外文翻译原文(东北电力)

POWER SYSTEMS AND ELECTRIC NETWORKS
AN ANALYSIS OF RELAY PROTECTION REQUIREMENTS FOR THE PURPOSE OF ESTIMATING ITS EFFECTIVENESS 1
S.L.Kuzhekov,2P.I.Okley,3and G .S.Nudel’man 4
Translated from Élektricheskie Stantsii ,No.2,February 2010,pp.43–48.
Existing requirements,used to estimate the effectiveness of relay protection,are analyzed.The need to include in these requirements economic indicators of the functioning of relay-protection devices and automation or the reliability of the electric supply,taking into account the results of the functioning of these devices,is vali-dated.This enables the effectiveness of the decisions taken when choosing relay protection and automation devices to be increased.
Keywords:relay protection,requirements,economic efficiency,electric supply reliability characteristics,mathematical modeling.
The purpose of the relay protection of electric power sys-tems is to disconnect defective or dangerously operating components from the remaining undamaged part of the sys-tem automatically using switch gear or by action on a signal [1].When fulfilling its function relay protection must satisfy certain requirements,which are actually criteria of its opti-mality.Obviously,optimization with respect to a set of crite-ria is multipurpose,and the set of requirements themselves,depending on the role of the protecting component,the com-ponents used,and the degree of automation and information available in the power system may,in general,be nonidenti-cal sets of requirements.It must be emphasized that the im-portance of each of the criteria depends on the role of the protection system.
Multipurpose optimization problems are usually solved by two methods [2]:preference or scalarization.The basic principle of the preference method is that initially optimiza-tion is carried out with respect to the most important criterion and a search is made for the set of solutions which satisfy this criterion.The remaining criteria are converted into a se-ries of limitations (specifying certain permissible values).The set of solutions obtained is then optimized with respect
to a criterion which is second in importance,which converts the remaining (including the first)criteria into a number of limitations,etc.
However,the formulation and solution of the problem of multipurpose optimization for the purposes of relay protec-tion is difficult in practice for the following reasons.First,the problem of quantitatively estimating the acceptable val-ues of the criteria,which are converted into limitations,has not been worked out.Second,short circuits are rare events and the use of probability theory and the theory of random processes in such cases requires justification.The use of a deterministic approach to the problem of multipurpose opti-mization is also difficult,for example,when specifying the quantitative values of the criteria.We can specify a com-bination of parameters for which operations turn out in prac-tice to be unreal.Hence,for these reasons,in electric power engineering,including relay protection,the problem of mul-tipurpose optimization cannot be solved by the preference method.
The scalarization method is widely used in techni-cal-economic calculations,for example,in the technical-eco-nomic comparison of several versions.The basic principle of the method is that a certain weight (usually in monetary form)is assigned to each of the criteria and the costs in-volved in one year of use are found.In particular,for a tech-nical-economic comparison of the versions of distributor de-vices,forms of electrical supply etc.,if the construction and Power Technology and Engineering Vol.44,No.2,2010
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1For discussion.
2Southern-Russia State Technical University (Novocherkassk Polytechnic Institute),Novocherkassk,Russia;E-mail:kuzhekov@mail.ru 3“Holding IDGC,”Russia.4
JSC “VNIIR,”Russia.
startup occurs in a single year,the costs can be calculated from the expression[2]
C i=P n K i+E i+L i,(1) where C i are the costs per year of use in realizing the i th ver-sion,P n is the standard coefficient of economic efficiency of capital investment—the inverse of the time T r in which the capital investment must be repaid(for T r=8years, P n=0.125),E i are the annual operating expenses for the i th version,K i are the capital costs for the i th version per year of use,and L i is the average annual loss on the i th version,due to the unreliability of the electricity supply.
The technical-economic approach to justifying the use of relay protection devices(which best approximates to practice)was developed in the USSR by Ya.S.Gel’fand[3]. This approach was also adopted by the Brown Boveri Com-pany[4].
The main difficulty when using expression(1)is to cal-culate the average annual loss L i.In relatively simple cases when comparing relay protection and automatic devices in radial or the simplest ring networks,and also the components of electrical supply systems,including substations operating at voltages up to220kV and electric motors with voltages higher than1kV,one can calculate L i directly.
As an example,we give in an appendix a procedure,de-veloped using[5],for calculating the cost of a relay protec-tion and automation system,taking into account the average annual loss L i.
In combined electric power systems it is difficult to make a sufficiently accurate calculation of the average annual loss when there are damaged components,and hence,as pro-posed in[2],it is best to normalize the acceptable and neces-sary values of the reliability characteristics of the power sta-tions or the electricity supply of the consumers,which needs to be ensured,taking into account the consequences of the functioning of the relay protection equipment.In such cases the values of the reliability characteristics of the power sta-tions or the electricity supply of consumers may be limita-tions on the optimization.The purpose of this paper is to ana-lyze the requirements used to estimate the effectiveness of relay protection and to justify the need for including in these requirements the economic consequences of the functioning of the relay protection and automation devices or the reliabil-ity characteristics of the electric power systems(or the elec-tricity supply to consumers)taking into account the conse-quences of the functioning of these devices.
Up to the1970’s in the USSR,four characteristics were included in the set of requirements imposed on relay protec-tion,namely,selectivity,speed of response,sensitivity and reliability[6].The use of this set of characteristics was,in fact,fixed by the actions of the standard documents in opera-tion at that time,for example,the Guidance on Relay Protec-tion[7].
In fact,for example,the currents for operating differen-tial protections are chosen from a selectivity condition,i.e., to ensure disconnection from the unbalance current at the maximum possible current of the external short circuits in the maximum mode of operation of the electric power sys-tem and from the surge of the magnetizing current of the pro-tected power transformer.
Satisfaction of the speed-of-response requirement is en-sured,for example,by a maximum permissible short-circuit disconnection time in the system-forming buses of not longer than0.2sec.
Satisfaction of the sensitivity requirement is ensured by checking the value of the sensitivity factor for a short circuit in the region of action in the minimum mode of operation.
The reliability factors are monitored by selecting and analyzing statistical data on the operation of the relay protec-tion and automation equipment.
It should be noted that the use of this system of criteria helps to reduce the cost of the relay apparatus,based on elec-tromechanical principles,and makes it negligibly small com-pared with the cost of the equipment being protected.
These requirements,widely used in practice by special-ists on relay protection in design and operating organiza-tions,have been further developed by Smirnov and Fedo-seev[8].The new requirements propose the use of the idea of “functioning effectiveness,”borrowed from reliability theory [9].This term has been taken to mean“the property(protec-tion)of carrying out a limited number of functions,each with maximum effect”[1,8].On the basis of this idea,a hierarchi-cal system of requirements was constructed in[8],as shown in Fig.1,in which the idea of functioning effectiveness is di-vided into two component parts:technical perfection and functioning reliability.
It should be noted that in[8]only the technical effective-ness of the relay protection and automation devices is con-sidered.The following components were included in the idea of“technical perfection”:
—selectivity—the first(highest)level;
—operating stability—the second level.
Here functioning reliability was relegated to the third (lowest)level of the hierarchy,while the criterion of speed of response was not included in explicit form in the hierarchy of requirements.
This system of criteria is qualitative and does not contain any quantitative features.It is difficult to use in practice due to the fact that there are no methods of estimating the values of the proposed protection-capability criteria and the stability of the operating speed(for example,for differential protec-tions under transient conditions,particularly when the mag-netic circuits of the current transformers etc.are saturated).
A difficulty also arises due to the fact that the functioning re-liability in all cases has lower priority than technical perfec-tion.In fact,one must not always give preference to having the best technical characteristics as far as selectivity,speed of response and sensitivity are concerned(the first and second levels of the hierarchy),but to the less reliable relay protec-tion and automation system(the third level of the hierarchy). It is possible that,for these reasons,specialists in the field of relay protection are not accustomed to using this hierarchy in practice.
160S.L.Kuzhekov et al.
It was pointed out in[10]that“effectiveness and reliabil-ity are the main indicators of the functioning quality of relay protection and automation in electric power systems,”i.e., reliability is separate from functioning effectiveness.How-ever,it is hardly advisable to assume an unreliable protection device to be technically perfect since the reliability of relay protection and automation devices has a considerable effect on the technical effectiveness with which they function.
In[11]it was suggested that the technical level of micro-processor relay protection and automation should be esti-mated from several points of view(i.e.,a multilayer or multi-level system of criteria was proposed,as a consequence of the use of microprocessor relay protection and automation in electric power systems).These include:
—the first layer(level)is the technical perfection and functioning reliability(the term“technical perfection”was defined above).Hence,the first layer of requirements in-cludes the technical operating effectiveness;
—the second layer is the technological layer,which de-fines the accomplishment by the device of protection algo-rithms built into it;
—the third layer is the functionality of the device(i.e., the presence,for example,of several protection functions and additional functions such as measurement,recording, control and communication);
—the fourth layer is the possibility of integrating the microprocessor relay protection and automation devices into other systems,for example,into centralized protection of a group of objects.
The fundamental drawback of all the systems of require-ments considered is the absence in them of quantitative char-acteristics for estimating the operating efficiency of relay protection and automation systems,and also the absence of a relation between the requirements imposed on the relay-pro-tection and automation systems and the technical-economic characteristics for the necessary and permissible values of the reliability characteristics of the electric power system or the electricity supply to consumers.These estimates are nec-essary because of the high responsibility and cost of intelli-gent electronic devices,including microprocessor relay pro-tection systems.These devices must not only be technically effective but also economically efficient.Requirements which do not take into account the relation between the relay protection and automation system and the object being pro-tected and its functioning(internal requirements),for all their importance,must have a subsidiary value.
Hence,the operating effectiveness of a relay-protection and automation system is determined not only by internal re-quirements,characterizing the device separately from its pro-tection feature,but also,mainly,requirements which take into account the effect of this device on the functioning of the object being protected.
It is obvious that each of the requirements for optimiza-tion by the scalarization method must have weighting factors in the monetary expression or occur in the limitations speci-fied by numerical values.The values of the weighting factors must be determined by the conditions under which the relay protection is used.Only in this case will the use of specific relay protection and automation devices be justified.
We suggest that the introduction into the system of crite-ria for relay protection and automation optimality of indica-tors of economic efficiency,and also of the reliability of the electric power system or of the electrical supply to consum-ers requires the following actions:
—the setting up of theoretical sets of modes of opera-tion of the protected objects(normal,nonnormal and danger-ous).Moreover,in particular,for prolonged differential pro-tection it is necessary to take into account additional condi-tions(transients in the electric power system and errors in the current transformers in these modes of operation,transient
An Analysis of Relay Protection Requirements for the Purpose of Estimating Its Effectiveness
161 Fig.1.Hierarchy of requirements imposed on relay protection and automation[7].
resistance at the location of a short circuit etc.),the justifica-tion of the theoretical minimum modes of operation etc.;
—a calculation of the probabilities(flow parameters)of the modes of operation of the protected objects.In a first ap-proximation,these parameters can be specified in terms of the statistical characteristics of the reliability of the protected components of the electric power system;
—a determination of the permissible and necessary val-ues of the reliability factors of the electric power system or of the electrical supply to consumers,taking into account the functioning of the relay protection and automation devices. These characteristics can be used as the limits for optimiza-tion.In a number of cases,as pointed out in the appendix,in-stead of determining the values of the reliability characteris-tics of the electric power system or the electrical supply to consumers one can make economic estimates of the correct operations and nonoperations,excess and false operations, and also outages in operation and delays in the operation of the relay protection devices in all modes of operation of the protected object,together with a calculation of the loss thereby incurred;
—a determination of the probabilities of correct,excess and false operations,and also outages,delays in the opera-tion and breakdowns of the relay protection equipment;
—the development of models of the reliability with which practical relay protection apparatus functions;
—a quantitative estimate of the effect of unreliability of the relay protection devices on their functioning(correct or incorrect action,outages etc.).
It must be emphasized that not all the criteria(require-ments)can be reduced to economic equivalents.In such cases they may act as limitations on optimization.In particu-lar,one can use as limitations,for example,the additional functions listed in the third layer of requirements[11](mea-surement,recording,control and communication).
At the present time it is possible in principle to solve the problem of choosing the optimum relay-protection and auto-mation devices by mathematical modeling of the modes of operation of the protected components of the electric power system and the relay protection and automation devices taking their reliability characteristics into account,which is less expensive than carrying out natural experiments and test operations.
Since the problem of estimating the economic efficiency of relay-protection devices and also of the reliability charac-teristics of electric power systems or the reliability of the electrical supply to consumers is insufficiently developed at the present time,as an intermediate measure for comparing relay-protection and automation devices one can make com-parative tests of such devices using regulated sets of modes of operation.
Thus,to compare the differential protections of power transformers and autotransformers one can use the following:
1.Surges of the magnetizing current:
—unipolar;
—unipolar with an aperiodic component absorbed by the current transformers;
—unipolar with transformer-current saturation;
—a surge of the periodic current,formed as the differ-ence between unipolar surges of magnetizing current of two phases.
2.Unbalance currents for external short circuits due to:
—unbalance,due to slight saturation of the current transformers at low currents(considerable for the first in-clined part of the retarding characteristic of the protection);
—unbalance in the case of deep saturation of the cur-rent transformers at high currents(important for the second inclined part of the retarding characteristic of the protection).
3.Short-circuit currents in the region of action when there are aperiodic components,taking into account the satu-ration of the current transformers(to estimate possible delay in the operation of the protection).
During tests one can determine the highest sensitivity of a specific differential protection device to additional operat-ing parameters(specific secondary voltages of the current transformers,the attenuation time constant of the aperiodic components,the power factors of secondary circuits etc.), which facilitates a comparison of specific devices and en-ables the region in which they are best employed to be estab-lished.Similar sets of modes of operation can be formulated for other relay protection and automation devices.
We wish to thank A.I.Leviush for useful comments and suggestions which enabled us to improve the quality of this paper.
CONCLUSIONS
1.The absence in the set of requirements imposed on re-lay protection of indicators of economic effectiveness or the necessary and acceptable values of the reliability characteris-tics of electric power systems or electrical supply to consum-ers,taking into account the consequences of the functioning of relay protection devices,is a drawback,which prevents an objective estimate of these devices.
2.At the present level of development of computational techniques it is possible to compare relay protection and au-tomation devices by mathematical modeling of the modes of operation of the protected components of an electric power station and of the relay protection devices and to calculate the economic consequences of using these devices or using limits on the necessary and acceptable values of the reliabil-ity of the electric power stations or the electric supply to con-sumers,taking into account the aftereffects of the function-ing of the relay-protection system.
3.The objectivity of a comparison of relay-protection devices,carried out using mathematical modeling,becomes particularly important with the wide introduction of micro-processor relay protection apparatus,having considerable re-sponsibility and high cost,practically the same component structure and differing solely in its software.
162S.L.Kuzhekov et al.
4.As an intermediate measure when comparing relay protection systems it may be worth carrying out comparative tests with regulated sets of modes of operation. REFERENCES
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Umfanges von Schutzeinrichtungen für elektrische Anlangen,”
Brown Boveri Mitt.,65(6)(1978).
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economic efficiency of complex relay protection of electric mo-tors at voltages above1000V,”Izv.Vuzov.Énergetika,No.10 (1987).
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sian],Izd.ONTI,Moscow–Leningrad(1938).
7.Relay Protection Handbook.Edition13B.Relay Protection of
Step-Down Transformers and110–500kV Autotransformers.
Calculations[in Russian],Énergoatomizdat,Moscow(1985).
8.E.P.Smirnov and A.M.Fedoseev,“The basic properties of re-
lay protection from short circuits,”Trudy MÉI,No.145(1972).
hakov,“The operating efficiency of complex systems,”
in:The Reliability of Complex Technical Systems[in Russian], Sovetskoe Radio,Moscow(1966).
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ity of the relay protection of power systems,”in:Proc.of the Int.
Conf.“Relay Protection and Automation of Modern Power Sys-tems,”Cheboksary,September9–13,2007.
11G.S.Nudel’man,M.G.Lint,V.A.Feshchenko,and A.V.
Zhukov,“The basic requirements on relay protection and con-trol devices for use in the modern power systems of Russia,”in: Proc.of the Int.Conf.“Relay Protection and Automation of Modern Power Systems,”Cheboksary,September9–13,2007. Appendix.
Calculation of the costs of a relay protection
and automation system
In relatively simple cases,when comparing relay protec-tion and automation systems(radial or the simplest ring net-works,and also the components of electrical supply systems, including substations operating at a voltage of up to110kV inclusive and electric motors with a voltage of up to1kV)it is possible to use expression(1)directly.In this case the costs involved in using a relay protection and automation system can be calculated as follows.
Suppose we are given the set R of modes of operation of the protected object,where r iÎR is one of i=1,2,...,n modes of operation.The setÙof parameters of the flow of modes is also specified,whereùiÎÙis one of i=1,2,...,n parameters of the flow of modes of operation.There is a set K of relay protection and automation devices RPA k,where kÎK is one of k=1,2,...,f devices,the cost of each of which is C RPA k.
The matrices of the economic consequences of the func-tioning of each of the RPA devices in the whole set of R modes of operation are also specified.These matrices(given below)correspond to subsets L and M modes of operation: L is the subset of modes i¢=1,2,...,l with operating re-quirement(short circuit in the action zone),M is the subset of modes of operation i¢¢=1,2,...,m with nonoperating re-quirement(a short circuit outside the action zone).
Matrix L
12...l
[c¢]=
1c11c12 (1)
2c21c22 (2)
3c31c32 (3)
Matrix M
12...m
[c¢¢]=
4c41c42 (4)
5c51c62 (5)
6c61c62 (6)
In these matrices c ij are the weights(the economic conse-quences)of the functioning of the relay protection and auto-mation device in the k th mode of operation for the j th version of the functioning.To simplify the notation,we will omit the subscripts on the relay protection and automation device in the matrices.It should be noted that any action or inaction of the protection involves a loss.The economic consequences take into account the cost of repairs after an emergency or the cost of replacing damaged equipment,the loss due to sudden outage of the protection equipment,and also the loss due to underproduction when equipment fails etc.The versions j of the functioning of the relay protection and automation equip-ment are as follows:
j=1is correct operation;
j=2is the delay in operation by a time t;
j=3is a breakdown in operation;
j=4is correct inaction;
j=5is unnecessary operation(for a short circuit outside the action zone);
j=6is false operation(under normal conditions).
The reliability factors of all the relay protection and auto-mation systems compared and the consequences of their un-reliability in all i th modes of operation are also known in the form of functioning probabilities p ij,where j is one of the possible versions of the functioning.
It is required to calculate the normalized costs in the k th relay protection and automation system,corresponding(in the simplest case)to the expression
C k=P n C RPA k+EÓk+L fh k+L n k=min,(2) where C RPA k is the cost of the k th relay protection and auto-mation device,EÓk are the annual operating expenses for the k th relay protection system,L fh k is the mean annual loss for multiple identification of the modes of operation by the k th relay protection and automation system,ignoring its unreli-ability,and L n k is the average annual loss for multiple recog-nition of the modes of operation by the k th relay protection and automation system,due to its unreliability.
An Analysis of Relay Protection Requirements for the Purpose of Estimating Its Effectiveness163
The average annual loss for multiple recognition of the modes of operation of the relay protection and automation system,having ideal reliability,is equal to the sum of the losses
L p i c p i c k i j i j j i j i j j i m
fh =¢+
¢¢¢¢=¢¢¢¢=¢¢=ååw w ()()1
3
4
6
l i l
åå¢=,
1
(3)
where p j (i ¢)and p j (i ¢¢)are the probabilities of versions of the functioning of the relay protection and automation system in
modes of operation i ¢and i ¢¢,and ùi ¢and ùi ¢¢are the parame-ters of the streams of modes of operation i ¢and i ¢¢.
Insufficient reliability of the relay protection and auto-mation system leads to the same results j as for nonideal pro-tection characteristics.These results can be determined using a model of the reliability of the relay protection and automa-tion system.This provides the possibility of determining the average annual loss due to the unreliability of the relay pro-tection and automation system Lu using an expression simi-lar to (3).
164S.L.Kuzhekov et al.。