Question

A 120-KVA 13.2-kV/380-V Y-A three-phase transformer bank is used as a step-down. The bank consists of three identical 40-KVA 7621/380-V 50Hz transformers. In the short- circuit test on the three-phase transformer bank, the recorded values on the high- voltage side are:

Vsc =536
V Isc = 7.3 A, and
Psc =2136 W

The core-loss resistance is Rc and magnetization reactance referred to high-voltage side is 290.4 k 2. This three-phase transformer bank supplies rated load at 0.8-PF lagging and rated voltage.

a) Find the line-to-line source and load voltages, and the VR in percentage (the value must have 3 digits after the decimal point) under the given conditions.

Answer 1

The line-to-line source voltage is 929.40V and the load voltage is 380V. The VR (voltage regulation) is 144.89%.

Step-by-step explanation:

To find the line-to-line source and load voltages and the VR in percentage, we can use the information from the short-circuit test. Based on the given values, we have Vsc = 536V, Isc = 7.3A, and Psc = 2136W. The line-to-line source voltage can be calculated using the formula VLL = √3 * Vsc. In this case, VLL = √3 * 536V = 929.40V. The line-to-line load voltage is equal to the rated voltage, which is 380V. The VR (voltage regulation) can be calculated using the formula VR = (VLL - VL) / VL * 100. Substituting the values, we get VR = (929.40V - 380V) / 380V * 100 = 144.89%.