Contingency Options: Modeling Basics

 

These options are all available on the Contingency Analysis dialog under the Contingency Options tab under the Modeling grouping.

Calculation Method

The calculation method defines how the power flow is solved during the contingency analysis. By default, Simulator uses a Full Power Flow for each contingency. For a large set of contingencies and a large case, this can take some time to complete. The Full Power Flow option can utilize either an AC solution or DC solution depending on whether or not the Power Flow Solution Options are set to Use the DC Approximation in Power Flow. Alternatively, the contingency analysis can be done by calculating the linear approximation of the impact of the contingencies by choosing either the Linearized Lossless DC or Linearized Lossless DC with Phase Shifters method. These two methods will both solve a set of contingencies much faster than the full power flow. The Lossless DC methods utilize sensitivities of devices to calculate the load flow in a linear fashion. The only difference between the two lossless DC methods is that the first method treats all phase shifters as free-flowing, while the method with phase shifters will hold all in-service phase shifters at their present MW flow value.

If the Power Flow Solution Options are set to Use the DC Approximation in Power Flow, the linearized methods will not be available. Also, if the DC approximation is in use, the option with the Limit Monitoring Settings to Treat Transmission Line Limits as Equivalent Amps will be ignored. Line limits will always be reported in MVA.

 

AC Method Options

The following options are available if using the Full Power Flow Calculation Method and the Power Flow Solution Options are NOT set to DC Approximation Power Flow.

Retry solution using the Robust Solution Process after a contingency solution failure

Checking this option will force the contingency analysis routine to attempt a robust solution following the failure of a standard Newton-Raphson solution. The robust solution attempt does not guarantee convergence, but will attempt to slowly approach a convergence solution if possible. This process is described in more detail under Simulation Control.

Using this option can greatly slow down the contingency solution when there are contingencies that will not converge. In general this option should not be used. If there are contingencies that fail after an initial run, they can always be attempted again using this method if desired.

The Robust Solution Process is not used regardless of how this option is set when solving contingencies as part of either the PV or QV analysis available with the PVQV add-on or ATC analysis with the ATC add-on.

Use specific solution options for contingencies

When checked, Simulator will use a different set of Solution Options when solving the contingencies defined in the contingency set. To define the solution options used during the contingency analysis, click the Define Contingency Solution Options button to open the Contingency Solution Options Dialog. If solution options have already been defined, the button will be labeled Modify Solution Options.

Do OPF solution for each contingency

Instead of using a standard power flow solution for each contingency, the Primal LP OPF algorithm will be solved. This will be solved with all of the option settings available with the OPF tool. This option can be used to mitigate violations. If flow constraints are being enforced, there will be no violations reported as long as there are no unenforceable constraints.

Do Not Use Post Power Flow Solution Action List

Checking this option prevents any globally defined post power flow solution actions defined with the case from being evaluated and performed in the post-contingency power flow solution during contingency analysis runs.

 

Disable Gen Drop Overlap

When using injection group contingency actions, there are very specific settings that will allow for the accounting of generation that is part of multiple injection groups that drop generation during a contingency. Check this option to disable this accounting. For a full description of how the generation drop overlap accounting works see the Contingency Element Type: Injection Group topic.

 

Make-Up Power

When solving a contingency, the make-up power defines how the post-contingency solution accounts for the change in system losses, generation, and load. There are three options for this make-up power.

Determine make-up using:

Area Participation Factors specified below

Simulator models this by temporarily switching to Island-Based AGC and using the Calculate Participation Factors from Area Make Up Power Values option during the contingency solution. The values specifying the CTG Make Up Gen for each area are used to determine the contribution of each area in an island to the amount of make-up power needed. Within each area, the individual participation factors of generators on AGC determine how much power will come from each generator.

Note that if all areas have CTG Make Up Gen equal to 0.0, then all make-up power will come from the island slack bus. This option generally yields faster solution times, but a concentration of make up power at the island slack bus may not accurately represent the response of the system following a contingency.The Calculate Participation Factors from Area Make Up Power Values section of Island-Based AGC describes this in further detail.

Generator Participation Factors From Entire Case Directly

Simulator models this by temporarily switching to Island-Based AGC and using the Use Participation Factors of Individual Generators option during the contingency solution. The individual participation factors of each generator within each island are used to determine how each generator meets the make-up power needs of the island. Area and super area interchange (ACE) requirements are ignored, and all generators on AGC are dispatched to account for the changes in system losses, generation, and load. This option is usually the best approximation of post-contingent system behavior, but may yield longer solution times than island slack bus make-up power (Area Participation Factors specified below with CTG Make Up Gen set to zero for all areas).

Same as Power Flow Case

This uses the area interchange options specified in the normal power flow.

When using the DC power flow or a linear calculation method and this option is chosen, Generator Participation Factors From Entire Case Directly will be used instead.

Make-up Power Tolerance

This specifies the tolerance of the Island-Based AGC used for both the Area Participation Factors specified below and Generator Participation Factors From Entire Case Directly options.

Prevent new island without enough controllable generation

This new step that can be optionally used in contingency analysis was added in Version 19, Build on January 9, 2017

Choose this option to try to prevent islands representing less than half the load in the case from being created during contingency analysis which do not have enough controllable generation available to prevent the island slack bus from operating outside of its limits. See the Advanced Power Flow Options help topic and the special topic on Island Creation for more information.