A 500MVA synchronous machine has H_{1 }= 4.6 MJ/MVA, and a 1500 MVA machine has H_{2} = 3.0 MJ/MVA. The two machines operate in parallel in a power station. The equivalent H constant for the two, relative to a 100 MVA base will be
We know that,
The load carrying capability of a long ac line is
Fast acting excitation systems
Fast field excitation system is one of the method to improve transient stability of the system.
A shunt reactor in general
Shunt reactors are used to reduce the effect of Ferranti effect when a medium or a long line is lightly loaded or is on noload. It doesn’t affect the steady state power transfer limit.
The angle swings during transients
If the inertia constant H = 9.0 MJ/MVA for a 50 MVA generator, the stored energy is
or,
K.E. stored = GH = 50 x 9 = 450 MJ
Bundled conductors in a transmission line will
Bundled conductors increases self GMD due to which the series inductive reactance is reduced as a result of which power transferred from sending end to the receiving end is increased. Hence, it improves the steady state stability of the system.
A 1500 MVA synchronous generator has an inertia constant of 5.0 MJ/MVA. The inertia constant of the machine relative to a 50 MVA base is
Since inertia constant,
∴
or,
If the initial acceleration power of a 100 MVA, 50 Hz synchronous generator having H= 5 MJ/MVA is Xpu, the initial acceleration in elecdeg/s^{2} and the inertia constant in M Js/eledeg respectively will be
From swing equation,
Also, inertia constant,
The critical clearing angle of a power system is related to
t_{cr} and δ_{cr} are related to transient stability limit. The fault in a power system must be cleared before δ reaches δ_{cr }and before t_{cr}.
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