Equal Area Criteria: Sudden Short Circuit on One of Parallel Lines

Q. A generator delivers power of 1.0 p.u. to an infinite bus through a purely reactive network. The maximum power that could be delivered by the generator is 2.0 p.u. A three-phase fault occurs at the terminals of the generator which reduces the generator output to zero. The fault is cleared after $t_c$ second. The original network is then restored. The maximum swing of the rotor angle is found to be ${\delta }_{max}=110$ electrical degree. Then the rotor angle in electrical degrees at $t=t_c$ is

1. 55
2. 70
3. 69.14
4. 72.4

Q. A generator with constant 1.0 p.u. terminal voltage supplies power through step-up transformer of 0.12 p.u. reactance and a double- circuit line to an infinite bus bar as shown in the figure. The infinite bus voltage is maintained at 1.0 p.u. Neglecting the resistances and susceptances of the system, the steady state stability power limit of the system is 6.25 p.u. If one of the double-circuit is tripped, then resulting steady stability power limit in p.u. will be

1. 12.5 p.u.
2. 3.125 p.u.
3. 10.0 p.u.
4. 5.0 p.u

Q. A 50 Hz 4-pole, 500 MVA, 22 kV turbo-generator is delivering rated MVA at 0.8 power factor. Suddenly a fault occurs reducing its electric power output by 40%. Neglect losses and assume constant power input to the shaft. The accelerating torque in the generator in MN-m at the time of the fault will be

1. 1.528
2. 1.018
3. 0.848
4. 0.509

Q. A 100 MVA synchronous generator operates at full load at a frequency of 50 Hz. The load is suddenly reduced to 50 MW. Due to time lag in governor system, the steam valve begins to close after 0.4 sec. The frequency at t = 0.4 sec is ______ Hz (Given H = 4 MJ/MVA)

1. 51.23