Chapter 11 AC Power Analysis

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Chapter 11AC Power Analysis

• Chapter Objectives
• Know the difference between instantaneous power
  and average power
• Learn the AC version of maximum power transfer
  theorem
• Learn about the concepts of effective or Rms
  value
• Learn about the complex power, apparent power and
  power factor
• Understand the principle of conservation of AC
  power
• Learn about power factor correction

Huseyin Bilgekul Eeng224 Circuit Theory
II Department of Electrical and Electronic
Engineering Eastern Mediterranean University
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Power Factor Correction

• The design of any power transmission system is
  very sensitive to the magnitude of the current in
  the lines as determined by the applied loads.
• Increased currents result in increased power
  losses (by a squared factor since P I2R) in the
  transmission lines due to the resistance of the
  lines.
• Heavier currents also require larger conductors,
  increasing the amount of copper needed for the
  system, and they require increased generating
  capacities by the utility company.
• Since the line voltage of a transmission system
  is fixed, the apparent power is directly related
  to the current level.
• In turn, the smaller the net apparent power, the
  smaller the current drawn from the supply.
  Minimum current is therefore drawn from a supply
  when S P and QT 0.
• The process of introducing reactive elements to
  bring the power factor closer to unity is called
  power-factor correction. Since most loads are
  inductive, the process normally involves
  introducing elements with capacitive terminal
  characteristics having the sole purpose of
  improving the power factor.

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Power Factor Correction
Increasing the power factor without altering the
voltage or current to the load is called Power
Factor Correction
Inductive Load with improved power factor
correction
Original Inductive Load
Effect of capacitor on total current
Power triangle of power factor correction
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Power Factor Correction

• Increasing the power factor without altering the
  voltage or current to the load is called Power
  Factor Correction.

Q1 S1 sin ?1 P tan ?1
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Power Factor Correction

• The process of increasing the power factor
  without altering the voltage or current to the
  original load is called power factor correction.
• Power factor correction is necessary for
  economic reasons.

• The capacitance value needed to change the pf
  angle from ?1 to ?2 .

• Similarly the inductance value needed to change
  the pf angle from ?1 to ?2 for a capacitive load.

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Power Factor Correction
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Power Factor Correction
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Power Factor Correction
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• Practice Problem 11.15 Find the value of the
  capacitance needed to correct a load of 140 kVAR
  at 0.85 lagging pf to unity pf. The load is
  supplied by a 110 Volt (rms), 60 Hz line.

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Wattmeter is the instrument for measuring the
average power. Two coils are used, the high
impedance Voltage coil and the low impedance
Current coil. Wattmeter measures the average
power given by
ApplicationsPower Measurement
Wattmeter
Wattmeter connected to the load
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Problem 11-74