Answer Happy

a) Explain mathematically how to covert impedance Z per unit using new MVA and kV base values. (6 Marks) b) A generator rated at 500 MVA, 22 kV has star-connected windings each with a reactance of 0.125 p.u. Find the ohmic value of the reactance of the windings. (2 Marks) c) A 10MVA rated, two winding, three-phase transformer has a transformation ratio of 24kV primary to 3.3kV secondary with a reactance of 1.50 referred to the primary side. Calculate the per-unit reactance values when using a 24kV base and 3.3kV bases. Compare your answers. (7 Marks) d) An 11kv/41 V, 3-phase transformer supplies a 20hp, 415V 3-phase motor with rated voltage and current via supply lines each with impedance 0.4 +j1.10. The efficiency and power factor for the motor are 90% and 0.8 lagging respectively. Using a single-line diagram for the system, calculate the per-unit value of impedance for the line and the per-unit value of motor and transformer secondary voltage. (10 Marks)