03'97aug

EEUG NewsEuropean EMTP-ATP Users Group e.V.

AUGUST 1997NUMBER 3VOLUME 3

C O N T E N T S

Editorial3 Instructions for Authors

EEUG Association6 Preliminary program of the EEUG Meeting97, Barcelona, November 9-11, 19977 Highlights of ATP Workshop, Osnabrueck, September 29, 1997

Program Information10 Whats New in ATP development? - W. Scott Meyer12 ATP related Internet resources - Lszl Prikler18 Short Introduction to NODA line model - Mustafa Kizilcay

Technical Note24 What are features of CABLE PARAMETERS different from CABLE CONSTANTS? - Akihiro Ametani

Discussion Corner27 CABLE CONSTANTS is not suitable model for naked, buried conductors 33 Nonconventional use of the synchronous machine model

People and Profiles36 Author of ATPDRAW - Hans-Kristian Hoidalen

Technical Papers38 Monte Carlo lightning backflash model for EHV lines - Gabor Furst47 Corona modeling for attenuation and distortion of lightning surges in overhead transmission lines - R. Ciudad, D. Alvira, F. Soto

2 EEUG News August 1997

EEUG Newspublished by European EMTP-ATP Users Group e.V. (EEUG), registered Association.

Editorial BoardMembers of the Executive Board of the EEUG.

EditorsDr. Mustafa Kizilcay, Dr. Juan A. Martinez-Velasco, Lszl Prikler

Editorial and administrative assistantCanan G. Kizilcay

Editors by E-mailMustafa Kizilcay [email protected]

[email protected] A. Martinez-Velasco [email protected] Prikler [email protected]

Mailing addressSubscription: Paper submission:EEUG e.V.c/o Prof. Dr. Mustafa Kizilcay Mr. Lszl Prikler Fachhochschule Osnabrck Technical University of BudapestFB Elektrotechnik Dept. of Electric Power Systems Albrechtstr. 30 Egry J. u. 18.D-49076 Osnabrck, Germany H-1111 Budapest, HungaryPhone +49 541 969-3065 Phone +36 1 463 3015Fax +49 541 969-3070 Fax +36 1 463 3013

EEUG News is published quarterly by the European EMTP-ATP Users Groupe.V., registered association in Offenbach am Main, Germany. All rights reserved.Copyright 1997 by the European EMTP-ATP Users Group e.V. SUBSCRIPTIONS: EEUG members: included in annual membership dues;Nonmembers: DEM 120, single copy DEM 35 (for Europe).

Editorial

EEUG News August 1997 3

5Instructions for Authors555First, middle and last name of the author Department / instituteOrganization name, Country Street / P. O. Box

Postal code, city, countryVoice tel. / fax number (optional)

Email address (if available)55

1 Technical contributions5The quality of a publication depends to a great extent on the uniformity of presentation. Rulesthat must be observed by authors of articles for EEUG News are as follow (this article can beconsidered as an example of a technical paper):5paper size DIN A4 format (21x 29.7 cm) or US standard format (8.5 x 11 inch) with left,

right, top and bottom margins of 2.5 cm or 1 inch.5page layout Single-column and single-spaced format is recommended. The first page should

have the title inside the top margin, and left aligned. The title is followed by thename (first, middle and last name) of the author, organization name and countryprinted left aligned, whereas address, voice tel./fax number (optional) and E-mailaddress (if available) of author(s) are printed right aligned.

5Section titles should be bold, with two blank lines above, and one blank linebelow, each such title. One line should be left blank between paragraphs, andindentation at the start of paragraphs should not be used.

5The contribution should not be paginated. A erasable pencil can be used tonumber the pages on the back side, or in the bottom-right corner.

5fonts Times New Roman, Roman or another proportional font similar to the font used

to create "Instructions for authors" is preferred.5

The title should be bold faced and in capital and small letters with font size of20 (points) as the title of this text given above.

5The names of the authors, organization name and country should be bold facedin font size 12. The address, voice tel./fax number and E-mail address ofauthor(s) should be in font size 11 as shown above.

5The body of the text should use font size 12. Titles of sections and subsectionsshould be bold in font size 14.

numbering Arabic numerals should be employed in numbering of sections, figures, tables,equations and references. The subsections are numbered by inserting a full stop"." between numbers, e.g. 1 1.1 1.1.3. All the figures, tables and equations

Editorial


should be numbered progressively. Equation numbers should be given inparentheses, such as (1) or (2-5), whereas numbers of references should bewritten between square brackets, such as [1].

5structure The structure of a technical paper usually is organized in the following parts, in

the given order: title, abstract (100 to 150 words), introduction, body,conclusions, references and annexes, if required.

5references A reference of a monograph should contain author(s), title, edition, publication

(place and publisher) and year. Example:5

[1] Karni, S.: Network Theory: Analysis and Synthesis, Boston, Allyn andBacon, Inc., 1966.A reference of a part of a contribution or to a monograph should containauthor(s), title of host, edition, part number, publication (place, publisher),year and location within the host documentation.

5Serials include periodicals, newsletters, annuals, and series of reports. Articlesin serials contain author(s), title, title of host document, location within host andpagination of the part, as shown below:

5[2] Clerici, A.; Marzio, L.: Coordinated Use of TNA and Digital Computer for

Switching-Surge Studies: Transient Equivalent of a Complex Network, IEEETrans. on Power Appar. and Systems, PAS-89 (1970), no. 8, pp.1717-1726

5The authors are requested to prepare up to 10 keywords for their contributions. Thekeywords should reflect the concepts, topics and methods included in the contribution.5Technical papers should be submitted primarily in printed form (three copies) ready to bephotocopied. Additionally, the text should be delivered on a MS-DOS floppy disk, if it is createdusing a word processor such as WordPerfect / CorelPerfect or MS-Word running underMS-DOS, MS-Windows 3.x or MS-Windows 95.55

2 Short articles, calls for help, suggestions, solutions, announcements5It is sufficient to provide the contribution by E-mail or on a DOS floppy disk (two copies)addressed each to the Editor and the Chairman of EEUG Association, who are responsible forthe edition. The text can be created using a plain text editor such as MS-DOS EDIT, or usinga word processor. When a word processor is used, WordPerfect 5.1/6.0, CorelPerfect 7.0 or MS-Word for Win3.x/95 2.0/6.0/7.0 format is preferred. Please state the rubric under which thearticle should appear.55

3 General remarks5Selection among contributions is done by the Executive Board of EEUG Association, butresponsibility for the content of a contribution rests with its author(s). If important editorialchanges seem necessary, the authors will be consulted prior to publication. No honorarium willbe paid any author.

Editorial


Technical papers should be submitted primarily in printed form ready to be photocopied. Pleasemail two copies of your contribution to the Editor and one copy to the Chairman, who act as thesupervising editor of EEUG News on behalf of the Executive Board:5Additionally, the text should be delivered to the Editor on an MS-DOS floppy disk or e-mailattachment in zipped form, if it was created using word processor such as WordPerfect orMS-Word running under MS-DOS, MS-Windows 3.x or MS-Windows 95.55Co-editors of EEUG News

Lszl Prikler Prof. Dr.-Ing. M. KizilcayTechnical University of Budapest Fachhochschule OsnabrckDept. of Electric Power Systems FB ElektrotechnikEgry J. u. 18. Albrechtstr. 30H-1111 Budapest, Hungary D-49076 Osnabrueck, Germany

Phone +36 1 463 3015 Phone +49 541 969-3065Fax +36 1 463 3013 Fax +49 541 969-3070/-2936

Email: [email protected] Email: [email protected]

EEUG Association


Preliminary program of the EEUG Meeting 97Barcelona/Spain, November 9-11, 1996

The annual European EMTP-ATP Users Group Meeting in 1997 will be held at the UniversitatPolitechnica de Catalunya.. The following papers will be presented in six session: ATPdevelopment and usage - Modelling - Overvoltages - FACTS and Rotating Machines -Validation tests - Protection/Miscellaneous.

* Current status of ATP development - Tsu-Huei Lui, W. Scott Meyer (USA) * The Latin American EMTP/ATP Users Group activities - M.P. Pereira (Brazil) * Services provided by EEUG to European ATP users via Internet - L. Prikler (Hungary)* Digital computation of electromagnetic transients in power systems. Current status - J.A. Martinez-Velasco (Spain) * Complete transformer model for very fast transient studies - M.H. Abdel-Rahman

(Kuwait), G.M.Abdel-Salam, E.A. Badran (Egypt)* Identification of rational function approximations for frequency domain responses by

vector fitting - B. Gustavsen, T. Henriksen (Norway)* A low-voltage varistor module for use within ATP-EMTP simulations - A. Larsson

(Sweden)* ATP load model of an antenna for satellite telecommunication - F. Muzi (Italy)* Determining overvoltage protection of an hydro power plant - I. Uglesic (Croatia)* Overvoltages due to switching off an unloaded transformer with vacuum circuit breaker - M. Popov, A. Causevski (Macedonia)* A simplified methodology for evaluating surge protection of distribution using metal oxide

arresters - J.A. Martinez-Velasco (Spain)* Lightning performance and switching overvoltages studies of an uprated transmission line - L. Prikler, G. Ban, G. Banfai (Hungary)* Teaching Power Electronics and FACTS using a data module approach - A.C. Siqueira de Lima (Brazil), J.A. Martinez-Velasco (Spain)* Modelling the TCSC using ATP Models - A.R.M. Tenorio (Brazil), N. Jenkins (United Kingdom), L. Prikler (Hungary)* Modelling and simulation of rotating machines using the ATP - J.A. Martinez-Velasco (Spain)* Simulation of induction motor behaviour during voltage disturbances using an aggregated model - J.J. Blanes Peiro (Spain)* Comparison of field measurements with transient simulations of an arc furnace - R. Bianchi Lastra, J. Barbero, A. Rifaldi (Argentina)* Comparison between the elements type 91 and 94 in the simulation of an electric arc from actual test data - W. Gimenez, O.P. Hevia (Argentina)* Energization of a 380 kV subnetwork - Comparison of EMTP simulations with

measurements - S.Groninger, M. Kizilcay, M. Losing (Germany) * Calling MATLAB from within ATP-MODELS - H. Wehrend (Germany)* Simulation of a series-compensation line for evaluation of relaying - algorithms - M. M. Saha (Sweden), E. Rosolowski, J. Izykowski, B. Kasztenny (Poland)* Developing feeder protection software within ATP-MODELS - H. Wehrend (Germany)* Grounding system design using EMTP - N.D. Hatziargyriou, M.I. Lorentzou (Greece)

EEUG Association


Highlights of ATP WorkshopOsnabrueck, September 29, 1997

EEUG Association


Program Information


Whats New in ATP development?

W.Scott MeyerCanadian/American EMTP User Group, USA E-mail: [email protected]

The former DEBUG.LIS has been renamed. For those who follow recommended standardpractice of KTRPL4 < 0, the diagnostic file will have new file type .DBG and name parallelto the input data file, when IPRSUP is zero. Negative values of IPRSUP are alsorecognized: -1 means diagnostic output should be minimal, -2 results in minimal diagnosticfile named DEBUG.LIS, -3 will result in normal diagnostic as value zero does, only to diskfile DEBUG.LIS (Can/Am EMTP News, April 1997, p. 2)

FOURIER ON of batch-mode plotting now is supported by a bar chart. The feature isinstallation-dependent in that a new vector-graphic module VECBAR is used, as called bymodule FSERIE which computes the Fourier coefficients and outputs the harmonic table ascharacter information. The new vector plot looks similar to the old SPY plot of harmoniccontent although the user has less control. (Can/Am EMTP News, April 1997, p. 3)

Disk file DEBUG.LIS produced by TPPLOT was changed back to DUMTPP.LIS as existedprior to that trial coupling of TPPLOT with ATP in the fall of 1994. Simultaneous executionof two or more Salford programs is the reason for the change.

(Can/Am EMTP News, April 1997, p. 3)

TPPDIR is a new DOS symbol that does for TPPLOT what ATPDIR does for ATP. IfTPPDIR is not defined, ATPDIR will be used as it has been in the past. So, for the user whowas happy with the old scheme of a single symbol for the two programs, nothing will change.But if ATP and TPPLOT are placed in different directories the single symbol ATPDIR willwork for one, but not the other. So, to accommodate two separate directories, the second symbolwas added. (Can/Am EMTP News, April 1997, p. 3)

An IEEE COMTRADE file can be used as input to the EXPORT command of TPPLOT tobe converted into one of the several formatted alternatives that are offered as outputs. Within theTPPLOT archive, COMTIN illustrates the conversion of COMTRADE.DAT and *.CFG intoa FORMATTED PL4 file. (Can/Am EMTP News, April 1997, p. 3)

A new Type-10 electric-network source has been provided to represent analytical functions.That is, the user simply supplies his algebra such as 303 * COS ( OMEGA * T - ALPHA)anywhere in columns 11- 60 as illustrated in DCNEW-19. However, imperfect operation of thePowell pocket calculator has temporarily limited usefulness. (Can/Am EMTP News, April 1997, p. 11)

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$PARAMETER is a new $-card that precedes an arbitrary number of definitions of symbols thatare defined by analytical functions. For any data card, any character string can be replaced bythe numeric evaluation of an expression. An illustration can be found in DCNEW-19. Again,reliance upon the Powell calculator has temporarily limited usefulness. (Can/Am EMTP News, April 1997, p. 11)

A new phase-domain synchronous machine model is now available in ATP-EMTP. It wasdonated by Tokyo Electric Power Co. (TEPCO) and Toden Software Inc. The new type-58 S.M.model improves numerical stability of EMTP simulation, which is demonstrated in thebenchmark data case DCN20.DAT. Data cards for the type-58 S.M. are fully compatible withdata cards for the type-59 S.M. (Can/Am EMTP News, April 1997, p. 12)

LIMCRD value of STARTUP ending in 999 (e.g., 6999) has special meaning. This is a specialswitch that overrides the predefined limit of DATA BASE MODULE punch card output.

(Can/Am EMTP News, July 1997, p. 1)

COMPTACS is a new DOS parameter that allows the user of compiled TACS to choosebetween MAKE and USE outside the data file. If COMPILED TACS MAKE or COMPILEDTACS USE is part of the data, the content of COMPTACS is immaterial. But in the absenceof a request in data, COMPTACS is used. There are 3 alternatives: 1)MAKE 2) USE; 3)anything else (nominally blank). (Can/Am EMTP News, July 1997, p. 2)

RMS is a new MATH command of TPPLOT that produces the RMS (root mean square) valueof a signal. The use is subject to an important restriction: the time instants of the input signalmust be uniformly spaced. The RMS meter has only one mandatory parameter: the floatingpoint time interval used for averaging. (Can/Am EMTP News, July 1997, p. 2)

Variable-dimensioning of the CABLE PARAMETERS code was completed on July 9th. (Can/Am EMTP News, July 1997, p. 8)

[R][L] and Z0Z1Z2 are the names of new Type-91 models that use compensation to representseries R-L branches. The limitation that both [R] and [L] must be symmetric in conventionalType-51,52,.. branches can be avoided. Type-91 branches are used to carry data, and MODELZ0Z1Z2 or MODEL [R][L] are to be keyed in the BUS3/BUS4 data fields of columns 15-24.

(Can/Am EMTP News, July 1997, p.12)

An extension to FREQUENCY SCAN has been implemented. Angles of Type-14 sinusoidalsources no longer must remain fixed as frequency is varied. Now, they, too, can be variedproportionally. The new fundamental frequency FREQFS on the FREQUENCY SCANrequest card will provide this if it is given a positive value. The effect can be seen in newstandard test case DCNEW-21. (Can/Am EMTP News, July 1997, p.16)

Program Information


ATP related Internet resources

Lszl Prikler Department of Electric Power SystemsTechnical University of Budapest, Hungary Egry J. u. 18.H-1111 Budapest, Hungary

Phone/Fax: +36 1 463 3015/-3013E-mail: [email protected]

This article primarily describes the ATP related Internet tools for those are not yet familiar withor not frequently use them. Since the available resources show an impressive growth, it is thehope of the author, that even the experienced users will find this report profitable. Further aim ofthis writing is to update and extend the content of the similar articles published years ago in thisperiodical [1, 2].

1 Short Internet history

The Internet had its beginnings in the 1960s when researchers began to experiment with linkingcomputers over telephone lines. Today, the Internet consists of the connections linking computersthroughout the world. Introducing hypertext markup language (HTML) and wide-spread use ofgraphical Web browsers were the next milestone in the Internet development in the beginning of1990s. Now if one picks up a newspaper or turn on the TV news there is something new about theInternet and World-Wide Web. The Internet can be used for a variety of purposes. A few of themore popular functions are:

electronic mail Telnet FTP World-Wide Web (WWW)

For further general information the reader is asked to read special literature about the Internet [3].There are some reports addressed especially to power engineers [4, 5, 6], too.

2 Electronic mail

Electronic mail is the most well-known feature of the Internet. By this way anyone, who has anaccount on a computer connected to the Internet can send messages to other users. For ATP usersthis provides an easy, efficient and very fast way of communication with other users all over theworld, including program developers, regional user group representatives or the author of thepresent article.

3 The ATP-EMTP Listserver

The listserver is an E-mail remailer program, which rebroadcast incoming messages to all membershave subscribed to the list. The ATP-EMTP listserver was being set up in September, 1991, byProf. Bruce Mork at the North Dakota State University, USA. Six years later the list has more than

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500 subscriber. Table 1 gives an overview of subscribers categorized by country. Table 1

Country # Country # Country # Country #

Argentina 3 Denmark 1 Japan 31 South Africa 26

Australia 24 El Salvador 1 Korea 9 Spain 20

Austria 1 Yugoslavia 1 Macedonia 1 Sweden 6

Belgium 5 Finland 1 Mexico 9 Switzerland 7

Brazil 28 France 5 Netherlands 1 Taiwan 11

Bulgaria 1 Germany 14 New Zealand 3 Thailand 2

Canada 19 Great Britain 23 Norway 9 Turkey 1

China 1 Greece 4 Peru 2 USA * 179

Colombia 4 Hongkong 2 Poland 7 Uruguay 1

Costa Rica 1 Hungary 1 Saudi-Arabia 1 Venezuela 6

Croatia 2 Indonesia 4 Singapore 1

Cyprus 1 Israel 1 Slovakia 1

Czech Rep. 7 Italy 13 Slovenia 1 * Including non-identifiable subscribers from domains like @compuserve.com or @aol.com

The list is actually maintained by its members, who add themselves, delete themselves and correcttheir own listing parameters (name, affiliation, country). Anyone who got an ATP licence has rightto subscribe to the ATP-EMTP Listserver, too. For subscription one has to send a single line emailto the following address:

[email protected]

The subject of the message can be left blank. The body of the text is shown next:

SUB ATP-EMTP Your Full Name, Institution, Country

Name, affiliation and country fields are limited to 39 characters total. Some minutes later the listserver program sends a confirmation letter to the address decoded from the From: filed of the firstmessage. It means that subscription is allowed and accepted only if one subscribes from his ownaccount. After subscription, any messages are sent to the address:

[email protected]

will be forwarded to all the others who has subscribed to this service. The listserver was being setup to support information exchange between ATP users, to provide a facility to help each other, andto have better access to program developers. The list is unmoderated, but a set of common senserules have to be applied. Dr. Morks collection of ATP-EMTP Listserver netiquette that all of ushave to follow in communication is shown next:

The aim of the listserver is to exchange quality information without the clutter of jokes, insults,self-aggrandizement, etc.

People must identify themselves when they subscribe. With only known professionals having acommon interest in using ATP, the "signal to noise ratio" can be kept much higher than internetnewgroups

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The intent is to limit discussions to licensed ATP users, so we can discuss and share informationwithout violating the terms of the license agreement.

Subscribers can add and remove themselves from the list, so it is self-maintaining. However, thelist "owner" (me) can step in and remove any subscriber who behaves in a non-professional orunethical manner.

Begin all messages with a short and to-the-point overview. None of us wants to spend any moretime reading our e-mail than we have to. Those who aren't interested in the topic can quicklydelete it and move on.

Do NOT send out any verbage from personal e-mail you've received from others, unless theyhave specifically given their approval for it to be distributed to all subscribers of the ATPlistserver.

Do NOT send out company advertisements, news of for-profit commercial endeavors, or othersolicitations. These are not related to ATP usage and development, and they reduce the signalto noise ratio.

If you want to write a long discussion on some topic, send it to the list owner, who will put it onthe ftp server and announce its existence.

Avoid sending out huge data cases to all subscribers. First send a short message asking for help.Send the related data case only to those who offer help. Do not forget to report the solution laterto the ATP community.

It is fine to voice opinions, but avoid insulting others in the process. Be professional in your actions, not just your words. Don't "cry wolf" too often. Getting into the habit of asking the other subscribers for help before

looking in the Rule Book, asking often for help but never helping others in return, etc., shouldbe avoided.

The traffic of the ATP-EMTP mailing list is automatically archived by the LISTSERV programon monthly basis. Past mailings are logged into separate disk files, LOGyymm, where "yy" and"mm" are the year and month, respectively. These files are available via the GET command of thelistserver. If one sends a message to the listserver at address: [email protected] a single line in the body, e.g.:

GET ATP-EMTP LOG 9703

after a while the listserver responds with a message and the requested file (mails delivered duringMarch, 1997) will be send to the requesters e-mail account.

The most important other listserver commands are:

SIGNOFF ATP-EMTP - Cancels subscription

REView ATP-EMTP - Returns e-mail addresses of all subscribers

SET ATP-EMTP options - Update your subscription options

INDex ATP-EMTP - Send the list of available archive files

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4 FTP

FTP is the method by which users can download or upload files from machines connected to theInternet. Anonymous FTP (or aFTP) permits a user to log-on to a remote computer and access filesothers have stored in a public directory. If the files are not publicly available a password is requiredto have access to files owned by someone else.

4.1 Anonymous ATP-FTP server

By using this service licensed users can download ATP related files from a remote computer to theirpersonal computer or workstation. The ATP-related materials (except for source code and theprograms themselves) are available over the Internet via anonymous ftp. This consists of pastnewsletters, latest revisions of Rule Book pages, utility programs, sample data cases, upcomingconference/seminar information, etc.

The address of the master aFTP site at the Michigan Technological University is :

ftp.ee.mtu.edu/pub/atp (IP: 141.219.23.120)

There are some mirror FTP sites of interest, for Europeans the most important is that operating atthe University of Hannover in Germany:

ftp.rrzn.uni-hannover.de/pub/mirror/atp (IP: 130.75.2.2)

New files are copied from the master site each Saturday. To access the files one has to login as"anonymous" and to give his personal e-mail address as the password. ATP materials are archivedin .ZIP files and kept in several subdirectories as shown below:

/canam -- Past issues of the Can/Am newsletter, in Word Perfectformat,

/course -- Announcements for past and future ATP courses andseminars

/util -- Utility programs useful to the ATP user. This includes gui/atpdraw-- Graphical preprocessor interface to ATP/gui/atpgen -- Graphical preprocessor interface to ATP/gui/show -- MS Windows postprocessor /dcase -- Sample data case files, to demonstrate ATP capabilities/license/canam -- ATP licensing form for CanAm users/license/eeug -- ATP licensing form for European users/models/tutor -- MODELS primer by Gabor Furst and manual by L. Dube /models/appl -- Sample MODELS-intensive ATP applications./ruleb -- Newest updated rule book chapters/ruleb/lecruleb -- LEC rulebook chapters, in original Lotus Manuscript format/ruleb/wpnofigs --LEC rulebook chapters, in WordPerfect 5.2, no figures./ruleb/wpwifigs -- LEC rulebook chapters, in WordPerfect 5.2, with figures/ruleb/updated -- Updated rulebook chapters

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4.1 Password protected FTP server

The European EMTP-ATP Users Group Association provides this service primarily for itsmembers. The latest ATP and TPBIG files (GIVE1 and GIVE2 disks) and DBOS install kit arestored on a publicly un-available directory on a Unix host of the Department of Electric PowerSystems at the Technical University of Budapest. Any potential user of this service is requested toidentify himself by sending his EEUG membership number and/or any relevant information on thesecond page of the ATP License Form via e-mail to the operator of this service at address:[email protected]. Until the world-wide ATP license data base is completed, the requesters arealso asked to send the xerox or scanned copy of the second page of the License agreement via e-mail or fax : + 36 1 463 3013.

5 World-Wide Web

The World-Wide Web is an unorganized collection of hypermedia documents that may containlinks to databases, papers, images, sound files, video clips and other resources. The key to theWebs popularity is its easy of use via a graphical browser that uses Hypertext Transfer Protocol(HTTP) as its language.

5.1 ATP Web servers in the Globe

Fig. 1 shows the geographical location of the available ATP related Web servers at present.

USA/Cananda(English)

Brasil(Portugal & English)

Argentina(Spanish)

Japan(Japanese & English)

Europe(English)

Fig. 1 - Location of ATP related Webservers

These Web servers were established primarily for supporting the ATP users in the region. However,originating from the nature of the Web, this services are not limited to the regional users. E.g theEuropean server introduces that the site has been established for the users of the royalty-free ATPversion of the Electromagnetic Transients Program (EMTP), without any geographicalconstraints.

The Web servers shown in the map can be reached by the following URLs:

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Europe: - http://www.vmt.bme.hu/eeug/USA/Canada:- http://www.ee.mtu.edu/atpBrasil: - http://www.furnas.gov.br/atpArgentina: - http://iitree.ing.unlp.edu.ar/estudios/caue/caue.htmlJapan: - http://www02.so-net.or.jp/~m_kan/index-e.htm

5.2 ATP WWWBOARD

The ATP bulletin board is a new initiatives originating from and operated in Japan. Theadvantage of the bulletin board over the e-mail listserver is told that tracking and searching the mailhistory is more comfortable. This service is primarily intended to serve the Japanese and East-AsianATP users, but not limited to them. In order to access these secure WWW pages, a username andpassword is required, however. Operators policy is that they inform only the users grouprepresentatives about the password, who is authorized to share it with other users in the region. Thepassword is updated regularly, in order to make this service secure. Operators other policy thatthey never respond for inquiries from individual users, instead they relay it to the regional usergroup. The ATP WWWBOARD is locatable at address: http://www.arienter.com/atpwww/. Twosoftware distribution servers are also in operation in Japan at the following URL:

http://beam.kisarazu.ac.jp:8080/~kasiwagi/atp/http://pels.pwr.eng.osaka-u.ac.jp/~atp/restricted/

6 References

[1] Mork, B.A.: New user-supported ATP news and help service via e-mail, Can/Am EMTPNews, Vol 91-4, October, 1991

[2] Wehrend. H.: Demonstration of ATP Related Internet Services, EEUG News, Vol. 1, No. 1-2, 1995

[3] Krol, E.: The whole Internet catalog and users guide, OReilly & Associates, Inc., 1996[4] Hirsh, P.M.: Exercise the power of the World Wide Web, IEEE Computer Applications in

Power, Volume 8, No.3, July 1995[5] Ramesh, V.C.: Browse the power engineering virtual Library, IEEE Computer Applications

in Power, Volume 8, No.4, October 1995[6] King, R.L.: Learning how to use the Internet and Web resources, IEEE Computer

Applications in Power, Volume 10, No.2, April 1997

Program Information


Short Introduction to NODA line model

Mustafa Kizilcay

Program Information


Technical Note


What are features of CABLE PARAMETERSdifferent fromCABLE CONSTANTS?

Akihiro Ametani

Technical Note


Discussion Corner


Discussion Corner is going to give a forum for short discussions call for help, suggestions andanswers of general interest. The most interesting discussion on the ATP-EMTP listserver willalso be reported here. We, the editors hope that those ATP users who can not follow thediscussion on the listserver will find this rubric useful.

Discussion topic:

CABLE CONSTANTS is not suitable modelfor naked buried conductors

M r. Carlos T. Mata Research Assistant at the Department of Electrical and ComputerEngineering, University of Florida initiated an interesting discussion about cable modeling onthe Listserver. The discussion has started with his message on 11th of September, 1997.

I tried to get the conductance and capacitance matrix for a two buried cable system. The system isvery simple, it is a counterpoise buried at 0.4 meters from the surface and a cable buried at 0.6meters (from the surface as well).

The results for different parameters are quite amazing. Using a ground resistivity of 4000 @m, andno insulator for the counterpoise I obtained: Self conductance = 0.0 (mho/m), Self capacitance =1.7858031E-7 (farad/m)Trying to understand what was going on, I increased the earth resistivity to 4.0e+10 @m just to seewhat effect that would have. Well, the results were the same as obtained before. Now the only thingI can conclude from here is that the program calculates the capacitance assuming perfect groundoutside the insulator layer. It doesn't matter what the ground resistivity is. So even when the soil isa very pour conductor this parameter is the same as if it was a perfect conductor.Does the cable constants program work with bare conductors?

Before midnight on the same day Robert Meredith of New York Power Authority replied. Thismessage has some general concerns related to cable modeling, so it is worth to quote in full:

You are attempting to deal with a counterpoise, presumably in continuous contact with the earth.This is an invalid condition for all calculation routines that use Carson's equations or a variation onthem to determine an earth return impedance. A recent IEEE paper, pointed out that Carson'sequations were derived for a conductor above the earth's surface and are NOT valid for a conductorin continuous contact with the earth's surface (or below it). To me it intuitively has to do with the lackof a calculable propagation velocity in the absence of a capacitance to the (ground) return path. Theactual reason may have to do with images or another aspect of Carson's derivation.

Although I don't believe Cable Constants uses Carson's equations, it is certainly constrained tocalculating a capacitance between the counterpoise and the surrounding earth in order to determinea propagation velocity, and consequently an impedance of the earth return path. High frequencyeffects will be most affected. If you are looking at lightning or switching transients, you need realisticcapacitances.

Discussion Corner


Your conclusion that earth outside any assumed insulation layer is assumed to be a perfect conductoris correct. Your variation of a miniscule thickness "insulating" layer will result in enormousvariation of the calculated capacitance. However, the result is unreasonable in any practicalsituation, since the insulating layer is an artifice introduced in a failed attempt to bypass thelimitations of Carson's equations. You will eventually want to ground the ends and possiblyintermediate points in an attempt to return to something closer to reality. Forget it, if you are dealingwith high frequencies. Between the grounded points the propagation velocity and the high frequencyimpedance of the counterpoise-earth return path will be heavily influenced by the capacitance valueyou have artificially determined. i.e. high frequency effects will likely be wrong.

There is no escape from the fact that capacitance within the surrounding earth must be realisticallycalculated to determine the high frequency impact of a counterpoise. Cable Constants is not designedfor that task. You might try finite elements. I hesitate to even think what effect dielectric breakdownof the "earth-as-insulator" model might add to a transients calculation involving a counterpoise. Wecertainly know that lightning can hit buried cables, clearly representing dielectric breakdown of theearth. The tests/experiments were done in Florida, weren't they?

You should also be aware that Cable Constants and all other "Line Constants" calculations ignore"end effects", which severely affects low frequency modeling accuracy. The calculations all assumethat the impedance from the point of earth contact to the depths at which low frequency currents floware negligible. For example a cable a 100 feet long could well be "calculated" to have earth returncurrents flowing several miles below the cable. How they get to those depths is not a concern of the"calculation". However the ability to reach great depths is solely responsible for the fact thatcalculated earth return resistance does not depend upon earth resistivity. In high resistivity earth thecurrents are just assumed to flow more deeply through semi-infinite cross sectional areas, ifnecessary, to hold the earth resistance constant for any given frequency.

If you are conducting low frequency modeling, you might consider that under the conditions of theCable Constants calculation your counterpoise is assumed to be in parallel with semi-infinite earthcross sections and may carry only a small part of the earth return current. In any event thecounterpoise will provide a resistively limited return path, while the deep earth provides aninductively limited return path. Counterpoise and earth return currents could be greatly out of phaseand in an overall inductive circuit the counterpoise current could be irrelevant (in the context usedby Cable Constants).

In short you will have different calculation errors at both high and low frequencies due to thecounterpoise. There is no realistic method of determining the high frequency effects in EMTP. Lowfrequency effects might be approximated by ignoring either the earth or the counterpoise, dependingon whether (unknown) grounding resistances are to be guessed as high or low. The counterpoise andpossibly the cable may be modeled as above the ground surface for conditions where capacitance toground is not critical. You could put a grounded ficticious high resistance sheath on any cable toreplicate the capacitive effect of surrounding earth, if the cable does not already have a groundedsheath.

Just a few thoughts on your very non-trivial, non-simple configuration....

Two days later Gabor Furst from G.B. Furst Consultants Inc, Canada confirmed that the solutiontechnique of CABLE CONSTANTS is not applicable to directly buried wires. His message also givessome more guidance to the counterpoise modeling:

Discussion Corner


The problem with a counterpoise is that its characteristic impedance is not constant but varies with

time from the initial value of the traditional surge impedance to the final dc groundingL C/resistance reached in about six times of the travel time of the counterpoise. An overall insight intothe performance of a counterpoise can be gleaned from Bewley's still invaluable 1933 text "TravelingWaves on Transmission Systems" chapters 8 and 10.

An in depth analysis of the counterpoise using field theory can be found in the text "EarthConduction Effects in Transmission Systems" by E.D. Sunde (1949). This text with its advancedmathematics is not for the faint hearted, but useful graphs and formulae for counterpoisecharacteristics are given for practical engineering applications.

Professor Martinez Lozano, Simon Bolivar University, Venezuela was the next contributor on 13th

of September, 1997:

I simulated the transients behavior of grounding electrodes in the ATP, using equivalent circuits,calculating the effect of resistivity, soil ionization and other phenomenon. The paper recommendedfor it: - Analytical Modeling of grounding electrodes (Transient Behavior) - R. Velazquez and D.Mukhedkar. IEEE Transactions PAS-103, No. 6, June 1984.

The closure of the story originates from Prof. Akihiro Ametani of Doshisha University in Kyoto,Japan, the author of the CABLE CONSTANT subroutine in ATP. He sent the following discussionon FAX which was forwarded to the Listserver by Dr. Scott Meyer on September 30th:

Carlos T. Matas problem of a naked (not isolated) buried conductor has reminded me of the caseof a propagation velocity greater than the light velocity in the year of 1976 just after the first versionof CABLE CONSTANTS was completed by myself. It was exactly the same problem as Carlos. Auser calculated propagation constants of a naked underground (buried) cable, and got thepropagation velocity greater than the light velocity.

1. Applicable Limit of CABLE CONSTANTS - Isolated Conductor CABLE CONSTANTS can not be applied, in theory, to a naked underground cable, i.e., to a not-isolated buried conductor. For an overhead line is always isolated by air from the earth, such aproblem never arises. CABLE CONSTANTS has adopted Pollaczeks impedance formula for anunderground cable, and Carsons formula for an overhead cable/line as same as LINE CONSTANTS.

J. R. Carson: Wave propagation in overhead wire with ground return, Bell Syst. Tech. J., Vol. 13, pp. 532-579, 1926. F. Pollaczek: Uber das Feld einer unendlich langen wechsel stromdurchflossenen Einfachleitung, E.N.T., Band 3, Heft 9 pp. 339-360, 1926

Both formulas were derived from the assumption of an isolated, infinitely long and infinitely smallconductor, see Chap. 4 and 5 of the EMTP Theory Book, B.P.A., Aug. 1986. Therefore the CABLECONSTANTS (CC hereafter) should not be applied to naked buried conductor. The LINECONSTANTS (LC) has no option to deal with a buried conductor.

A KILL code was originally introduced to avoid problems such as Carlos case, and it was statedthat CC could not handle a naked buried conductor, i.e., the case of ri+1 (outer radius of the i-th

Discussion Corner


conductor) = ri+2 (outer radius of the conductor outer insulator). However, there exists, in a physicalreality, a thin layer of a copper or aluminum oxide on the conductor surface if it is directly buried.This thin layer behaves like an insulator up to a certain limit of a conductor current and voltage, forexample until dielectric breakdown. Because of the fact, in the case of ri+1 = ri+2 , CC automaticallymodifies ri+2 to be greater than ri+1 , i.e., ri+2 = ri+1 + (epsilon, a small value) to avoid anumerical instability due to the term of log ( ri+2 / ri+1 ). This is explained as DegenerateConfigurations and Special Cases in the ATP Rule Book. .....2. Models of Naked Buried Conductor

Thanks to Bob Meredith for his valuable comments to Carlos problem. It is very true that dielectricbreakdown occurs between a conductor and the earth when a lightning current flows into a nakedburied conductor such as a counterpoise and a grounding rod (not necessarily lightning hits theburied conductor and scarcely hits because the conductor is underground).

My research group has carried out a number of experiments of an impulse (lightning)voltage/current characteristic of buried conductor (Ref. 1). The experimental results clearly indicateda current-dependent nonlinear characteristic of the buried conductor impedance. Also, we havefound that current distribution along the conductor is nonlinear due to radial current penetration tothe earth. As same as Bobs question to Carlos, such the tests/experiments were done in Florida,werent they?

2.1 Sundes formula

To simulate such a phenomenon, one approach is to adopt Sundes resistance and surge impedanceof a naked buried conductor as Gabor Furst suggested.

E.D. Sunde: Earth Conduction Effects in Transmission Systems, Dover Pub. Co., New York, 1949, pp 75-89 and 263-266

At the first stage of CC development, considering the case mentioned in the front of this note, Ithought to include a naked buried conductor option adopting Sundes formula. But I gave up the ideabecause of the following reasons: (1) Sundes formula is for the resistance and the surge impedance,but not for the impedance and admittance. (2) the resistance and surge impedance formulas have notbeen verified by experimental results.

For the EMTP has been widely used all over the world, implementation of a formula and/or a modelas a subroutine (fixed long-term) of the EMTP needs the condition that the formula and the modelhave experimentally well verified and/or theoretically proved, and also the limitation (assumption,applicability) is clear.

2.2 My Approach

Presently, I am representing a naked buried conductor as a cascade connection of N isolatedconductors:

each line length x = x / N, x: total length,sending end of the i-th line connected to the earth through resistance Ri Ri evaluated from an experimental result or Sundes resistance formulaparameters of each isolated line evaluated from CC

Discussion Corner


m4

0 m4

0f(x) dx1dx2

mx1

0 mx2

0f(x) dx1dx2.

ZCarson' mx1

0 m4

0f(x)dx1dx2 > Zfinite' m

x1

0 mx2

0f(x) dx1dx2

Simulation results using the model by the ATP agrees rather well with experimental results as faras a current into the conductor is small, i.e., in the region of no dielectric breakdown.

3. End Effect mentioned by Bob Meredith

It is true that the impedance and admittance of a short overhead line are significantly different fromthose given by Carsons formula because it assumes an infinitely long and infinitely small conductor.I have derived impedance and admittance formulas of a finite length conductor, and investigated theeffect of the finite length.

A. Ametani & A. Ishihara: Investigation of impedance and line parameters of a finite- length multiconductor system, Trans. IEE Japan, Vol. 113-B, No. 8, pp. 905-913, 1993 (in Japanese) A comparison with measured results (R. Velazquez et. el. : Earth-return mutual coupling effects ingrounding grids, IEEE Trans., PAS-102, No. 6, p. 1850-, 1983 mentioned by Prof. Martiez Lozano)clearly show that Carsons impedance of an infinitely long conductor is greater than the finite-lengthconductor impedance which agrees well with the measured results. ..... The shorter the line length,the greater the error of Carsons impedance as expected. The higher the frequency, the lower theerror as Bob pointed out. The characteristic is theoretically explained. Carsons impedance formulais given in the form of

while a formula of a finite-length conductor is

It is clear that Carsons formula can not be applied to a finite-length conductor, because Carsonsimpedance is given for per-unit length, i.e., Zcarson [ohm/m], which has already been doubly-integratedfrom 0 to infinity. When the impedance of conductor 1 with length x1 is considered; Carsons formulaassumes the conductor 2 being infinitely long, while the finite conductor impedance takes intoaccount the length x2 , i.e.,

Finally, I acknowledge to Carlos T. Mata, Bob Meredith, Gabor Furst and Prof. Martinez Lozanofor the critical and valuable comments related to the CABLE CONSTANTS. Also, thanks to Mr.Masahiro Kan for sending me the copy of their E-mail discussions by Fax, because I have not openan E-mail for myself. I do not want to receive a hundred pages of ATP outputs by E-mail askingwhats wrong, that was my experience ten years ago. If a user of the ATP CABLE CONSTANTS hasa question to me, could you please send the question by Fax to the number: +81 - 774 - 65 - 6801.

Discussion Corner


References:[1] S. Sekioka, T. Hara, A. Ametani: Development of a Nonlinear Model of a Concrete PoleGrounding Resistance, IPST95-International Conference on Power Systems Transients, Lisbon,pp. 463-467, 1995.

Discussion Corner


Discussion topic:

Non-conventional use of SM model

The next discussion topics is a continuation of the main subject (machine modeling) of theprevious issue of EEUG News. Mr. Bruno Ceresoli, ENEL S.p.A. Electric Research Center, Italyraised a question related to inadvertent synchronous machine energization on 18th of April, 1997,which resulted first in a discussion and then a collaboration with the machine expert Gabor Furst,G.B. Furst Consultants Inc., Canada. The results of this cooperation are reported here:

Mr. Ceresoli asked:

we are currently simulating the inadvertent energization on a 370 MVA synchronous generator (byclosing the busbars breaker with the machine at very low (about zero) speed and voltage). Use of SM59 ATP model shows low currents flowing through the armature windings (i.e. less than 0.1 the ratedcurrent), which seems to be not correct. Has anyone some experience or ideas on the matter (bothATP simulation and "field experience")?

Gabor Furst has had (unfortunate) field experiences as he shared this with Listserver subscribers inhis mail on 18th of April:

I had one unfortunate experience with this type of incident many years ago in Australia, when a150 MW hydro generator was inadvertently energized at rest. The result was that the amortisseurwinding in the rotor disappeared in a puff of smoke.

.I was working recently on U.M. simulation of induction motors and I also happened to do somestudies for a big pulp and paper company in New Brunswick on across the line and reactor startingof 30 000 hp synchronous motors. I had done some EMTP simulation of starting currents and startingtorques which were in a very good agreement with the information supplied by ABB. I would be verysurprised if your initial results were correct.

If you send me the machine parameters, the short circuit level of the system at machine terminals, andthe speed at which the breaker was closed, and a brief description of what happened, I would beinterested to do a simulation for you. It might be useful if you could also send me the d and q axisequivalent diagram of the machine, which would save me the effort of converting d and q axisreactances and time constant into the parameters of the equivalent diagram, which I would use forthe simulation for U.M. rather than the SM59 model.

The results of the cooperation between experts in Italy and Canada was being summarized in twoemails submitted on May 16 and June 5, 1997. Because the second significantly modifies someconclusions of the first, here an edited version of this two electronic messages are published:

Discussion Corner


Inadvertent energization of synchronous machines

Bruno Ceresoli Via A. Volta, 1Ettore De Berardinis 20093 Cologno Monzese (MILANO)ENEL S.p.A. Electric Research Center, Italy E-mail: [email protected]

[email protected]

Gabor B. Furst Vancouver B.C. CanadaConsulting Engineer, G.B. Furst Inc., Canada [email protected]

T he following report summarize some results obtained in the attempt to model an inadvertentenergization of a Synchronous Generator when still (or at very low velocity) without applicationof the field voltage. They aim to be, above all, a possible starting point for further discussion that willbe welcome, especially from machine experts. We hope in any case this can be useful for other users.

1 Physical response of a synchronous machine to inadvertent energization

All people involved and references confirm that for any sudden application of voltage to the stator,regardless whether the rotor is spinning or is at standstill, the voltage applied will see transiently thesubtransient reactance or something close to it. So, a simple manual calculation can be done in orderto have a first approximation results of the stator currents. This behavior is physically due to thepresence of the damper windings (or bars) that are in fact short-circuited on the rotor, with a behaviorsimilar to the starting of an asynchronous motor. Note that this is true also for the field winding thatis short- circuited as well, when no excitation is present. In conclusion, in the case of an inadvertentenergization large currents are generated in the field and damper windings (or bars), well beyond towhat these windings were designed for. This can cause damage if protections do not trip in time.

2 Experiences using Universal Machine (UM) model

If properly used, the U.M. model shows good results, with "high" stator currents regardless the initialspeed of the machine. Inadvertent energization can be obtained at any speed with a virtually zerovoltage (e.g. 1 V) in the UM data; the results of the energization do not substantially depend on theinitial speed. Note that the U.M. simulation is correct in the context of the basic modeling, whichrefers all coil inductances and mutual inductances to the stator, and uses a star equivalent for thesimulation. The currents in the stator coils will be "REAL" currents, while the currents in the rotorcircuits are currents referred to the stator side. In other words, the model refers all the currents to thestator coils. The conversion factor can be easily found only for the field winding from the machinespecification (by means of the no load field current on the air gap line). On the other hand, thecalculation of the damper currents is not simple, and can only be done from special data obtainedfrom the manufacturer.As regards the machine parameters, it is worth noting that the UM model response is obtained usingthe resistances and inductances calculated at rated speed (50 Hz for us). As the UM model results

Discussion Corner


seem to be correct also at very low speed, this suggest that these 50 Hz values are substantiallyadequate in the 0-50 Hz range.

3 Initial experiences with the SM-59 model

The SM-59 model, used with the PARAMETER FITTING option, seemed not to be suitable tosimulate energization of a synchronous machine at standstill or even at a low frequency. The statorand corresponding field currents obtained from the model were low at low frequency, and grew upwith the frequency. The reason of this behavior was not clear for the authors initially. While the 50Hz PARAMETER FITTING results are reasonable, using the same conversion at differentfrequencies. e.g. 1 Hz, different values ware obtained:

- stator resistances with the SAME values (good!); - rotor resistances with value 50 times GREATER than at 50 Hz; - the SAME values (in Ohm!) for all the reactances (that means, rotor self inductances 50 times GREATER than at 50 Hz, it seems...)

4 Further investigation of the machine models (SM-58, SM-59, UM)

Authors have continued to investigate the problem using all the available SM-58, SM-59 and UMmodels. The initial conclusion reached was that all the SM59 like data inputs produce incorrectresults, whereas the standard UM type #1 model, with coil inductance inputs, gives the right answer,which, as far as the stator inrush current is concerned, can easily be checked by a simple manualcalculation.

After performing a variety of tests, authors concluded that the problem could be a data error ratherthan a bug in the SM59 or the new SM58 model. And this assumption was correct: the SM59simulation used the per unit L version of input. In calculating the per unit L's, it was assumed that themodel converts from per unit L's to inductances using the frequency 50 Hz, specified or implied inthe data file as the power frequency, and not the initial rotor speed (frequency) which was specifiedas 1.0 Hz. However it should be noted that the per unit inductances have to be referred to aninductance base which is a function of : Lbase=Zbase/ with Zbase=V

2/S. So, dividing the per unitinductances by initial/ 50Hz = 1/50, the correct results were obtained also with the SM59 or SM58 model.

5 Conclusion

The simulation yields the correct stator currents for both the SM59 and UM models, and the correctfield current using the SM58/59 model. Using the standard UM type #1 model, the field current hasto be scaled manually or via TACS/MODELS, based on a subsidiary run or a SM59 no load run.Neither of the two models give the true currents in the damper windings as these windings aremodeled by equivalent coils, the characteristics of which, such as number of turns etc. are not knownand indeed may not even exist as in the case of the equivalent coil for the rotor steel of a round rotorunit.

People and Profiles


Author of AtpDRAWThe rubric People and Profiles aims for introduction of ATP users to readers. In this issue theauthor of the AtpDraw program and his Institution are introduced.

H ANS -KRISTIAN HOIDALEN was born in a small place called Drangedal located in the Telemark county (cradle of skiing) in thesouthern part of Norway in 1967. He received a M.Sc. degree in electricalengineering from the Norwegian Institute of Technology, Norway, in 1990.For 1 1/2 year he further work at this institute as a scientific assistant andduring this period development of ATPDraw started. In 1992 he beganworking at the Norwegian Electric Power Research Institute (EFI), mainly inthe field of electric transients, power lines and covered conductors.Development of ATPDraw continued during this period, financed byBonneville Power Administration. From 1994 he has been on a leave fromEFI to work on a PhD on the subject of lightning-induced voltages with focus on problems in the low-voltage system. Personal interests are music (singing and guitar playing), skiing, orienteering andbridge (not basketball).

ATPDraw is a graphical preprocessor to the ATP-EMTP on the MS Windows platform. In theprogram the user can build up an electric circuit, using the mouse, by selecting predefined componentsfrom an extensive palette. Based on the graphical drawing of the circuit, ATPDraw generates the ATPfile in the appropriate format based on "what you see is what you get". All kinds of standard circuitediting facilities (copy/paste, grouping, rotate, export/import) are supported. Circuit node naming isadministrated by ATPDraw and the user only needs to give name to "key" nodes. More than 65standard components and 25 TACS objects are available, and in addition the user can create newobjects based on MODELS or Data Base Modularization. ATPDraw has a standard Windows layout,supports multiple documents and offers a large Windows help file system. which explains the mostbasic rules. Other facilities in ATPDraw are: a built-in editor for ATP-file editing, support ofWindows clipboard for bitmap/metafile, output of MetaFiles/Bitmaps files or PostScript files notlimited to circuit window size, a new module for using Line/Cable Constant punch files directly inATPDraw, a tool-bar below the main menu containing the most used selections together with the last9 selected components, an extensive UnDo/ReDo handling with up to 100 steps, etc.

Along with ATPDraw comes a program called ATP_LCC which supports Line/Cable Constants inthe ATP-EMTP. In this program the material and geometric data are specified in dialog windows andthe cross section is display in the main window. The program ATP_LCC generates correct ATP-fileswhich processed by ATP produce punch files which in most cases are readable by ATPDraw.

The ATPdraw program is royalty free and can be downloaded free of charge from the ftp serverftp.ee.mtu.edu (user: anonymous, password: your e-mail address). The property of the programbelongs to Bonneville Power Administration (BPA) which has financed the program developmentand the Norwegian electric Power Research Institute (EFI).

Some fact about Mr. Hoidalens empoyer: EFI was established in 1951 and has developed intoan independent research company and centre of expertise in energy supply and electric powertechnology. EFI is internationally recognized as a neutral test and certification body for electro-

People and Profiles


technical equipment. EFI is an important partner for the electric manufacturing industry in developingNorway's energy supply and it has close cooperation with the Norwegian University of Science andTechnology (NTNU) in Trondheim in the field of applied and theoretical technological developments.EFI have developed numerous models for studies of electric power systems, and devoted considerablelaboratory work to research and development of materials and components. EFI's staff is active ininternational standardization bodies and international cooperation which are relevant to energy supplyand the industry as a whole. EFI is now organized in 4 research divisions and their main activity areasare listed below:

Power Generation and Market Strategic energy studies Hydrology Expansion planning and operation planning of hydro thermal systems Market modelling, Contract evaluations Demand forecasting Data communication New reneable energy sources, Decentralised generation

Power Transmission Systems Transmission system planning Security assessment System dynamic studies, System protection Power flow control using FACTS devices Control and operation of AC/DC systems Power transmission lines Electrical and mechanical design of components and plants Insulation coordination, including voltage transients Lightning detection and location

Power Distribution and Apparatus Distribution system planning Distribution automation and protection Power system quality, Power electronics Faults statistics EMC/EMI Field calculations Energy control in buildings and industrial processes Electrical installations for ships, offshore and industry Lighting technique Maintenance and refurbishment planning

Materials Technology Cable technology, Insulation materials and systems Condition monitoring and diagnostic methods Electrical fire technology Components development support Testing of electrical components Operate EFI's heavy laboratories

For more information about EFI visit their home page at address: HTTP://www.efi.sintef.no

Technical Papers


Monte Carlo Lightning Backflash Model for EHV LinesA MODELS Application Example

Gabor B. Furst #203-1745 Martin DriveConsulting Engineer Surrey (Vancouver) B.C.Vancouver B.C. Canada V4A9T5

[email protected]

Abstract: The tripout rate of ehv double circuit transmission lines due to lightning causedbackflashes cannot be calculated accurately by the traditional simplified methods. This paperpresents a method using EMTP simulation of the physical system combined with MonteCarlo simulation of the significant random variables affecting backflash, using MODELS.New features of ATPs MODELS which were added recently, facilitating the Monte Carlosimulation of multiple independent probability distributions, and a self terminating MonteCarlo process are discussed. Corona was not built into the backflash model, its effect wasonly simulated by separate runs with line models incorporating the increased couplingbetween phase and shield wires. The central focus of the paper is to present an applicationexample of new MODELS features. The backflash problem is used as a vehicle for this, acomprehensive coverage of the backflash problem is beyond the scope of this paper.

1 Introduction

The lightning backflash caused tripout rate of hv and ehv transmission lines with towers ofmoderate highest of about 35 m or less, can be analyzed using the conventional simplifiedapproach which lends itself to manual calculations. A typical example of this method isshown in [1]. The concept is illustrated in Figure 1. The lightning surge striking the towertop sees the parallel connection of the surge impedance of the shield wires and the towergrounding resistance. The tower surge impedance or inductance is usually neglected. Thesurge discharges through this equivalent surge impedance and raises the tower top potential toEtp. A percentage of this potential which also propagates down the shield wires, is coupledto the equivalent phase wire, which is represented by the phase wire having the greatestaverage distance from the shield wires. This coupled potential is Ecp. The power frequencypotential used is the 50% probability value of the potentials on the three phases, which is 87%of the maximum phase to ground potential. This component is Eph.. The voltage stress acrossthe gap between the phase wire and the tower can be written as

Es = Etp - Ec - Eph (1)

The magnitude of the voltage stress is a function of the lightning surge current. Theamplitude of the surge for which the voltage stress exceeds the strength of the tower gap andcauses a backflash, is the critical surge current Is . The probability of the surge currentexceeding this value can be determined from typical lightning surge probability distribution

Technical Papers


curves. The number of backflashes per year per 100 km line, called the backflash tripout rate,can be determined from:

Tripout = P(Is) . Nline ( 2)

where Nline is the expected number of lightning strikes to the line per 100 km per year.

Z s h

R g

E c p + E p h

E s

Is

E tp

Figure 1 Equivalent for Simplified Study

2 ATP - Semi-Probabilistic Approach

An improved method using ATP/MODELS was described by D. Alvira in [2]. Figure 2 is asimplified illustration of the concept.

Transmission lines on both sides of the tower hit by lightning is modeled by one of theEMTP line models, usually by either the JMARTI or the constant parameter distributed linemodel. In [2], the JMARTI setup is used to model one span on both sides of the tower with along line connected to these spans. The lightning surge is represented by a 13 type 2/50mscurrent source.

Istroke

Rg

Istroke%Prob.

ln( Istr / imean )

%Prob.

1 2 3

Px

JMARTI or

Distr. par.

Ztower

Ea,b,c =f(angle)2us surge

Vflo

Figure 2 ATP - Systematic Model

The tower is represented by a surge impedance terminated in a tower footing resistance. Thethree phase potentials are produced by the steady state EMTP solution.

Technical Papers


An excellent discussion on the representation of towers and lines for lightning studies can befound in [3].

The electric strength of the insulator string or the gap from the phase wires to the tower isrepresented by flashover switches set to the 50% impulse flashover voltage of the insulatorstring.

A systematic ATP run is used for the step wise increase of the amplitude of the lightningsurge current until one of the flashover switches operate, which is monitored in MODELS.The magnitude of the surge current at which the first switch operation occurs is the criticalsurge current from which the probability of backflash can be determined as in the simplifiedmethod. The surge current obtained is the value for the phase potential distribution obtainedfrom the steady state solution. As systematic or Monte Carlo simulation does not restart fromsteady state, separate sets of systematic runs have to be carried out to simulate the effect ofdifferent phase rotation. this was done in [2] by step wise increase of the power frequencyreference angle from zero to 360 deg. If the phase rotation is increased in n equal increments ,then the probability of backflash is

p I k p kb s sk

n

==

( ) ( )1

(3)

where pb is the total probability of backflash over the 0 - 360 deg. range of power frequency reference angles; Is (k) is the critical flashover current for the kth reference angle .

To find the critical surge current from ATP/MODELS run, the lightning surge source wasconnected to the tower top via a systematic switch, stepped by small time intervals. Thevalue of sequence number of energization, KNT, was calculated in MODELS from theclosing instant of the switch, passed to MODELS. The surge current was then generated as afunction of the switch closing time, with the magnitude increased in steps until backflashoccurred in one phase. This was monitored in MODELS by passing the position of theflashover switches.

This method assumes constant phase to tower flashover voltages in the three phases, and afixed surge front time for which a typical value of 2 micro seconds was used. In addition, ituses a 13 type source, which is not ideal for lightning surge simulation.

In terms of ATP runs, the evaluation of equation (3) requires a number of passes(energizations) equal to the product of the number of steps used in increasing the strokecurrent in a pre-determined range times the number of steps used for scanning the range ofangle reference for the phase potentials. Assuming 20 for both , the number of passes is 400.In addition each step for changing the phase angle requires a separate systematic run, hencethe full evaluation of (3) has to be done outside ATP.

3 Double Circuit HV/EHV Lines

The methods described above give reasonably good results for HV and EHV lines with towerheights not exceeding approximately 35 meter, which would be the case with most singlecircuit tower lines with horizontal configuration. For double circuit lines, and with the towerheight exceeding this value, field experience indicated that the simplified method may give

Technical Papers


overly optimistic or conservative results, depending on the simplifying assumptions made. Ifcompared with the ATP systematic method described above, the following additional factorsmay be considered:

(a) The probabilistic distribution of the front time of the lightning surge current and theshape of the rising part.

(b) The variation in the tower gap 50% flashover voltage in the three (or more) phases,together with the dispersion of the flashover voltage around the 50% value.

(c) The different crossarm heights carrying the individual phases.

(d) The variation in the tower footing resistance.

(e) The effect of corona on increased coupling between shield and phase wires.

Including the variables considered in the systematic approach, the random variables and theirprobability distribution considered, for the purpose of the example discussed in this paper,are:

Lightning surge current log-normal distribution Lightning surge rate of rise log-normal distribution Phase potentials (reference angle)uniform distribution Tower gap (insulator flashover) normal distribution Tower footing resistance uniform distribution

The phase potentials are related to only one random variable , the phase rotation angle, whilethe tower gap flashover voltages are considered to be independent in the three phases. Thisgives a total seven independent probability distributions. To handle this problem with asystematic approach, also referred to as method of enumeration, and if only five discrete stepswere considered for each variable, the total number of passes to be run would be 57 = 78125passes. Apart from the excessive computer time, the effort in evaluation the results outsideATP would be substantial, and/or a separate computer program would have to be used to doit. It seems to be logical, therefore, to explore the benefits of a Monte Carlo type simulation.

EMTP is designed to perform normal (Gaussian) or uniform distribution of closing oropening of circuit breaker poles either in a SYSTEMATIC manner or by random simulationusing STATISTICS with the Monte Carlo technique. The ATP Rule Book warns the useragainst the potentially enormous number of energizations with the SYSTEMATIC optiondepending on the step times used for breaker closing or opening.. The breaker opening orclosing logic is controlled internally by ATP, the user enters only the appropriate values forstepping with SYSTEMATIC or s with STATISTICS. For backflash simulation suchEMTP internal logic does not exist, and the user has to perform the random choice of themagnitudes of probabilistic variables from TACS or MODELS. This involves, as a startingpoint, the monitoring of the value KNT, the sequence number of the current energization(pass). To eliminate the cumbersome way of calculating KNT as discussed in Section II, thewriter approached Dr. Meyer about the possibility of passing EMTP constants and variablesto TACS or MODELS, for use or even modification by the user. Changes wereimplemented in both TACS and MODELS (by L.Dub), which gave MODELS a verypowerful additional capability to manipulate ATP variables from inside MODELS.

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To demonstrate the new features and the use of Monte Carlo simulation in MODELS anexample data case was created for the backflash analysis discussed above. The mainfeatures of this example data case, which will be available on the Fargo Server , are describedbelow.

4 A Sample Data Case for Backflash Analysis using MODELS

(a) Network and Tower Representation

The line used in the example was a double circuit steel tower construction for 345 kV,barrel configuration with two overhead shield wires, but only one side of the towerstrung, similar to the arrangement used in the systematic approach described above.Two 200 m half spans were represented on both sides of the tower assumed to be strickenby lightning, with a three km section on the source side and ten km on the other side.The circuit arrangement is shown in Figure 3. The line sections were modeled asuntransposed distributed parameter lines (K.C.Lee model) at 500 kHz. In an actualengineering study the user may want to use the JMARTI setup but in the writers opinioneven a lossless line would give satisfactory results.

Figure 3 Circuit Arrangement in Data Case

The tower was modeled as a single phase distributed parameter line of four sections,corresponding to the sections between crossarms and from the bottom crossarm to thetower footing.

No steady state energization is used. A randomly selected angle for phase A is used tocalculate the instantaneous potentials of the three phases, which is then applied to thephase wires at the source end in the time loop. As the line is longer than the simulationtime of 6ms, there are no reflections from the line ends, which makes this approach a validequivalent to changing the phase angle in the phasor solution.

(b) Lightning Surge

For modeling the lightning surge current a simplified version of the Type 15 Bernd Steinsource was used generated in MODELS. The three variable parameters of the surge areamplitude, front rate of rise and tail time to 50% amplitude. The tail time was fixed to 50ms, and the mean value of rate of rise was calculated as a function of the surge amplitude[4]. Both the amplitude was assumed to have a log-normal distribution with a mean of25kA, both the amplitude and a rate of rise were assumed to have a s of 0.7. A typicallightning surge current shape is shown in Figure 4.

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Figure 4 100 kA , 2/50 ms surge

(d) Tower Gap Flashover

A uniform 50% impulse flashover voltage was assumed for the three phases equal to 1500kVp, typical of 345 kV lines in North America. The probability distribution was assumedto have a s of 3%, with the three phases being probabilistically independent.

5 Monte Carlo Simulation Techniques in Models

Recent improvements to MODELS made it possible to run Monte Carlo simulation fromMODELS in a very efficient way. Two functions were added to MODELS which enabledperforming Monte Carlo simulations from MODELS for simultaneous simulation of severalindependent random processes with different user defined probability distributions, and tomonitor the progress of the simulation. These two functions are: atp and deposit

The function atp is used to pass the value of an EMTP constant or variable to MODELS,whereas the function deposit enables the user to modify an EMTP constant or variable andpass it back to EMTP. This means that if an EMTP array is set aside for temporary storage,variables can be passed from a trial (energization) KNT(i) to the next simulation trialKNT(i+1). In the past, this could be done in an EMTP Monte Carlo simulation by a muchmore laborious and slower way of using SPY. Highlights of the method are given below,details can be found in the liberally annotated example data file BACKFL.DAT which will beavailable from Prof. Morks site.

(a) Random Number Generation

The example data has six variables with independent probability distributions. It ispossible to use the consecutive throws of the same dice to generate the random numbersfor selecting the value of the variables in each trial. In the example, two random numbergenerators were used. One was the internal random number generator of MODELS, theother was a user defined random number generator which was used to select the value ofthe amplitude of the lightning surge current. This generator is seeded in the INIT groupby the user in the first pass. The xi value is stored in a selected EMTP array using thedeposit statement. For getting xi+1 the atp function is used to recall xi and the user definedrandom number generator calculates xi+1. The usefulness of having more than onerandom number generator in the Monte Carlo simulation is beyond the scope of thispaper.

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(b) Keeping Track of Values and Events

With the atp and deposit statements it is possible to keep track of array values and events(e.g. breaker operations) from the previous trials, which has not been possible with thebatch mode EMTP Monte Carlo simulation. In the backflash example at hand, thevariables to store and monitor, are points on the cumulative probability distribution curveof a selected variable, and the number of backflashes which occurred.

(c) Termination of the Simulation

In principle, the simulation is terminated when the probability distribution of the resultingevent of interest becomes stable, i.e. it does no longer change with repeated trials,meaning that the process converged. In the case of the backflash simulation this meansthat the calculated value of the line tripout rate no longer changes with increasing numberof the trials. This simple concept could be difficult to implement when dealing withevents of a very low probability. The in depth theoretical treatment of this problem,discussed in texts on the accuracy of Monte Carlo simulations, is beyond the scope of thispaper.

The backflash and hence the tripout rate is an event which depends of a usually very lowprobability of the combination of high lightning surge current and the front time of thesurge. This probability for EHV lines is in the order of one percent. This means that themonitored tripout rate, within an accuracy band, could appear to have converged and nochange occurs for a relatively large number of consecutive trials, before true convergencewas obtained. The approach tested was the monitoring of the convergence of the tripoutrate and the convergence of the obtained cumulative distribution of the lightning surgeamplitude. The convergence of the lightning surge amplitude was determined from themonitoring of three points on the cumulative distribution curve in the 75 kA t 125 kArange, using an accuracy defined for each of the three points. Convergence was deemedto be obtained when both the tripout rate and the lightning surge distribution converged.This approach was tested for large number of trials beyond the point of convergence, andwas found acceptable from the point of view of engineering accuracy, bearing in mindthe accuracy of the data for this type of analysis. When convergence is reached MODELSsets NERG to KNT(i) +1, and the simulation is terminated. It should be noted, however,that the method used only establishes a general concept of an automatic termination of theMonte Carlo simulation. For other type of studies, and with the event or its probabilitydistribution having different sensitivities to the random variables, the method of testingconvergence would change.

(d) Optimization of Number of Trials and Individual Run Times

The total time required for the Monte Carlo simulation depends on the number of trials(energizations) required to achieve convergence, and the run time TMAX used for asingle simulation.

The number of trials can be reduced if the range of simulation of the cumulativedistribution functions is restricted based on a knowledge by experience or by preliminarycalculations. An example using the surge amplitude log-normal distribution illustrates

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this. There is a minimum value of lightning surge current below which backflash will notoccur regardless of the steepness of the surge front. Assuming that this value for a givenline voltage class is 75 kA, only the >75 kA range of the distribution curve needs to besimulated. For the log-normal distribution of lightning currents, the probability of a surgeamplitude being greater than 75 kA is 5.8%. This reduces the required number of trials toapproximately 5.8% compared to the simulation of the whole range. Because of therandom nature of the simulation this is not the exact reduction but it is a reasonableestimate.

Another possibility to reduce the overall simulation time is to abort individual runs, onceit is recognized that the combination of values of random variables cannot cause abackflash. This happens if the combination of surge amplitude and the steepness of thesurge front is such that from prior knowledge, backflash would not occur. If such acondition is detected the deposit function is used to change the value of tmax to t+deltat.The two methods described reduced the total simulation time for the backfl.dat exampleby a factor of four.

6 Screen Display During Running

Once the simulation started, the user has lost control, as MODELS cannot be run in the SPYmode. It is useful, however, particularly during the testing stage of the model, to observe onthe screen the progress of the simulation and some of the interim results of an individual run.This information can be useful for debugging and/or improving and changing input data, andprovide some information for insulation coordination. The display is flashed on the screenduring each pass, generated by MODELS write statements, and is available in the .LIS filefor examination. In addition, by observing the display, the user may terminate the run fordata modifications. The screen display for monitoring random variables and backflash isshown below.

KNT = 158SURGE CURRENT 153 KASURGE FRONT 1.6 USPHASE POTENTIALS PH. A, B, C 321, 56, 264 KVTOWER GAP FLASHOVER PH. A, B, C 1578, 1670, 1524 KVBACKFLASH IN PHASE CTIME TO FLASHOVER 2.5 USBACKFLASH COUNT = 5TRIPOUT RATE 0.95/100 KM / YEAR

In the above listing the front time of the surge is calculated from the random steepnessassuming that the rate of rise is constant between zero and maximum amplitude. Phasepotentials are calculated from the random phase A reference angle. Tower gap flashovervoltages are calculated from the random variation around the 50% flashover value. Shouldbackflash occur, the timing of the backflash and the phase in which it occurred is recorded.The number of backflashes are accumulated and the tripout rate is calculated from the entereddata of isokeraunic level and tower dimensions. Further details are given in theBACKFL.DAT data file.

In the BACKFLASH example, after the first 100 passes and then following blocks of 20passes, the convergence of Monte Carlo simulation is checked. In the BACKFLASH

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example, this is done by checking the error between three points on the surge currentcumulative probability curve obtained by the simulation, against the theoretical values. If allthree errors are less than the specified errors, the run is terminated. This is run, or and theerror can be checked for more than one random variable if desired.

KNT = 121CHECK PROGRESS NOWTARGET CUMULATIVE PROBABILITIES 75, 100, 125 KA 5.8 2.4 1.1 % CURRENT VALUES : 4.5 1.2 0.8 %SURGE CURRENT 56 KASURGE FRONT 1.8 USPHASE POTENTIALS PH. A, B, C 336 , 225, 111 KVTWR GAP FLASHOVER PH. A, B, C 1618, 1673, 1603 KVBACKFLASH COUNT = 3TRIPOUT RATE 0.74 / 100 KM / YEAR

7 Conclusions

The paper shows an engineering example of utilizing some of the new features of theMODELS language which were added recently. While the data demonstration data fileBACKFL.DAT is an example only rather than an engineering template for performinglightning backflash studies, it is nevertheless a useful starting point for those who wishdevelop Monte Carlo simulations for backflash studies, or other type of simulations such asswitching surge studies using random modeling of tower gap flashover voltages and lightningarrester simulations. Further work is required to include a suitable corona model.

8 Acknowledgment

Acknowledgment is due to Ing. David Alvira of the Red Espana, Madrid. whose emaildescribing the SYSTEMATIC approach gave the incentive to the development presented, andto Laurent Dube for his assistance in the implementation of the new MODELS features in thedata file.

9 References

[1] Transmission Line Reference Book 345 kV and above, EPRI, 1975[2] David Alvira: Backflash Simulation for a 400 kV Double Circuit Line using

ATP/MODELS. ATP-EMTP List-server Email , January 1996.[3] T. Yamada et al. : Experimental evaluation of UHV Tower Model for Lightning Surge

Analysis, IEEE Transmission and Power Delivery, Vol.10, No. 1, January 1995.[4] R.B. Anderson, A.J. Erikson : Lightning Parameters for Engineering Application,

Technical Brochure, CIGRE, Electra, No.69, 1982.[5] J.G. Anderson, Monte Carlo Computer Calculation of Transmission Line Lightning

Performance, Power Apparatus and Systems, Part III,Vol. 80, 1961.[6] M.A. Sargent, Monte Carlo Simulation the Lightning Performance of Overhead

Shielding Networks of high Voltage Substations, IEEE Trans., Vol. PAS-91, 1972.[7] IEEE Working Group Report: Estimating Lightning Performance of TransmissionLines II - Updates and Analytical Models , IEEE Transactions on Power Delivery, Vol.8,No.3, July 1993.

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Corona Modelling for Attenuation and Distortion ofLightning Surges in Transmission Lines

Juan L. Ciudad, David Alvira, Fernando Soto Power System Studies DepartmentRed Elctrica de Espaa, S.A. , Spain P/ Conde de los Gaitanes, 177

La Moraleja, 28109 Madrid (Spain)[email protected]

Abstract: Red Elctrica de Espaa, S.A. (REE) is interested in travelling wave attenuationcaused by corona, specially in lightning surges. Knowing how the overvoltage, produced by alightning strike, attenuates until it reaches the near substation, allows to evaluate the criticallightning distance. In this paper it is shown a corona model for the Electromagnetic TransientProgram (EMTP/ATP) developed by REE, suitable for lightning surges. This model is basedon linearized charge-voltage cycles and on the division of the transmission line into sections.After building the model, some validations are done.

Keywords: Corona, Lightning Surges, Attenuation, Distortion, EMTP.

1 Introduction

Two of the most important effects of corona in overhead transmission lines are the power lossincrease and the attenuation of travelling waves. This paper presents a model that cansimulate the attenuation of the amplitude and wave front of lightning type surges travelling ina High Voltage transm

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