Binding constraints

Report notes

1. Constraints in the SPD model fall into one of three categories:
   • Branch constraints - a group of transmission lines between two locations combined into a single constraint
   • Branch limits - a constraint on the transfer capacity of a single transmission line between two locations
   • Market node constraints - restrictions on machines providing frequency keeping services.
   Only the instances of the above constraints that are binding in the SPD solution for final pricing are presented in this report. A constraint is determined to be binding if its associated shadow price is positive. On any given day, there may well be no binding constraints of any or all of the three constraint types. Binding branch limits are quite rare.

2. Limit (MW) denotes the megawatt value of the transfer capacity parameter for branch constraints and branch limits, and the generating machine limit net of the frequency keeping requirement in the case of market node constraints (i.e. the right-hand side of the constraint).

3. Shadow price ($/MWh) is a measure of the cost to the system of a binding constraint. Conversely, a constraint that is not binding will have a zero shadow price and imposes no cost on the system. More technically, the shadow price represents the decrease (increase) in the SPD objective function value that would be associated with a 1 MW increase (decrease) in the limit of the constraint. Shading is set between zero (white), $100 (yellow), and $200 (red) on the shadow price as a visual cue indicating the severity of boundedness. Historically, approximately 80% of all binding constraints have a shadow price of less than $200/MWh.

4. The components that the constraint is composed of (i.e. the left-hand side) can be viewed by clicking on the plus sign at the left to expand the row:
   • The factor represents the technical coefficient or parameter on each component of the constraint
   • The MW value of each component denotes the value attained by the transmission flow variable for branch constraints and branch limits and the generating variable for market node constraints.
   The sum (over all components) of the factor multiplied by the MW for each component will equal the limit or right-hand side parameter for a constraint that is binding.

5. If a branch or branch limit constraint spans two zones, the constraint will appear in the report twice; once for each zone.

6. Downloading the report as a CSV or PDF does not capture the components of the constraints. To obtain all details of binding constraints, including its components, and to select binding constraints for more than a single day, please use the underlying data report (icon at upper right of screen).