Real-time Adaptive Load Shedding based on Probabilistic Overload Estimation

JAIME CEPEDA; DIEGO RAMIREZ; D. GRACIELA COLOMÉ

Medellín

Congreso; IEEE Transmission and Distribution Latin America 2014; 2014

IEEE PES Colombia

In recent years, important efforts to improve monitoring, protection and control of power systems have been explored. In this connection, several novel approaches for assessing vulnerability and improving security in real time have been developed. However, most of the work is commonly focused on tackling stability phenomena, while the possible overloads are often treated as negligible in real-time power system security. But sometimes, high electric post-contingency currents might provoke overloads which could increase the system security problem. This paper tackles the possible overload issues by applying a novel adaptive load shedding (ALS) method. First, the possibility of fast post-contingency overloads is evaluated using Statistical Distribution Factors (SDFs) that allow computing an Overload Index (OVI) in real time. The results are then used for triggering an adequate ALS scheme that allows improving the system security level when the OVI reaches a critical value. For this purpose, Monte Carlo-based contingency analysis is firstly performed to iteratively calculate ac Distribution Factors (ac-DFs). After, SDFs are defined by the mean of ac-DFs. These SDFs are then used together with principal component analysis (PCA) and support vector machine classifier (SVM-C) in order to structure a table-based real-time post-contingency overload estimation algorithm, which allow computing OVIs depending on the actual operating state and the type of contingency. In the cases where OVI reaches inadmissible levels, an ALS scheme is triggered using a centralized strategy. The aim is to alleviate the current in overloaded transmission lines before the local overload protection acts, since it might initiate a cascading event that would eventually drive the system to a blackout. The proposal is structured to act in coordination with the traditional underfrequency and undervoltage load shedding. For this purpose, PMU measurements of voltage phasors and frequency are used for evaluating the event evolution in order to determine the adequate amount of load to be shed due to overload problems. The scheme also determines the location of the load to be shed by analyzing the participation of each load in the overloaded line via the computation of electrical distances between the overloaded-line receiving-end bus and the load bus. The proposal is tested on the IEEE New England 39-bus test system. Results show the feasibility of the methodology in alerting about possible overloads and defining an appropriate ALS scheme that allows alleviating the current in the possible overloaded lines.