Electrical Power Systems

306 Electrical Power Systems
H
pf
d
2
dt
d
2
= P m–P e
b 1 2g
where H = HH 1 2
H + H
P m =
P e =
H2P - H1P H + H
m1 m2
1 2
H2P - H1P H + H
e1 e2
1 2
11.11. A 4 pole, 60 Hz synchronous generator has a rating of 200 MVA, 0.8 pf lagging. The moment of
inertia of the rotor is 45100 kg-m 2 . Determine M and H. Ans: M = 8.5 MJ-rad/sec.
H = 4.0 MJ/MVA.
11.12. A 50 Hz synchronous generator with inertia constant H = 2.5 sec and a transient reactance of
0.20 pu feeds 0.80 pu real power to an infinite bus (voltage 1.0 pu) at 0.8 power factor lagging via
a transmission network with an equivalent reactance of 0.25 pu,
A three-phase fault is sustained for 0.15 sec across generator terminals.
Plot the swing curve and calculate the torque angle d, 0.25 sec after fault initiation.
Ans: 63.36º
11.13. A 50 Hz, 500 MVA, 400 KV generator (through transformer) is connected to a 400 KV infinite
busbar through an interconnector. The generator has H = 2.5 MJ/MVA, voltage behind transient
reactance of 450 KV and is loaded 460 MW. The transfer reactances between generator and
busbar under various conditions are:
Prefault: 0.5 pu, During fault: 1.0 pu and Postfault: 0.75 pu. Plot the swing curve using intervals
of 0.05 sec and assuming that the fault is cleared at 0.15 sec. Ans: System remains stable
11.14. A power plant has four identical generator sets each rated 50 MVA and each having an inertia
constant of 5 MJ/MVA. A second power plant has three identical generator sets each rated
100 MVA and having an inertia constant of 3 MJ/MVA. If the two power plants are tied together
at one end of a long tie-line, calculate the equivalent inertia on a base of 100 MVA.
Ans: 19 MJ/ MVA.