Chapter 3: 32MCQ (page 143)
Question: For the same output, the autotransformer (with not too large a turns ratio) is smaller in size than a two-winding transformer and has high efficiency as well as superior voltage regulation.
(a) True
(b) False
Answer
Therefore, the correct answer is (a) True
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The leakage reactance of a three-phase, transformer is 0.06 per unit based on its own ratings. The Y winding has a solidly grounded neutral. Draw the per-unit equivalent circuit. Neglect the exciting admittance and assume the American Standard phase shift.
A single-phase three-winding transformer has the following parameters: and per unit. Three identical transformers, as described, are connected with their primaries in (solidly grounded neutral) and with their secondaries and tertiaries in . Draw the per-unit sequence networks of this transformer bank.
Rework Example 3 .12 for a tap, providing an increase for the high-voltage winding.
Three single-phase two-winding transformers, each rated , with
a 0.10 per unit leakage reactance, are connected as a three-phase extendedautotransformer bank, as shown in Figure 3.36 The low-voltage A winding has a 110 volt rating. (a) Draw the positive- sequence phasor diagram and show that the high-voltage winding has a 479.5 volt rating. (b) A three-phase load connected to the low-voltage terminals absorbs 6kW at 110 volts
and at 0.8 power factor lagging. Draw the per-unit impedance diagram and calculate the voltage and current at the high-voltage terminals. Assume positive-sequence operation.
Rework Example 3.5; using and.
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