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

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

A single phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at half load at the same power factor is

A dc series motor driving an electric train faces a constant power load. It is running at rated speed and rated voltage. If the speed has to be brought down to 0.25 p.u. the supply voltage has to be approximately brought down to