.jpg)
Fig. Ripples on the ocean surface
BASICS OF SINUSOID
14
![Page 15: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/15.jpg)
15
The terms which we most commonly use:
Waveform: The variation of a quantity such as voltage or current
shown on a graph to a base of time is a waveform.
Cycle: Each repetition of a variable quantity, recurring at equal
intervals, is termed a cycle. Period: The duration of one cycle is termed its period.
Fig. Cycles and Periods
BASICS OF SINUSOID
![Page 16: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/16.jpg)
16
BASICS OF SINUSOID
Instantaneous value: The magnitude of a waveform at any instant in
time. They are denoted by lower-case symbols such as e, v and i.
Peak value: The maximum instantaneous value measured from its
zero value is known as its peak value.
Peak-to-peak value: The maximum variation between the maximum
positive instantaneous value and the maximum negative instantaneous
value is the peak-to-peak value.
Fig. Peak Values
![Page 17: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/17.jpg)
17
BASICS OF SINUSOID
Peak amplitude: The maximum instantaneous value measured from the
mean value of a waveform is the peak amplitude.
Frequency: The number of cycles that occur in 1 second is termed the
frequency of that quantity. Frequency is measured in hertz (Hz)
Fig. Effect on waveforms by varying frequency
![Page 18: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/18.jpg)
Sinusoids, play an important role in the analysis of periodic signals
The derivative and integral of a sinusoid are themselves sinusoids.
For these reasons, the sinusoid is an extremely important function in
circuit analysis
BASICS OF SINUSOID
Consider the sinusoidal voltage,
( ) sinmv t V t Where, Vm = the amplitude of the sinusoid
ω = the angular frequency in radians/s
ωt = the argument of the sinusoid18
![Page 19: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/19.jpg)
It is evident that the sinusoid repeats itself every T seconds thus, T is
called the period of the sinusoid
From the figures, we observe that ωT = 2π2
T
Fig. Vm sin ωt as a function of ωt Fig. Vm sin ωt as a function of t
BASICS OF SINUSOID
19
![Page 20: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/20.jpg)
The fact that v(t) repeats itself every T seconds is shown by replacing t
by t + T,( ) sin ( ) sin ( )
2m m
Tv t T V t T V t
sin( 2 ) sin ( )m mV t V t v t
Hence, ( ) ( )v t T v t
Thus, v has the same value at t + T as it does at t and v(t) is said to be
periodic.
A periodic function is one that satisfies f (t ) = f (t + nT ), for all t and
for all integers n
BASICS OF SINUSOID
20
![Page 21: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/21.jpg)
The period T of the periodic function is the time of one complete cycle
or the number of seconds per cycle
The reciprocal of this quantity is the number of cycles per second,
known as the cyclic frequency (f) of the sinusoid. Thus,
1f
T
2 f
While ω is in radians per second (rad/s), f is in hertz (Hz)
Therefore,
BASICS OF SINUSOID
21
![Page 22: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/22.jpg)
A more general expression for the
sinusoid is,
( ) sin( )mv t V t
where, (ωt+ϕ) is the argument and
ϕ is the phase
Let us examine the two sinusoids,
1 2( ) sin( ), ( ) sin( )m mv t V t v t V t
Fig. Two sinusoids with different phases
BASICS OF SINUSOID
Both argument and phase can be in
radians or degrees
22
![Page 23: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/23.jpg)
23
Fig. Two sinusoids with different phases
BASICS OF SINUSOID
The starting point of v2 in Fig.
occurs first in time
Therefore, v2 leads v1 by ϕ or v1 lags
v2 by ϕ
If ϕ ≠ 0, v1 and v2 are out of phase
Moreover, if ϕ = 0 then v1 and v2 are
said to be in phase as they reach their
minima and maxima at exactly the
same time
![Page 24: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/24.jpg)
A sinusoid can be expressed in either sine or cosine form
When comparing two sinusoids, it is convenient to express both as
either sine or cosine with positive amplitudes using,
sin( ) sin cos cos sin
cos( ) cos cos sin sin
A B A B A B
A B A B A B
With these identities, it is easy to show that,
sin( 180) sin ,cos( 180) cos
sin( 90) cos ,cos( 90) sin
t t t t
t t t t
Using these, sinusoid can be transformed from sine form to cosine form
or vice versa.
BASICS OF SINUSOID
24
![Page 25: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/25.jpg)
A graphical approach can also be used to
relate or compare sinusoids as an alternative
to using the trigonometric identities,
The horizontal axis represents the
magnitude of cosine, while the vertical axis
(pointing down) denotes the magnitude of
sine
Angles are measured positively counter
clockwise from the horizontal, as usual in
polar coordinates
BASICS OF SINUSOID
25
Fig. A graphical means of relating
cosine and sine,
cos(ωt − 90°) = sin ωt
![Page 26: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/26.jpg)
Similarly, by adding 180° to the argument of sin ωt gives −sin ωt, or
sin(ωt + 180°) = −sin ωt as shown below,
BASICS OF SINUSOID
Fig. A graphical means of relating cosine, sin(ωt + 180°) = −sin ωt26
+ sin ωt
![Page 27: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/27.jpg)
The graphical technique can also be used to add two sinusoids of the
same frequency when one is in sine form and the other is in cosine
form
BASICS OF SINUSOID
27
To add A cosωt and B sinωt as shown,
Here, A is the magnitude of cosωt
while B is the magnitude of sinωt
Fig. Adding A cosωt and B sinωt
cos sin cos( )A t B t C t
where, 2 2 1, tanB
C A BA
![Page 28: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/28.jpg)
SOLVED NUMERICALS ON SINUSOIDS
28
![Page 29: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/29.jpg)
29
Numerical 1: Determine frequency in Hz, angular frequency in rad/s,
and the amplitude of the harmonic voltage signals as shown.
Solution: All four signals in Fig. have the same amplitude of 0.6 V,
the same frequency of f = 1 kHz, and the same angular frequency
of ω = 2πf = 6283.1 rad/s.
![Page 30: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/30.jpg)
30
Numerical 2: Determine the frequency, amplitude, and phase of the
harmonic voltage signal as shown versus the base cosine signal.
Solution: The amplitude by inspection is observed to be Vm = 1.0V.
The frequency is determined by observing the entire interval from
0 to 3 ms containing three full periods; hence T = 1 ms, and
f = 1/T = 1000 Hz =1 kHz.
![Page 31: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/31.jpg)
31
For the phase determination, we note that the first maximum occurs later
in time than for the base cosine, which already peaks at t = 0.
Therefore, the phase must be negative, that is, φ < 0. The absolute value
of the phase is,
2T
T
which gives |φ| = π/3 for ΔT = T/6
Alternatively, the same result can be obtained by observing that the
cosine function is equal to 0.5 Vm at t = 0, so that φ = -cos-1 (0.5) = -π/3.
![Page 32: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/32.jpg)
Numerical 3: Find the amplitude, phase, period, and frequency of the
sinusoid v(t) = 12 cos(50t + 10°) V.
Solution:
The amplitude is Vm = 12 V
The phase is ϕ = 10°
The angular frequency is ω = 50 rad/s
The period T =2π/ω =2π/50= 0.1257 s
The frequency is f = 1/T= 7.958 Hz
32
Numerical 4: Given the sinusoid 45 cos(5πt + 36°), calculate its
amplitude, phase, angular frequency, period, and frequency.
Solution: 45, 36°, 15.708 rad/s, 400 ms, 2.5 Hz
![Page 33: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/33.jpg)
Numerical 5: Calculate the phase angle between v1 = −10 cos(ωt + 50°)
and v2 = 12 sin(ωt − 10°). State which sinusoid is leading.
Solution: METHOD 1- In order to compare v1 and v2, we must express
them in the same form. If we express them in cosine form with positive
amplitudes, v1 = −10 cos(ωt + 50°) = 10 cos(ωt + 50° − 180°)
v1 = 10 cos(ωt − 130°) or v1 = 10 cos(ωt + 230°)
33
v2 = 12 sin(ωt − 10°) = 12 cos(ωt − 10° − 90°)
v2 = 12 cos(ωt − 100°) = 12 cos(ωt − 100° + 360°) = 12 cos(ωt + 260°)
It can be deduced that the phase difference between v1 and v2 is 30°
Thus, it can be observed v2 leads v1 by 30°
![Page 34: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/34.jpg)
METHOD 2- Alternatively, we may express v1 in sine form:
v1 = −10 cos(ωt + 50°) = 10 sin(ωt + 50° − 90°)
= 10 sin(ωt − 40°) = 10 sin(ωt − 10° − 30°)
34
But v2 = 12 sin(ωt − 10°). Comparing the two shows that v1 lags v2 by 30°.
This is the same as saying that v2 leads v1 by 30°
METHOD 3- We may regard v1 as simply
−10 cos ωt with a phase shift of +50°.
Similarly, v2 is 12 sin ωt with a phase shift
of −10°.
Therefore, as observed v2 leads v1 by 30°.
![Page 35: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/35.jpg)
BASICS OF PHASORS
35
![Page 36: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/36.jpg)
BASICS OF PHASORS
A phasor is a complex number that represents the amplitude and phase
of a sinusoid.
Phasors provide a simple means of analysing linear circuits excited
by sinusoidal sources
A complex number z can be written in rectangular form as
z x jy
where j = √(−1), x is the real part of z, y is the imaginary part of z
36
![Page 37: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/37.jpg)
The complex number z can also be written in polar or exponential
form as,jz r re
Where, r is the magnitude of z, and ϕ is
the phase of z
,z x jy z r
Rectangular form Polar form
The relationship between the
rectangular form and the polar form
is shown in Fig.,
BASICS OF PHASORS
Fig. Representation of a complex
number37
![Page 38: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/38.jpg)
Where, x axis represents the real part and the y axis represents the
imaginary part of a complex number
BASICS OF PHASORS
Given x and y, we can get r and ϕ as
2 2 1, tany
r x yx
, cos , sinwhere x r y r
Thus, z may be written as
(cos sin )z x jy r r j
The idea of phasor representation is based on Euler’s identity
cos sinje j 38
![Page 39: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/39.jpg)
cos Re( ),sin Im( )j je e
BASICS OF PHASORS
Given a sinusoid v(t) = Vm cos(ωt + ϕ),
( )( ) cos( ) Re( )j t
m mv t V t V e
Thus, ( ) Re( )j tv t Ve where,j
m mV V e V
By considering cos ϕ and sin ϕ as the real and imaginary parts of e jϕ,
39
![Page 40: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/40.jpg)
BASICS OF PHASORS
The plot of Vejωt = Vmej(ωt+ϕ) on the complex plane can be observed as,
Fig. Representation of Vejωt sinor rotating counter clockwise and its projection on the real axis as
a function of time.
40
As time increases, the sinor rotates on a circle of radius Vm at an
angular velocity ω in the counter clockwise direction
![Page 41: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/41.jpg)
BASICS OF PHASORS
Phasors V = and I = are graphically represented,
Such a graphical representation of phasors is known as a phasor diagram
41
mV mI
![Page 42: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/42.jpg)
BASICS OF PHASORS
By suppressing the time factor, we transform the sinusoid from the
time domain to the phasor domain. This transformation is summarized
as follows,
( ) cos( )m mv t V t V V
Besides time differentiation and integration, another important use of
phasors is found in summing sinusoids of the same frequency
42
![Page 43: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/43.jpg)
SOLVED NUMERICALS ON PHASORS
43
![Page 44: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/44.jpg)
Numerical 1: Transform these sinusoids to phasors,
(a) i = 6 cos(50t − 40°) A
(b) v = −4 sin(30t + 50°) V
Solution:
(a) i = 6 cos(50t − 40°)A has the phasor,
(b) Since, −sin A = cos(A + 90°),
v = −4 sin(30t + 50°) = 4 cos(30t + 50° + 90°) = 4 cos(30t + 140°) V
The phasor form of v is 4 140oV V
6 40I A
44
![Page 45: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/45.jpg)
Numerical 2: Express these sinusoids as phasors,
(a) v = −14 sin(5t − 22°) V
(b) i = −8 cos(16t + 15°) A
Solution: (a) (b)
Numerical 3: Find the sinusoids corresponding to these phasors,
(a) (b)
Solution: (a) v(t) = 25 cos(ωt − 140°) V or 25 cos(ωt + 220°) V,
(b) i(t) = 13 cos(ωt + 67.38°) A
8 165I A 14 68V V
25 40V V (12 5)I j j A
45
![Page 46: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/46.jpg)
Numerical 4: Given i1(t) = 4 cos(ωt + 30°) A and i2(t) = 5 sin(ωt − 20°) A,
find their sum.
Solution:
Current i1(t) is in the standard form. Its phasor is
We need to express i2(t) in cosine form. The rule for converting sine to
cosine is to subtract by 90°,
i2 = 5 cos(ωt − 20° − 90°) = 5 cos(ωt − 110°)
and its phasor is
4 30oI A
2 5 110oI A
46
![Page 47: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/47.jpg)
If we let i = i1 + i2, then
I = I1 + I2 =
= (3.464 + j2) + (-1.71 - j4.698)
= 1.754 − j2.698
=
4 30 5 110o A
3.218 56.97 A
Transforming this to the time domain,
we get i(t) = 3.218 cos(ωt − 56.97°) A
47
![Page 48: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/48.jpg)
AVERAGE AND RMS VALUES OF
AN ALTERNATING CURRENT
48
![Page 49: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/49.jpg)
AVERAGE AND RMS VALUES OF AN ALTERNATING
CURRENT
Let us first consider the wave shown as shown, which is typical current
waveform produced by a transformer on no load,
Fig. Average and RMS values 49
![Page 50: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/50.jpg)
If n equidistant mid-ordinates (i1, i2, ...) are taken over either the
positive or the negative half-cycle, then average value of current over
half a cycle is,
AVERAGE VALUE OF AN ALTERNATING CURRENT
1 2 ... nav
i i iI
n
Or, alternatively, average value of current is,
50
=𝐴𝑟𝑒𝑎 𝑒𝑛𝑐𝑙𝑜𝑠𝑒𝑑 𝑜𝑣𝑒𝑟 ℎ𝑎𝑙𝑓 − 𝑐𝑦𝑐𝑙𝑒
𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑏𝑎𝑠𝑒 𝑜𝑣𝑒𝑟 ℎ𝑎𝑙𝑓 − 𝑐𝑦𝑐𝑙𝑒
![Page 51: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/51.jpg)
AVERAGE AND RMS VALUES OF AN ALTERNATING
CURRENT If Im is the maximum value of a current which varies sinusoidally as
shown,
Fig. Average and RMS values of a sinusoidal current51
![Page 52: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/52.jpg)
AVERAGE AND RMS VALUES OF AN ALTERNATING
CURRENT
The instantaneous value i is represented by,
sinmi I
where, θ is the angle in radians from instant of zero current
For a very small interval dθ radians, the area of the shaded strip is
i · dθ ampere radians
The use of the unit ‘ampere radian’ avoids converting the scale on
the horizontal axis from radians to seconds
52
![Page 53: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/53.jpg)
Therefore, total area enclosed by the current wave over half-cycle is,
AVERAGE VALUE OF AN ALTERNATING CURRENT
0 0 0
sin cos
( 1) 1 2
m m
m m
i d I d I
I I
Therefore, average value of current over a half-cycle is Iav
2 mI
Iav = 0.637Im
53
![Page 54: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/54.jpg)
RMS VALUE OF AN ALTERNATING CURRENT
If i is the instantaneous current through the resistance, the average
power dissipated is,
Therefore, 0.7072
mm
II I
It is normal practice to omit the RMS subscript, and just denote IRMS as I
54
< 𝑖2𝑅 > = 𝐼𝑅𝑀𝑆2 𝑅 wher𝑒 < 𝑖2 >= 𝐼𝑅𝑀𝑆
< 𝑖2 >=1
𝜋 0
𝜋
𝐼𝑚2 𝑠𝑖𝑛2 𝜃 𝑑𝜃 =
𝐼𝑚2
2
IRMS
![Page 55: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/55.jpg)
AVERAGE AND RMS VALUES OF AN ALTERNATING
CURRENT
RMS value of a sinusoidal current or voltage is,
0.707 mI I
Form factor (= RMS/Average) of a sine wave is,
Form factor =0.707 ∗ maximum value
0.637 ∗ minimum value1.11fk
Peak or crest factor (= Amplitude/Average) of a sine wave is
Peak factor =maximum value
0.707 ∗ maximum value1.414pk
55
![Page 56: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/56.jpg)
NUMERICALS ON AVERAGE AND RMS VALUES
56
![Page 57: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/57.jpg)
Numerical 1: An alternating current of sinusoidal waveform has an RMS
value of 10.0 A. What is the peak-to-peak value of this current?
Solution:
The peak-to-peak value is therefore 14.14 − (-14.14) = 28.28 A
1014.14
0.707 0.707m
II A
57
![Page 58: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/58.jpg)
Solution: The relation is of the form v = Vm sinωt and by comparison,
( ) 141.4 2ma V V V Hence, 141.4
1002
V V
(b)Also by comparison,377
377 / 2 , 602
rad s f f Hz
(c)Finally, 141.4sin 377v t
when t = 3 × 10−3 sec,
3141.4sin(377 3 10 ) 141.4sin1.131
141.4 0.904 127.8
v
V
58
Numerical 2: An alternating voltage has the equation v = 141.4 sin 377t,
what are the values of (a) RMS voltage (b) frequency
(c) the instantaneous voltage when t = 3 ms?
![Page 59: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/59.jpg)
Numerical 3: A current has the following steady values in amperes for
equal intervals of time changing instantaneously from one value to the
next (Fig. 32):
0, 10, 20, 30, 20, 10, 0, −10, −20, −30, −20, −10, 0, etc.
Calculate the RMS value of the current and its form factor.
Fig. Waveform of current59
![Page 60: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/60.jpg)
Solution: 𝐼𝑎𝑣 =area under curve
𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑏𝑎𝑠𝑒
2 3 2 4 3 5 4 6 50 0 10 20 30 20 10
6 6 6 6 6 6 6 6 6 6 6
0
15A
2 2 2 2 2 2
2
2 3 2 4 3 5 4 6 50 0 10 20 30 20 10
6 6 6 6 6 6 6 6 6 6 6
0
I
60
316
316 17.8
17.81.19
15.0f
av
I A
Ik
I
![Page 61: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/61.jpg)
STEADY STATE AC RESPONSE FOR A
PURE RESISTIVE CIRCUIT
61
![Page 62: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/62.jpg)
STEADY STATE AC RESPONSE FOR A PURE RESISTIVE
CIRCUIT
Consider a circuit having a resistance R ohms connected across the
terminals of an AC generator G as shown,
Fig. Circuit with resistance
62
![Page 63: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/63.jpg)
If the value of the voltage at any instant is v volts, the value of the
current at that instant is given by,
STEADY STATE AC RESPONSE FOR A PURE RESISTIVE
CIRCUIT
vi
R
When the voltage is zero, the current is also zero and since the current
is proportional to the voltage, the waveform of the current is exactly
the same as that of the voltage
63
![Page 64: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/64.jpg)
The two quantities are in phase as
they pass through their zero values
at the same instant and attain their
maximum values in a given
direction at the same instant
Hence the current wave is as
shown,
STEADY STATE AC RESPONSE FOR A PURE RESISTIVE
CIRCUIT
Fig. Voltage and current waveforms for a
resistive circuit
64
![Page 65: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/65.jpg)
STEADY STATE AC RESPONSE FOR A PURE RESISTIVE
CIRCUIT
If Vm and Im are the maximum values of the voltage and current
respectively, it follows that
mm
VI
R
But the RMS value of a sine wave is 0.707 times the maximum value,
so thatRMS value of voltage=V=0.707Vm
RMS value of current=I=0.707Im
65
![Page 66: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/66.jpg)
STEADY STATE AC RESPONSE FOR A PURE RESISTIVE
CIRCUIT
Substituting for Im and Vm we have,
0.707 0.707
I V VI
R R
Hence, Ohm’s law can be applied without any modification to an AC
circuit possessing resistance only
If the instantaneous value of the applied voltage is represented by,
sinmv V t
66
![Page 67: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/67.jpg)
STEADY STATE AC RESPONSE FOR A PURE RESISTIVE
CIRCUIT
Then instantaneous value of current in a resistive circuit is
sinmV ti
R
The phasors representing the voltage and current in a resistive circuit
are shown below,
Fig. Phasor diagram for a resistive circuit
The two phasors are actually coincident, but are drawn slightly apart
so that the identity of each may be clearly recognized67
![Page 68: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/68.jpg)
UNSOLVED PROBLEMS
68
![Page 69: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/69.jpg)
Question 1: Given the sinusoidal voltage v(t) = 50 cos (30t + 10°) V, find:
(a) the amplitude Vm, (b) the period T, (c) the frequency f, and (d) v(t) at t =
10 ms.
Question 2: A current source in a linear circuit has is = 8 cos(500πt - 25°) A
(a) What is the amplitude of the current?
(b) What is the angular frequency?
(c) Find the frequency of the current.
(d) Calculate is at t = 2 ms.
Question 3: Express the following functions in cosine form:
(a) 4 sin(ωt - 30°) (b) −2 sin(6t)
(c) −10 sin(ωt + 20°)
69
Ans.2: (a) 8 A, (b) 1570.8 rad/s,
(c) 250 Hz, (d) -7.25 A
Ans.3: (a) 4 cos(ωt-120°), (b) 2
cos(6t+90°), (c) 10 cos(ωt+110°)
Ans.1: (a) 50 V, (b) 209.4 ms, (c)
4.775 Hz, (d) 44.48 V, 0.3 rad
![Page 70: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/70.jpg)
Question 4: Given v1 = 20 sin(ωt + 60°) V and v2 = 60 cos(ωt − 10°) V,
determine the phase angle between the two sinusoids and which one lags
the other.
Question 5: For the following pairs of sinusoids, determine which one
leads and by how much.
(a) v(t) = 10 cos(4t − 60°) and i(t) = 4 sin(4t + 50°)
(b) v1(t) = 4 cos(377t + 10°) and v2(t) = −20 cos 377t
(c) x(t) = 13 cos 2t + 5 sin 2t and y(t) = 15 cos(2t − 11.8°)
70
Ans.4: 20º and v1 lags v2
Ans.5: (a) i(t) leads v(t) by 20° (b) v2(t) leads
v1(t) by 170° (c) y(t) leads x(t) by 9.24°
![Page 71: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/71.jpg)
Question 6: Find the phasors corresponding to the following signals:
(a) v(t) = 21 cos(4t − 15°)V (b) i(t) = −8 sin(10t + 70°) mA
(c) v(t) = 120 sin(10t − 50°) V (d) i(t) = −60 cos(30t + 10°) mA
Question 7: Transform the following sinusoids to phasors:
(a) −10 cos(4t + 75°) (b) 5 sin(20t - 10°)
(c) 4 cos (2t) + 3 sin (2t)
Question 8: Two voltages v1 and v2 appear in series so that their sum is v
= v1 + v2. If v1 = 10 cos(50t − π∕3) V and v2 = 12 cos(50t + 30°) V, find v.
71
Ans.6: (a) 21∟-15 ° (b) 8∟-160 ° (c) 120∟-140 ° (d) 60∟-190 °
Ans.7: (a) 10∟-105° (b) 5∟-100 ° (c) 5∟-36.87 °
Ans.8: 15.62 cos(50t-9.8°) V
![Page 72: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/72.jpg)
Question 9: A linear network has a current input 10 sin(ωt + 30°) A and a
voltage output -65cos(ωt+120°) V. Determine the associated impedance.
Question 10: If the waveform of a voltage has a form factor of 1.15 and
a peak factor of 1.5, and if the peak value is 4.5 kV, calculate the average
and the r.m.s. values of the voltage.
Question11: An alternating current was measured by a DC milliammeter
in conjunction with a full-wave rectifier. The reading on the milliammeter
was 7.0 mA. Assuming the waveform of the alternating current to be
sinusoidal, calculate: (a) the r.m.s. value; and (b) the maximum value of
the alternating current.
72
Ans.11: 7.8mA, 11 mA
Ans.10: 2.61kV, 3 kV
Ans.9: 6.5 Ω
![Page 73: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/73.jpg)
Question 12: An alternating current has a periodic time 2T. The current
for a time one-third of T is 50 A; for a time one-sixth of T, it is 20 A; and
zero for a time equal to one-half of T. Calculate the RMS and average
values of this current.
Question 13: A triangular voltage wave has a periodic time of (3/100)
sec. For the first (2/100) sec, of each cycle it increases uniformly at the
rate of 1000 V/s, while for the last (1/100) sec, it falls away uniformly to
zero. Find (a) its average value; (b) its RMS value; (c) its form factor.
73
Ans.12: 30 A RMS, 20 A average
Ans.13: 10 V, 11.55 V, 1.155
![Page 74: Introduction to Electrical Engineering L 13: SINGLE PHASE ...web.iitd.ac.in/~vivekv/ELL100/L13_VV.pdf1 in sine form: v 1 = −10 cos(ωt+ 50°) = 10 sin(ωt+ 50°−90°) = 10 sin(ωt](https://reader035.vdocuments.us/reader035/viewer/2022070216/611a6d2116ed6819eb237a4d/html5/thumbnails/74.jpg)
REFERENCES
[1] Edward Hughes; John Hiley, Keith Brown, Ian McKenzie Smith,
“Electrical and Electronic Technology”,10th Ed., Pearson Education
Limited, 2008.
[2] Alexander, Charles K., and Sadiku, Matthew N. O., “Fundamentals of
Electric Circuits”, 5th Ed, McGraw Hill, Indian Edition, 2013.
74