Principles of Automatic Emergency Control

by V. A. Venikov

The emergency control consists of individual (self-contained) devices. It should be remembered, however, that all those devices respond to the parameters of a single electro-mechanical transient process evolving in the system and control it. The devices, therefore, become interrelated through the controlled process. We may therefore consider the emergency control as an integrated system, though certain of its apparatus perform individually. In its progress, the emergency control technology tends to overcome this disintegration of apparatus and become integrated in all respects.

With the emergency control schemes considered as an integrated system, we may say that its main purpose during disturbances of the normal operating conditions is to keep those conditions within the permissible range or get them back into the range. Comparing it with other control systems; we may draw a parallel with the modern systems of optimal control which control the motion along certain paths subject to the movement speed and energy change. The processes in power systems are rapid, and to obtain the desired results the control has to use all of its utmost means.

Attempts to optimally control electromechanical transients in power systems have revealed a specific feature of a power system. In most cases the effect caused on it by the emergency control can be of one sign only. Thus, power plant generators, for instance, can be rapidly switched off only, whereas their reconnection takes far more time, measured in minutes and sometimes in tens of minutes. The same case is with the steam turbines which are quick only in stopping steam admittance, while its readmittance takes much longer time. Such installations make a majority in electrical utilities, whereas the abilities of control actions in either direction (forcing and deforcing generators, for instance) at equal or close speeds are scarce exceptions, though fairly useful.

At the same time all methods of optimal control theory use, as a rule, alternating actions of both signs. Hence, the application of optimal control theory to the emergency control produces as yet fairly modest results. Basic concepts and techniques in this field most often employ conventional methods of analyzing electromechanical transients in power systems, i.e. stability studies and the investigation of measures to improve the stability.

The study of emergency control automatic equipment falls into several closely interrelated problems which involve the analysis of contingencies in power systems of diverse configurations, study of methods to control electromechanical transients that can be utilized at power stations and networks of different types, and also familiarization with the methods of detecting emergency situations and aids for the containment for emergencies under such circumstances. In parallel with optimal control theory the latter operation is known as search for control strategy, the control being any action of the emergency control on a power system.

Problems of the emergency control theory are concerned with the study of stability or form part of it. However, the emergency control equipment is called upon not only to assess the stability level of a given real operating condition or conditions taken as a whole, but also to reveal measures providing the required value of this level (or a maximally possible level, if the required value cannot be achieved).

Lately many stability studies have been done with reference to, the design of emergency control (structure and settings) with a view of providing control over the process.

Generally calculations of steady-state, and transient stability are carried out for substantially simplified models in which system parts are substituted by their electric, magnetic, and mechanic equivalents. This simplification is used because the process flow can be clearly traced, a method of a process control can be chosen, and emergency control automatic facilities can be properly arranged only in a model of simple configuration.

Venikov, V. A. Electric Power Systems: Automatic Power Systems Control /translated from  Russian by Y. M. Matskovsky. – Moscow: MIR Publishers, 1982. – 445 p. (Pp. 362-364).

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