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J. Wang
4/3/2011
1
Topic 1: Ac power and three phase concepts
ECE341 Energy Conversion (Spring 2011)
s
Ac power, phasor, power factor
s
Active and reactive power
s
Capacitor vs. Inductor
s
Why three phase
s
Wye and Delta connection
s
Per phase analysis
s
Unbalanced three phase
Facts
J. Wang
4/3/2011
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Ohio’s “renewable portfolio standard,” which originated in the Republicanled
state Senate in 2008, requires that
25 percent of Ohio’s energy come from
renewable sources by 2025
, and
that half of that renewable portion be
created instate.
Its passage — along with grants from a state program known
as the Ohio Advanced Energy Fund — essentially jumpstarted an alternative
energy industry in the state.
Already, the impact is visible across Ohio. Farmers, homeowners and small
companies put up solar panels and wind turbines; several largescale
renewable projects, including a
12megawatt solar field in northern Ohio
and planning for a
50megawatt field in the southeast, got underway
; wind
companies moved ahead with plans for
five new wind farms around the
state and five turbines in Lake Erie
; hundreds of companies either started up
or got involved in the manufacturing supply chain for renewable energy; the
city of Toledo emerged as a hub for research and manufacturing of thinfilm
solar cells.
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Notation  Power
J. Wang
4/3/2011
3
• Power: Instantaneous consumption of energy
• Power Units
Watts
= voltage x current for
dc
(W)
kW
–
1 x 10
3
Watt
MW
–
1 x 10
6
Watt
GW
–
1 x 10
9
Watt
• Installed U.S. generation capacity is about
900 GW ( about 3 kW per person)
Notation  Energy
J. Wang
4/3/2011
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• Energy: Integration of power over time; energy is what people
really want from a power system
• Energy Units
–
Joule = 1 Wattsecond (J)
–
kWh
= Kilowatthour (3.6 x 10
6
J)
–
Btu
= 1055 J; 1 MBtu=0.292 MWh; 1MWh=3.4MBtu
– One gallon of gas has about 0.125 MBtu (36.5 kWh); one
gallon
ethanol as about 0.084 Mbtu (2/3 that of gas)
• U.S. electric energy consumption is about 3600 billion kWh
(about 13,333 kWh per person)
3
Symbols in the Ac Circuits
J. Wang
4/3/2011
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t
ϖ
sin
2
100
Phase Angles in Ac circuits
J. Wang
4/3/2011
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• Angles need to be measured with respect to a
reference  depends on where we define t=0
• When comparing signals, we define t=0 once and
measure every other signal with respect to that
reference
• Choice of reference is arbitrary – the
relative
phase
shift is what matters
• Relative phase shift between signals is independent
of where we define t=0
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Example: Phase Angle Reference
J. Wang
4/3/2011
7
•
Pick the bottom wave as the reference
1
sin
4
v
V
t
π
ϖ
=
+
( 29
2
sin
0
v
V
t
=
+
( 29
1
sin
0
v
V
t
=
+
2
sin
4
v
V
t
=

1
2
4
θ

=
1
2
4

=
•
Or pick the top as the reference it does not matter!
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This note was uploaded on 04/01/2012 for the course ECE 341 taught by Professor Keyhani during the Fall '08 term at Ohio State.
 Fall '08
 Keyhani

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