Virtual Bus Angle for Phase Angle Monitoring and its Implementation in the Western Interconnection

With the deployment of PMUs, phase angle difference monitoring becomes essential to provide situational awareness of the system stress level. In today's control rooms, many physical angle pairs are selected and monitored based on previous operation knowledge. However, under different system operating conditions, the correlation between system stress level and a physical angle pair may change. To solve the challenge to select the most correlated angle pairs under various conditions, this paper proposes the virtual bus angle concept for a transfer path or cut plane. The proposed approach adopts a weighted angle difference that is theoretically highly correlated to the system stress level. Historical measurement data is used to validate the high correlation between the virtual angle difference and path flow. After the validation, virtual angle is implemented in Peak Reliability's OSIsoft PI system for online monitor and in real time transient stability tool, online TSAT, for dynamic limit calculation. The implementation of the virtual bus angle shows promising results as demonstrated through two recent system events in the Western Interconnection.