Transient Stability Program Research Articles

Computational Aspects in Practical Application of Lyapunov Method to Power Systems

For online transient security monitoring quick determination of critical clearing time is one of the most important requirements. Repeated integration of system equations, for this purpose, is ruled out. Recent approaches have favoured Lyapunov method. However,the work on fast and accurate determination of stability region by this method is not yet complete. In this paper, available control theory for systems with single nonlinearity is extended to multi-nonlinear systems and is applied to multimachine power systems. It has been shown that a vast majority of points, searched hitherto, for computing the minimum of Lyapunov function, are not necessary. The approach drastically reduces the number of search points and gives reasonable estimates of stability regions even in those cases where other methods have not succeeded. This is illustrated by a 5 machine and a 13-machine system. It is hoped that this method will provide a basis for online transient stability programs.

Verification of Synchronous Machine Modeling in Stability Studies: Comparative Tests of Digital and Physical Scale Model Power System Simulations

The adequacy of digital models of synchronous machines in conventional transient stability programs has been of continuing interest and concern to engineers involved in system planning and operating studies. To verify the adequacy of such models a comparative test approach is taken by running a series of tests on the AEP Transient Stability Program and on the MIT Physical Scale Model facility which closely approximates actual system dynamic performance characteristics. The paper summarizes the results of these studies and shows good correlation between the two simulations. Also, the results confirm the findings of others that existing models and associated parameters may need to be improved for certain types of dynamic performance studies and operating conditions.

An efficient algorithm for simulation on transients in large power systems

The simulation of the transient response of a large interconnected power system involves the solution of a very large system of differential-algebraic equations under a great variety of initial conditions and disturbances. The demands imposed on a digital transient stability program to i) study larger power system interconnections, ii) provide a more detailed representation of the power system components, and iii) permit the simulation of longer time periods, have the effect of increasing the computing time. The importance of, and the need for, efficient computational schemes is apparent. The method presented in this paper makes detailed use of the structural properties of the differential-algebraic system representation. The nonlinear differential-algebraic system is split into a nonstiff part with long time constants coupled to a stiff part with a sparse Jacobian matrix whose longest time constant is shorter than that of the first part. These two parts are linear in their respective states, i.e., the system is semilinear. With the nonstiff part removed, a smaller set of stiff equations with a smaller conditioning number than the original system is obtained. Consequently, longer stepsizes can be used so as to reduce the computation time. The proposed multistep integration schemes exploit the stiffness and semilinearity properties. Numerical results on a small test problem indicate that these schemes operate with good accuracy at stepsizes as large as 100 times those necessary to ensure numerical stability by more conventional schemes.

Dynamic equivalents from on-line measurements

This paper presents the results of a feasibility study of a technique for identifying dynamic equivalents of portions of a power system from measurements made only within a restricted Study System without intentional perturbation of the system. The Maximum Likelihood technique is used to identify parameter values for a specified equivalent structure which is suitable for direct use in standard transient stability programs. The identifier was tested using measurements from simulations tuned to match field measurements. The field measurements, identification algorithm, and program test results are described. The expected benefit of this technique is in overcoming a major block in the development of an on-line technique for the evaluation of transient stability contingencies by power system operators.

Solution methods for transient and dynamic stability

The transient stability study is used to examine the dynamic behavior of a power system following a disturbance. Transient stability programs have grown in the size of the power system under study, in the duration of the study, and in the magnitude of the disturbance. Each prime mover is represented by as few as two or as many as forty ordinary differential equations. These equations are coupled to a set of algebraic equations (two per node) which describe the network. Available programs frequently use explicit fixed step integration methods and the sequential solution of the differential and algebraic equations. Recent advances in solution methods have been directed toward implicit integration techniques and the simultaneous solution of the whole set of differential-algebraic equations. The transient stability problem, the unit models currently in use, and recent advances in solution methods are briefly reviewed. A dynamic stability program is described which incorporates comprehensive dynamic models of prime movers; the results of several experiments using this program are presented.

A Non-Iterative Transient Stability Program Including the Effects of Variable Load-Voltage Characteristics

Techniques are developed for improving the speed of solution of transient stability studies which include the effects of synchronous machine amortisseur circuits and nonlinear variable-voltage loads. A fast, non-iterative method of solving the algebraic equations involving only direct matrix multiplication is discussed. Results of computer tests on a complex multi-machine system demonstrating the importance of load modelling and the effectiveness of the new proposed non-iterative solution technique are presented.

New Techniques for the Calculation of Dynamic Stability

A 100-machine transient stability program has been developed which represents the effects of machines much more completely than has been available previously. Both d-and q-axis quantities are fully represented and saturation effects in both axes are incorporated. The speed-governing and voltage-regulating systems available are extensive and complete, thus allowing a very close approximation to any physical system. Facilities for nonlinear loads and induction motor transients are also included.

A Digital Transient Stability Program including the Effects or Regulator, Exciter, and Governor Response

A Digital Transient Stability Program including the Effects or Regulator, Exciter, and Governor Response