A three phase transformer is used for ancillary services in a thermal power plant. It shows the following nameplate data: 30 MVA, 20/6.6 kV, and an impedance of 8%. The transformer has 21 taps to change the tap ratio in 1% increments. Neglect the transformer resistance. a) If the voltage at the high side is 18.5 kV, determine the tap ratio that must be used under a full load condition at unity power factor. b) What is the number of the actual tap? Assume you start counting from the lowest possible tap.

A three phase transformer is used for ancillary services in a thermal power plant. It shows the following nameplate data: 30 MVA, 20/6.6 kV, and an impedance of 8%. The transformer has 21 taps to change the tap ratio in 1% increments. Neglect the transformer resistance. a) If the voltage at the high side is 18.5 kV, determine the tap ratio that must be used under a full load condition at unity power factor. b) What is the number of the actual tap? Assume you start counting from the lowest possible tap.

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.27P: A three-phase transformer is rated 1000MVA,220Y/22kV. The Y-equivalent short-circuit impedance,...

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A single-phase 50-kVA,2400/240-volt,60-Hz distribution transformer is used as a step-down transformer at the load end of a 2400-volt feeder whose series impedance is (1.0+j2.0) ohm. The equivalent series impedance of the transformer is (1.0+j2.5) ohms referred to the high-voltage (primary) side. The transformer is delivering rated load at a 0.8 power factor lagging and at a rated secondary voltage. Neglecting the transformer exciting current, determine (a) the voltage at the transformer primary terminals, (b) the voltage at the sending end of the feeder, and (c) the real and reactive power delivered to the sending end of the feeder.
A single-phase two-winding transformer rated 90MVA,80/120kV is to be connected as an autotransformer rated 80/200kV. Assume that the transformer is ideal. (a) Draw a schematic diagram of the ideal transformer connected as an autotransformer. showing the voltages, currents, and dot notation for polarity. (b) Determine the permissible kVA rating of the autotransformer if the winding currents and voltages are not to exceed the rated values as a two-winding transformer. How much of the kA rating is transferred by magnetic induction?
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For an ideal 2-winding transformer, the ampere-turns of the primary winding, N1I1 is equal to the ampere-turns of the secondary winding, N2I2 (a) True (b) False
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