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C6811 Pages: 3

A two area system connected by a tie line has the following parameters on a 1000
MVA common base.
Area

Frequency sensitive load co-efficient

Inertia constant

Governor time constant

Turbine time constant 0.5 | 06 |
The units are operating in parallel at a nominal frequency of 60 Hz. The
synchronizing power co-efficient is given as 2.0 pu. If the load in areal increases by
187.5 MW, determine the new steady state frequency and the change in tie-line flow.

PART D
Answer any two full questions, each carries 10 marks.
Prove that the maximum permissible sudden increase in load is 72.5% of the steady
state limit if the machine is initially at no load.
Explain Equal Area criterion and state the assumptions made.

Derive the expression for transmission losses as a function of power generation.

What is unit commitment problem? What are the constraints and the solution
techniques for unit commitment problem involving thermal plants?

Find the energy stored in the rotor of a three phase, 50 Hz. 250 MVA turbo alternator
with H=7.5 MJ/MVA. Determine the value of the inertia constant M. The generator is
initially supplying a steady power of 150 MW. If the mechanical power input to the
turbine is suddenly decreased to 100 MW, evaluate the initial acceleration of the rotor

neglecting all losses. Assume 6 poles. Also find the rotor speed after 10 cycles.
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