A 500 kVA, 3-phase transformer has iron loses of 300 W and full load copper losses of 600 W. The percentage load at which the transformer is expected to have maximum efficiency is

Figure shows an ideal three-winding transformer. The three windings 1,2,3 of the transformer are wound on the same core as shown. The turn's ratio N₁:N₂:N₃ is 4:2:1. A resistor of 10 Ω is connected across winding-2. A capacitor of reactance 2.5 Ω is connected across winding-3. Winding-1 is connected across a 400 V, ac supply. If the supply voltage phasor $$\overline V=400\angle0^\circ$$, the supply current phasor $${\overline I}_1$$ is given by

Figure shows an ideal single-phase transformer. The primary and secondary coils are wound on the core as shown. Turns ratio $$\left(\frac{N_1}{N_2}\right)$$=2. The correct phasors of voltages $$E_1,\;E_2$$ currents $$I_1,\;I_2$$ and core flux $$\phi$$ are as shown in

Figure shows a $$\triangle$$ - Y connected 3-phase distribution transformer used to step down the voltage from 11000 V to 415 V line-to line. It has two switches S₁ and S₂. Under normal conditions S₁ is closed and S₂ is open. Under certain special conditions S₁ is open and S₂ is closed. In such a case the magnitude of the voltage across the LV terminals a and c is