Chapter 3: Q2MCQ (page 140)
For an ideal transformer, the efficiency is
(a) 0%
(b) 100%
(c) 50%
Therefore, the correct option is (b): 100%
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Determine the positive- and negative-sequence phase shifts for the three phase transformers shown in Figure 3.36.
Does an openconnection permit balanced three-phase operation?
(a) Yes
(b) No
Consider the adopted per-unit system for the transformers. Specify true or false for each of the following statements:
(a) For the entire power system of concern, the value ofis not the same.
(b) The ratio of the voltage bases on either side of a transformer is selected to be the same as the ratio of the transformer voltage ratings.
(c) Per-unit impedance remains unchanged when referred from one side
of a transformer to the other.
The "Ohm's law" for the magnetic circuit States that the net magneto-motive force (mmf) equals the product of the core reluctance and the core flux.
(a) True
(b) False
Consider the oneline diagram shown in Figure 3.40. The three-phase transformer bank is made up of three identical single-phase transformers,each specified by (on the low-voltage side), negligible resistance and magnetizing current, and turns ratio . The transformer bank is delivering at 0.8 p.f. lagging to a substation bus whose voltage is 230 kV.
(a) Determine the primary current magnitude, primary voltage (line-to-line) magnitude, and the three-phase complex power supplied by the generator. Choose the line-to-neutral voltage at the bus,role="math" localid="1655206659086" as the reference. Account for the phase shift, and assume positive-sequence operation.
(b) Find the phase shift between the primary and secondary voltages.
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