Electrical engineeringLesson 1 of 1 in the course AC power

Three-Phase Power: Circuits, Distribution, Loads, and Safety

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

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Summary

Three-phase power is the standard form of AC used by electrical grids to generate, transmit, and distribute electricity. This lesson introduces the system, its phase relationship, and the terms used to describe its conductors and voltages.

A three-phase system is a polyphase AC system with three live conductors. Each carries an alternating voltage and current of the same frequency, while the three waveforms are offset from one another. The system is widely used because it can deliver power smoothly and economically, especially to industrial equipment and over transmission networks.

All flashcards

What is three-phase electric power?
An AC system with three same-frequency phases separated by 120∘120^\circ, commonly used for generation, transmission, distribution, and heavy loads.
What is a line conductor?
A conductor connecting a source to a load, excluding neutral and protective conductors.
How do line-to-line and line-to-neutral voltage differ?
Line-to-line voltage is measured between two line conductors; line-to-neutral voltage is measured between one line conductor and neutral.
What does 230/400 V indicate?
It indicates 230 V line-to-neutral and 400 V line-to-line in the stated convention.
What are star and delta connections?
Star (Y or wye) connects phase windings to a common point; delta (Δ\Delta) connects them in a closed loop.

Quiz questions

  1. In a balanced star-connected three-phase system, how are line-to-line voltage and line-to-neutral voltage related?Answer: VLL=3VLNV_{LL}=\sqrt{3}V_{LN}
  2. What happens to a three-phase motor's rotation when any two supply phases are interchanged?Answer: The direction of rotation reverses.
  3. What can happen to line-to-neutral voltages if a neutral breaks while loads are unbalanced?Answer: Some lightly loaded circuits may experience elevated voltage.
  4. What must match before two three-phase sources are connected in parallel?Answer: Their phase sequence and corresponding phase identities.
  5. What voltage does each branch of a delta-connected load receive?Answer: Line-to-line voltage.

Based on the Wikipedia article Three-phase electric power, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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