Impacts of Constraint Relaxations on Power System Operational Security

Constraint relaxations by definition mean that certain constraints are allowed to be violated in energy market models for a pre-determined penalty price. System operators utilize this mechanism in an effort to impose a price-cap on shadow prices in the markets. In addition, constraint relaxations can serve as corrective approximations that help to reduce the occurrence of infeasible or extreme solutions in market models. This paper aims to capture the impact constraint relaxations have on AC operating conditions. Moreover, this analysis also provides a better understanding of the correlation between DC market models and AC systems, and analyzes how relaxations in market models propagate to system operations. This information can be used to assess the risk associated with constraint relaxations. The practice of constraint relaxations was replicated in this paper using a test case and a real-life large-scale system, while capturing both the energy market aspects and AC system performance. System performance investigation included static and dynamic security analyses for base-case and post-contingency conditions.