ac power analysis 3-phase
TRANSCRIPT
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AC Power Analysis 3-Phase
Prepared for
Electrical Engineering Laboratory II, ECE L302
by
Mohammed Muthalib
Center for Electric Power Engineering
Drexel University
(http://power.ece.drexel.edu) 1
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Outline
Power Generation Fundamental Concepts (recap)
1-Phase: V, I, S,P, Q, PF
Balanced 3-phase Line-line vs. line-neutral voltage 3-phase power
S3Φ, P3Φ, Q3Φ,
Why 3-phase? This weeks experiment Power lab safety
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Generation
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Nuclear plant Hydro plant
Coal plant Fossil fuel plant
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Generation
Conservation of energy
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Generation
Fossil Fuel: Burn fuel Steam Turbine Generator
Nuclear: Nuclear reaction Steam Turbine Generator
Hydro: P.E. of reservoir K.E. of water Turbine Generator
Wind: K.E. of wind rotational K.E. of blades in turbine Generator
Solar: Solar radiation semiconductor energy transfer Electron flow
Solar and wind require storage and AC/DC conversion
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Generation
Turbine – Generator Turbine provides mechanical torque to the rotor of the generator Stator has coils that react to the electro-magnetic field variations
6 http://dcacmotors.blogspot.com/2009/03/basic-generator.html
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Generation
3-phase generation Stator has 3 coils wound 120° out of phase
7
ECE Department, University of Minnesota http://www.ece.umn.edu/users/riaz/animations/alternator.html
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Fundamental Concepts
AC voltage and current Sinusoidal time varying waveforms
Phasor representation (time invariant)
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( ) ( )( ) ( )
peak V
peak I
V
I
v t V sin t
i t I sin t
voltage phase anglecurrent phase angle
= ω + θ
= ω + θ
θ −
θ −
V
I
jV
jI
peak
V V e
I I e
Where V and I are rms values
V (amplitud ) V
V
I
e 2
θ
θ
= ∠θ =
= ∠θ =
=
Voltage and current phasors (polar coordinates)
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Fundamental Concepts
Voltage and current waveforms
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Voltage and current phasors (polar coordinates)
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Fundamental Concepts
Instantaneous power: Product of v(t) and i(t)
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( ) ( )( ) ( )( ) ( ) ( )
( ) ( )
( ) ( )
( ) ( ) ( )
V
I
V I
V I
V I V I
v t 2 V sin t
i t 2 I sin t
p t v t * i t
2 V I sin t sin tuse trigonometric identity2sin usin v cos u v cos u vu t , v tp t V I cos V I cos 2 t
= ω + θ
= ω + θ
=
= ω + θ ω + θ
= − − +
= ω + θ = ω + θ
= θ − θ − ω + θ + θ
time invariant (constant)
time varying with frequency 2ω
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Fundamental Concepts
Instantaneous power
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( ) ( ) ( )p t v t * i t=
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Fundamental Concepts
Complex power: Is a representation of power in a complex vector space Denoted S with units of VA
|S| - apparent power
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2 2S P Q V I= + =
( )( ) ( )
( ) ( )
V I
*
jV I
V I V I
S VI *denotes complex conjugate
S V I V I eusing Euler's formulaS V I cos j V I sin
P jQ
θ −θ
=
= ∠ θ − θ =
= θ − θ + θ − θ
= +
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Fundamental Concepts
Real power: Real power = Average power
Denoted P with units of Watts Power absorbed by the resistive components of the system
Reactive power: Denoted Q with units of VAR Power absorbed by the reactive components of the system Example, Inductance and Capacitance
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( )AVG V IP P V I cos= = θ − θ
( )V IQ V I sin= θ − θ
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Fundamental Concepts
Power Factor: Is a measure of how effectively a system component draws real
power. It is the ratio between real power and apparent power
PF is presented as a real number between 0 and 1 with a leading/lagging denotation for the PF angle o Lagging - current angle lags the voltage angle, θV>θI
o Leading - current angle leads the voltage angle, θV<θI
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( )V IPPF cosS
= = θ − θ
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Fundamental Concepts
Power Factor: Which figure represents a load with a lagging PF?
o What kind of load has a lagging power factor? Which figure represents a load with a leading PF?
o What kind of load has a leading power factor?
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Fundamental Concepts
PF=1 indicates that all the power consumed in the system is real power. A load with PF=1 emulates a resister Reactive power draw is zero
Is PFC necessary? Why?
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Fundamental Concepts
PFC by injecting reactive power
Reactive power injection is done by adding capacitive and inductive loads to the system. Capacitive – supply reactive power Inductive – consume reactive power
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Balanced 3-phase
Balanced 3-phase circuit All components, loads, lines, etc. are assumed to be identical
Balanced 3Φ circuits are analyzed through a single phase equivalent analysis
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Balanced 3-phase
Balanced 3-phase voltages
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( )( )( )
an an
bn an
cn an
V 2 V sin t 0 Volts
V 2 V sin t 120 Volts
V 2 V sin t 120 Volts
= ω + °
= ω − °
= ω + °
( )( )( )
a a I
b a I
c a I
I 2 I sin t 0 Amps
I 2 I sin t 120 Amps
I 2 I sin t 120 Amps
= ω + θ + °
= ω + θ − °
= ω + θ + °
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Line-line voltage
Line-line voltage Voltage measure between phases, Vab, Vbc, Vca
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( )( ) ( )
ab an nb
a
ab an b
n bn
n
an
ab an
V V cos 30 V cos 30
3 V
V V VV
V V 30
V= +
= +
= ° + °
=
∠ = ∠ +
−
°
an
bn
ab
V 120 0 VV 120 120 VV 208 30 V
= ∠ °
= ∠− °
= ∠ °
Example:
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3-phase power
Real Power P3Φ= PA+ PB+ PC
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( )( )( )
( ) ( )( )( )
A A A V,A I,A
B B B V,B I,B
C C C V,C I,C
V,B V,A I,B I,A
V,C V,A I,C I,A
A B C A B C
B A A V,A I,A
A A V,A I,A
A
P V I cos Watts
P V I cos Watts
P V I cos Watts
120 , 120120 , 120
V V V , I I I
P V I cos 120 120
V I cos
P
= θ − θ
= θ − θ
= θ − θ
θ = θ − ° θ = θ − °
θ = θ + ° θ = θ + °
= = = =
= θ − ° − θ − °
= θ − θ
=
Balanced 3-phase voltage phasor
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3-phase power
Real Power
Reactive power
Complex Power
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( )( )
3 A B C
3 an a V,A I,A
3 LL L V,A I,A
P P P P Watts
P 3 V I cos Watts
P 3 V I cos Watts
Φ
Φ
Φ
= + +
= θ − θ
= θ − θ
( )( )
3 A B C
3 an a V,A I,A
3 LL L V,A I,A
Q Q Q Q VAr
Q 3 V I sin VAr
Q 3 V I sin VAr
Φ
Φ
Φ
= + +
= θ − θ
= θ − θ
Balanced 3-phase voltage phasor ( )*3 A A
3 3 3
S 3V I VAS P jQ VA
Φ
Φ Φ Φ
=
= +
LL ab anV V 3 V= =
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Why 3-phase?
Electrical energy has to be transmitted/distributed over long distances Cables are heavy (engineering problem to string up in the air) and
lossy
23
https://www.osha.gov/SLTC/etools/electric_power/illustrated_glossary/transmission_lines.html
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Why 3-phase?
Neutral Current (balanced 3-Φ)
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( )( )( )
( ) ( ) ( )( )( ) ( ) ( )( )( ) ( ) ( )( )( ) ( ) ( )( )
a a I
b a I
c a I
n a b c
a I I I
a I I I
a I I
a I I
I 2 I 0 Amps
I 2 I 120 Amps
I 2 I 120 Amps
I I I I
2 I cos cos 120 cos 120
j 2 I sin sin 120 sin 120
2 I cos 2cos cos 120
j 2 I sin 2sin cos 120
0
= ∠ θ + °
= ∠ θ − °
= ∠ θ + °
= + +
= θ + θ − ° + θ + °
+ θ + θ − ° + θ + °
= θ + θ − °
+ θ + θ − °
=
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Why 3-phase?
Transmission of power in balanced 3-phase can be done without a neutral conductor
More efficient and economical since: less losses from conductor Less cost with respect to material and construction
NOTE: Distribution systems are unbalanced and require a neutral
conductor Connect back to local electrical substations Supplied through distribution transformers
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Electrical Supply
Transmission/Distribution
26 http://www.avalon-energy.com/sample.aspx?C1=28
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Electrical Supply
Residential connection
27
http://waterheatertimer.org/See-inside-main-breaker-box.html
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Lab Experiment
Simulating a 2-bus power system (Transmission) Measure voltages and currents; calculate power Observe effects of loading
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Lab Experiment
Test system with 3 load types Resistive Load (4 – 20 bulbs) RL (20 bulbs + 0 - 5 inductors) RC (20 bulbs + 0 - 4 capacitors) Nonlinear Load
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Lab safety
You will be dealing with voltages and currents of 120V and 25A
Adherence to safety and conduct guidelines is imperative Please read the Power Lab Safety document Please watch lab safety video
http://power.ece.drexel.edu/videos/
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Thank you
Questions are most welcome