Question

A three-phase, 415 V load takes a line current of 800 A from a 3300/415V delta – star transformer. The 3300V system is supplied from an 11000/3300V star – star transformer. Draw the circuit diagram and, assuming no losses, find both line and phase values of voltages and currents in each part of the circuit. What will be the turns ratios of both transformers?

Answer 1

$U_{1ph}=\frac {U_1}{\sqrt3}=6350.85V;\\U_{2ph}=\frac {U_2}{\sqrt3}=1905.26V;\\\frac{W_2}{W_1}=\frac{U_{2ph}}{U_{1ph}}=0.3;step-down \;transformer;\\U_{3ph}=U_3=3300V;\\U_{4ph}=\frac {U_4}{\sqrt3}=239.6V;\\\frac{W_4}{W_3}=\frac{U_{ph4}}{U_{ph3}}=0.073;step-down \;transformer\;too\\I_{4ph}=I_4=800A\\I_{3ph}=I_{4ph}\times\frac{W_4}{W_3}=58.4A;\\I_3=I_{3ph}\times\sqrt3=101.15A;\\I_{2ph}=I_2=101.15A;\\I_{1ph}=I_1=I_2\times\frac{W_2}{W_1}=30.35A.$