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Polyphase Power Systems
14 questions By Tony R. Kuphaldt
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Question 1 of 14
Explain the difference between a balanced polyphase system and an unbalanced polyphase system. What conditions typically cause a polyphase system to become unbalanced?
Reveal answerA “balanced” polyphase system is one where all line voltages are equal to each other, and all line currents are also equal to each other. “Unbalanced” conditions usually stem from unsymmetrical loads, although severe imbalances may be caused by faults in the system.
Notes:Ask your students which type of three-phase system (balanced or unbalanced) is easier to analyze, and why that is so.
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Question 2 of 14
What is polyphase electric power, and how does it differ from single-phase power?
Reveal answerIn polyphase systems, there are multiple voltages phase-shifted apart from each other so as to be intentionally “out of step.”
Notes:Although the rationale for polyphase electrical power may not be apparent from either the question or the given answer, your students need to be aware of its existence.
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Question 3 of 14
All large electric power generating systems in the world today produce three phase power, rather than single phase power. Explain why this is so, in terms of advantages of distribution and use.
Reveal answerGenerating and distributing AC power in three-phase form is more efficient than if it were done in single-phase form.
Notes:Please do not accept the given answer as a student response! This answer is very shallow, not communicating much meaning. Ask your students to explain why polyphase power systems enjoy greater efficiencies than monophase power systems. There is more than one correct answer to this question!
