Simulator 16 User Guide - PowerWorld

When doing contingency analysis and the Power Flow Solution Options are set to Use the
DC Approximation in Power Flow, this option will be ignored. Line limits will always be reported in
MVA when using the DC approximation.
Limiting End of Line
Specified as higher or lower, this field determines whether the higher or the lower flow amount on
the element is used for reporting a limit violation. If you use higher, it is possible that the lower flow
is not violating the line limit. If you use lower, then you are guaranteed that the element limit is
being violated at both ends of the element.
% of Limit for Reporting (Interfaces)
The percentage to which Simulator’s study tools will limit an interface. Typically this is 100%, but it
can be modified. In Contingency Analysis, interfaces will be flagged as violated if they exceed this
percentage. In performing an Optimal Power Flow, all attempts will be made to keep the interface
below this percentage.
Interface Rating Set
You may define eight different ratings to an interface. Change this value to specify which rating set
should be used for interfaces in the limit group.
Interface Contingency Rating Set
This field specifies the rating set used for post-contingency monitoring of Interfaces during
Contingency Analysis.
% of Limit for Reporting (Nomograms)
The percentage to which Simulator’s study tools will limit a nomogram.
Use Limit Cost
If this field is checked, you are enabling the capability to have a cost function associated with
enforcing constraints. This cost function can be viewed as similar to a generator cost function, in
that as the constraint becomes overloaded by larger amounts, the marginal cost of enforcing the
constraint will increase.
Once the box is checked, the table for defining the limit cost function will become enabled. The
starting point (% Flow) must be at or above 100%. You can then begin inserting additional points in
the piecewise linear curve by right-clicking in the table and selecting Insert Point from the popup
menu, followed by entering the new percent flow and marginal cost. Note that the cost function
must be strictly increasing, meaning the next marginal cost value must be equal to or greater than
the immediately previous value.
When constraints are given the ability to use this limit cost curve, it effectively gives the optimal
power flow the ability to "dispatch" the limit of the elements according to the marginal costs of the
limit cost curve. You are determining the point on the limit cost curve where the shadow price of
enforcing the constraint is met. Thus the OPF routine will determine how much you will allow the
element to be overloaded by giving the element the piecewise linear curve. The OPF will solve the
problem, and optimize the constraints as it determines shadow prices for each constraint and adjusts
the limit accordingly during the iterations of the routine. Since these are somewhat flexible limit
assignments to the elements, they are sometimes considered "soft" constraints.
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