[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx 1 Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected] Engineering 43 Thevenin/Norton AC Power
Feb 26, 2016
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx1
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engineering 43
Thevenin/NortonAC
Power
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx2
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Thevenin’s Equivalence Theorem Resistance to
Impedance Analogy
LINEAR C IRC U ITM ay contain
independent anddependent sources
with their co ntro ll ingvariablesPART A
LINEAR C IRC U ITM ay contain
independent anddependent so urces
with their contro ll ingvariablesPART B
a
b_Ov
i
LINEAR C IRC U IT
PART B
a
b_Ov
i
THR
THv
PART AThevenin Equivalent Circuit for PART A
OOv V
IiTHTHV V
THTHR Z
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx3
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
AC Thevenin Analysis Same Circuit,
Find IO by Thevenin Take as “Part B” Load
the 1Ω Resistor Thru Which IO Flows
Now Use Src-Xform The Thevenin Ckt
VjjA
x
x
)22()1(02
VV
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx4
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
AC Thevenin Analysis cont. The Xformed
Circuit Another
SourceXform
Find ZTH by Zeroing the 8+j2V-Source
Now the Combined 8+j2 Source and all The Impedance are IN SERIES• Thus VOC Determined by
V-Divider
j28
2610)28(
)1()1(1 jj
jjj
OC
V
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx5
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
ReDraw the Voltage Divider
The V-Divider Formula:
OV1Z
2Z
212 ZZZVV SO
2
22882
128)1()1(
1282jjjjj
jjjjOC
V
jjjjjjjOC 35
2610
22828
22288 2
V
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx6
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
AC Thevenin Analysis Find ZTH by Zeroing the
8+j2 V-Source
IO is Now Simple
So The Thevenin Equivalent Circuit
122
111
1111
)1(||)1(
2j
jjjjjj
TH
TH
TH
Z
Z
Z
)(235
111
AjO
OC
TH
THO
I
VZ
VI
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx7
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Norton’s Equivalence Theorem Resistance to
Impedance Analogy
OOv V
IiNNi I
NNR Z
LINEAR C IRC UITM ay contain
independent anddependent sources
with their co ntro ll ingvariablesPART A
LINEAR C IRC U ITM ay contain
independent anddependent so urces
with their contro ll ingvariablesPART B
a
b_Ov
i
LINEAR C IRC UIT
PART B
a
b_Ov
i
NRNi
PART ANorton Equivalent Circuit for PART A
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx8
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
AC Norton Analysis Same Circuit,
Find IO by Norton Take as the “Part B”
Load the 1Ω Resistor Thru Which IO Flows
Possible techniques to Find ISC:• Loops or Nodes• Source Transformation• SuperPosition
Choose Nodes
Shorting the Load Yields Isc= IN
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx9
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
AC Norton Analysis cont Short-Ckt Node On The
Norton Circuit
Use ISC=IN, and ZN to Find IO
• See Next Slide
As Before Deactivate Srcs to Find ZN=ZTH
)(1
281
0602 Ajj
jSC
I
1)1(||)1( jjZTH
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx10
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
AC Norton Analysis cont.2 The Norton
Equivalent Circuitwith LoadReattached
Same as all the Others
Find IO By I-Divider
2
351
44
11
14
14
1111
22
2 jj
jjj
jj
jj
jj
O
O
SC
NSCO
I
I
IZ
II
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx11
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Outline – AC Steady State Power Instantaneous Power Concept
• For The Special Case Of Steady State Sinusoidal Signals
Average Power Concept• Power Absorbed Or Supplied During an
Integer Number of Complete Cycles Maximum Average Power Transfer
• When The Circuit is in Sinusoidal Steady State
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx12
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Outline – AC SS Power cont. Power Factor
• A Measure Of The Angle Between the CURRENT and VOLTAGE Phasors
Power Factor Correction• Improve Power Transfer To a Load By
“Aligning” the I & V Phasors Single Phase Three-Wire Circuits
• Typical HouseHold Power Distribution
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx13
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Instantaneous Power Consider in the Time
Domain a Voltage Source Supplying Current to an Impedance Load
Now Recall From Chp1 The Eqn for Power
In the General Case
vip
iM
vM
tItitVtv
cos)(cos)(
Then at any Instant for Time-Varying Sinusoidal Signals
ivMM ttIV
titvtp
coscos
Now Use Trig ID
)cos()cos(21coscos yxyxyx
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx14
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Instantaneous Power cont. Rewriting the Power Relation for Sinusoids
Examine the TWO Terms of the Power Equation
)2cos(2
)cos(2
)(
)2cos()cos(2
)(
ivMM
ivMM
ivivMM
tIVIVtp
tIVtp
• The First Term is a CONSTANT, or DC value; i.e. There is No Time Dependence
• The Second Term is a Sinusoid of TWICE the Frequency of the Driving Source
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx15
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example For the Single Loop Ckt Use Phasors To find I
Assume
302302604 AV
ZVI
302604
60cos4)(
ZV
andVor
tVtv
To Obtain the Time Domain current Take the Real Part of the Phasor Current
30cos22Re302Re)( 30
tAmptieeti tj
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx16
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example cont Thus for This case In the Power Equation
Or
30602cos3060cos4
)(tW
titvtp
306024
iv
MM AIVV
The Amplitudes and Phase Angles
902cos446.3)( tWWtp
See Next Slide for Plots• v(t)• i(t)• p(t) = v(t)•i(t)
60cos4 tV j732.1
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx17
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Sinusoidal Power Example 9.1
-4
-2
0
2
4
6
8
0.000 0.003 0.006 0.009 0.012 0.015 0.018 0.021 0.024 0.027 0.030
Time (S)
v(t)
or i
(t) o
r p(t)
v(t) (V) i(t) (V) P(t) (V)
file =Sinusoid_Lead-Lag_Plot_0311.xls
p(t) Calculated by p(t)=v(t)•i(t)
Avg-p = 3.46W
Max-p = 7.46W
NEGATIVE POWER – Inductive Load can Release stored Energy to the Circuit
p = 0 if either i or v are zero
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx18
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Average Power For ANY Periodic Function, It’s Average Value Can be
calculated by Integrating Over at Least ONE COMPLETE PERIOD, T, and Then Dividing the Integrated Value by the Period
Then the Average POWER for Electrical Circuits With Sinusoidal Excitation
timeBaseLinearbitary an )(10
0
0
tdttxT
XTt
t
0
0
0
0
0
0
coscos1
11
tT
t ivMM
tT
t
tT
t
dtttIVT
dttitvT
dttpT
P
And Recall 2T
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx19
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Average Power cont Also For ANY Periodic Function, the Average value May
be Calculated over any INTEGER number of periods. This is, in Fact, How most Electrical Power Values are MEASURED. Mathematically:
Now Sub Into the Average Power Integral The Simplified (n =1) Expression for Instantaneous Power
0
0
coscos1 tnT
t ivMM dtttIVnT
P
0
0
0
0
0
0
)2cos(2
1)cos(2
1
)2cos()cos(2
1
tT
t
tT
t ivMM
ivMM
tT
t ivivMM
dttIVT
dtIVT
P
dttIVT
P
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx20
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Average Power cont.2 Examine the Two Terms from the Average Power Eqn
Thus the First Term is a CONSTANT that depends on the Relative Phase Angle
Also by Trig: cos(−) = cos()• Thus for the First Term It Does NOT Matter if the Current
LEADS or LAGs the Voltage
)cos(2
cos2
1
1)cos(2
1)cos(2
1
11
1
0
0
0
0
0
0
ivMMtT
tivMM
tT
tivMMtT
t ivMM
IVPtIVT
P
dtIVT
dtIVT
P
viiviviv coscoscoscos
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx21
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Average Power cont.3 The Second Term from the Average Power Eqn
• As the The Integral of a sin or cos over an INTEGER number of periods is ZERO
Thus the Average Power is Described by the FIRST TERM ONLY
0)2cos(2
1 0
02
tT
t ivMM dttIV
TP
cos2
)cos(2
)cos(2
MM
viMM
ivMM
IVP
IVPIVP
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx22
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Resistive & Reactive Power For a Purely
RESISTIVE Circuit There is NO Imaginary Component of the Impedance and thus no Phase Shift Between i & v. So for sinusoids
For A Purely REACTIVE Circuit i&v are ±90° out of phase• So then Avg Power eqn
Thus the Resistors Absorb, or Dissipate, Power (as Heat) only
2MM
resIVP
!090cos2
MMreact
IVP Thus Purely reactive
Impedances absorb NO Power on Average• They STORE Energy
over one Half-Cycle, and then RELEASE it over the NEXT
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx23
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Avg Power For This Circuit The Power Parameters
FIND: The Dissipated Power
Use Phasor Algebra to Find the Current
)(1554.3458284.2
601022
6010 Aj
V
I
1560
54.310
iv
MM AIVV
The Power Calculation
WWP
AVP
IVP ivMM
5.1245cos7.17
1560cos2
54.310
)cos(2
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx24
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Avg Power cont Since Only the Resistor
Dissipates Power, Check the Previous Calc by using Pres=vres•i
Alternatively by OHM
Use Phasors for VR
WWP
AVP
IVP iv
MRM
5.12200.25
1515cos2
54.307.7
)cos(2,
RV
)(1507.7601022
2 VVVjR
V
For a Resistor the Current & Voltage WITHIN the Resistor are IN-PHASE; thus
1507.71554.32 VARR IV
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx25
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Cap Circuit For This Circuit Find the Total
Impedance Across the V-Source
Find The Dissipated Power in Each Resistor
Start by Finding The Current In the Ckt Branches that Contain the Resistors
Then The total Current I
I
2I
565.264721.44524
6.713.2544
168844)4(42
jjj
jj
TZ
6.8668.26.2647.4
6012
A
V
TZVI
• i(t) LEADS vS(t)
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx26
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Cap Circuit cont
So the 2Ω Resistor Power Dissipation
Then the Power Absorbed by the 4Ω R
I
2I
WRIP M 20.768.2221
21 22
2
6.4190.1
6.8668.24524
90444
42 II
jj
WP
WP
20.7
)(90.1421
4
24
Now Find I2 by Current Divider
2
,
21
0cos21
cos2
MR
MMR
ivMRM
R
RIP
IRIP
IVP
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx27
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Maximum Avg Power Transfer Recall From the Study
of Resistive Ckts The Criteria for Max Power Xfer to a Load Resistor
Where RTH is the Thevenin Equivalent Resistance for the Driving Ckt
Now Try to Develop a Similar Relationship for Impedances
Consider This General Thevenin Equivalent Ckt
THL RR pwrmax,
For This Ckt the Avg Pwr Delivered to the Load
)cos(21
LL ivLLL IVP
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx28
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Max Avg Power Transfer cont Now by Phasors
WhereLTH
LOCL
LTH
OCL
ZZZVV
ZZVI
Now By Euler Rln Recall
THTHTH
LLL
jXRjXR
ZZ
ZVVZ
VZZV
andMM
zVMM
ZV
ZV
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx29
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Max Avg Power Transfer cont.2 Then the Load Voltage
& Current Magnitudes
Similarly Also by Euler
OCTHL
LL
THL
LL
VZZ
ZVor
OCV
ZZZV ||
L
LL Z
VI And
LIV
LVIVL
LLILLLL
Z
ZV
ZVI
LL
LLL
L
But
ZVI
LLLLLL RXZjXR tanZ Now a Useful Trig ID
LLLIV
IVIV
RXZLL
LLLL
tantanBut
tantantan11cos 2
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx30
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Max Avg Power Transfer cont.3 ReArrange Trig ID to
Find
Again the Power Eqn Or
Substitute to Find And
22
2
)cos(
1
1)cos(
LL
LIV
LL
IV
XR
RRX
LL
LL
)cos(21
LL ivLLL IVP
2221
LL
L
L
OCTHL
L
OCTHL
LL
XR
RZ
VZZ
Z
VZZ
ZP
222
2
21
LL
L
THL
OCLL
XR
RZZVZP
222 )()(
)()(
THLTHLTHL
THLTHLTHL
XXRRZZ
XXjRR
ZZ
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx31
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Max Avg Power Transfer cont.4 Finally The Power Eqn
Restated
Now To Maximize the Power Transfer, Set the Partial Derivatives to 0
at LAST The Optimized Load
• The Complex Conjugate And the Power
Transferred at Optimum
22
2
)()(21
THLTHL
LOCL XXRR
RVP
THL
THL
L
L
L
L
RRXX
RPXP
0
0
*TH
optL ZZ
TH
OCL R
VP42
1 2max
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx32
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Max Avg Power Transfer cont.5 Check
At the Max Condition
22
2
)()(21
THLTHL
LOCL XXRR
RVP
THL
THL
L
L
L
L
RRXX
RPXP
0
0
TH
OCL
TH
OC
TH
THOC
TH
THOCL
THTHTHTH
THOCL
RVP
RV
RRV
RRVP
XXRRRVP
8
8421
0)2(21
)()(21
2max
2
2
2
22
2max
22
2max
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx33
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Maximum Power Xfer Find ZL for the
Maximum Power Xfer And The Max Pwr Xfer
Recall The Max Power Criteria
Need to find • VOC = VTH
• RTH
*TH
optL ZZ
THOCL RVP 82max
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx34
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Max Pwr Xfer cont. Remove Load and Find
VOC by Loop Current And by Ohm’s Law in
the Frequency Domain
Using KVL on the Loop
OCV
I
56.71974.1861812)1(92
0122
Vjjj
jOC IV
4573.12)1(98
)22(36022012024
jjj
I
II THZ
Find ZTH by Source Deactivation (Zeroing)
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx35
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Max Pwr Xfer cont.2 Then ZTH
Taking The Conjugate
THZ
22
42)2||2(2jjjjjTHZ
)(18
8822
4
jj
jTHZ or
)(1 joptLZ
Then The Power Transferred to this Load
W
WV
RVP THOCL
458
36018
974.18
82
2max
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx36
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Power Factor Consider a Complex
Current Thru a Complex Impedance Load
The Current and Load-Voltage Phasors (Vectors) Can Be Plotted on the Complex Plane
By Ohm & Euler
in the Electrical Power Industry θZ is the Power Factor Angle, or Simply the Phase Angle
LZiMI
vMV
iv
VIz
ivz
izv
or
IZV
ZIV
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx37
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Power Factor cont The Phase Angle Can
Be Positive or Negative Depending on the Nature of the Load
Typical Industrial Case is the INDUCTIVE Load• Large Electric Motors are
Essentially Inductors Now Recall The
General Power Eqn
Measuring the Load with an AC DMM yields• Vrms
• Irms
Zrmsrmsivrmsrms
ZMM
ivMM
IVIVP
IVIVP
cos)cos(
cos22
)cos(21
0MVV
e)(capacitivleadscurrent
090 z
)(inductivelagscurrent
900 z
ZZZVI
0
V is the BaseLine
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx38
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Power Factor cont.2 The Product of the
DMM Measurements is the APPARENT Power
The Apparent Power is NOT the Actual Power, and is thus NOT stated in Watts.• Apparent Power
Units = VA or kVA
Now Define the Power Factor for the Load
Some Load Types
rmsrmsapparent IVP pfIVP
PPpf
rmsrmsactual
zivapparent
actual
and
cos)cos(
inductive pureinductiveor lagging
resistivecapacitiveor leading
capacitive pure
90900
010
0109010
900
z
z
z
pf
pf
pf
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx39
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
pf – Why do We Care? Consider this
case • Vrms = 460 V• Irms = 200A• pf = 1.5%
Then• Papparent = 92kVA• Pactual =1.4 kW
This Load requires The Same Power as a Hair Dryer or Toaster
However, Despite the low power levels, The WIRES and CIRCUIT BREAKERS that feed this small Load must be Sized for 200A!• The Wires would be nearly an INCH in
Diameter
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx40
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Power Factor The Local Power
Company Services this Large Industrial Load
Find Irms by Pwr Factor
Then the I2R Loses in the 100 mΩ line
Improving the pf to 94%
1.0
kW100010V5
Power company
rmsrms
rmsrms
rmsrms
VkWIVpfPIpfIVP
480707.0100
22
22 1
pfVRPRIPrms
linelinermslosses
234.4
)(707.01
4801.010)707.0( 22
10
kW
WpfPlosses
13.134.4
)(94.01
4801.010)94.0( 22
10
kW
WpfPlosses
kWkWPsaved 77.334.487.0
I lags V
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx41
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example - Power Factor cont For This Ckt The
Effect of the Power Factor on Line Losses
1.0
kW100010V5
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx42
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Complex Power Consider a general Ckt
with an Impedance Ld Mathematically
For this Situation Define the Complex Power for the Load:
Converting to Rectangular Notation
*rmsrmsIVS
Ziv
ivrmsrms
irmsvrms
irmsvrms
IVIVIV
:recall
*
SSS
)sin()cos( ivrmsrmsivrmsrms IVjIVS
PActive Power
QReactive Power
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx43
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Complex Power cont Thus S in Shorthand Alternatively,
Reconsider the General Sinusoidal Circuit
S & Q are NOT Actual Power, and Thus all Terms are given Non-Watt Units• S→ Volt-Amps (VA)• Q → Volt-Amps,
Reactive (VAR) P is Actual Power and
hence has Units of W
First: U vs. Urms
jQP S
rmsrms
Mrms
M
UUU
U
U
U
2and
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx44
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Complex Power cont.2 Now in the General Ckt
By Ohm’s Law
In the Last Expression Equate the REAL and Imaginary Parts
And Again by Ohm
iviv
rmsrms
ivrms
rms
irms
vrms
rmsrms
jZZj
soZIV
IV
IV
sincosImRe
and
ZZZ
Z
IVZ
Z
Z
iv
iv
Z
Z
Imsin
Recos
ZVI
ZV
ZV
rmsrms
irms
iv
vrmsrms
rmsrms
So
I
ZVI
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx45
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Complex Power cont.3 And by Complex Power
Definition
Using the Previous Results for P
Similarly for Q
ivrmsrms
ivrmsrms
IVQIVP
jQP
sinImcosRe
then
SS
S
RIIP
IZV
ZIVP
rmsrms
rmsrms
rmsrms
22 Re
Re
ReRe
Z
Z
ZS
XIIQ rmsrms22 Im Z
So Finally the Alternative Expression for S
ZS 2rmsI
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx46
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Complex Power Triangle The Expressions for S
Plotting S in the Complex Plane
From The Complex Power “Triangle” Observe
ZSS
2rmsI
jQP
PQ
iv tan Note also That Complex
Power is CONSERVED
kkrmsktot I ZSS 2,
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx47
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example - Complex Power For the Circuit At Right
• Zline =0.09 Ω + j0.3 Ω• Pload = 20 kW• Vload = 2200°• pf = 80%, lagging• f = 60 Hz → ω = 377s-1
Lagging pf → Inductive
From the Actual Power
Thusinductive
capacitive
pfSP iv )cos(||Re SS
kVAkWpfPSL 25
8.020
And Q from Pwr Triangle
kVAR15222 QPSQ L
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx48
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example - Complex Power cont Then SL
Recall the S Mathematical Definition
Alternatively
87.36251520 kVAkVAjLS
*LLL IVS
Note also that [U*]* = U In the S Definition,
Isolating the Load Current and then Conjugating Both Sides
)(86.3664.1130220
87.3625 **
AV
kVA
L
L
LL
IVSI
)(18.6891.90220
000,15000,20 *
Aj
j
L
L
I
I
Lagging
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx49
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example - Complex Pwr cont.2 Now Determine VS
Then VS Then The Phase Angle
To find the Src Power Factor, Draw the I & V Phasor Diagram
)(220)18.6891.90)(3.009.0(0220)3.009.0(
Vjjj
S
LS
LlineS
VIV
VVV
86.453.24914.2163.248
22014.2163.28
rmsS
S
S
Vjj
VVV
86.4
86.36
SV
LI
7464.0
72.41coscosalso and
Load Inductive V Lags I 72.4186.3686.4
pfpf iv
iv
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx50
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example - Complex Power kVAR For the Circuit At
Right, Determine• Real & Reactive Power
losses in the Line• Real & Reactive Power
at the Source Lagging pf → Inductive
From the Actual Power
Thusinductive
capacitive
kVAkWpfPSL 62.47
84.040
And by S Definition
laggingpfkW
84.040
1.0 25.0j
pfSP iv )cos(||Re SS
rmsL
LL A
VSI )(45.216* VIS
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx51
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example - Complex kVAR cont. Also from the S
Relation & Pythagorus
Now the PowerFactor Angle Then for Line Loses
Quantitatively
laggingpfkW
84.040
1.0 25.0j
)(839,25|||| 22 VARPLL SQ
86.3284.0acosiv
pf = cos(θv − θi); hence
2
** )(
Lline
LLlinelinelineline
IZ
IIZIVS
VAjj
line
line
117134685)45.216)(25.01.0( 2
SS
I Lagging V
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx52
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example - Complex kVAR cont.2 Find Power Supplied
by Conservation of Complex Power
Then to Summarize the Answer• Pline = 4.685 kW• Qline = 11.713 kVAR• PS = 44.685 kW• QS = 37.552 kVAR
laggingpfkW
84.040
1.0 25.0j
kVAkVAj
j
jjSup
04.4037.58 552.37685.44
839.25713.1140685.4
839.2540713.11685.4S
LoadlineSupplied SSS
In this Case
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx53
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Power Factor Correction As Noted Earlier, Most
Industrial Electrical Power Loads are Inductive• The Inductive
Component is Typically Associated with Motors
The Motor-Related Lagging Power Factor Can Result in Large Line Losses
The Line-Losses can Be Reduced by Power Factor Correction
To Arrive at the Power Factor Correction Strategy Consider A Schematic of a typical Industrial Load
Intentionally Added
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx54
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Power Factor Correction cont. Prior to The Addition
of the Capacitor
For The Capacitive Load
)cos(||
oldold
oldoldoldoldold
pfSjQPS
22
2
C
Im
90
LL
CCC
LC
LLLC
L
CVC
CVIQ
CVI
CVCj
Z
VZVI
After Addition of the Capacitor
)cos(||
newnew
newnew
Coldold
Coldnew
pf
jQjQPS
SSS
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx55
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Power Factor Correction cont.2 Find θnew
• Cap is a Purely REACTIVE Load
The Vector Plot Below Shows Power Factor Correction Strategy
old
new
old
Coldnewtan
PQ
PQQ
Use Trig ID to find QC to give desired θnew
2tan1
1cos
1cos
1
new2
old
Cold
PQQ
QL
QC
QL-QC
P
Qnew
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx56
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Trig ID Digression Start with the ID
2tan11cos
Solve for tan
old
Coldnewtan
PQQ
Recall tanθnew
1cos
1
new2
old
Cold
PQQ
Or
new
new2
new2
new2
new2
new2
new2
old
Cold
coscos1
coscos1
coscos
cos1
P
But: cosθnew = pfnew
new
new
pfpf 2
new
1tan
1cos
1tan 22
Substituting
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx57
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example pf Correction Kayak Centrifugal
Injection-Molding Power Analysis• Improve Power Factor
to 95%
Find Sold
Now Qold
Adding A Cap DoesNOT Change P• Use Trig ID to Find Tan(new)
And by S Relation
laggingpfVkW rmsL
8.00220,50
Roto-molding
process
pfSSP iv )cos(Re S
kVAkWpfPSold 5.62
80.050
)(5.37|||| 22 kVARPoldold SQ
329.01
tan95.0cos2
new
newnewnewnew pf
pfP
Q
kVARPQP
Qnew
new 43.16329.0
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx58
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example pf Correction cont Then the Needed QC
Recall The Expression for QC
laggingpfVkW rmsL
8.00220,50
Roto-molding
processkVAQQQQ
C
newoldC
07.2143.165.37
CVQ LL 2CC |||| IV
Then C from QC
FFCVQC
L
C
1155)(001155.0)220()602(
1007.212
3
2
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx59
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
All Done for Today
PowerFactor
Correction
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx60
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
WhiteBoard Work
Let’s Work Problem similar to P5.78• Determine at the input
SOURCE – Voltage & Current– Complex Power– Δθ & pf
19V220 rms
60 kVA
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx61
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx62
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx63
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx64
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx65
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx66
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx67
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx68
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx69
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx70
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx71
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx72
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx73
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx74
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
WhiteBoard Work
Z L1 20 V
2 j1
- j2
2 I x
I x
F ig u re P 9 .3 2
Let’s Work This Nice Problem
Find ZL for Pav,max, & the value of Pav,max
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx75
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Use Nodal Analysis
to Find VO
The KCL at Node-1
Subbing for V1 Yields
Now KCL At VO
1V
0212
3012 1111
jjOVVVVV
O
OO
jj
VV
VVV
1
01
1
1
Multiply Node-1 KCL by 2j to Obtain
0)(22)3012( 1111 Ojj VVVVV
Factoring out VO Yields 3012901))1)(31(2( Ojj V
3012)1)(221(2 jjjj OO VV
75121.245657.5
1201244
12012
Vj
O
O
V
V
Isolating VO
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx76
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Alternative This Time Use Thevenin
to Find VO
Take Cap & Res in Series as the Load Find VOC by V-Divider
Deactivate V-Src to Find ZTH
2.06.062
62462
4232
342||1||2
22
j
jjj
jj
jj
TH
TH
TH
Z
Z
Z
3012)2||1(2
2||1j
jOCV
30122)21(2
2jj
jOCV
435.48795.33112012
6212024
Vjj
OC
OC
V
V
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx77
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example Alternative cont. Now Apply the Thevenin
Equivalent Circuit to the Load
Calculate VO By V-Divider
+-OCV
THZ 1j
1
0V
00.75121.2435.48795.3565.26559.0
8.06.11
12.06.01
11
VV
j
jj
jZ
O
O
OCO
OCO
OCTH
O
VV
VV
VV
VV
2.06.0 j
Same as Before
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx78
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
P5.57 Graphics
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx79
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
P5.81 Graphics