Answered: A 5000-kVA 230/13.8-kV single-phase…

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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Question

A 5000-kVA 230/13.8-kV single-phase power transformer has a per-unit resistance of 1 percent and
a perunit reactance of 5 percent (data taken from the transformer’s nameplate). The open-circuit
test performed on the low-voltage side of the transformer yielded the following data:
VOC = 13.8 kV; IOC = 15.1 A; POC = 44.9 kW.

(a) Find the equivalent circuit referred to the low-voltage side of this transformer.
(b) If the voltage on the secondary side is 13.8 kV and the power supplied is 4000 kW at 0.8 PF
lagging, find the voltage regulation of the transformer. Find its efficiency

Expert Solution

Step 1

(a) The open-circuit test was performed on the low-voltage side of the transformer, so it can be used to directly find the components of the excitation branch relative to the low-voltage side.

$\begin{array}{rcl} |Y_{E X}| & = & |G_{C} - j B_{M}| \\ = & \frac{15.1}{13.8 \times 10^{3}} \\ = & 0.0010942 \end{array}$

The angle is,

$\begin{array}{rcl} θ & = & \cos^{- 1} \frac{P_{O C}}{V_{O C} I_{O C}} \\ = & \cos^{- 1} \frac{44.9 \times 10^{3}}{13.8 \times 10^{3} \times 15.1} \\ = & 77.56 ° \end{array}$

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