Chapter 2, Problem 2.12P

Three 20-kVA, 24,000/277-V distribution transformers are connected in $\Delta -\text{Y}\text{.}$

The open-circuit test was performed on the low-voltage side of this transformer bank, and the following data were recorded: $V_{\text{line,}\text{OC}}=480\text{V}{I}_{\text{line}}=4.10\text{A}{P}_{3\varphi ,\text{OC}}=945\text{W}$

The short-circuit test was performed on the high-voltage side of this transformer bank, and the following data were recorded:

$V_{\text{line,}\text{SC}}=1400\text{V}{I}_{\text{line,}\text{SC}}=1.80\text{A}{P}_{3\varphi ,\text{SC}}=912\text{W}$

1. Find the per-unit equivalent circuit of this transformer bank.
2. Find the voltage regulation of this transformer bank at the rated load and 0.90 PF lagging.
3. What is the transformer bank’s efficiency under these conditions?