The power system studies done with the purpose of meeting the NERC (North American Electric Reliability Corporation) standards address the issue of assessing power system performance, following normal and contingency conditions. The results of these studies must ensure that the transmission system performance meets the NERC Reliability Standards, and that the upgrades to meet future system needs are developed such that the reliable and secure operation of the transmission system is maintained.
The Transmission Planning (TPL) standards define reliable system performance following the loss of a single bulk electric element, two or more bulk electric elements, or following extreme events.
The loss of two elements has been historically performed using N-2 contingency analysis, which corresponds to the loss of two bulk electric elements simultaneously.
A forthcoming, more stringent, NERC TPL standard also requires N-1-1 contingency analysis, which corresponds to the loss of two elements consecutively. The system adjustments should be performed after the 1st N 1 contingency, and may be performed after the 2nd N-1 contingency in each N-1-1 contingency pair.
There is a growing need to provide the system planners with fast automated process to effectively perform NERC-compliance studies. The framework for N 1 1 and N 2 contingency analysis should have the capability to perform the following computations within one simulation run:
• Identify critical contingencies that cause violation of voltage, thermal and steady-state stability limits;
• Determine transmission system bottlenecks;
• Determine potential cascading modes;
• Compute minimum amount of necessary system adjustments;
• If load shed is required, minimize the amount of load curtailment in order to maintain reliable operation of the power system;
• Provide automatic reporting capabilities.
System adjustments may include: MW dispatch, MVAr dispatch, transformer tap change, phase shifter adjustment, capacitor and reactor switching, line switching, and load curtailment.
It is of the utmost importance to ensure that the analysis framework is based on the AC analysis methodology that allows to monitor voltage, thermal and steady-state stability limits.
Since a variety of N-1-1 scenarios may be implemented, the analysis tool should be very flexible in order to be quickly and easily adjusted to the need and specifics of a particular utility or an ISO.
The strategy to perform massive N 1 1 AC contingency should focus on providing the Planning engineers with a solution that has the following capabilities:
• Automatic creation of N 1 1 contingency lists;
• Automating the process of N 1 1 contingency analysis;
• Allowing the user to implement various sets of system adjustments within a single run;
• Incorporating the analysis of cascading outages;
• Providing easy and flexible reporting and post-processing consistent with the utility/ISO practice.
In addition, this process should be used to assist the planners in optimizing the transmission system expansion which will reduce the blackout risk and improve transmission system reliability. Therefore, the solution should have the capability to perform massive contingency analysis – hundreds of thousands to millions of contingencies – per single run.
For more details on the use of Physical and Operational Margins (POM) Suite for N-1-1 contingency analysis, please visit http://www.vrenergy.com.