A three-phase grounded wye-delta connected transformer supplies a load. The load voltage is 480 V (line-to-line), the loads are: Phase ab is 25 kW with power factor 0.8 lagging; Phase bc is 10 kVA with power factor 0.75 lagging; and Phase ca is 47 kW with power factor 0.85 lagging. The transformer is rated 50 kVA, 12.47 kV / 480 V, 9.2%. Calculate: (a) the unbalanced delta currents in each phase (Iab, Ibc, Ica), (b) the unbalanced wye currents (IA, IB, IC), (c) the required supply voltages per phase (both line-to-line and line-to-neutral), and (d) the ground current at the wye side. Hint: place the transformer impedance at the wye side in series in each phase.

Amass of 1.5 kg of air at 120 kpa and 24°c is contained in a gas-tight, frictionless piston-cylinder device. the air is now compressed to a final pressure of 720 kpa. during the process, heat is transferred from the air such that the temperature inside the cylinder remains constant. calculate the boundary work input during this process.

Amass of m 1.5 kg of steam is contained in a closed rigid container. initially the pressure and temperature of the steam are: p 1.5 mpa and t 240°c (superheated state), respectively. then the temperature drops to t2= 100°c as the result of heat transfer to the surroundings. determine: a) quality of the steam at the end of the process, b) heat transfer with the surroundings. for: p1.5 mpa and t 240°c: enthalpy of superheated vapour is 2900 kj/kg, specific volume of superheated vapour is 0. 1483 m/kg, while for t 100°c: enthalpy of saturated liquid water is 419kj/kg, specific volume of saturated liquid water is 0.001043m/kg, enthalpy of saturated vapour is 2676 kj/kg, specific volume of saturated vapour is 1.672 m/kg and pressure is 0.1 mpa.

The y form of iron is known as: a) ferrite b) cementite c) perlite d) austenite