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GATE 2016 EE – Question 31

Electrical Machines · Synchronous machines: cylindrical and salient pole machines, performance and characteristics, regulation and parallel operation of generators, starting of synchronous motors · 1 mark · Multiple choice

Consider a system consisting of a synchronous generator working at a lagging power factor, a synchronous motor working at an overexcited condition and a directly grid-connected induction generator. Consider capacitive VAr to be a source and inductive VAr to be a sink of reactive power. Which one of the following statements is TRUE?

  1. Synchronous motor and synchronous generator are sources and induction generator is a sink of reactive power.
  2. Synchronous motor and induction generator are sources and synchronous generator is a sink of reactive power.
  3. Synchronous motor is a source and induction generator and synchronous generator are sinks of reactive power.
  4. All are sources of reactive power.

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Show answer and explanation

Correct answer: (A) Synchronous motor and synchronous generator are sources and induction generator is a sink of reactive power.

Explanation

A synchronous generator at a lagging power factor supplies inductive current, which makes it a source of reactive power. An overexcited synchronous motor draws leading current, so it also supplies reactive power. A grid-connected induction generator needs magnetising current from the grid, so it is a sink.