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Esc201: Introducton To Electronics: Sinusoidal Steady State Analysis

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ESc201 : Introducton to Electronics

Sinusoidal Steady state Analysis

Dept. of Electrical Engineering


IIT Kanpur

1
Recap
Canonical Form x(t )  xm cos(t   )
Phase difference is usually considered between -180 to 180o

2
Average Power Vrms
Vrms 
Vm Vm2
pavg  pavg 
R 2 2R
Im 1 2
I rms  pavg  Im R
2 2

Phasor
v(t )  Vm cos(t   ) Vm 
2
Recap Complex Impedances
Inductor

VL  I L  Z L Z L  j L

3
Resistor R

v(t)

v(t )  VM cos(t   ) i (t )  VM cos(t   )


R
VM
VR  VM  IR  
R
VR
IR 
R
4
Example-5 i(t) L=0.1H R=50

v(t)

v(t )  2 cos(200t  45) V   200 rad/s

j20 50

Z L  j L

VS  245 V 5
Example-5 contd.
50+j20
Zeq

VS  245 V

245 245
I    0.03723.2 A
50  j 20 53.8521.8

i (t )  0.037 cos(200t  23.2) A

6
j20 50

VS  245 V

50
VR  2 45  V
50  j 20

Concept of voltage or current division can be used as before

7
Capacitor
v(t )  VM cos(t   )

dvc
ic  C
dt

i(t )   CVM sin(t   )


i(t )  CVM cos(t    90 ) o

VC  VM  I C  CVM   90
In a capacitor, current leads voltage by 900 8
Capacitor
VC  VM 

I C  CVM   90

I C  C90 VM 

I C  jCVC

1 1
VC  I C  ZC ZC  j
jC C

9
10
Example-6

11

12
A

13
V

VS  10030

I  0.707  15

14
Example-7

15
V

 V

16
Currents Z RC  50  j 50 

A
A
17
Example-8

18
19
Example-9

20
21
Example-10

22
23
25
Superposition Theorem is also applicable for independent
sinusoidal sources
26
27
Example-11

28
29
Power dissipation in RLC Circuits
For Resistance T
v (t ) 2 1 v(t ) 2
0 R dt
R
p pavg 
R T
v(t) 2
Vrms
pavg 
R
Vm
Vrms 
2

pavg  I rms
2
R
Im
I rms 
2 30
L

v(t)

pavg  0
31
C

v(t)

pavg  0

32
General Rule v(t )  VmCos(t )
i(t )  I mCos(t   )

T
1
p
T  v(t )  i(t )dt
0

For a resistor PF = 1, while for inductor and capacitor it is 0


1 1
j L   L 90 ;  j    90
C C
 is phase difference between voltage and current 33
Find the average power drawn from the supply

0.1
I Rrms   0.071
Where is this power dissipated? 2

P  VRrms  I Rrms cos   I 2


Rrms  R  0.5W 34
Average power dissipated through the inductor
VL  j100  I 14.14  45
    45  135  90
P 0
1
PI  R  0.5W P  I Rrms R 
2 2 2
Rrms
IR R
2 35
Should a Power company charge a person even though power
consumed is zero?

L Power
v(t)
Meter

pavg  0
Rwire

L Power
v(t)
Meter
Power is dissipated and
somebody has to pay for it.
Rwire 36

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