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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 field excitation system is one of the method to improve transient stability of the system.
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.
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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