Scoping Study Report on Improving Load and Generator Response Models (Real-Time Grid Reliability Management PIER Final Project Report Appendix G)

This report is a scoping study to examine research opportunities to improve the accuracy of the system dynamic load and generator models, and data and performance assessment tools used by California ISO operations engineers and planning engineers, as well as those used by their counterparts at the California utilities, to establish safe operating margins.

Model-based simulations are commonly used to assess the impact of credible contingencies to determine system operating limits (path ratings, and so forth) to ensure compliance with North American Electric Reliability Corporation (NERC) and Western Electricity Coordinating Council (WECC) reliability requirements. Improved models and a better understanding of the impact of uncertainties in these models will increase the reliability of grid operations by allowing operators to more accurately study system voltage problems and the dynamic stability response of the system to disturbances.

Secure operation of the grid relies on advanced planning for credible contingencies. Anticipatory studies are used to establish operating limits for secure operation as established by NERC and WECC reliability criteria. The criteria have very specific goals, for example, "The interconnected power system shall be operated at all times so that general system instability, uncontrolled separation, cascading outages, or voltage collapse, will not occur as a result of any single contingency or multiple contingencies of sufficiently high likelihood." This famous N-1 criterion, by itself, does not provide specific guidance to achieve this goal. Additional criteria are concretely specified in terms of measurable system quantities such as voltage, frequency, active and reactive power flows, and other measures derived from these. For the initial response after an event, reliability criteria specify the allowable ranges for transient deviations in voltage and frequency. Adherence to these criteria should prevent catastrophic failures. To study these transient events, model-based computer simulations are required to predict the system response to possible contingencies. It is the adequacy of these models that is the subject of this report.