T. Van Cutsem

Definition and classification of power system stability IEEE/CIGRE joint task force on stability terms and definitions

The problem of defining and classifying power system stability has been addressed by several previous CIGRE and IEEE Task Force reports. These earlier efforts, however, do not completely reflect current industry needs, experiences and understanding. In particular, the definitions are not precise and the classifications do not encompass all practical instability scenarios. This report developed by a Task Force, set up jointly by the CIGRE Study Committee 38 and the IEEE Power System Dynamic Performance Committee, addresses the issue of stability definition and classification in power systems from a fundamental viewpoint and closely examines the practical ramifications. The report aims to define power system stability more precisely, provide a systematic basis for its classification, and discuss linkages to related issues such as power system reliability and security.

A method to compute reactive power margins with respect to voltage collapse

A method of computing the reactive power margin-i.e. the difference between the maximum reactive load and the corresponding base case value-for a given set of load buses of a power system is proposed. This margin is aimed at assessing the system robustness with respect to voltage collapse. The corresponding collapse point is directly obtained as the solution of an optimization problem with the load increase as the objective, the nonoptimized loads as equality constraints, and the generator reactive limits as inequality constraints. The CRIC electrical decoupling yields a voltage-only problem. The latter is solved using the Newton approach and a procedure is given to deal with the inequality constraints efficiently. A simple illustrative example and simulation results obtained on the Belgian 520-bus, 41-generator system are given. >

A simple direct method for fast transient stability assessment of large power systems

A method for online transient stability assessment of large power systems is proposed. It consists of: replacing the multimachine system by a two-machine dynamic equivalent, further amenable to a one-machine-infinite-bus system; reducing the stability problem to a sole algebraic equation, devised from the equal area criterion, or equivalently from the Lyapunov direct criterion; and using this equation to derive one-shot stability analysis strategies. A technique for system admittance matrix reduction is developed that proves efficient, especially for large systems and multiple-contingency evaluation. The methods main appeal is rapidity: it is about one order of magnitude faster than the most efficient direct criterion. Other attractive features are flexibility and ability to encompass various simulation conditions. Extensions to online sensitivity analysis and control are suggested. >

Wide-Area Detection of Voltage Instability From Synchronized Phasor Measurements. Part I: Principle

This two-part paper deals with the early detection of an impending voltage instability from the system states provided by synchronized phasor measurements. Recognizing that voltage instability detection requires assessing a multidimensional system, the method fits a set of algebraic equations to the sampled states, and performs an efficient sensitivity computation in order to identify when a combination of load powers has passed through a maximum. The important effects of overexcitation limiters are accounted for. The approach does not require any load model. This first part of the paper is devoted to theoretical foundations of sensitivity calculation along the system trajectory, derivation of the algebraic model, and illustration on a simple five-bus system involving the long-term dynamics of a load tap changer and a field current limiter.

A comprehensive analysis of mid-term voltage stability

This paper proposes a comprehensive approach to mid-term voltage stability, combining fast simulation, instability diagnosis and corrective control determination. The fast simulation approximates the mid-term evolution by a succession of equilibrium points, thereby offering a good compromise between efficiency and accuracy. The instability diagnosis and corrective control determination consist of fast sensitivity analyses at some points of the simulated system trajectory, in order to identify critical points and determine the smallest changes in power injections required to recover stability. The method is illustrated on a real-life 1200-bus modelling of the French Western system. >

An approach to corrective control of voltage instability using simulation and sensitivity

This paper deals with the diagnosis of power system voltage collapse situations, following large disturbances and/or load increases. A method is proposed to identify the set of buses where load restoration is responsible for the collapse and to determine the corresponding corrective actions. It has been implemented in a fast voltage stability simulator, using sensitivity techniques. Tap changer blocking and load shedding are illustrated on a real-life 410-bus system. >

Securing Transient Stability Using Time-Domain Simulations Within an Optimal Power Flow

This paper provides a methodology to restore transient stability. It relies on a well-behaved optimal power flow model with embedded transient stability constraints. The proposed methodology can be used for both dispatching and redispatching. In addition to power flow constraints and limits, the resulting optimal power flow model includes discrete time equations describing the time evolution of all machines in the system. Transient stability constraints are formulated by reducing the initial multi-machine model to a one-machine infinite-bus equivalent. This equivalent allows imposing angle bounds that ensure transient stability. The proposed optimal power flow model is tested and analyzed using an illustrative nine-bus system, the well-known New England 39-bus system, a ten-machine system, and a real-world 1228-bus system with 292 synchronous machines.

Validation of a fast voltage stability analysis method on the Hydro-Quebec system

This paper reports on tests validating a fast voltage stability analysis method, envisaged for operational planning and real-time applications. The simulation method relies on quasi-steady-state approximation, replacing the transient dynamics with equilibrium equations and focusing on the long-term dynamics. Various comparisons have been performed with full time simulation, on the 514-bus Hydro-Quebec system. The accuracy is equivalent while the new method is up to 3 orders of magnitude faster.

Wide-Area Detection of Voltage Instability From Synchronized Phasor Measurements. Part II: Simulation Results

This two-part paper deals with the early detection of an impending voltage instability from the system states provided by synchronized phasor measurements. Recognizing that voltage instability detection requires assessing a multidimensional system, the method fits a set of algebraic equations to the sampled states, and performs an efficient sensitivity in order to identify when a combination of load powers has passed through a maximum. This second part of the paper presents simulation results obtained from detailed time-domain simulation of the Nordic32 test system, without and with measurement noise, respectively. Several practical improvements are described such as anticipation of overexcitation limiter activation, and use of a moving average filter. Robustness to load behavior, non-updated topology and unobservability is also shown. Finally a comparison with Thevenin impedance matching criterion is provided.

An educational simulation tool for power system control and stability

This paper presents a Simulink-based educational tool developed for the purpose of illustrating power system control and stability notions as well as introducing students to realistic, though tractable in size, design problems. Relevant courses are taught to last-year undergraduate as well as graduate students at the University of Lie/spl grave/ge, Belgium, and the National Technical University of Athens, Greece. After a brief description of the corresponding curricula, the paper describes the simulation tool and gives examples of problems and assignments given to the students.