GATE EE 2015 Set 1 — Question 51
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Power Systems → Economic Operation & Compensation → Economic Load Dispatch
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Question
Consider the economic dispatch problem for a power plant having two generating units. The fuel costs in Rs/MWh along with the generation limits for the two units are given below: ;
; The incremental cost (in Rs/MWh) of the power plant when it supplies 200 MW is ________.
; The incremental cost (in Rs/MWh) of the power plant when it supplies 200 MW is ________.
Correct answer
20 to 20
Solution
The incremental fuel costs for the two units are:Total demand .Check the incremental costs at the lower limits:
At , .
At , .Since , we should ideally load unit 2 more and unit 1 less. However, unit 1 is already at its minimum limit of . To satisfy the total demand of , we must have:
and .At this operating point, the incremental cost of the plant is determined by the unit that would meet the next increment in demand. Since unit 1 is at its lower limit and unit 2 is within its limits (), any small increase in demand will be met by unit 2.
Therefore, the incremental cost of the plant is:
At , .
At , .Since , we should ideally load unit 2 more and unit 1 less. However, unit 1 is already at its minimum limit of . To satisfy the total demand of , we must have:
and .At this operating point, the incremental cost of the plant is determined by the unit that would meet the next increment in demand. Since unit 1 is at its lower limit and unit 2 is within its limits (), any small increase in demand will be met by unit 2.
Therefore, the incremental cost of the plant is:
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