Simulator 16 User Guide - PowerWorld

Tutorial: OPF Marginal Cost of Enforcing Constraints Page 5 of 6
Similar to the bus marginal cost, you can also calculate the marginal cost of enforcing a line constraint.
For a transmission line, this represents the amount of system savings that could be achieved if the
MVA rating was increased by 1.0 MVA.
Select OPF Case Info > OPF Lines and Transformers from the OPF ribbon group on the Add
Ons ribbon tab. The OPF Constraints Records dialog opens.
Note the column displaying MVA Marginal Cost displays 6.0 for the line from Bus 1 to Bus 3. This is
determined based on the following:
With no change in system load:
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Pg1 + Pg2 = 0
If we allow one additional MVA to flow on the line from Bus 1 to Bus 3:
(2/3)Pg1 + (1/3)Pg2 = 1
Solving the above system of equations results in:
Pg1 = 3 MW and Pg2 = -3 MW
cost = (Pg*LMP) = [(3 MW)*(10.00 $/MWh) + (-3 MW)*(12.00 $MW/h)] = -6.00 $/hr, a net
savings of 6.00 $/hr.
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