A Pilot Project for the Survey of Sag Performance of the Brazilian Transmission System

D. M. Coneia , , Fellow IEEE. and D. 0. C. Brad

Abslrod Considering the ample institutional experience in Brazil, ONS, the exelusive Brazilian I S 0 - Independent System Operator has been working diligently to bring into lorce all previous concerns with respect to Power Quality. To this end, regarding voltage sags and swells, it has been observed that the amount 01 information available in Brazil at this time was not enough to permit solid conclusions to he safely made. For that reason, B special measurement survey Pilot Project has been initiated. This Project has as one 01 its prime objectives the identilication of the mein causes and mechanism regarding the propagation 01 sags and swells occurring in the Brazilian transmission system as well as to subsidize the definition and Characterization 01 the phenomenon and its indices.

The partial resulta obtained so far are presented in this paper.

Index Term-Power Quality; voltage sags and swells; perlormance indices; statistics.

1. INTRODUCTION

T H E Brazilian electric energy market can be

characterized as a functionally unbundled model, which implies that generation, transport - transmission and distribution - and commercialization activities are segregated.

Considering the ample institutional experience in Brazil, ONS - the exclusive Brazilian ISO, Independent System Operator - has been working diligently to bring into force all the previous concems with respect to the question of Power Quality. To this end and with the support of ANEEL - the Brazilian Electric Energy Regulating Agency - ONS has been stimulating a broad sectorial debate. Agents that require access to the transmission system, govemment organs, universities and research centers have been taking part in this debate.

Regarding voltage sags and swells, it has been clearly observed that the amount of information readily available in Brazil was not sufficient as to permit conclusions to be safely made. For that reason, a Pilot Project, a measurement survey instrument, has been initiated. This project has as its prime aim to defend the quality of power at the end consumer and will strive to achieve the immediate objectives of identifying the main causes and mechanisms of sag and swell propagation in

D. M. Comia is with ONS - Operador Nacional do Sinema El%co, Rio

D. 0. C. Brari! i s with ONS - Operador Nacianal do Sistema Ei&mco, de Janeiro. Brazil (e-mail: delmocorr~ia~ans.org.br).

Rio de Janeiro. Brazil (e-mail: docb@ons.org.br).

0-7803-767 I -U0215 17.00 02002 IEEE 582

the system, as well as to subsidize the definition and characterization ofthe phenomenon and its indices.

11. DESCRIPTION OF THE PROJECT

The project has foreseen the selection of survey points spread over Brazil and the installation of measurement instruments. The information thus obtained will be supplied to ONS and treated statistically on two levels. Technical analysis of the results will have broad divulgation and will be aggregated in order so as to not permit the identification of the locations involved. On a more detailed level, only the companies involved in the subsystem will have access to the complete information.

The aim of this general program, whose finality is to improve the quality of electrical energy received by the end- consumer, is to reach the following objectives: - To promote a better understanding ofthe concepts involved and a leveling among the Brazilian electrical community; - To subsidize the definitive characterization ofthe phenomenon; - To define the adequate indices for the phenomenon, and to recommend reference standards; - To define the adequate methodology for obtaining these indices; - To identify the main propagation causes and mechanisms of the phenomenon in the same voltage level and between different voltage levels; - To bring to light in a national context, the peculiar characteristics of regional systems; - To publish the performance results on the transmission system busbars.

Finally, by the conclusion of the pilot monitoring program, the intention is to reach decisions conceming the statistical sampling criteria; the bus performance analysis and propagation analysis.

The project is divided in areas and each area in subsystems. In each subsystem, points are selected for measurement. The project covers the areas listed in Table I

111. MAIN DEFINITIONS

All the main definitions and recommendations are included in the Grid Procedures. These Procedures contain a set of documents elaborated by ONS together with the agents and whose final version must be approved by ANEEL. They establish the procedures and technical requirements for the implementation. use and operation of the transmission systems

and define the responsibilities of ONS and all other players

TABLE I AREAS AND SUBSYSTEM S INCLUDED M THE PROGRAM

. . P0i"lS S"b.

SrjtemJ kea Agents involved

Mato Gmuo do SUI Minas G m i r

Pam"i

Pemamhueo Rio de Janeiro Rio Grandc do SUI

sa0 Paul0

TABLE 2 SHORT VOLTAGE VAUTIONS- BWILLAN CLASSIFICATION

Classification Duration = d AmpliNde = a

Momentaneour lnleMptionr d < 3 I. a<0,1 p" voltage "ari*tiO"S

sags I cycle 5 d < 3 s. 0,I pu 5 a < 0,9 pu

Swells l c y c l e < d < 3 ~ . 1 , 1 p u < a ENERSUL 1 5

CEMIG- Dislrihuition 8 l 2 Temporary lntermptianr l ~ < d _ E I m . a<O.lpu and CEMIG - Transmission COPEL - Dirlrihuilion. I 5 sags 3 s c d 5 1 mn. 0.1 pu i a < 0.9 pu COPEL - Tmrmirrion and GERDAU

voltage vanations

CELPE, CHESF and GERDAU 3 7 Swells 3 s < d 5 i m n . 1 ,1pu<a LIGHT and Cosipa I I AES-SUI. RGE. ELETROSUL 4 11 and GERDAU V. DATA MADE AVAILABLE T O O N S

30 For every measurement point surveyed, the following data BANDEIRANTE, CTEEP, ELEKTRO, 6 ELETROPAULO and EF'TE 20 Agents 24 ,] were registered:

- point of installation; - voltage level;

According to the Module 2 of Grid Procedures - Performance Standards and Minimum Requirements for the Transmission System - voltage sags and swells are collectively

transducer characteristics; alteration in the State of the (in and out of

sprv irp , . "_. . .--, , called short voltage variations and are defined as a significant voltage amplitude deviation during short intervals of time. The amplitude is defined as the extreme rm5 voltage value during

instrument characteristics; rrigger configuration.

the variation in pu of a reference voltage at the point considered. The duration of the short voltage variation is defined as the time interval measured from the instant at which the rms value in pu crosses a certain pre-established voltage limit up to the instant at which the same variable crosses again the same limit.

In order to better relate the variation to its causes a division of the phenomenon in different band durations has been adopted. Momentaneous voltage variations are events shorter than or equal to 3 seconds, while temporary voltage variations are events longer than 3 seconds up to and including one minute. In momentaneous and temporary intemptions all three voltages must be below IO % of the nominal voltage.

Taking these considerations into account, the phenomena have been classified as per Table 2.

1V. CHARACTERIZATION OF THE PERFORMANCE OF A BUSBAR IN REFERENCE TO SHORT VOLTAGE VARIATIONS

The parameters duration and amplitude were used to characterize the severity of a certain short voltage variation. The performance o f a bushar with reference to this phenomenon was characterized by the frequency of occurrence of pairs amplitude-duration in a given period of time during which the bus has been monitored. These were divided in bands.

In order to make it possible to evaluate the propagation of the phenomenon over the system, the waveforms were recorded, so that the data could be manipulated according to different criteria in the future.

The following data were recorded for every event: - event identifier; - instant of occurrence; - cause: - pre-fault voltage.

If possible, all waveforms were recorded, so that ONS could compare different calculation algorithms and aggregation criteria.

VI. TREATMENT OF UNAVAILABILITIES

The total survey period is forecasted as one and a half years. Besides that. each instrument was installed as different instants and may undergo at the beginning of operation some weeks of adjustment. For that reason, it is very important to consider the real availability of each point of measurement.

The way in which unavailability was considered is hener illustrated in an example as shown in Fig. 1. This figure represents a system comprised of four points (PI to Pa). The aim is to take a statistical survey for the time between instants to and t4. The horizontal lines in the figure represent the availability of each point. For instance point PI became unavailable before the initial time and became available again at instant t2

Given a survey period of time (ta and t4). the methodology applied divides it in as many periods as there are availabilityiunavailability commutations of all points. In the example shown in Fig. 1. three such instants were identified giving rise to four time intervals. For each time interval ti., to I,, the quantity of points available is expressed by A;. For example, between t, and 4 there are three points available and An is equal to 3.

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I so, 1

Voltage rag Amplitude [ pu ]

PI F2 F3 F4 Fig. I , Example of availability of a survey compired of four p i n t s

00.20 00.30 00.40 00 .50 m0.60 00.70 m0.80 0 0 . ~ 5 00 .90

The distribution Fjofthe parameters amplitude and duration is obtained for every time interval ti.l to 1,. Example: between t , and t2 there are F2 sags, where F is a matrix representing the bands in which these parameters have been divided.

The total distribution for the time interval 1, to t2 is obtained as the average of all intervals with availability different from zero, weighted by interval duration and availability. By illustration, the frequency average matrix F i n the example presented in Fig. 1 is given by ( I )

Fig. 2. Average number of disturbances detected per point per month

700 600 500 2 400 300 200 100

0

v1

(1 1 A I A3 A4 F = 11 - f o + / 4 - 1 2

VII. MAIN RESULTS

A . Statisfica/ Universe The survey universe is composed of 223 pointmonths,

divided as follows: - 13.8-34.5 kV: 84 pointmonths; - 69-88 kV: 84 pointmonths; - 138 kV: 84 point.months; - 230 kV: 84 pointmonths;

Although measurement points of voltage greater than 230 kV are foreseen, they have not yet been included in the survey.

Fig. 2 gives an idea of the average amount of disturbances detected per point per month. From this amount not all represent shorl voltage variations.

An estimate of the size of the file related to a disturbance can be viewed in Fig. 3. It shows that due to the diversity of instruments used, there are archives very rich in information and others considered very simple.

E. Occurrence Distribution

Fig. 4 presents the absolute frequency distribution of sag amplitudes detected by voltage class. To illustrate, the 138 kV busbars surveyed presented about eleven sags of amplitude below or equal 0.9 pu. The 13.8 kV busbars surveyed presented approximately four sags of amplitude below or equal 0.4 pu.

Voltage Clas [ kV 1

Fig. 4. Absolute average frequency dirtibution per point per month for each voltage e l u s . having voltage w g amplitude as a pvrametei

The same information in relative values is given in Fig. 5. It can be concluded from the figure that 30 % of the voltage sags demonstrated voltage amplitude below or equal 0.85 pu. This signifies that 70 % of the sags had an amplitude between 0.85 and 0.9 pu. One possible conclusion to be drawn from this fact is that the trigger configuration is not adequate. It would have been more representative to have used , for instance, a Rigger related to the pre-fault voltage.

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Voltage rag AmpliNde I pu I 0 0 . 5 0 810.60 00 .70

100,0%

90,0% ._ 'i - 80.0%

% E -a 60,0% 6 0 ~ , 50.0%

$ 1 70,0%

I 40,0% U : .- > CL 30,0%

4 20.0%

10.0%

0.0%

- - -

Voltage Clasr [ kV I

Fig. 5: Relative average frequency dislribution per point per month for each voltage class, using voltage rag amplitude ai a parameter

C. Volrage Class The division between voltage classes of the sag occurrence

frequency for different voltage amplitudes can be seen in Fig. 6. For example around 40 % of the sags of amplitude below or equal 0.7 pu occur on 13.8-34.5 kV busbars, 16 % on 69-88 kV busbars and 14 % o n 230 kV busbars.

0 1 3 . 8 - 3 4 . S k V m 6 9 - 8 8 k V 0138kV 0 2 3 0 kV

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.85 0.9

Voltage rag ampliNde 1 PU 1

Fig. 6: Relative average frequency distnbulion per poinl per month for each voltage sag amplifude. using voltage class as a paramerer

D. Avai/obi/i/y In order to evaluate the effect of the unavailability of

instruments on the statistics, two cases were compared. Fig. 4 corresponds to an average availability of 4 0 % of the instruments. It means that some points began to be monitored only at the end of the year. Had this unavailability not been taken into account, the results obtained for 138 kV busbars would be the ones presented in Fig. 7. The same comparison for 69-88 kV busbars is presented in Fig. 8.

These figures lead to the conclusion that especially at the beginning of a measurement program, it is very important to take into account the real availability of the points monitored.

.40% Available

0,2 0.3 0,4 0,5 0.6 0,7 0.8 0.85 0.9

Voltage sag Amplitude [ pu I

Fig. 7: Absolute avenge frequency dirtibution per point per month for each voltage rag amplitude and 230 kV busbarr. considering that the instlvmenrs areavailable 1W%and40%ofthet ime

Availability 1 0 100% Available 1 .40% Availsblc

7.0 I

0.2 0.3 0.4 0.5 0.6 0.7 0,s 0.85 0.9

Voltage sag Amplitude I pu I

Fig. 8: Absolute avenge frequency dismibution per point per month for each vollage rag ampliNde and 69-88 kV busban. eonsidenng that the initmments are available I W % and 40 % ofthe time

VIII. ACKNOWLEDGMENT

For their important work on the Pilot Project, the authors gratefully acknowledge the contributions of ABRACE - Joe0 Morganti; AES Eletropaulo - Alexander Tenorio and Leandro R. de Souza; AES SUI - Carlos Eduarrlo Figueirrdo; CELPE - Samuel Marinho Costa. Simane Neiva Coelho and Wider

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Basilio Santos: CEMIG-DistribuiqBo - Gilberto Abdo Rocha and Tatiana Nesralla Ribeiro: CEMIG-Transmissso - Angelica da Costa 0. Rocha, Carlos Alberto de Freitas Mello and Jeder Francisco de Oliveira: CHESF - Herivelto S . Bronzeado and J. IX. REFERENCES Jlilio A. Lins Leitio: COMPANHIA PlRATINlNGA DE [ I ] ONS ~ Operadoi ~ a c i o n r l do Sirtcme, ',Procedimentor de ~ e d ~ . FORCA E LUZ S. A. - S e w Ahn and Belemar Cardoso da M6du.a 2.2 - Padrks de Desempenho e Requiritos M i n k " para as Silva; COpEL-Distrihuiqgo ~ Mauricio Robles Onega; Instala~ker da Rede Bisicr (Grid Procedurre. Module 2.2 -Performance COP~L~Transmissio . Miguel A, S . Mikilita; cosIPA ~ Standards and Minimum Requiremenu for the Basid Grid

Gerald0 Tressoldi: CPFL - Dalton Pereira Dias and Jose Luiz Brines: CTEEP-EPTE - Antdnio A. C.Armda, Diogo Kataoka and Nelson da Silva Vilares: EFEl -Jose Maria de Carvalho

Innrllationr)." Rio de Janeiro. Nov. 1999.

X. BlOGR4PHES

Filho and Thiago Cle de Oliveira; ELEKTRO - Emesto A. Mertens Jr.: Eletrosul - Anilson Luiz Duarte, Evenon Pizolatti Medeiros, lldo Wilson Griidner and Ruy Luiz Machado; Enersul - Alexsandro Alves Martins and Carlos Alberto de Oliveira: GERDAU - Adriano Dutra de Uchoa, Alberto de Moraes Barbosa, Andre de Souza Almeida, AntBnio Claudio lgnacio Silva, Carlos Roberto Maycr, Edvei da Silva Pontes, Elias Boutros Sater, &CO Teodoro Sommer, Sergio Augusta Strartmann and Walter Ries: INSTRONIC - Gilberto Queiroz and Mauricio Perez: GRUPO VOTORANTIN -Jose Roberto Pires Freire: JOULE - Ubiratan F. Castellano; LIGHT - Jorge Alexandre Zaiden and Luiz Oscar Rodrigues Jobim; ONS - Andre Vidal de Negreiros, Heloiza Helena X. M. Menezes, Jose Marcilio C. ValenCa, Jose Robeno de Medeiros and Laercio Guedes: Reason - Jurandir Paz de Oliveira: RGE - Lucian0 A. Brasil da Silva, Sergio J. Scortegagna Filho and Vinfredo E. Koch: Siemens - Marcio Aralijo and Rogirio Bo1eta:Cosigua - Alvaro Ferreira de Azevedo.

Correia, D. M. was bom in Rio de Janeiro. Bmii. on December I. 1953. He completed his underpduate studies PI the Universidade Federal Ruminenre. Niter&. B-1, graduated from the Uniwsidndc Federal de Pemambuco. Recife. Brazil and was awarded his Doclorate degree from the Technixhe Univerritji Hsmbug-Harburg. Hamburg. Germany

His emplopen1 expedence includes ONS ~ the Independen! System Operator in Brazil,

Univmidade de SPo Paulo. Technixhe Univerri t i t Hamburg-Harburg. Themag Engenhada LIB.. and IESA. His special fields of interest include cleclromagnetic compeibility. power quality. electromagnetic lnterfmnce and equipment engjneedng.

B i d , D. 0. C. ulils bom in SPo Paulo. B m i l on May 27, 1949. He obtained his Elcctdcvl E n g i n d n g degree from the Escolv Politicnica da Unwersid.de dc SBo Paulo. Brazil in 1972 and his M.Sc degree t o m Univerridade Federal de Pemambuco. Brazil in 1996. At this time he works for ONS IS Transmission Adminislmtion Mnnager.

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