This document contains 6 practice questions related to generators and power systems. Question 1 asks to find the steady state power limit of a system with a generator synchronous reactance of 0.4 pu connected through a series reactance of 1.0 pu to an infinite bus at 1.0 pu. Question 2 asks to calculate the acceleration in rpm/sec of a 30 MVA generator given its inertia constant and input and output power. Question 3 asks to calculate the shaft power, stable and unstable rotor angles, and oscillation frequency for a generator supplying 1.2 pu power through a reactance of 0.8 pu. Question 4 asks to find the critical clearing angle for a generator initially supplying 1.5 pu power where faults reduce the

1. Unit V Practice Questions
Q1. Find the steady state power limit of a system consisting of a generator with a synchronous
reactance of 0.4 pu connected to an infinite bus through a series reactance of 1.0 pu. The terminal
voltage is held at 1.0 pu and the infinite bus voltage is 1.0pu [0.957]
Q2. A 30 MVA, 15KV, 4 pole, 50 Hz turbo-generator has an inertia constant of 10KW-sec/KVA. If the
input power and the output power are 25MW and 20MW respectively, find the acceleration in
rpm/sec [12.5]
Q3. A 50Hz synchronous generator having H constant as 5MJ/MVA is supplying 1.2pu power to an
infinite bus. The emf of the generator is 1.6pu in magnitude and the voltage at the infinite bus is
1.0+j0 pu. The reactance through which the power is getting transmitted is 0.8pu. Calculate the
following:
(i) The shaft power(neglecting the rotational losses)
[1.2]
(ii) The rotor angle for stable and unstable operation [36.86, 143.13]
(iii) The frequency with which the generator oscillates during a disturbance
[1.128Hz]
Q4. A generator is supplying 1.5pu power to an infinite bus. There is a 3 phase fault occurring at a point
which reduces the steady state power limit. The fault is cleared by a circuit breaker and the power
transmission is resumed but the maximum limit is different from the pre-fault conditions. The power
angle equation pertaining to the three conditions are :
Pre – fault: 2.1 sinδ; During– fault: 0.8 sinδ ; Post – fault: 1.8 sinδ
Find the critical clearing angle [57.6]
Q5. A 60 Hz generator is supplying 60% of maximum power to an infinite bus through a reactive network.
A fault occurs which increases the reactance of the network between the generator internal voltage
and the infinite bus to 400%. When the fault is cleared the maximum power that can be delivered is
80% of the original maximum value. Determine the critical clearing angle for the conditions
described. [61.64]
Q6. A 60 Hz turbo alternator rated 500MVA, 22KV has H=7.5MJ/MVA. Find:
(i) K.E. stored in the rotor at synchronous speed
[3750]
(ii) The angular acceleration if the electrical power developed is 400MW when the input less the
rotational losses is 740,000HP [36.5rpm/sec]
.