C. Concordia

Concepts of Synchronous Machine Stability as Affected by Excitation Control

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.

Tie-Line Power and Frequency Control of Electric Power Systems - Part II [includes discussion]

In a previous paper [ibid., vol. 72, pt. III, June 1953, pp. 562-71], the authors presented the results of a study of the performance of two interconnected steam-electric power-generating areas as affected by frequency and tie-line power controllers. The present paper extends this study to include hydroelectric power generating areas as well. As before, the object is to determine theoretically the best values of controller gains, that is, to find those controller settings that will result in best over-all system performance. The principal criterion of good performance is, also as before, the minimizing of any oscillations in tie-line power or system frequency resulting from load disturbances to either area. Thus, stability, rather than rapidity of response, is preferred, since the system actually is continually being disturbed by small and more or less random changes of load, rather than by the step load change used as a test disturbance in the study.

Analysis of Series Capacitor Application Problems

IN THE past several years series capacitors for the compensation of line drop in power circuits have found increasing use,1–9 because improved and automatic voltage regulation can, in many cases, be obtained more economically by this method than by any other means.

Self Excited Torsional Frequency Oscillations with Series Capacitors

The application of series capacitors to compensate long-distance high-voltage transmission lines introduces potential modes of dynamic instability caused by interactions with synchronous machines and turbine-generator shaft torsional resonance. This paper describes the modes of ihstability and analytical methods used to predict the combinations of parameters which may lead to instability. Insight into the phenomena of modal interaction, a factor causing one of the unstable modes, is provided.

Steady-state stability of synchronous machines as affected by voltage-regulator characteristics

STEADY-STATE stability of synchronous machines is an old subject, and the fact that voltage regulators may on occasion increase the stability limit is more or less well known.1 The present paper, however, aims to contribute to the knowledge of the subject by:

Self-Excited Oscillations in a Transmission System Using Series Capacitors

Self-excitation can result from using series capacitors in EHV transmission circuits if the series compensation is large and the circuit resistance small. Such a condition can be realized in a highly compensated transmission line using bundle conductors. An analytical approach to solve for the borderline conditions between stability and instability is presented. The analysis presented is suitable for the simultaneous consideration of both electromechanical (hunting) and primarily electrical (self-excitation) oscillations using lumped circuit constants, or for cases of distributed circuit parameters (long lines and/or solid-rotor generators). Numerical examples are included.

Negative Damping of Electrical Machinery

This paper presents (1) a more nearly complete and exact criterion of instability or hunting of a synchronous machine as influenced by its armature or tie line resistance, (2) a general stability criterion which includes in one formula three previously separately treated cases: the usual steady state power limit, rotor hunting produced by armature resistance, and self-excitation produced by series capacitance in the armature circuit, and (3) an indication, by means of a numerical example, of the limitations of the previously used approximate criterion for hunting due to armature resistance. In previous treatments, hunting, self-excitation, and loss of synchronism have been considered only separately, neglecting their mutual interactions. The present paper, on the other hand, considers their mutual effects and thus provides a general analysis by reference to which the limitations and proper fields of application of the approximate formulas may be found. Application of the complete criterion given is however rather laborious, and it is not suggested for general use in place of the approximate forms.

Synchronous Machine With Solid Cylindrical Rotor

Discussion of a paper by C. Concordia and H. Poritsky published in the January 1937 issue, pages 49–58, and presented for oral discussion at the synchronous machinery session of the winter convention, New York, N. Y., January 27, 1937.

The Doubly Fed Machine

SYNCHRONOUS machines, operating with a-c excitation on both stator and rotor are used in many applications, for example, as induction frequency converters, as power and instrument Selsyn drives, and as variable speed power drives. Reference 1 has mentioned particularly the variable speed fan drive, and presented equations for the small oscillations of one such doubly fed machine. Reference 2 has also previously given the equations of hunting of the doubly fed machine (part XIV, section IV) in connection with the general study of oscillations of rotating machines. However, since the present authors have been using in their own work equations which seem to them to be more convenient and simpler in form for calculations, and since it now seems desirable to present not only general equations but also some of the more fundamental and significant performance characteristics of these machines, it is thought that this paper may now be appropriate. The form of the equations developed possesses the additional novelty of facilitating the setting up of equivalent circuits for hunting on the a-c network analyzer, and allowing the quick determination of the damping and synchronizing torques directly by wattmeter readings.

Effect of Restriking on Recovery Voltage

IT IS well known that when any portion of an electrical circuit is either opened or closed a transient condition will usually exist for some period, depending on the damping, before the circuit assumes its new steady state. In power circuits, such switching operations are the application and removal of faults or loads and the connecting or separating of various parts of a system. The transient conditions resulting from these switching operations give rise in some cases to overvoltages, which can be calculated by straightforward and more or less well-known methods, if the transient circuit parameters are known. However, in some instances voltages much higher than those predicted by such calculations have been obtained, and various explanations1–9 have been offered for these occurrences.