Abstract
For transient stability analysis of a multi-machine power system, the Extended Equal Area Criterion (EEAC) method applies the classic Equal Area Criterion (EAC) concept to an approximate One Machine Infinite Bus (OMIB) equivalent of the system to find the critical clearing angle. The system-critical clearing time can then be obtained by numerical integration of OMIB equations. The EEAC method was proposed in the 1980s and 1990s as a substitute for time-domain simulation for Transmission System Operators (TSOs) to provide fast, transient stability analysis with the limited computational power available those days. To ensure the secure operation of the power system, TSOs have to identify and prevent potential critical scenarios through offline analyses of a few dangerous ones. These days, due to increased uncertainties in electrical power systems, the number of these critical scenarios is increasing, substantially, calling for fast, transient stability analysis techniques once more. Among them, the EEAC is a unique approach that provides not only valuable information, but also a graphical representation of system dynamics. This paper revisits the EEAC but from a modern, functional point of view. First, the definition of the OMIB model of a multi-machine power system is redrawn in its general form. To achieve fast, transient stability analysis, EEAC relies on approximate models of the true OMIB model. These approximations are clarified, and the EAC concept is redefined with a general definition for instability, and its conditions. Based on the defined conditions and definitions, functions are developed for each EEAC building block, which are later put out together to provide a full-resolution, functional scheme. This functional scheme not only covers the previous literature on the subject, but also allows to introduce several possible new EEAC approaches and provides a detailed description of their implementation procedure. A number of approaches are applied to the French EHV network, and the approximations are examined.
Highlights
To ensure the secure operation of the power system, Transmission System Operators (TSOs) perform offline Transient Stability Analysis (TSA) for a few dangerous scenarios and design remedial actions for the critical ones, i.e., the ones with lower Critical ClearingTime (CCT) (CCT is the maximum fault elimination time without the system losing its capability to recover a normal operating condition [1])
For a multi-machine power system, the idea of Equal Area Criterion (EEAC) was proposed in the late 1980s
All One Machine Infinite Bus (OMIB)-based transient stability analysis methods rely on the observation that the loss of synchronism involves the irrevocable separation of generators into two groups: critical generators and non-critical generators [1]
Summary
To ensure the secure operation of the power system, Transmission System Operators (TSOs) perform offline Transient Stability Analysis (TSA) for a few dangerous scenarios and design remedial actions for the critical ones, i.e., the ones with lower Critical Clearing. (i) power system classical model is valid and (ii) the angles of machines within each of the groups are equal to the center of angle of the group These assumptions lead to a time-invariant OMIB model on which the EAC can be applied. The various approaches proposed differ in many respects, but they all rely on the same concept, the OMIB transformation These days, power systems are operating closer to their security limits and the uncertainties are increasing. Though the recent significant reduction, time-domain simulation computational time is still restrictive for the growing list of case studies, calling for fast, transient stability analysis techniques once more. A number of the approaches are applied to two test systems to provide a detailed comparison
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