Exam question: synchronous motor excitation

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Discussion Overview

The discussion revolves around a multiple choice exam question regarding forms of excitation in synchronous motors. Participants explore different modes of operation and characteristics of synchronous motors, including under and over excitation, and how these relate to other types of motors.

Discussion Character

  • Homework-related
  • Debate/contested

Main Points Raised

  • One participant notes that synchronous motors can operate in under or over excited modes, with over excitation referred to as a synchronous condenser due to its ability to supply reactive power.
  • Another participant questions the implications of under excitation, seeking clarification on its effects.
  • A further response suggests that under excitation leads to operation akin to an induction motor, characterized by a lagging power factor.
  • Another participant reiterates the point about under excitation, emphasizing that while it operates with a lagging phase, it remains a synchronous motor without phase slippage, contrasting it with induction motors.

Areas of Agreement / Disagreement

Participants express differing views on the implications of under and over excitation, with some asserting that under excitation resembles induction motor behavior, while others clarify the distinctions between synchronous and induction motors. The discussion remains unresolved regarding the correct forms of excitation as per the exam question.

Contextual Notes

There are unresolved assumptions regarding the definitions of excitation types and the specific characteristics of synchronous versus induction motors. The discussion does not reach a consensus on the correct answers to the exam question.

tobiascarter
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Here is a multiple choice question i was completely stumped on, and still can't find the right answer for in my textbooks...

Name 2 forms of excitation with respect to synchronous motors:
a) under and over excitation
b) dc & ac variation
c) dc excitation and load variation
d) armature and stator reversal

Any clues or certain answers would be appreciated
 
Last edited:
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Synchronous motor can be operated in under or over excited modes. If operated in over excitation mode, it is also called as synchronous condenser, because it supplies reactive power to the source.
 
and if it is under excited??
 
Last edited:
it is Induction motor.(it works on lagging p.f.)
 
hmparikh1990 said:
it is Induction motor.(it works on lagging p.f.)
When running as a synchronous motor, it is still synchronous, and the armature has a lagging phase. There is no phase slippage, like in an induction motor. It has synchronously-excited salient poles on the armature, not a squirrel cage like induction motors.

Bob S
 

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