Electrical engineeringLesson 2 of 2 in the course AC power

Power Factor in AC Systems: Phase, Harmonics, Correction, and Measurement

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Power factor describes how effectively an AC electrical system converts the apparent power flowing through it into real power that can do useful work. This lesson introduces the main power quantities and the basic power-factor equation.

Real power, PP, is the average rate at which electrical energy is transferred to perform work or produce heat. It is measured in watts (W). In an AC circuit, it is the average of the instantaneous product of voltage and current over time.

All flashcards

Real power
The average rate of electrical energy transfer into work or heat; measured in watts.
Complex power
The combination of real and reactive power, written S=P+jQS = P + jQ.
Distortion power factor
With sinusoidal supply voltage, the ratio of fundamental RMS current to total RMS current: I1/IrmsI_1/I_{rms}.
Current total harmonic distortion
The RMS combination of harmonic currents divided by the RMS fundamental current.
Synchronous condenser
An unloaded synchronous motor that provides adjustable reactive power through changes in field excitation.

Quiz questions

  1. How is apparent power related to real power PP and reactive power QQ in the power triangle?Answer: ∣S∣=P2+Q2|S| = \sqrt{P^2 + Q^2}
  2. Under the convention in which inductive loads have positive reactive power, what describes their usual power factor?Answer: Current lags voltage, and reactive power is positive.
  3. How can a capacitor connected near an inductive motor load improve power factor?Answer: It supplies reactive power that offsets some of the load’s reactive demand.
  4. What does active power-factor correction do to input current?Answer: It uses power electronics to shape current so it more closely follows line voltage.
  5. Why must an overall power-factor measurement convention be specified for an unbalanced polyphase circuit?Answer: Its power factor is not uniquely defined without a chosen overall measurement convention.

Based on the Wikipedia article Power factor, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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