Q2: Correct the wrong statement if any: 1-The series filed of a series de generator is excited by armature current. 2- The developed power in DC generator armature is function to load current. 3-The commercial efficiency of DC generators is relationship between output mechanical power and developed power in armature winding. 4- If the source frequency subjected to primary windings increased, the iron losses also decreased. 5-In transformers short circuit test primary voltage will be greater than secondary voltage.

In a DC generator, the effect of armature reaction on the main field is to * reverse it O distort it O reduce it O both (b) and (c)

With the aid of diagrams describe the basic topology of a wound field 3 phase synchronous generator and outline the relationship between the excitation voltage and rotor current. Q2 (a) (b) Outline with the aid of a suitable diagram the necessary power conversion stages required to interface a small permanent magnet (PM) generator to a stand alone DC system. A star connected 3 phase wound field synchronous generator with a synchronous reactance of 20 N is connected to a 6.6 kV (phase voltage) grid and supplies 1.5 MW at 0.95 lagging power factor at its terminals. Calculate the phase current and resultant voltage across the synchronous reactance (Vxs), and from a scaled phasor diagram graphically determine the required excitation voltage (Eph) and load angle (8). (c) The load is now increased to 3 MW with the Excitation Voltage kept constant. Using the phasor diagram drawn in part (c) graphically determine the resultant phase current, power factor and load angle. (d)