The phenomena of stability of synchronous machines under small perturbations is explored by examining the case of a single machine connected to an infinite bus through external reactance.

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Concepts of Synchronous Machine Stability as Affected by Excitation Control

This paper provides a detailed account of analytical work carried out to determine the parameters of power system stabilizers (PSS) for the Darlington nuclear generating station presently under construction in eastern Ontario. The results presented are, however, of general interest and provide a comprehensive analysis of the effects of the different stabilizer parameters on the overall dynamic performance of the power system. They show how stabilizer settings may be selected so as to enhance the steady-state and transient stability of local plant modes as well as inter-area modes in large interconnected systems. In addition, it is shown that the selected parameters result in satisfactory performance during system islanding conditions, when large frequency excursions are experienced. Darlington GS, when completed by 1992, will comprise four 1100 MVA, 0.85 p.f., 1800 RPM turbine generators with "CANDU-PHW" reactors, moderated and cooled by heavy water. The station will be incorporated into the 500 kV network through three double-circuit lines. The units will be equipped with transformer-fed thyristor excitation systems and Delta-P-Omega type PSS [1, 2].

Application of power system stabilizers for enhancement of overall system stability

This paper demonstrates the use of genetic algorithms for the simultaneous stabilization of multimachine power systems over a wide range of operating conditions via single-setting power system stabilizers. The power system operating at various conditions is treated as a finite set of plants. The problem of selecting the parameters of power system stabilizers which simultaneously stabilize this set of plants is converted to a simple optimization problem which is solved by a genetic algorithm with an eigenvalue-based objective function. Two objective functions are presented, allowing the selection of the stabilizer parameters to shift some of the closed-loop eigenvalues to the left-hand side of a vertical line in the complex s-plane, or to a wedge-shape sector in the complex s-plane. The effectiveness of the suggested technique in damping local and inter-area modes of oscillations in multimachine power systems is verified through eigenvalue analysis and simulation results.

Simultaneous stabilization of multimachine power systems via genetic algorithms

This part of a three-part paper deals first with the performance objectives of power system stabilizers in terms of the type of oscillations for which they are intended to provide damping, the operating conditions for which the requirement for stabilization is greatest, the need to accommodate multiple modes of oscillation, and the significance of interplant modes of oscillation. It next treats stabilizer tuning. General tuning guidelines are developed as well as variations required for different input signals. The operating conditions under which each type of stabilizer should be tuned are identified. The relationship between phase compensation tuning and root locus analysis is presented. Finally, the relative performance characteristics of the three types of stabilizers are examined for both small perturbations and large disturbances.

Applying Power System Stabilizers Part II: Performance Objectives and Tuning Concepts

For an optimal linear regulator design a performance function of the quadratic form must be chosen. The question arises of how to decide the weighting matrix Q of the performance function. A new method is developed in this paper to determine Q in conjunction with a left shift of the dominant eigenvalues as far as the practical controllers permit. The method is then applied to the optimal control design of a typical power system. Three cases are investigated, the first with an optimal excitation control uE, the second with optimal governor controls uG and uG, with and without the dash-pot, and the third with uE plus uG control. The stabilizing signals thus obtained are given nonlinear tests on the same power system. It is found from the results that the optimal controls are more effective than conventional excitation control, that the optimal governor control without dash-pot is just as good as the optimal excitation control, and that the optimal uE plus uG control is the best way to stabilize a power system.

Optimal Power System Stabilization Through Excitation and/or Governor Control

A device to provide a signal proportional to changes in generator speed has been developed by Ontario Hydro. Field tests have been performed to demonstrate that use of this signal with a high-speed rectifier excitation system results in dynamic stability limits which approximate those which can be obtained with a zero reactance generator. Transient stability limits are greater than those obtainable with high-response conventional excitation systems. Results from the field tests and a computer study are compared.

Effect of High-Speed Rectifier Excitation Systems on Generator Stability Limits

Excitation systems which utilize controlled rectifiers supplied directly from the generator terminals for the main exciter are in service at four remote generating stations. Due to the nature of the power system, these excitation systems were designed to withstand high ac overvoltages and to provide simultaneous control of a number of parallel generators. Experience in testing and operating these excitation systems is described.

Kenneth R. McClymont

Papers

Effect of High-Speed Rectifier Excitation Systems on Generator Stability Limits

Experience with high-speed rectifier excitation systems