Unit 16 Inductance in AC Circuits

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Unit 16 Inductance in AC Circuits

• Objectives
• Discuss the properties of inductance in an
  alternating current circuit.
• Discuss inductive reactance.
• Compute values of inductive reactance and
  inductance.
• Discuss the relationship of voltage and current
  in a pure inductive circuit.

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Unit 16 Inductance in AC Circuits

• Objectives
• Be able to compute values for inductors connected
  in series or parallel.
• Discuss reactive power (VARs).

3
Unit 16 Inductance in AC Circuits

• A continually changing magnetic field induces a
  voltage into any conductor.

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Unit 16 Inductance in AC Circuits

• As current flow increases through a coil, a
  magnetic field is created around the coil.

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Unit 16 Inductance in AC Circuits

• As current flow decreases through a coil, the
  magnetic field collapses.

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Unit 16 Inductance in AC Circuits

• The applied voltage and induced voltage are 180
  out of phase.

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Unit 16 Inductance in AC Circuits

• Inductive reactance is the current-limiting
  property of an inductor.
• The inductive reactance symbol is XL .
• The unit of measurement is in ohms, just like
  resistance, and Ohms law formulas can be used.

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Unit 16 Inductance in AC Circuits

• Inductive Reactance
• XL 2pfL
• XL inductive reactance
• 2 a constant
• p 3.1416
• F frequency in hertz (Hz)
• L inductance in henrys (H)

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Unit 16 Inductance in AC Circuits

• Coils with turns close together produce more
  inductance than coils with turns far apart.

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Unit 16 Inductance in AC Circuits

• Three factors that determine induced voltage
• 1. The number of turns of wire.
• 2. The strength of the magnetic field.
• 3. The speed of the cutting action.

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Unit 16 Inductance in AC Circuits

• Circuit current is limited by inductive
  reactance.
• XL 2pfL 377 x .8 301.6 ?
• I E / XL 120 V / 301.594 ? 0.398 A

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Unit 16 Inductance in AC Circuits

• Inductors connected in series.
• LT L1 L2 L3
• XLT XL1 XL2 XL3

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Unit 16 Inductance in AC Circuits

• Inductors connected in parallel.
• 1/LT 1/L1 1/L2 1/L3
• 1/XLT 1/XL1 1/XL2 1/XL3

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Unit 16 Inductance in AC Circuits

• In a pure inductive circuit, the current lags the
  applied voltage by 90.

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Unit 16 Inductance in AC Circuits

• Reactive Power
• VARs EL x IL
• VARs EL2 / XL
• VARs IL2 x XL
• EL voltage applied to an inductor
• IL current flow through an inductor
• XL inductive reactance

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Unit 16 Inductance in AC Circuits

• Review
• Induced voltage is proportional to the rate of
  change of current.
• Induced voltage is always opposite in polarity to
  the applied voltage.
• Inductive reactance is a countervoltage that
  limits the flow of current, as does resistance.

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Unit 16 Inductance in AC Circuits

• Review
• Inductive reactance is measured in ohms.
• Inductive reactance is proportional to the
  inductance of the coil and the frequency of the
  line.
• Inductive reactance is symbolized by XL.
• Inductance is measured in henrys (H) and is
  symbolized by the letter L.

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Unit 16 Inductance in AC Circuits

• Review
• When inductors are connected in series, the total
  inductance is equal to the sum of all the
  inductors.
• When inductors are connected in parallel, the
  reciprocal of the total inductance is equal to
  the sum of the reciprocals of all the inductors.

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Unit 16 Inductance in AC Circuits

• Review
• The current lags the applied voltage by 90 in a
  pure inductive circuit.
• Reactive power is measured in VARs.