ELECTRIC CIRCUITS ECSE2010 Spring 2003 Class 25

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ELECTRIC CIRCUITSECSE-2010Spring 2003Class 25

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ASSIGNMENTS DUE

• Today (Thursday)
• Activities 25-1, 25-2 (In Class)
• Next Monday
• Homework 9 Due
• Activities 26-1, 26-2 (In Class)
• Next Tuesday/Wednesday
• Experiment 8 Report Due
• Activities 27-1, 27-2 (In Class)

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REVIEW

• Bridge Circuits are circuits used to accurately
  measure R, L and Cs
• Wheatstone Bridge Measures R (AC or DC)
• Maxwell Bridge Measures L (AC Only)
• Balance the Bridge gt Determine Ru, Zu
• Practiced with Experiment 8

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AC POWER

• To date, we have been concerned with finding
  v(t), i(t) in AC SS
• Find V, I gt Write down v(t), i(t)
• Now focus on AC Power Calculations
• RMS Values
• AC Power Systems
• Power Factor Correction

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RMS VALUES
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RMS VALUES
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RMS VALUES

• RMS Value is a Scalar
• Not a Phasor!
• Convenient way to describe Current, Voltage in AC
  Steady State
• Convenient way to calculate Power
• All residential AC electricity is described in
  terms of RMS Values
• 120 V 120 Volts, RMS

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AC POWER
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AC POWER
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AC POWER
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AC POWER
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IMPEDANCE TRIANGLE
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AC POWER
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ACTIVITY 25-1
LOAD
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REAL AND REACTIVE POWER
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REAL AND REACTIVE POWER
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REAL AND REACTIVE POWER
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REAL AND REACTIVE POWER

• Q is a measure of the rate of change of energy
  stored in Reactive Elements (L, C)
• Power companies must worry about Q since they
  supplied this energy
• Supplied Q over their Lines gt Real Cost
• Power companies want customers to have Low Q
• Big issue for a large user - like Rensselaer
• Fans all use Motors - Motors are Inductive
• Get charged for Q, not just P

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REAL AND REACTIVE POWER
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REAL AND REACTIVE POWER

• Notes on Reactive Power
• Real Power P is always gt 0
• Reactive Power Q can be gt 0 or lt 0
• For Inductive Load, X gt 0 gt Q gt 0
• For Capacitive Load, X lt 0 gt Q lt 0

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POWER SYSTEMS
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POWER SYSTEMS

• Complex Power

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POWER TRIANGLE
Imaginary
S
jQ
Real
P
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POWER SYSTEMS

• Significance of S Complex Power
• For Several Loads gt STotal S1 S2 S3
• STotal (P1 P2 ) j ( Q1 Q2 )
• Regardless of how loads are connected!
• Just Add Complex Powers
• Add Ps and Qs
• Makes AC Power calculations much easier

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POWER SYSTEMS

• Do Most AC Power Calculations Straight from Power
  Triangle
• Will do Activity 25-2 shortly to practice
• Lots of Definitions Easy calculations

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POWER FACTOR
Imaginary
S
Q
Real
P
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POWER SYSTEMS
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POWER SYSTEMS
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ACTIVITY 25-2
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ACTIVITY 25-2

• Input Represents Commercial Power
• Keeps amplitude of voltage to circuit constant
• Model with Ideal AC Voltage Source in Series with
  Source Resistance, Rs
• /V/ 500 Volts (RMS)
• Input frequency is 60 Hz
• Standard for Residential/Commercial Power