Discuss the importance of reactive power control in power systems. What devices and methods are used to regulate reactive power, and why is it essential for system reliability?

2. A 250 kVA, 480 V, 50 Hz, delta-connected alternator with a rated field current of 5 A was tested and the following test data were obtained: • Open circuit terminal voltage from OC test data is 540 V at the rated IF. • Short circuit current from SC test data is 300 A at the rated IF. • A dc current of 20A is flowing through any two stator armature terminals, when a DC voltage of 10 V was applied to two of the terminals. Evaluate the following from above tests data the armature resistance, the approximate synchronous reactance and voltage regulation at rated load and 0.7 pf lead.

Q4: Answer the following questions: 1-A single-phase 100 kVA, 600V, 50 Hz alternator has effective armature resistance and leakage reactance of 0.072 and 0.18 ohm respectively. At rated terminal voltage and kVA load, determine internal induced emf at 0.75 p.f. lagging. 2-A 4-pole, 3-phase, 50-Hz, star-connected alternator has 60 slots, with 4 conductors per slot and coils are short-pitched by 3 slots. If the phase spread is 60°, calculate the line voltage induced for a flux per pole of 0.943 Wb. distributed sinusoidally in space.

Solve Q4 and Q5 only

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]