Chapter 3: Q33 MCQ (page 87)
The direct electrical connection of the windings allows transient overvoltages to pass through the autotransformer more easily, and that is animportant disadvantage of the autotransformer.
(a) True
(b) False
Therefore, the correct answer is (a) True
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A single-phase transformer has 2000 turns on the primary winding and 500 turns on the secondary. Winding resistances are , and ; leakage reactanceโs are, and . The resistance load on the secondary is .
(a) If the applied voltage at the terminals of the primary is , determine at the load terminals of the transformer, neglecting magnetizing current.
(b) If the voltage regulation is defined as the difference between the voltage magnitude at the load terminals of the transformer at full load and at no load in percent of full-load voltage with input voltage held constant, compute the percent voltage regulation.
Consider three ideal single-phase transformers (with a voltage gain of )put together as a three-phase bank as shown in Figure 3.35. Assuming positive-sequence voltages forfindin terms ofrespectively.
(a) Would such relationships hold for the line voltages as well?
(b) Looking into the current relationships, expressin terms
of,respectively.
(c) Let and be the per-phase complex power output and input,
respectively. Find in terms of .
With the American Standard notation, in either a or transformer, positive-sequence quantities on the high-voltage side shall lead their corresponding quantities on the low-voltage side by .
(a) True (b) False
It is stated that
(i) balanced three-phase circuits can be solved in per unit on a per-phase basis after converting-load impedances to equivalent Y impedances.
(ii) Base values can be selected either on a per-phase basis or on a three phase basis.
(a) Both statements are true.
(b) Neither is true.
(c) Only one of the above is true.
A low value of transformer leakage reactance is desired to minimize the voltage drop, but a high value is desired to limit the fault current, thereby leading to a compromise in the design specification.
(a) True
(b) False
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