New developments in systems for transmission and distribution substation control and protection

Electric Power Systems Research, 5 (1982) 21 - 34

21

New Developments in Systems for Transmission and Distribution Substation Control and Protection*

B DON RUSSELL

Electrzc Power Instrtute, Texas A & M Unwers~ty, College Statmn, T X 77843 (U S A )

(Received July 20, 1981)

SUMMARY

Thzs paper contains the edzted records of four presentatzons on Transmtsszon and D~stnbutton Substatzon Automatzon. These presentations were made at the 1980 Summer Power Meeting of the Power Engineering Society under the sponsorship o f the Apphcatzon of New Technologzes Working Group of the Automatic and Supervisory Systems Subcommzttee o f the PES Substatzons Commzttee The organzzatmn and structure of transm~sszon and dzstnbutzon control and protectzon systems utzhzmg computer based technology are described m detad The perspectwe of ut~hty companzes concerning the need and practzcahty of such systems zs described The problem o f electromagnetzc interference m transm~sszon substatzons ~s also presented INTRODUCTION

Since the advent of relatively Inexpensive computer systems, power systems engineers have attempted to define h o w such systems could be used to automate dlstnbutmn and transmmsmn substations. Improvements in control, protectmn, and data acqumltlon are desirable m an attempt to prove the overall rehabfllty and operatmn of the utility system The purpose of the panel discussion held at the 1980 Summer Power Meeting was to descrlbe t w o projects currently attempting to utlhze several new technologies to automate *Record of Panel Presentations, 1980 Summer Power Meeting, orgamzed by Apphcatlon of New Technologms m Substatmn Control Working Group, Automatm and Supervmory Systems Subcommittee, Substatmns Committee 0378-7796/82/0000-0000/$02 75

substations Representatwes of two manufacturers, a utlhty, and a umverslty were asked to present an overall pmture of substation automation and the detmls of their individual research efforts. All of the research described was co-sponsored and partially funded by the Electrm Power Research Institute. The panel was organized as followsPanel Moderator G E Short, Boeing Instrument and Control Panel Members Jennmgs Bunch, General Electric Company 'Integrated digital systems for dlstnbutmn autom atmn' John L. McCoy, Texas Electrm Servme Company 'Dmtnbutmn a u t o m a t m n from the utility w e w p o m t ' E n k A Udren, Westmghouse Electric Corporatmn 'Design of a transmlssmn substatmn automatmn system' B Don Russell, Electric Power Institute, Texas A&M Umverslty 'Electromagnetic transmnt measurements m transmlssmn substatmns' A summary text of each of the above presentatmns follows

' I N T E G R A T E D DIGITAL S Y S T E M S B U T I O N A U T O M A T I O N ' (GEC)

F O R DISTRI-

In 1973, General Electmc mltlated the PROBE Project to determme the technmal feaslblhty of digital electronms for substation and dmtmbutlon feeder automation. Workmg m partnership with Commonwealth Edison, a m m m o m p u t e r research faclhty was estabhshed m the LaGrange Park Substation of the Commonwealth Edmon Company to provide actual substation operating reqmrements and environment Subsequently, Niagara Mohawk © Elsevmr Sequoia/Printed in The Netherlands

22 and Pubhc Service Electric & Gas of New Jersey joined the project to prowde technical and fmancml support Results to date have demonstrated the technmal feaslblhty of eleven substation automation functions which cumulated in a successfully staged fault test on Friday, October 13, 1978 Current efforts are tamed at demonstrating the technical feasibility of identifying and isolating feeder faults and restoring services to unfaulted sections by automatic operation of feeder sectmnahzmg switches This automatm feeder control will be coordinated with the necessary substation automation functions, such as automation breaker reclosmg, and will use radio to communmate with and control feeder devines An alternative d i s t n b u t m n line carner commumcatlon system will also be assessed P R O B E Prolect --Phase 1 (1973 - 1978) The PROBE Project was mitmted m anticlpation of utility needs for more timely onhne information and better controls for distribution substations and feeders The primary ratmnale was that analog electromechanmal and static relay technologms appeared to have inadequate capablhty to fulfill these needs and that continued decreasing cost made digital electromcs potentially attractive The application of digital technology can take two paths (1) a one-for-one replacement of analog components, or (2) an integrated system approach The one-for-one replacement philosophy, while more familiar, would not utlhze fully the performance or the low cost potential of digital technology The integrated system approach, on the other hand, promises to fully utilize the low cost potential of digital technology but requires a fundamental reexamination and perhaps a change in tradltmnal approaches to substation functmns General Electric and its utility partners elected to pursue the integrated system approach with the followmg objectives (1) To determine and to define the functmnal specification of substatmn functmns from a digital implementation perspective (2) To develop an integrated digital system approach, the concept of a c o m m o n substatmn data base, for substatmn a u t o m a t m n (3) To verify the integrated system approach by demonstrating a broad class of substation and d l s t n b u t m n feeder functions m an actual field installation

The functions selected to carry out the above objectives are hsted below P R O B E d~stnbutton automatton functions Phase 1 Alarm annunciation Automatic reclosmg Automatm bus sectlonahzmg Breaker failure protection Fault recording Instrumentation Remote control and data reporting Sequence-of-events recording Synchronism check Transformer load capability monitoring Transformer LTC control Phase 2 Automatic feeder sectmnahzmg and development Integrated Volt/VAR control

Many of these functions, such as synchromsm check, are more hkely to be required for transmission rather than for distribution substations Thus, as a research project, PROBE spanned the total substation automation requirements Initial field installation and evaluation of the PROBE system began m 1976 and demonstrated (1) The functional performance of the above eleven substation automation functions (2) The generation and mmntenance of the c o m m o n substation data base built from highspeed sampled raw current, voltage, temperature and status reformation The data base was maintained through all other electrical noise at LaGrange Park Substation (3) The successful demonstration of the integrated and coordinated execution of interrelated substation functions m a staged fault test This test staged a transmnt fault (apprommately 3000 A) at approximately 1 6 miles on a distribution feeder by shorting one phase of the feeder to ground through a fuse PROBE automatic functions were initiated by the instantaneous overcurrent relay The coordinated actions of automatic breaker reclosing, breaker fmlure protection, sequenceof-events recording, fault recording, and instrumentatlon and alarm annuncmtion were correctly executed

23

The potential advantages of digital technology in provldmg tnnely operatmnal reformation to utlhtms were shown b y the demonstratmn of digital parallel transformer LTC control Two large (40 MVA) substatmn transformers were instrumented and controlled by the PROBE system In normal operatmn, these transformers were controlled by an analog LTC control system based on the principle of mlmmlzmg the circulating reactive current The PROBE parallel transformer LTC control implemented the same control strategy Dunng the test, the operation of the transformers was first controlled by the analog LTC control system and then by the PROBE system. The comparative performance of the parallel transformer LTC control is hsted below Parallel transformer L TC control Circulating currents (kVAR) Transformer 72 Analog control 2900 lead PROBE control 500 lead

Transformer 73 2200 lag 230 lead

In this experiment, the results do show the performance advantage of the digital versus analog lmplementatmn In addltmn, the results suggest that with an integrated digital system, the remote control and data reporting functmn can mform operators of any off-tune performance of any substation functmn so that mmntenance can be scheduled to 'tune-up' the performance of specific distribution devices. Capacitor bank switching, originally a planned functmn of Phase 1, was deferred because no switched capacitors existed wlthm LaGrange Park Substation and because of the desire to Investigate the coordmated control of transformer LTC and capacitor bank, 1 e. Integrated V o l t / V A R control, usmg remotely controlled feeder capacitor switches m the next phase of the project. PROBE Project -- Phase 2 (1977 - 1980) Dunng the course of the PROBE Project, technmal exchange with utflltms seemed to mdmate the high beneSt potential of dlstn-

butlon feeder automation; that is, automatic feeder sectzonahzmg and d e p l o y m e n t can minimize servme outage time, p m p o l n t faulted sections for faster repmr with fewer hne crews, and defer Incremental substation transformer and feeder investment by permitting the shanng of load within and between dlstnbutlon substations In addition, with commumcatlon and control capablhtles added to feeder dewces, it now becomes posmble to coordinate the switching of feeder capacitor banks with substation transformer LTC control band on the actual operating conditions rather than on calender clock We call this capablhty zntegrated V o l t / V A R control It has the potential to maintain tighter bandwidth in voltage regulations and to minimize dlstnbutmn feeder losses -- t w o functions of mterest for energy conservatmn Two primary techmcal challenges m achmwng the above functmns are (1) the commumcatlon and the automatm control algorithm of remote feeder sectmnallzlng and capacitor bank switches, and (2) the coordinated control of substation functmns with these distribution feeder functmns. The PROBE Project selected radm and dlst n b u t m n hne carner as the commumcatlon media Experimental mmroprocessor-based pole-mounted remote umts using these medm were built to sense fault detectors, contact inputs and to provide control outputs and running averages of feeder voltages Data reductmn capabflltms such as average voltage were placed m these pole-mounted umts to increase the accuracy of the sensed data and in antmlpatmn of the low-data-rate capablhty of the developing dlstrlbutmn communmatlon systems For broad apphcatmn to various dlstnbutmn substatmns and feeder conflguratmns, a generalized automatm feeder sectmnahzmg and deployment algorithm is needed A generalized algorithm can be apphed to a variety of feeder conSguratmns without reprogrammmg. Unhke typmal computer-based SCADA systems, automatin feeder sectmnallzmg will normally operate without operator mterventmn. The operator is outside the control loop. Thus, the algorithm has to be systematmally programmed and exhaustively evaluated Based on the onglnal work by C Castro of Pubhc Servme E l e c m c & Gas, a generalized algorithm was developed and succesfuUy demonstrated with

24 a feeder n e t w o r k simulator It is now under simulator and field evaluatmn Au to matic feeder sectmnalizmg and deploym e n t is intimately tied to substatmn functmns such as automatic breaker reclosmg and to substation operating parameters such as transf o r m e r load capablhty The result of automatin recloslng, successful or not, mdmates a transient or a persistent fault and, thus, the need for feeder sectmnallzmg In addition, faster sectmnallzmg can be accomphshed if the fault d etect i on process is initiated upon breaker tripping rather than wmtmg for unsuccessful reclosmg T r a n s f o r m e r load capablh t y is needed to determine w he t he r addltmnal feeder sections can be pinked up w i t h o u t overload Similar c o o r d m a t m n between substation and feeder a u t o m a t i o n is also necessary for integrated V o l t / V A R control in which the switching o f feeder capacitor should be coordinated with substatmn transformer LTC control To clarify the logic operations of coupled functions, a distributed processing a u t o m a t i o n architecture was evolved The PROBE Phase 2 system consists of dual-mmmomputers m whmh one is used for substatmn signal collect m n and processing, data base mmntenance and substation a ut om at m control Relevant m f o r m a t m n is passed to the second minicomp u ter which Is the cont r ol focus of the dlstnbutton c o m m u m c a t m n interface and the feeder a u t o m a t m n functmns Necessary substation control for completing the ope r at m n o f feeder a u t o m a t i o n function is passed back to the first m m m o m p u t e r for e x e c u t m n

PROBE System The PROBE System consists of a dualm m m o m p u t e r system with distributed highspeed data acqulsltmn and processmg units The main c o m m u n i c a t i o n medium for feeder a u t o m a t m n is radio C o m m u n m a t m n interface and r e m o t e control is carried out by microprocessor-based pol e - m ount e d control units Some o f these units also have d l s t n b u t m n hne c ar n er mo d ems as adjuncts to radms to assess canner for feeder a u t o m a t i o n As shown m Fig 1 the PROBE System uses only raw substation m f o r m a t m n sensed by auxlhary current and pow e r transducers and by digital contacts I n s t r u m e n t a t i o n parameters necessary for all cont r ol f unc t m ns are calculated from raw sampled data either by the

PROBE 1 m m m o m p u t e r or by a high-speed processing unit This latter unit is a specialized high-speed m m roprogram m ed processor with hard-wired mult~pher In keeping with the distributed processing philosophy, the c o m m u n i c a t i o n interface to the feeder units 0 e p r o t o c o l and error checking) is carried out by a microprocessor c o m m u n l c a t m n controller The PROBE 2 m i n i c o m p u t e r is then primarily used for system coordination and for the e x e c u t m n of automat~c feeder sectionallzmg and integrated V ol t / V A R control algorithms Commercml mobile radio {approximately 150 MHz) t echnol ogy is the basis for the experimental p o l e - m o u n t e d control umts The microprocessor coordinates the e x e c u t m n of c o m m u m c a t m n p r o t o c o l together with fault det ect i on and switch operation In the case of capacitor bank switching where feeder voltages are measured, the microprocessor averages the measured voltages to assure a more reliable readmg and to reduce the c o m p u t a t m n load on the PROBE 2 m m m o m p u t e r s Because extensive actual field operations are lmpractmal, the PROBE Project has built a substation breaker simulator and a feeder system simulation for more extensive evaluat m n of the control functmns In addition, a fmld test box was also developed to md m the fmld installation and c h e c k o u t of the rem ot e pol e-m ount ed control units

Concluding remarks With the PROBE System research project complete, the E P R I / G E Integrated Distribution Control and P r o t e c t i o n Project will cont m ue to develop a u t o m a t i o n technology. The PROBE project has shown the technmal feaslblhty of an integrated digital system approach for substation and distribution feeder automation However, it remmns for the E PRI/ G E Project t o dem onst rat e the distract advantages of such an a u t o m a t i o n system and to develop hardware and software for practmal Implem ent at i on Techmcal exchanges with utlhtms have usually rinsed the followmg three questions (1) What are the operational advantages of digital technology ~ (2) How to assess the possible cost/benefit of this technology ~ (3) What are the n e x t steps to make this technology available to utlhtms~

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I COMMUNIC CONTROL LER

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CARRIER SUBST UNIT

PROBE1 MINICOMPUTER

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Fig 1 P R O B E S y s t e m a r c h z t e c t u r e

The posszble specffm operatmnal advantages such as better control of parallel transformer load tap changers have been cited above. However, the essentml potentzal advantage of dzgltal technology zs the abdzty to prowde more control functmns at comparable or lower costs, and m prowdmg new functmns such as automatm feeder sectmnahzmg whmh is not posszble wzth analog technology. By collecting all necessary substatmn mformatmn at once m a data base, mtegrated dzgltal systems can potentmlly decrease much of the new substatmn deszgn, wrong, and thus constructmn costs. In conjunctmn with load management and dzstnbutmn c o m m u m c a t m n dewces, integrated dzgital systems for dzstnbutzon control and protectmn can prowde realtzme operatmnal m o m t o n n g and control capabdztms throughout a dzstnbutmn system down to customer sites. Thzs real-tzme control capabflzty appears to be essential ff utflltms are to actzvely manage the:r loads m the future

Cost/benefit evaluatzon zs essentially a quantztatzve method of assessing the potentials of new technologms. General Electric zs currently working with a utzhty to develop a procedure for determining the dollar value of the potentzal benefits of dzstnbutzon automatzon. Some potential benefits can be placed m four general categories" (1) Save investment by d e f e m n g new feeders, new substations or new transformers by operating the e q m p m e n t closer to zts maxzm u m ratings rather than to some preset assumed hmlts (2) Reduce interruption related cost by reducing hne crew tzme for fault location and servme restoratzon (3) Reduce operatzonal cost by reducmg distribution system losses. (4) Improve customer relatzonshlp by decreasing mterruphon tzme, better voltage control and zdentffymg low-voltage feeder sectmns.

26 The o th er side of benefits is cost In fulfilling the possible requirements of various utilities, our c o n t m u e d interaction with utilities has indicated t hat an integrated digital system for distribution a u t o m a t i o n should have the following characteristics

Flexible and compatible automatzon system archttecture so t hat a utility can i m p lemen t d l s t n b u t l o n a u t o m a t i o n little by httle (1 e in piecemeal} for a variety of distribution system configurations Low cost and rehable components so the utility can afford to implement distribution a u t o m a t i o n on a wide scale Structured software destgn so that the automation system will operate reliably and be easily mamtmnable by utilities S tr u ctu r ed software design described the philosophy of programming the digital system so th at normal updates and modifications can be d o n e by utlhtms w i t h o u t reprogrammmg, and th at the e q u i p m e n t m a n u f a c t u r e r can fill a u t l h t y order w i t h o u t excessive programming cost Generalized algonthms for control functions is an approach to attmn the above objective Other necessary c o m p o n e n t s to structured design are, for example, well t h o u g h t - o u t and systematic arrangement of data in the data base (e g data pointers and tables), and the clear logical partition of program modules for the various control functions An equally imp o r t a n t result of structured design is that the logic and systematic approach to programming will help to ensure the reliability of the result a n t software It is h o p e d that the E P R I / G E Integrated Distribution Control and Pr ot e c t i on Project will fully d emo ns t r at e the technical e c onomi c feasibility o f substation and feeder a u t o m a t i o n

'DISTRIBUTION AUTOMATION F R O M THE UTILITY VIEWPOINT' (TEXAS ELECTRIC SERVICE COMPANY) Texas Electric Service C om pany (TESCO) is an investor-owned electric utility serving a pp r o x imately 500 000 customers with a peak d eman d of about 3800 MW in nort h central and west Texas Along with sister companies, Texas Power and Light and Dallas Power and Light, we are a m e m b e r of the Texas Utilities C o m p a n y system, which serves a b o u t one-third o f the population of Texas

Our service area reaches from F o r t Worth on the east to the Midland-Odessa area on the west Electric service to our customers was, m the past, provided entirely by gas/oil generatlon However, because of the fuel-changing program begun by Texas Utilities m the late 1960s, a b o u t one-half of our generation now is fueled by hgnlte coal These efforts m reducmg the use of natural gas as a boiler fuel were rewarded m 1978 when Texas Utilities received the electric u t l h t y mdustry's highest award, the Edison Award, given annually by the Edison Electric Institute TESCO has long been c o m m i t t e d to the d e v e l o p m e n t of new techniques and technologies in m any areas related to our industry We are completing, with Rockwell International, a D e p a r t m e n t of Energy feaslblhty study on the solar repowermg of an existing generating u m t using the central receiver concept In the late 1950s we pioneered in the develo p m e n t of a c o m p u t e r i z e d distribution data base which uses a coordinate grid system to locate any c o m p o n e n t of p r o p e r t y to within ten feet This data base finds uses m plant accounting, m engineering, m customer services, and in trouble dispatching This t ype of data base could eventually interface with the distribution a u t o m a t i o n systems for bot h onand off-hne uses The support of research organizations in our industry has always been of importance to TESCO In addition to the work of the Electric Power Institute, we also provide funding t o organizations at the Universities of Texas at Arlington and Austin and at Texas A&M University In our role as advisor on the EPRI Transmission A u t o m a t i o n Project (RP1359), we have participated m substation electromagnetic interference tests c o n d u c t e d for EPRI by the Electric Power Institute at Texas A&M In the latter part of 1979, we were chosen to serve as host utility for the EPRI project dealing with the a u t o m a t i o n of distribution substations and systems (RP1472}

Host utlhty project stte The located tion m station

test substation for this project is at the Handley Steam Electric StaF o r t Worth, Texas. Generation at this consists of t w o small umts connect ed

27 to the 69 kV system, and one 400 MW base load gas/off u m t and two 425 MW gas/off peakmg umts connected to the 138 kV system A 69 kV switching statmn connects the small umts to two 69 kV hnes. An autotransformer connects thxs switching statmn to the 138 kV switching statmn where a double bus arrangement connects ten 138 kV transmlss:on hnes. The busses are operated trod or spht, depending upon the generating umts on hne at any given time. The 138/12.5 kV substation is normally connected to the 138 kV D-bus through a clrcmt breaker A normally open mr switch prowdes an alternative source to this substatmn from the 138 kV C-bus. Three 20 MVA transformers serve three sectmns of 12.5 kV switchgear whmh are connected by normally open bus tm circuit breakers. Each sectmn of swltchgear, m turn, serves two dlstmbutmn feeders. Each delta-wye, load tap changing transformer is protected by percentage dffferentml and sudden pressure relays The differential relays also protect the lowmde transformer leads. Each sw:tchgear statmn is protected by an instantaneous overcurrent equipment ground relay connected to a current transformer located electrically between the msulated swltchgear frame and statmn ground. Providing phase protectmn are t:me overcurrent relays connected to current transformers m each totallzmg c~rcmt breaker The 12.5 kV fuse-coordinated feeders are protected by instantaneous and time overcurrent relays and are reclosed by a camoperated time delay reclosmg relay. Each feeder cubmle has assocmted with it a completely e m p t y spare cubmle, the product of an engineering/operating philosophy of the past It is m these spare cubmles t h a t we propose to install some of the automated systems. The master u m t will be located m a small vacant brink building near the swltchgear. The radial d : s t n b u t m n feeders leave the substatmn underground and extend to a riser pole approximately one thousand feet from the substatmn where they become an overhead wood pole crossarm type of constructmn The two test feeders are approxLmately four miles long and are each d:wded by normally closed sectmnal~zmg sw~tches into three load blocks of about 3 MW each. Normally open switches also prowde emergency tins between

the test feeders and also to adjacent feeders It is proposed to automate these sectmnallzmg sw~tches for fault :solatmn, load restoratmn, and load balancmg. Power factor correctmn to u m t y is accomphshed by a c o m b m a t m n of fixed, time controlled, and t~me-temperature controlled feeder capacitor banks On the test feeders there are seven switched capacitor banks. It is proposed to automate these capacitor banks as a part of the mtegrated Volt/VAR control system

D~stnbution automation system requzrements Present day d l s m b u t l o n control and protectlon systems use time-proven concepts and equipment whmh is extremely rehable and dependable The automated systems of the future will be required either to match the record of conventional devines or provide such expanded capablhtms so as to give the user a trade-off. Fail-safe techmques and selfdlagnostm routines, while not enhancing rehablhty in the strmt sense of the word, will provide lmmedmte acknowledgment of a possible problem before a dlsabhng fmlure occurs. However, the obwous questmn is "What happens when the watchdog dms~". The most severe threat to rehablhty will be the environment m whmh the electromc systems will have to function The temperature and humidity extremes antmlpated m switchgear cubmles will test the demgner's ability m this area. A substatmn has always been a hostile enwronment for electronm equipment, w:th both conducted and radmted electromagnetm interference generated by occurrences such as power faults, switching surges, and relay operatmns. The Handley substation was chosen as a test site because of the adverse enwronment brought on by the heat of the Texas sun, the proximity of the 138 kV switchyard with its 40 000 A fault d u t y , and the presence of the generating umts, two of whmh are switched dmly for summer peaking purposes. The rehabfllty of most equipment depends, m part, on the quahty and quantity of mmntenance done on the equipment. An automated control and protectmn system will require mamtenance, though probably a great deal less than the present electromechanmal devines The system should be designed to facilitate that mamtenance whmh is required

28 Utflltms normally install substatmn equipment m a pmcemeal manner, as needed for load growth An automated system should support this philosophy Flexibility and modularity both m hardware and m software are required so that even major addltmns and modffmatmns can be easily implemented without disturbing those areas whmh are unaffected by the changes A system should be des:gned such that the utility can make its own modffmatmns w i t h o u t extensive personnel trmnmg Closely related to flexibility and modularity is the compatlbfl:ty requ:red among different supphers and classes of equipment A utility, once it purchases the equipment of one suppher, does not want to be trod down to that one suppher for the hfe of a substatmn The ability to readily interface equipment with different trademarks is essent:al, not only to provide a second source for techmcal reasons, but also to provide the economm benefits arising from competltmn Compatlbfl:ty is also necessary between d l s t n b u t m n class and transmlssmn class equipment For a c o m b m a t m n substatmn, a utility may choose to mstall one master u m t to control the entire statmn through both transm:sstun and d : s t n b u t m n slave umts On the other hand, separate master umts could be used whmh would commumcate through a data hnk In either case, compat:bfl~ty of the different classes of equipment ~s necessary Slmphc~ty of operatmn ~s also ~mportant, because of the numerous personnel that may be required to utfl:ze the system A complicated operating m e t h o d would necessitate extensive personnel training, something whmh could be costly and t~me consuming Probably most ~mportant m the eyes of management, an automated d~stnbutmn system should be cost effective The cost/ benefit ratm of th~s new generatmn of equ:pment should compare favorably w:th that of the present e q m p m e n t The expected savings should be proven through studms and actual fmld expermnce

background, the General Electric Company has classffmd these potentml benef:ts mto four categorms -- investment related, operatmns related, mterruptmn related, and customer related

Investment related benefits (1) Deferred mvestments due to increased loa_dmg of equipment resulting from automatm load balancing (2) Deferred investments resulting from a reductmn m d l s t n b u t m n losses due to :mproved VAR control (3) Sawngs due to improved plannmg w:th more timely data and improved data management (4) W:th favorable cost trends, an mtegrated a u t o m a t m n system can rival conventional equipment on a dollar-for-dollar basis

Operatzons related benefits (1) Production cost savings resulting from reduced losses through better VAR control (2) Savmgs m manpower due to longer mmntenance mtervals eventually expected from an electromc system (3) Improved operatmns brought about through enhanced, more t:mely data and remote control of feeder devines (4) Detection of mc:pmnt equ:pment fmlures before the fmlure has caused a load mterruptmn

Interruption related beneftts (1) Savings m manpower required to locate and :solate faulted sect:ons, and restore servme to unaffected areas (2) Mm:mlzatlon of lost revenue by prompt restorat:on of servme to unaffected areas (3) Reduction m damage clmms due to customer outages (4) Improved fault detection mtelhgence with high impedance ground fault sensing (5) Mm:mlzatlon of repetitive trapping through fault location and signature analysis (6) Detection and prevention of inherent system problems such as sympathetm tripping

Customer related benefits Potentml benefzts Several orgamzatmns, including utflltms and supphers, have analyzed the benefits to be gamed from the use of an automated dlst n b u t m n control and protectmn system With their expermnce from the PROBE Project as

(1) Improved avmlab:hty of servme to customer (2) Improvement m customer relations through better voltage control, reduced interruption time, and ~mproved customer records

29 (3) Reductmn m customer complmnts armng from lengthy mterruptmns and voltage variations Conclusion The partmlpatmn of Texas Electrm Servme Company as host utility for the EPRI Automated Dlstnbutmn Project RP-1472-1 was presented through a descnptmn of the test substatmn The desired design and performance requirements for such a system were discussed, along with potential benefits which a utility could expect to gmn from automated dlstnbutmn The automated systems discussed here are, without questmn, a 'whole new ball game', and will require considerable thmkmg on the part of utility engineers m developing their own phflosophms related to these systems. There are still many questmns whmh reqmre answers and d e c m o n s whmh need to be made There is no questmn, however, that the computer technology of t o d a y and t o m o r r o w will ultimately be utilized to control dlstnbutmn substatmns and systems Fully integrated systems offering substatmn and feeder automatron functmns, load management and other customer-oriented functmns, and addltmnal functmns not even defined y e t are just around the corner We as utility engineers fred ourselves m a positron comparable to that m which the pmneers of our industry found themselves around the turn of the century when standardlzatmn was being argued It is our important task to learn all the lessons and answer all the questmns, while we are still on the ground floor lookmg up

'DESIGN OF A TRANSMISSION SUBSTATION AUTOMATION SYSTEM' (WESTINGHOUSE ELECTRIC CORPORATION)

The Electric Power Research Institute (EPRI) is presently sponsonng the design and constructmn of an integrated, mmroprocessor based system to perform all relaymg, control, and interface functmns for transmlssmn-class substatmns. Work is presently being carned out by Westinghouse Industry Systems Dlwstun, with support from the Relay-Instrument Dlwsmn and the Research and Development Center

The project investigators have just completed the general system and functmnal design phase of the project, work is now proceeding on the detailed design and constructmn of a commercml-prototype demonstratmn system The demonstratmn, whmh will consist of a subset of the full complement of hardware and functmnal features designed for the system to date, is to be installed m a 500/230 kV substatmn of Pubhc Servme Electrm and Gas Company (PSE&G) m New Jersey In addltmn to PSE&G, five other utility adwsors from around the U m t e d States have overseen the development project effort and contributed to the specffmatmn of the system. Prolec t o blec twes The following goals were estabhshed at the outset of the project. (1) To take advantage of new hardware technology -- especially mmroprocessors, LSI support devines, and digital optmal-flber commumcatmns {2) To provide improved performance for functmns now done by conventmnal control equipment, using refmed, programmed mtelhgence (3) To add new functmns and capabflltms whmh become practmal with the new architecture and hardware (4) To fred a flemble architecture whmh combines effective mtegratmn of the system with adaptability to a varmty of substatmn arrangements and apphcatmn needs (5) To reduce hfetlme cost by paying attentmn to ease of manufacture, installation, and mmntenance The control o f transm~szon substattons The proposed system design is based on the distractive features of the particular apphcatlon. These include large distances among the controlled or monitored power devines m the switchyard, a hostile electromagnetm environment, and a high probablhty of multiple expansions or changes of lay-out over the hfe of the station. A relatively sophlstmated complement of control and protection devines is presently installed, with extensive faclhty for remote control. Also, utlhty engineers want comprehensive reformation on the operatmn and status of power and control equipment The new system design descnbed below addresses a number of the shortcommgs of

30 present e q u i p m e n t T h e d i f f i c u l t y and expense o f g e n e r a t m n o f even minimal o p e r a t i n g inf o r m a t i o n f o r t h e user is p r o b a b l y o n e o f the m o r e frustrating limitations o f the existing e q u i p m e n t , as c o m p a r e d to w h a t is p r o m i s e d b y the new t e c h n o l o g y O t h e r relative disadvantages Include the high cost of lnstalhng c o m p l e x i n t e r c o n n e c t m n wiring, the isolated intelligence o f each c o n t r o l device or s y s t e m acting I n d e p e n d e n t l y and unable to c o o r d i n a t e with others, and d u p l i c a t e d h a r d w a r e in d i f f e r e n t systems which does n o t yield the b e n e f i t o f true r e d u n d a n c y Also, a longr e c o g n i z e d disadvantage o f existing relays and o t h e r low d u t y - c y c l e c o n t r o l s is t h a t t h e y are idle virtually all o f the time, giving n o assurance t h a t t h e y will w o r k p r o p e r l y w h e n called u p o n Thus, c o m p r e h e n s i v e testing programs are n e e d e d SystemCtr I Control Man-Machine . ~ Interface

Stat,on Computer

SC

Data H,ghway I

I

I I

II

II

) Cluster I

I ]/~~]'*~

Other Processor Clusters

|Funct,on

"pr°cess°r(s)

/ / r ~ ? a t a Bus / I I , I [~ 1 I ~l~J.--Lm k

H ghway I ~ ~ ~ -I Contro,,;rl I I t I C°ntr°"ers

Jl', Data 1 Opt,cla/::ber ~ , ~ . I DA l Lm Other DA Acqu s t on i Package I Un,ts C°nt r°l [Lt]~] ..II " ~ Status Fig 2 Architecture of the substatmn control and protectmn system (SCPS)

Archztecture o f the substation control and protectmn system (SCPS) Figure 2 shows the essence o f the archit e c t u r e o f t h e h a r d w a r e e l e m e n t s for the new SCPS T h e f r o n t line for the system consists o f a set o f s w i t c h y a r d - r e s i d e n t data-acquisition packages such as t h a t labelled DA in Fig 2 T h e DA m o d u l e has inputs f r o m c u r r e n t and voltage t r a n s d u c e r s (e.g CTs and CVTs), status or c o n t a c t d a t a f r o m c o n t r o l l e d p o w e r apparatus, and o u t p u t c a p a b l h t y for driwng the c o n t r o l circuits o f t h a t a p p a r a t u s DAs are installed in the s w i t c h y a r d t o m i n i m i z e wiring

runs Each DA u n i t c o n n e c t s to a limited area o f the s w i t c h y a r d -- f o r e x a m p l e , t o one b r e a k e r with its c u r r e n t t r a n s f o r m e r s , c o n t r o l circuits, and adjacent isolating switches or, alternatively, t o several breakers in one bay or on one bus o f the substation I n p u t s to each DA are digitized and t h e n f o r m a t t e d by a m m r o p r o c e s s o r - b a s e d c o n t r o l l e r into serial message blocks for transmission over the optmal-fiber link In the c o n t r o l house, the optical d a t a are received b y a s e c o n d link c o n t r o l l e r interface which feeds a cluster o f c o n t r o l m i c r o p r o cessor m o d u l e s o n a c o m m o n bus A n u m b e r o f DA units at diverse locations m a y d e h v e r t h e d a t a u t i h z e d b y each processor cluster Each p r o c e s s o r P in the cluster o f Fig 2 imp l e m e n t s specific c o n t r o l and p r o t e c t i o n functions All o f the p r o c e s s o r clusters are c o n n e c t e d via a m u l t l d r o p coaxial-cable d a t a highway to a s u b s t a t i o n c o m p u t e r SC, also located in the c o n t r o l house SC serves as an overall system supervisor, as a central p o i n t f o r a h u m a n o p e r a t o r , as the interface p o i n t for a r e m o t e system c o n t r o l center, as an historical d a t a base, and as an a p p h c a t l o n - f u n c t I o n p r o c e s s o r f o r those f u n c t i o n s requiring global access to substation d a t a T h e critical p r o t e c t i o n f u n c t i o n s , such as relaying transmission lines, t r a n s f o r m e r s , and buses, d e m a n d the highest p r i o r i t y In the a r r a n g e m e n t o f d a t a flow and processing m the integrated system A p r o c e s s o r in a cluster assigned to p r o t e c t a specific apparatus acquires all the digitized d a t a samples it requires directly f r o m the DA units in the s w i t c h y a r d Decisions to trip, or take o t h e r c o n t r o l action, are t r a n s m i t t e d over a r e t u r n link t o the a p p r o p r i a t e DA u m t where the req u e s t e d c o n t r o l o u t p u t IS energized N e i t h e r the d a t a highway n o r the station c o m p u t e r need be in o p e r a t m n for these critical functions F a u l t - d e t e c t o r or arming r o u t i n e s are used t o activate relaying programs In a P processor w h e n a d i s t u r b a n c e or fault s y m p t o m ~s observed in the AC signals These relaying programs o c c u p y m o s t or all o f the processor's t i m e w h e n r u n n i n g H o w e v e r , w h e n t h e r e has b e e n n o r e c e n t disturbance, the p r o t e c t i o n p r o c e s s o r is avmlable to p e r f o r m less critical low-speed p r o t e c t i o n and c o n t r o l f u n c t i o n s , and to pre-process or c o n c e n t r a t e the mass o f

31

mcommg data samples into compact representatmns (e.g., phasors} for transmission over the data highway to the station computer Thus, the P processors and the connected network of DA units provide sensmg and executive functmns for the station computer SC The entire SCPS normally runs m synchromsm A central clock signal, distributed from the clusters to the DA umts, triggers samphng of AC and status pomts throughout the substatmn New samples of each input are taken 16 times per power cycle, or one set of samples every 1.04 ms This high rate is needed for high-performance relaymg; the data are concentrated at the cluster level for functions needing less detailed input reformation, as mentioned above The cluster architecture facilitates the use of several P processors to handle a single large protectmn job, ff this is necessary with the parhcular processor used. Powerful new 16-bit microprocessors will be used as the P devines m Fig 2 The investigators have evaluated several types for basra performance, and also for availability of predesigned modules and support hardware which will speed up the SCPS prototype development Finally, an important flexibility feature n o t shown in Fig 2 is the optmn of a cluster w:th direct local {control house) inputs and outputs, as opposed to the cluster of Fig 2 whose I/O is provided only through data hnks to the switchyard DA umts A cluster may m fact have both local and switchyard I/O interfaces This provides the means for the SCPS to connect to signals and control clrcmts prevmusly wired to the control house Such connections are reqmred when the SCPS is mstalled as part of an addition to an existing station, where exmtlng control and relay circuits are left m servme for the old p o r h o n of the statmn

System functions Westinghouse, EPRI, and six utflltms have developed a full design specification for all the functmns whmh might be prowded by the SCPS Table 1 hsts the functmns Only a subset of these will be Implemented for the lmtml demonstratmn at PSE&G, but basic design work has been done for all of them The I/O reqmrements of each have been allowed for so that the system can be expanded to include them at a future time

TABLE 1 System functmns Fault protectlon Transmission hne relaying, including dlrectlonalcomparison pilot capabfllty Transformer faultprotectmn Bus faultprotection Shunt reactor protectmn Transfer-tnpplng logm and interfaces Power apparatus momtorlng and control Load momtormg, load sheddmg, mtertm trippmg Transformer overload monltormg Local voltage and V A R flow control Out-of-step protectmn M o m t o r m g and control of breakers, disconnects, clrcmt switchers,etc Automatm recloslngfollowing hne faults Synchronism checking and automatic synchronizer closlng User-speclfmd automatic swltchmg sequences Interfaces for u h h t y users Local man-machine interface Remote commumcatlons interfaces Alarming and sequence-of-events recording Logging and dmplay of data Oscillography Line fault locatmn eshmatlon Interchange revenue metering System eqmpment checking Self-checking of processors Checking of input data sources Differential measurement check (substahon state estnnation) Pilot and transfer-trip channel momtormg and testing

Rel~abd~ty and redundancy A great deal of the project effort has been devoted to investigation of rehablhty and hardware fmlures Hardware failure rates for various subsystems have been estimated; these results p o m t to areas where special des:gn attention is needed Also, detmled analysis of funchonal rehablhty with various redundantarchitecture schemes has been done to show what measures must be taken to provide reliability and security for cntmal protection functions.

Concluszon benefits of the SCPS The EPRI-sponsored development of an Integrated substation control and protection system is now progressing into the implementation phase In the design work completed so far, new hardware technologies such as 16-blt microprocessors, LSI support, and optical-

32 fiber commumcations have been integrated into a flexible arch:tecture whmh interfaces to new or expanding substations Many utility advisors have taken part in the definition and specffmation of the system functions The proposed SCPS offers important improvements over conventional substation control e q m p m e n t The improved performance of existing functions -- adaptive behavior, refined logic and characteristics, greater apphcation-oriented mtelhgence New functions, not practical or economic with existing equipment The coordinated response of diverse functions The sharing of data eliminates duphcated measurements or calculations Modularity facilitates expansion The potential for improved functional rehablhty and faster trouble-shooting through selfchecking Detailed logs, reports, fault data retention, and equipment performance evaluatmns, all of whmh can be telecommumcated to utility headquarters if desired Constructmn and wrong savings from factory assembly and test of system, and from switchyard multiplexing of signal and control traffic A favorable hardware cost trend

'ELECTROMAGNETIC TRANSIENT MEASUREMENTS IN TRANSMISSION SUBSTATIONS' (ELECTRIC POWER INSTITUTE, TEXAS A&M UNIVERSITY) Introduction The new technologies being applied to power substations for automation, control, and protection require t h a t we carefully look at the environment as it relates to potential system degradatmn and factors such as extreme temperature ranges and high humidity must be considered when dealing with electromc equipment in substatmns In addltmn, a very speclfm concern of system designers :s the potential for electromagnetm mterference with equipment operation While damage to electronm equipment is of some concern, the primary consideration is to insure that automatin equipment can operate properly m the hazardous substatmn e n w r o n m e n t

The problem of electromagnetm interference :n power substatmns has been known for many years As more electric equipment has been introduced into general usage, the reports of system failures and m:soperatmn have increased Some groups have attempted to produce design and test standards for substation equipment, but largely this actlv:ty has been ineffective For the most part, these efforts were doomed to failure owing to the lack of specific and quantltat:ve data related to the transmnt electromagnetic noise in power substatmns While the continuous wave and steady state background no:se in the substatmn must be considered, the transient noise produced by sw:tchmg activity is the area of primary concern Until recently, the sophistication and expense of the measurement equipment required to produce a technically acceptable trans:ent data base were excessive Under the sponsorship of the Electric Power Research Institute and the project direction of Mr Stlg Nflsson, a data base has been gathered and analyzed for future use by utlhtms and equipment manufacturers Measurement pro blem The electromagnetic transmnts produced by the switching of equipment such as disconnects and breakers are particularly difficult to measure The transients produced contain slgmflcant electrm and magnetm field amphtudes over a broad frequency range To properly characterize the electromagnetm transients, it :s necessary to make independent electric and magnetm fmld measurements m the time dommn This requires that spec:flc attention be given to the sensors and transducers used d u n n g measurement Additionally, the high fmlds produced have a hab:t of interfering directly w:th the equipment bemg used to measure those very fmlds Therefore, slgnlfmant attention must be given to the shmldlng and design of the measurement equipment When these and other problems such as fmld portability of the equipment and the need to capture the entire transient including pretransmnt field levels are considered, the result is a highly sophlst:cated measurement system The Electrm Power Institute of Texas A&M Umverslty, in cooperatmn with several eqmpment manufacturers, developed a portable

33 m s t r u m e n t a t m n system to solve the above problems The equipment, called TRUCC (Transient Recorder Utihzmg Computer Control}, is shown in Fig. 3 m a substation prepared to take measurements The system consists of a double shmlded screen room on the back of the truck shown The major components of the transient capture system are a microwave data link, transient dlgttlzers, a minicomputer, and various freespace field sensors

Edztmg Analysis of the electrical, physmal, environmental, and operating reformation taken when the transient was captured Data enhancement Specific selection of the transient, selection of approprmte pre-event data, adjustment for DC offset, and adjustment for off-scale peaks Cahbrat~on pulse correction Calculation of the gmn through the microwave transmitters and correction of the data set accordingly Tzme tying Correlation of waveforms from several digitizers to produce one waveform

Fig 3 TRUCC substation measurements Measurements can be made up to three hundred feet from the TRUCC and are transferred to the TRUCC system using dmlectnc wavegulde The transient signals are captured usmg transient digitizers and the m f o r m a t m n is subsequently stored on disk using the minicomputer. The system is capable of capturing electric and magnetm fields or conducted transients up to approximately 130 mHz The system has a broad dynamm range and is capable of recording the amplitude of any transient which can be produced m the power substation

Data reductton and analyszs Subsequent to the collection of data by the TRUCC system, the data are analyzed using analytical software developed specifically for that purpose The data are transferred from the TRUCC to other computer systems by transferring data disks. The reduction software first converts the data taken by TRUCC into time and frequency dommn representatmns of the original transient. This software consists of several stages mcludmg the following

Fourier transforms After the waveforms have been corrected and adjusted for a uniform sample rate, a fast F o u n e r transform is performed and the data are corrected to remove the effects of the system transfer function An inverse Fourier transform is used to obtain the corrected time dommn waveform Data output The data are stored on magnetic disks and hard copies are made of the corrected time and frequency plots F~eld measurements Measurements have been taken at various voltage levels m the substations of Pubhc Service Co of New Mexmo, Texas Electrm Service C o , Public Service Electric Gas of New Jersey, Northern States Power/Minnesota Power & Light, etc Measurements typically consist of the opening and closing of various breakers and switches including speclfmally the switching of capacitor banks, reactors and transformers Also, staged faults have been measured. An example of a typmal transmnt IS shown m Figs 4 and 5 This partmular transmnt resulted from the closmg of a 500 kV circuit breaker which energized a short section of bus The measurement was taken in the Deans Switching Station of Pubhc Servme Electric and Gas of New Jersey Figure 4 shows the electric field c o m p o n e n t and Fig. 5 the magnetic field.

34 1000

600 O0

f

800.

r

400 O0

f 6 Off

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-40000

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000

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040

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0 80

1 O0

120

140

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tl"

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020

040

060

000

100

120

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Fig 4 Electrm field vertmal component

Fig 5 Magnetm field perpendmular component

As can be seen, this transient exhibits very high frequency components which are superimposed on a longer term, low frequency oscillation The amphtudes are slgmfmantly high, yet the transmnts die out rather rapidly Analysis of these and similar transmnts is underway and should lead to specffm ranges of frequency and amplitude which can be expected from switching events in transmlssmn substations

transients Once data analysis is complete, it is hoped that manufacturers, utihtms, and others can utlhze the results to insure that automation, control, and protection equipment can be built to properly withstand substation environments

Conclusion A sophisticated instrumentation system and technique for measunng substation transients has been developed A data base of typmal switching events m substations has been acquired and analysis of the data is underway Prehmmary results indicate that present electromagnetm interference standards are madequate and extstmg test and design specffmatlons for substation automation equipment do not properly charactenze radiated substation

SUMMARY OF PRESENTATIONS These presentations show that slgmfmant progress is being made m the identification of proper procedure and techmques for substation automation Numerous system designs are being studmd and state-of-the art technologres are being apphed Ancdlary considerations such as electrical environment are also being studied Under the direction of the Electric Power Research Institute it is expected that these efforts will result m technically and economically feasible designs for improving the operatlon and performance of power substations