1978_spectrum_stress_strain.pdf

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LARGE SYSTEMS

P o w e r / e n e r g y- - - -

Operat ing unders t ress and s t ra in

This, part two of the blackout series, defines controlobjectives for various levels and types of emergencies

In the U.S. today, complex power systems are able to pro-

vide reliable electric service at low cost with the help of

automatic control-simultaneously tracking the random-

ly varying system load, optimizing generation to minimize

cost, and coordinating the action of many independent

control centers. When an develops in one of

these systems, however, the picture changes completely

and new control objectives must be met if the system is to

be restored successfully to normal operation.

The control objectives of a power system are related

to the level of security at which the system is operating,

and (see box 50) as this level decreases below an ac-ceptable threshold, preventive measures must be taken to

restore the system to a robust state. It is rare that a major

system failure is the result of one catastrophic disturbance

that wipes out an apparently secure system. Usually such

failures are brought about by a reduced level of security

that renders the system vulnerable to the cumulative ef-

fects of a sequence of moderate disturbances. The systems

have been designed and built to operate as efficiently as

possible under normal circumstances. In the event of the

loss of a piece of major equipment (whether due to an in-

ternal fault or an external event) with its resultant instan-

taneous surges of power, the system must be to

sorb these stresses without further damage and to find a

new balance of flows. Coincidence of disturbances

and/or hidden weaknesses in system components or con-

trol functions can combine to produce momentary local

stresses beyond any level of endurance to which the

system could possibly be designed within reasonable

economic limits.

Emergencies can strike suddenly-or build slowly. Dur-

ing these emergencies, the system operator (human or

automatic) struggles to keep the system under control-to

maintain balance between load and generation, or de-

mand and supply, through all available means. However,

there are two factors that can doom these efforts to

failure: time constraints-the inability to quickly

enough; and capacity constraints-demand outstripping

available supply. Recent blackouts have been in the first

category. Hut in January 1977, several interconnected

utilities appeared to be headed toward a failure of the se-

cond kind when, in some areas of the U.S., unusually

severe winter temperatures froze such crucial resources as

coal piles and waterways and greatly limited generating

System frequency, a sens i t ive of

discrepancy between load and generation, sagged to 59.84

Hz, and remained below 60 Hz for almost seven hours.

- -

Lester H. U.S. Department of Energy

Carlsen General Electric Company

During this period, the available power supply was re-

duced to a critical level.

When the ca re fu l l y cons t ruc ted and ma in ta ined

dynamic system structure (see box on 51) begins

to reel under the impact of a major disturbance, and is on

the verge of disintegrating, the regimes

normal circumstances are no longer adequate, or rele-vant, and new controls are necessary. However, before

such controls can be discussed, the general states of

operation of a power system should be considered.

States of operation ,

Power sys tem cond i t ions are descr ibed by f ive

operating states, as shown in Fig. Three sets of generic

equations-one differential and two algebraic-govern

operation: The differential set encodes the

physical laws governing the dynamic behavior of the

systems components. The two algebraic sets

equality constraints, which refer to the systems total

load and total generation, and inequality constraints,

which state that some system variables, such as currents

and voltages, must not exceed maximum levels

tidg the limitations of physical equipment.

the a l l constra in ts are

satisfied, indicating that the generation is adequate to

supply the existing total load demand, and that no equip-

ment is being overloaded. In this state, reserve margins

(for transmission as well as for generation) are sufficient

to provide an adequate level of security with respect to the

stresses to which the system may be subjected.

If the security level falls below some threshold of ade-

quacy, or if the probability of increases, then

the system enters the this state, all

straints would still be satisfied, but existing reserve

margins would be such that some disturbance could result

in a violation of some inequality constraints; e.g., equip-

ment would be overloaded or less severely above its

rated capabilities. In this (insecure) alert state, preventive

action can be taken to restore the system to the normal

state (see Table I).

If a sufficiently severe disturbance takes place before

preventive action can be taken, the system enters the

Here, inequality constraints are violated,

and system security would have been breached since the

security level would be below zero and practically

nonexistent. The system, however, would still be intact,

and emergency control action (heroic measures)

be initiated in order to restore the system to at least

alert state. If these measures are not taken in time, or are

ineffective, if the initiating disturbance or a

one is severe enough to overstress the system, the

system then starts to disintegrate and is ( s e e


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I). this staie, equality as well as inequality con-

straints have been violated; the system would no longer be

intact, and major portions of the system load would be

lost. Emergency control action should be directed toward

salvaging as many pieces of the system as possible from

total collapse. Once the collapse had been halted, if there

were any remaining equipment operating within rated

capability, or some equipment had been restarted follow-

ing total collapse, the system enter the restorative

with control action being taken to pick up all lost

load and reconnect the system. From this state, the system

could transit to either the alert or to the normal state,

depending on circumstances.

So far, precise definitions characterizing the several

states discussed have not been provided. Without such

definitions, the indicated framework can be of heuristic

value only; judgment as to whether the system has moved

from one state to another will be subjective at best, and

possibly arbitrary. Nevertheless, even at this level this

framework can contribute significantly not only by clari-

fying analyses of the histories of disturbances but, more

important, by providing some guidance as to the controls

to be effected under certain circumstances or the operator

decisions to be implemented (see Fig. 1).

Given a consistent set of definitions of each state,

necessary and/or sufficient conditions for state

the problem involved in on-line security assessment

could provide considerable insight into the design of con-

trol strategies proper to several states.

preventionHistorically, system security been approached by

way of reliability; planning and building systems that

could be inherently robust in the face of credible (and

some incredible) disturbances. Typically, the assessment

was carried out in the planning stage by way ofsimulating

the response of the projected system to a of

hypothesized severe (worst case) disturbances. Such

have served as a means to measure the strength andcapacity of a system to withstand the entire of

disturbances under stress conditions. Systems designed to

such criteria have proved reliable under all but

unusual circumstances.

However, no absolute guarantee of reliable perfor-

mance can be provided by the system planner for even the

best planned and constructed system. The system

operator is ultimately responsible for maintaining effec-

tive operation of the system under all circumstances.

Following the Northeast blackout of 1965, increasing

System operating states.

Reduction in reserve

and/or increasedprobabi l i ty of disturbance


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Table I). In this state, equality as well as inequality con-

straints have been violated; the system would longer be

intact, and major portions of the system load would be

lost. Emergency control action should be directed toward

salvaging as many pieces of the system as possible from

total collapse. Once the collapse had been halted, if there

were any remaining equipment operating within rated

capability, or some equipment had been restarted follow-

ing total collapse, the system enter the

with control action being taken to pick up all lost

load and reconnect the system. From this state, the system

could transit to either the alert or to the normal state,

depending on circumstances.

So far, precise definitions characterizing the several

states discussed have not been provided. Without such

definitions, the indicated framework can be of heuristic

value only; judgment as to whether the system has moved

from one state to another will be subjective at best, and

possibly arbitrary. Nevertheless, even at this level this

framework can contribute significantly not only by clari-

fying analyses of the histories of disturbances but, more

important, by providing some guidance as to the controls

to be effected under certain circumstances or the operator

decisions to be implemented (see Fig. 1).

Given a consistent set of definitions of each state,

necessary and/or sufficient conditions for state

could be identified. Such definitions could simplify

the problem involved in on-line security assessment and

could provide considerable insight into the design of con-

trol strategies proper to the several states.

Emergency prevention

Historically, system security has been approached byway of reliability; planning and building systems that

could be inherently robust in the face of credible (and

some incredible) disturbances. Typically, the assessment

was carried out in the planning stage by way of simulating

the response of the projected system to a number of

hypothesized severe (worst case) disturbances. Such tests

have served as a means to measure the strength andcapacity of a system to withstand the entire spectrum of

disturbances under stress conditions. Systems designed to

such criteria have proved reliable under all but the

unusual circumstances.

However, no absolute guarantee of reliable perfor-

mance can be provided by the system planner for even the

best planned and constructed system. The system

operator is ultimately responsible for maintaining effec-

tive operation of the system under all circumstances.

Following the Northeast blackout of 1965, increasing

System operating states.

Reduction in reserveand/or increased

of disturbance

- - - - - - _ _

- -

System not System

E:


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was to the problem security

assessment-the provision of data-gathering and

-processing systems that would assist the operator in an-

ticipating potential trouble and then deciding how to pre-

vent it or to minimize its impact. Naturally, the problem

has been approached as suggested by established planning

procedures. Present test procedures consider the given cir-

cumstances (loads, line flows, generating capacity, spin-

ning then check to see whether the system

can withstand possible specific disturbances-such as the

loss of a major generating unit or station or of one or

more major transmission lines.

This planning-oriented approach to such security

assessment involves two operations: gathering informa-

tion about the present status of the system (the power

system state estimation problem), and calculating whether

the system will maintain stable operation in the face of a

designated list of severe disturbances. These operations,

straightforward in a planning environment, become very

difficult to handle in an operating, real-life situation by

virtue of the vast amount data that

must be processed, the practically limitless number of

contingencies (possible combinations of equipment losses)

State estimation programs filter incoming data on

generation, bus loads, on-line currents, and/or bus

voltages in order to provide an Accurate picture of the

systems condition. Contingency lists are carefully

assembled. The ability of the system to maintain stable,

steady-state operation following a disturbance is assessed

either by inspection of precalculated distribution factors

(approximate but very rapid) or by on-line load flows

(more accurate but more time consuming). However,

because of the time required for simulation, it is not prac-

tical to calculate the systems stability performance during

the transient period between the predisturbance and

postdisturbance steady state.

These procedural problems-the amounts of data, the

number of contingencies, and the time required to assess

transient stability-could be resolved at a more basic level

by taking a more operator-oriented approach to security

assessment.

As has been mentioned, system disruptions

almost invariably result from the inability of a system

operating at a reduced level of security to endure the con-

sequences of a series of less than major disturbances.

Consider the possibility of a sequence of rather minor

that must be considered, and the length of time needed to events that may result in the removal of equipment such

determine by simulation the response of the system to any as transmission lines or generation units. This sequence of

one (let alone all) of these contingencies. Despite these events will gradually reduce the security level or the

procedural difficulties, rudimentary security assessment robustness of the system to such an extent that even a

programs are being developed and some have been mal contingency may be all that is needed to cause aplemented. drastic system failure. Even under normal operation, the

Basic definitions

Reliability, security, and stability are related terms. For relatively modest disturbances whose cumulative impact

the purposes of this article, is considered as on the system can be severe.referring to the probability (in the heuristic sense of Cons ider a we l l -known example-the New York

relative frequency over the long run) of satisfactory blackout of July 13, 1977. Initially, the Consolidatedsystem performance. This is a function of the sion system was experiencing a normal summer peak.

average performance of the system, and its achievement Most of the generation was located in a northern sectionis a system planning problem. By contrast, security is of the service area and considerable power was imported

considered to be an instantaneous, time-varying the north. Hence the situation was fairly typical for

that is a function of the of the system Con Edison. However, at the same time, the area withinrelative to imminent disturbances. a narrower the Con Edison System was experiencing a severecondition concerning the continuance of parallel, thunderstorm. Under those conditions, lightning struckchronous operation of all operating units (synchronous lines connecting Con togenerators) of a is a very Important factor in north of New York. This constituted a very severesecurity. disturbance and may be regarded as a multiple

Security, therefore, is an operating problem. Obviously, cy due to the resulting loss of two major transmissionreliability and security are related: A system built to be lines. The system did hold together and recover, but thereliable will not be vulnerable to run-of-the-mill distur- newly established operating situation was at abances and hence will evidence a reasonable degree of siderably lower security level. In addition, the weather insecurity most of the time. At times, it will pass through the New York area was still very bad. At this reducedperiods of relative insecurity. If major disturbances do not security level, subsequently another section of theoccur during insecure periods, or if the system manages system was struck by lightning and the resulting

ride them out whenever they do occur, the system will ing operations isolated additional equipment. Underhave proved reliable even though sometimes less than normal conditions, this contingency by itself would notsecure. By contrast, an unreliable system will be subject have been difficult to contend with. However, due to theto frequent complete breaches of its security. extreme reduction in the security level of the system at

Thus defined, the security (or security level) of a system this time, this additional disturbance caused a number ofis determined by the relationship between its reserve critical transmission-line overload situations, which

margin (i.e., the margin between actual line power flows eventually to the total collapse of the system. (Thisand the corresponding line power transfer capabilities) on discussion has been simplified in order to illustrate thethe one hand, and the contingent probability of concept of security level. For more complete details,bances on the other. seems clear that under normal see the February issue of Spectrum, pp. 38-46.)conditions a given system could be considered secure Finally, it may be helpful to distinguish betweenwith relatively modest reserve margins, whereas under assessment and security enhancement . Secur i tymore risky (unusual) circumstances (e.g., severe storms), assessment refers to the evaluation of system-derivedmuch higher margins would be required for comfort. The data assess its relative robustness in its present state.threat posed by severe storms involves not only an in- Security enhancement refers to specific operationscreased probability of more severe disturbances, but, tine to improve system robustness, and to raise themore important, an increased probability of a sequence of formance level of system security.


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outage of individual pieces of equipment due failure,

inadequate maintenance, etc., often reduces the system to

a less secure, less than its design level.

is necessary to distinguish between the static descrip-

tion of reliability (which serves as a basis for

system design and in large measure is still utilized as a

basis security and the dynamic interplay in

real time between a fluctuating level of security as a

system responds to sequences of events and the continual-

ly contingent probability of disturbances. In

light of these the role of security assess-

ment might be viewed as providing to the operator infor-

mation on the changing reserve margins of his equipmentand the continually changing probabilities of possible

disturbances. Thus, the traditional system planning ap-

proach, as well as the system operators approach, must

be used in emergency prevention.

In addition to security assessment security enhancement

must be taken into account. The system operator

operate the system with (just) enough margin to pro-

vide insurance against the ultimate loss of power to a large

portion of his customers. He must take into account not

only the security level of his system but also the possibility

of disturbances that may threaten and disrupt the system.

Thus, security enhancement must remain the sole domain

of the operator. Experienced system operators continually

make structural readjustments to the system, increase or

adjust level of operating reserves, and reschedule

generation to maintain necessary levels within critical

geographical areas. They take actions to provide the

necessary assurance that, with the given physical state of

the and with the given contingent level of pro-

bability of disturbances, the system will be to react

reliably and to maintain its equilibrium. Table II lists,

under the alert state, control means that are appropriate

and available to the system operator for achieving his ob-

jectives in securi ty enhancement.

Emergency control

Once a system has entered the emergency state, the

deliberate control decisions and actions that are ap-

propriate to the normal, and even the alert, state are no

longer adequate, and more immediate action may be

called for

Power engineering literature over the half-century

is replete with discussions of problems related to transient

stability, and the steady increase in our understanding of

those problems has been a major factor in the achieve-

ment of the reliable systems to which we have become ac-

customed. In recent years, the scope of those discussions

has extended to the detailed study of large systems, which

have been modeled in detail in order to simulate their

response to specific disturbances.

Until very recently, emergency control was iden-

tified with local reflexive action for the prevention oftransient instability of individual machines. However,

machine instabilities do not constitute-and may not even

bc fac tors in -major sys tem b lackouts . As

earlier, if the particular incident triggering the tran-

sition to the emergency state has only local significance

(such as the ins tab i l i ty and shutdown o f a smal l

generator), return of the system to the alert state may be

effected solely by local control action-e.g., through

operation of protective devices. Even the loss of a major

unit may be accommodated by a sufficiently robust

system without serious aftermath. If, however, the

dent that triggered the state transition had been sufficient:

ly severe to the systems security level, reflexive

local control action, whether or not successful in preven-

ting damage to the equipment involved, not adequate-

ly restore the overall balance of the system. Lines or other

major equipment wilt be seriously overloaded, and more

powerful, action wilt be required.

Table II also lists control methods appropriate to the

emergency state that are at least potential candidates for

inclusion in emergency control regimes. Of all the im-

mediate and heroic means listed, fault clearing

has a long history of application. Underfrequency relay-

ing for load shedding has come into fairly widespread use

during the past decade (with performance that has not

always been satisfactory, or even acceptable) and a large

dynamic brake has been installed on the Bonneville Power

Administration system in the northwestern part of the

U.S. Although the possibility of using other devices has

been discussed, they have all been viewed primarily as

candidates for more powerful local control action. They

are, however, of widely diverse characteristics, and may

be c lass i f ied accord ing to a var ie ty o f c r i te r ia :

some involve interference with the flow of

real energy into or out of the (electrical) system, whereas

others only affect the paths of flow through the system.

The U.S. power system

The electric energy system of the United States in-c ludes app rox ima te ly 6000 gene ra t ing un i ts ,600 000 km of bulk power transmission lines, 12 000s ub st at i on s, a n d i n n u me r a b l e l o w e r -v o l t a gedistribution lines and transformers. The electricenergy processed by this system is produced, not

to schedule, but in response to the instantaneousdemands of some million customers. At the pre-sent state of the art, it is not feasible to control thisincredibly complex system monolithically, and

there are theoretical indications that it may neverbe efficient to do so. This entire total of intercon-

nected systems is presently controlled by some 117

independent control centers, some groups of whichfunc t ion in a coo rd ina ted manne r . Thus , anoperating utility may control from one to 300generating in a tightly coordinated manner; a

power pool of interconnection may consist of fromtwo to 37 operating utilities, which operate in a

and regional councilsthe operation of several contiguous Inter-

connections. Finally, the North American PowerSystems Commi t teereviews the common operating problems of all U.S.interconnected systems. A control area may con-sist of anything from a single utility to a power pool,and an interconnection can include more than onepool.

Under normal c i rcumstances, power sys temcontrollers must: continually adjust plant out-puts to match the continuous random fluctuation incustomer demand for power (a complex trackingproblem); (2) continually adjust plant controls(valves, governors, burner tilts, rod positions, etc.)t o m a i n t a i n t he b a l a n c e o f p r o c e s svariables-steam temperatures and pressures,etc.-within individual plants, and the balance ofpower levels (loads) among all the plants at theirmost efficient level (an optimization problem); and(3) avoid conflict between the thousands of controlactions performed more or less independently byindividual control centers each minute (a coordina-tion problem).


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From a time-domain perspective, all can be very fast ac-

ting, but most can be of only short duration, whereas the

rest can be sustained indefinitely. Each distinction pro-

vides a useful perspective frdm which to consider the

devices relative usefulness, but incorporation of such

diverse control means into effective automatic control

regimes poses a variety of unsolved problems.

The inability to gather, analyze, and respond to data

reflecting the state of an entire system, combined with the

futility of trying to preanalyze and prepare open-loop

control actions to take care of the literally infinite number

of emergency situations that could occur, has led us to

focus exclusively on local emergency control. As a result

of this limitation, extreme cases, the operator is left to

cope as best he can with the overall situation without the

aid of generalized emergency control.

The picture is now changing, however. Improved

understanding of power systems dynamics, advances in

communication and data-processing technologies, and re-

cent contributions of modern control theory have all con-

tinued to make feasible the development of general

automatic control regimes appropriate to the emergency

state.

class of problems resulting from the interaction of

individual methods of control deals with the achievement

of effective coordination in the use of multiple control

means within an area, in the functioning of local and cen-

tral (higher-level) control regimes, and in transitions be-

tween the several operating states. Particularly vexing are

the problems involved in achieving rapid coordinated ac-

tion from widely dispersed control techniques responding

individually to locally available information. Pending fur-

ther useful developments in the theory of decentralized

control, coordination between control centers must be

sought heuristically, but it cannot be altogether neglected.

Another class of problems involves coordination be-

tween means and ends. A definition of control objectives

tha t a re bo th adequa te to sys tem ope ra t iona l re -

quirements and practicable for use in control synthesis

must be developed. addition, associated control

algorithms for achieving those objectives must be for-

mulated. A number of possible approaches have already

been suggested, mostly in the of normal state con-

trol, and more will undoubtedly emerge for considera-

tion. In this connection, one consider-ation merits special

mention. The pervasively nonlinear and time-varying

nature of power systems, their inordinate complexity,

which requires that analytic models must be grossly

simplified to be usable, and the many contingencies that

must be handled combine to make the use of

type (possibly even adaptive) control algorithms practical-

ly indispensable. Classical optimal control methods

generating open-loop nonfeedback controls do not ap-

pear practicable at present.

must be stressed, however, that the emergency con-

trol problem transcends the transient stability problem,

and that when the system is in the emergency state,

whether or not following a unit in transient stability,

coordinated systemwide action must be taken to restore it

to at least the alert state.

Recovery from emergencies

Once an emergency has progressed the loss of system

integrity, return to the normal state realized by a

Uncontrolled state transitions

Normal-,

Nature of the transition: in security level(Once the system has been stressed, and until an adequate margin has been restored, it is more vulnerable to subsequent disturbances

Possible causes:

1. Reduction in supply margin, possibly due to: unusual load increase, of generating units, of generating unit,derating due to environmental constraints, derating due to auxiliary failure, rescheduled maintenance

2 Reduction in delivery margin, possibly due to: loss of transmission line or transformer, unusual distribution of load, increase in power

wheeling, derating due to unusually hot weather

3. Increased probability of disturbance, possibly due approach or arrival of severe storms, natural disasters (such as floods, earth-

quakes), civil disturbances, accidents

Alert -emergency

Nature of the transltion: violation of inequality constraints

Relevant constraints: line flows (emergency ratings), component loads (emergency ratings), voltage levels, system frequency, machine or

bus voltage angles

Proximate cause: malfunction and/or loss, temporary or permanent, of a major piece of equipment

Potential triggers: internal electrical or mechanical failure, malfunction of protective or control device, external events such as lightning,plane crash, etc.

Emergency- in extremisNature of the-transition: loss of system integrity; violation of equality constraints

Proximate cause: of tles resultlng in formation of system island(s) that are uncontrollable and/or unable to carry their internal load

Potential triggers: prolonged overloading of critical ties, malfunction of protective equipment, successive disturbances during emergency

II. Control methods

A. Alert state: preventive (deliberate) control to restore adequate reserve margins: generation shifting (security dispatch), increasedreserves, tie-line manning of normally unmanned (sub) stations. voltage reduction (not always effective or desirable)

B. Emergency state: immediate control to clear equipment overloads: fault clearing, fast valving, dynamic braking, exciter control, dcmodulation, load control, capacitor switching, plus all controls mentioned in the alert state

C. In extremis: heroic action to contain the disruption of the entire system: all of above, plus load shedding, controlled islanding

D. Restorative state: deliberate (corrective) control to reestablish a viable functioning system: unit restartlng and/or synchronization, load

restoration, resynchronization of areas

5 2


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system restoration. the

of the art, this remains a manual process that re-

quires careful thorough advance planning if it is to be

achieved at all promptly. The design of the system must

be such equipment lost from service during the final

of an emergency, while the system is in be

protected from unnecessary damage. In addition, all

necessary means be available for a systematic restart

of the system, even from a complete blackout, and the

operators be thoroughly familiar with the pro-

cedures for such a restart. The system must lend itself to

sectionalizing so thr load that has been lost can be

in blocks small enough to be manageable;

simultaneously, local energy sources at generating stations

must provide adequate power to auxiliaries (such as

pumps, exciters, etc.) required for unit start-up.

Careful advance planning for system recovery follow-

ing a widespread blackout can do much to minimize its

duration and hence to limit the

Ongoing research

Control design has focused primarily on the normal

state, in line with the philosophy of designing the system

to be strong enough to withstand normal contingen-

cies. The consideration of control during the emergency

s ta te has been based ma in ly on the o f t h echaracteristics and application of individual devices.

However, an attempt to view the emergency state as a

control regime and to develop an integrated control

strategy for it came early in 1975 when the Energy

Research and Development Administration (now part of

the U.S. Department of Energy) issued a Request for Pro-

posals for research this area. Presently, four research

projects on various aspects of emergency control are

underway within that subprogram Oct. 1977,

p. 21).

One project, at Wayne State University, addresses pro-

blems associated with maintaining the synchronous

operation of generators when subject to severe distur-

bances such as system short circuits (faults). An optimala im ing s t ra tegy a t temp ts to gu ide the uns tab le

generators back to equilibrium with the rest of the system.

Considerable testing in a simulation and prototype en-

vironment is needed before actual system implementa-

tion, but the approach promises to be superior to existing

open-loop approaches.

In another project, Washington University (St. Louis,

MO.) has developed a new state space called the local

equilibrium state, which is mathematically equivalent to

the existing one. It is a new equivalent system description

that can be obtained with local information only, thus

simplifying the simultaneous measurement problem. The

project will demonstrate the practicability of this new

state space and use it to develop strategies for coordinated

control of the during emergency situations.

A third project, at the Massachusetts Institute of

Technology, is addressing slower-speed aspects of system

emergencies. The projects objective is to develop a

framework for emergency control by considering the re-

quirements for information flow and modeling at various

levels in the system-including individual generating

plants, transmission system buses, and the system control

center.

The fourth project, at Systems Control, Inc., aims at

assessing the stability of a system when subjected to a

This company been successful in apply-

basic mathematical theory (originally developed by

Lyapunov) to the analysis of power system stability. The

problem of conservative results, high computational

and the need for initial system time simulation

assoc ia ted w i th Lyapunov s theo ry have a l l been

eliminated or reduced to a point where the new method

may play a significant role in both the planning and

operation of future power systems. The method can assess

the relative stability of a system in a given operating state

with limited computational burden, which may lead to an

effective application in the security assessment of power

systems. Subsequently, other program areas have been in-

itiated that will have an impact upon the design and

operation of systems during the non-normal system

operating state. A subprogram entitled System Effec-

tiveness Analysis is attempting to develop a framework

and methodology to integrate system with

structural reliability, cost, and worth of service to the

customer when planning future systems.

Other programs, sponsored by the Electric Power

Research Institute are developing tools and fur-

ther knowledge that will be required to handle the

problems of system operation during emergencies.

For example, a large-scale computer program is being

used in one project to develop improved simulation of the

dynamics of turbine boiler systems, their auxiliary equip-

and their during emergencytions such as reduced voltage and system frequency. Such

a program can be instrumental in dealing effectively with

system emergencies. As a matter of fact, the understan-

ding developed through its design and use is already

becoming a factor in system operation.

A concerted effort to develop an approach to system

planning, design, and operation that properly recognizes

all the system operating states and the state-transition

mechanisms is needed. The success of this effort requires

not only the cooperation of the nations utilities, but of

the U.S. Government, and major U.S. manufac-

turing and consulting firms as well.

L. Fink (F) is Assistant Director for SystemsManagement and Structuring with the U.S. Depart-ment of Energy, Electric Energy Systems Division.His main interests are in the application of systemstheory to the planning, design, and operation ofelectric energy systems. He has also worked in theapplication of field theory to energy systems and inthe modeling, and control of generating

plants and of individual and interconnected powersystems. He has received the B.S.E.E. and M.S.E.E.degrees from the University of Pennsylvania.

Carlsen (M) is a manager of systems analysis

In the Electric Utility Systems Englneerlng Depart-ment (EUSED) at the General Electric Company inSchenectady, N.Y. He has worked with the ERDA asa Branch Chief for Systems Control and has plan-ned, developed, initiated, and managed research in

the area of control and operation of future electricenergy systems. He has developed models andcomputer analysis tools for use in the investigationof subsynchronous resonance and shaftand has worked in the areas of excitation systemsand gene ra l dynamic pe r fo rmance o f powersystems. He received the from PurdueUniversity and the M.S.E.E. and Ph.D. from theUniversity of Wisconsin.

1978_spectrum_stress_strain.pdf

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