A 100-kVA, 3,000-V, 50-Hz, 3-phase star-connected alternator has effective armature resistance of 0.2 Ω. A field current of 40 A produces short-circuit current of 200 A and an open-circuit e.m.f. of 1040 V (line value). Calculate the full-load percentage regulation at a power factor of 0.8 lagging.

A 500-V, 50-kVA, single-phase alternator has an effective resistance of 0.2 Ω. A field current of 10A produces an armature current of 200A on short-circuit and emf of 450V on open circuit. Calculate (a) the synchronous impedance and reactance and (b) the full-load regulation with 0.8 p.f. lagging.

By comparing the principle of operation of a "three" phase generation system with a single-phase system, state what are the bendfits of three phase systems? In your own words, define the "skin effect" in transmission lines and discuss how can it be minimised? Name three advantages of AC transmission in comparison to DC transmission. What are the units of active, reactive and apparent power? The current in a single-phase motor lags 50° behind the voltage. What is the power factor of the motor?

A 1500KVA, 8KV, three-phase wye-connected alternator has an effective resistance of 0.502 and a reactance of 62 per phase. It delivers full-load current at 0.8 lagging power factor at rated voltage. What will be the terminal voltage for the same excitation and load current, if the power factor is 0.8 leading?

Show that an alternator running in parallel on constant-voltage and frequency bus-bars has a natural time period of oscillation. Deduce a formula for the time of one complete oscillation and calculate its value for a 5000-kVA, 3-phase, 10,000-V machine running at 1500 r.p.m. on constant 50-Hz bus-bars. The moment of inertia of the whole moving system is 14,112 kg-m2 and the steady short-circuit is five times the normal full-load value. ANSWER IS [1.33 second]

A 3Ø, Y-connected alternator is rated at 1,600KVA, 13.5KV. The armature effective AC resistance per phase is 1.5Ω. The percentage regulation for a load of 1,280kW at unity power factor is 3.5%. Determine:(a) synchronous reactance of the alternator(b) %VR at full-load 0.8pf leading(c) What is the effect on %VR value if taken at half-load lagging pf? Justify andexplain briefly your answer on one(1) sentence.

2MVA, 2.3kV 3Ø Y-connected alternator operates at rated kVA at a power factor of 80%. The DC armature winding resistance between terminals is 0.08Ω. The field takes 70A at 125V from an exciter equipment. Friction and windage loss is 20kW, iron losses 36kW and stray load losses are 2kW. Calculate the efficiency of the alternator. Assume the effective armature winding resistance is 120% of the DC resistance.