Questions

1. The kinetic energy stored in the rotor of a 75MVA, four pole, 50Hz synchronous machine is 200 MJ. The input to the machine is 40MW at a developed power of 37.5MW. Calculate the accelerating power and acceleration?
2. If the acceleration remains constant for 10 cycles. What is the power angle at the end of the 10 cycles?
3. The generator has an internal voltage (E) of 1.1pu and is connected to an infinite bus operating at a voltage of 1.04pu through a 0.25pu reactance. A three phase short circuit occurs on the line (with an equivalent reactance of 3pu). Subsequently the circuit breakers operate and the reactance between the generator and the bus becomes 0.4pu.

a) Calculate the critical clearing angle?

b) Plot the swing curve for the machine

c) Find the critical clearing time in ms.

d) If the circuit breaker operates within 70ms is this sufficient to ensure stability is not lost?