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1074 IEEE Transactions onPower Systems,Vol. 4, No. 3, August 1989

RELI ABI LI TY ASSESSMENT OF GENERATI ON SYSTEMS CONTAI NI NGMULTI PLE HYDRO PLANT USI NG SI MULATI ON TECHNI QUES

R. N. Al l an, Fel l ow J . Roman

UM ST l nst de I nvest i gaci on Tecnol ogi caManchest er, Engl and Madri d, Spai n

Abstr act

The studi es report ed i n thi s paper descri be model sand eval uati on techniques based on Monte Carl osi mul ati on for the rel i abi l i ty assessment of mxedhydro-thermal generati on system. I n part i cul ar i tconsi ders the ef f ects that systemoperati ng and watermanagement pol i ci es have on the rel i abi l i ty i ndices.These effects are descri bed and di scussed usi ng thebasi c I EEE Rel i abi l i ty Test System( RTS) extended byaddi t i onal hydro pl ant data. The outcome of thesestudies i s an i mproved underst andi ng of the effectsthat operati onal pol i ci es have on the behavi our ofmxed hydro- thermal system and, i n part i cul ar, ani mproved know edgeof the response of the RTS.

I NTR3IXKTI ON

Rel i abi l i ty assessments are a necessary part ofpower system studi es i n order to assi st manageri aldeci si ons of howmuch shoul d be spent on the qual i ty ofthe servi ce, howmuch capaci ty to i nstal l and when.Engi neers should carry out rel i abi l i ty studi es in thepl anni ng, desi gn, operati on andmai ntenance stages i norder to achi eve an acceptabl e l evel of rel i abi l i ty ata reasonabl e cost. Tool s to carry out these studi eshave been developed duri ng the l ast decades. At presentseveral model l i ng and evaluat i on techniques areavai l abl e [l -31. Choosi ng the most conveni ent andef fecti ve techni ques w l l determne the qual i ty of therel i abi l i ty assessment and must ref l ect the operati ngcharacteri sti cs of the system

Most evaluati on methods are di rect anal yti caltechni ques whi ch generate system or subsystem ri ski ndi ces. The devel opnent and uti l i sati on of mor epowerf ul di gi tal computers has al so l ed to i measi ng

use of si mulati on methods (general l y known as MonteCarl o methods) . Both methods have advantages anddi sadvantages. D rect anal yti cal techni ques aregeneral l y f aster and very sui tabl e when sensi t i vi tystudi es are needed. Gn the other hand these techniquesmay have to approxi mate some system ef f ects, such asoperati ng pol i ci es whi ch are not normal l y recognised i nthese techniques or, as i n the case of hydro generat i ngsyst ems, the random i npt of energy i nto the systemSimulati on techniques can take i nto account mostaspects i nherent i n the operati on of a power systemandprovide the probabi l i st i c di stri buti ons associ ated w ththe rel i abi l i ty i ndi ces. The maj or short comng of thesetechni ques i s that general l y they requi re a l argeamount of computi ng t i me.

89 WM 126 -4 PWRSby t he I EEE Power Syst em Engi neer i ng Comm t t ee of t heI EEE Power Engi neeri ng Soci ety f or present ati on at t heI EEE/PES 1989 W nter Meet i ng, New York, New York,J anuar y 29 - Febr uar y 3, 1989. Manuscri pt subm t t edSept ember 2, 1988; made avai l abl e for pr i nt i ngNovember 29, 1988.

A paper r ecommended and appr oved

Rel i abi l i ty studi es of power syet eme have beent radi t i onal l y perf ormed in parts, now known ashi erarchi cal l evel s [ 4 1 . Thi s study i s concernedwthhi erarchi cal l evel I (HLI ) , . e. the generati ng systemRel i abi l i ty eval uati on at HLI negl ects the network andpool s al l sources of generati on and al l l oads together.The probl emi s to eval uate the abi l i ty of the systemtosuppl y the l oad demand taking i ntoaccount the l oadvari ati on and the random events (such as f orcedoutages) that aff ect equi pment capaci ty.

generati on fraa a hydro system depeds on the

past hi story of water i nf l owa i nto the hydropl ants, t heoperati ng pol i cy and the evoluti on of the l oad up tothe i nstant being anal ysed 151. h he other hand, thegenerati on of a thermal system depends on thecondi t i ons that exi st i n t he pl ants f romi nstant toi nstant . These are essent i al di f f erences when tackl i ngrel i abi l i ty eval uati on of the system and must berecogni sed by the model s used to represent theoperat i on of a hydro-thermal or al l - hydro system

studi es report ed in thi s paper concern model sand evaluati on techni ques associ ated wth mxedhydro-thermal generati on system. I n part i cul ar i t

consi ders the ef fects t hat systemoperati onal pol i ci eshave on rel i abi l i ty i ndi ces. These ef fects aredescri bed and di scussed usi ng the basi c I KEERel i abi l i ty Test System ( RTS) extended by addi t i onalhydro pl ant data. The outcome of t hese studi es i s ani mproved understandi ng of the ef fects t hat operati onalpol i ci es have on the behavi our of mxed hydro- thermalsystem and, i n part i cul ar, an i mproved knowedgeofthe response of them.

The

The

SI MULATIONAND PDDKLLI NGPRDCBDURBS

Concepts

I n the case of hydro-el ectr i c system, thegenerati ng capaci ty avai l abl e w l l depend upon pl anndand f orced outages and the water st orage l evel . Thestorage l evel determnes the energy state of thesystem Operati ng defi ci enci es i n these system may becaused by an energy defi ci t due to l i mt s on the waterstorage of the hydro pl ants or by a power def i ci t dueto l i mts on the peak capaci ty of the hydro pl ants.

The energy state of the hydro-el ectr i c system i sdetermned by the past hi story of st reaml ows, theoperati on pol i cy and the evoluti on of l oad up to theyear bei ng anal ysed. The capaci ty avai l abl e i n ahydro-el ectr i c system i s di rect l y af f ected by theenergy state of the system This i s because thecapaci ty avai l abl e at each hydro pl ant depends not onl yon the i nstal l ed generati ng capaci ty but al so on thereservoi r head. The random f actors af f ecti ng the energyst ate of the syst emmake Monte Carl o si mul ati on methods

very sui tabl e approaches for anal ysi ng these types ofsyst em. These methods can take i nto amount vi rtual l yal l cont i ngenci es i nherent i n the system and can al sosi mulate the operati on of a hydro-thermal system underthese condi t i ons. The rel i abi l i ty of the systemcan

then be examned by si mul ati ng a suff i ci ent peri od ofthe operati ng hi story.

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Simulati on Procedures

Detai l s of Monte Carl o si mul ati onand stochasti csi mul ati on techni ques can be f cxnd i n References 16-81.Al a0 a detai l ed di scussi on of how these methods havebeen appl i ed to thi s generati on rel i abi l i ty probl emi sgi ven i n Ref erences [9-121. Theref ore i t i s suf f i ci ent

to surmari se that the concepts usedi nthepreaentdel l i ng and evaluati on techniques were besed on :

a) the mul ti pl i cati ve c o m t method f or generat i ng

pseudo- randomnunbers

b) the i nverse traneformmethod for converti ng these tothe rel evant probabi l i ty di st r i bt i on

c) the sequenti al si nni l ati on approach i n order torepresent the t i me dependent sequenti al process ofthe hydro-pl ant.

Thesyst emoperat i on i s si mul ated over a l ongperi od of t i me whi ch i s subdi vided into referenceperi cda of one year. Eech year i s di vided i nto basi ct i me i nterval s duri ng which the s t a t e of the systemi sassuned to be const ant. The present model works on anhourl y basi s whi ch means that changes i n the syatemarea s s 4 o occur at the beginni ng of every hour.

Generati on Model

The generati on system i ncl udes t h e 4 and hydropl ants. A t h e d pl ant i s represented as a si ngl egenerati ng uni t. A hydro pl ant however i ncl udes i tsreservoi r and turbi ne-generator set, the model s forwhich are descri bed i n the next secti on. Both t h e 4and hydro gener at M uni ts have the model forrepresent i ng forced outages and repai rs.

Thi s assunes that [131 the t i mebetween forcedoutages of generati ng uni ts and the durati on of theuni t f orced outages are i ndependent ard exponenti al l ydi str i buted and that a f orced outage of any uni t causesl oss of the total capeci ty of the uni t. I t al a0 assumesthat 1133 repai r i s undertaken as soon as a uni t f ai l s,there are enough repai rmen to work on al l f ai l ed uni tssi mul taneousl y, r epai r t i me i s i ndependent of any otherrepai rs or f ai l ures and repai r i s al ways successf ul andrestores the camponent to as good as new

The f ul l rati ng capeci ty of a the& uni t i sconsi dered when i t i s i n the up state. The avai l abl e

capeci ty a hydro uni t i n the up state may be lawert hen i ts f ul l rati ng capeci ty however de on therel evant hydropl ant parameters. Thi s i s di scussed i nthe next secti on.

of

HYDRD PLANT MODELLING

Water I nfl owModel s

The source of energy i n ahydmsyat em s thewater i nf l ows whi ch usual l y come f ran rai nf al l , pel tedsnow etc. The water can be stored i nreservoi rsl ocated along the ri vers and i ts potenti al energy

transformed i nto el ectr i c energy by means of t urbi nesand el ectr i c generators. Theref ore, f ran the el ectr i cenergy producti on point of vi ew a hydro plant woul d bethe basi c el ement of producti on, whi l e the set of hydropl ants located on the same ri ver woul d be theexploi tati on scheme of the whol e ri ver, the el ements ofwhi ch are the main ri ver or i nf l ow i ts tri butari es or

si de i nf l ows and the hydm pl ants ( reservoi rs andturbi ne-generator sets). Thi s scheme i s def i ned as ahydrochai n.

The i nf l ow of water i nto secti on k (k= for maini nf l ow k> f or ai de i nf l ows) of the ri ver i srepresented by:

Wk = h & k + & ( 1)

Ii k =w k/N (2)

where:

Wk : i nf l owof water into secti on k duri ng i - th peri odi i k : rai nfal l i n secti on k duri ng i - th peri odh,&: l i near corr el ati on coef f i ci ents f or secti on kIi k : hourl y i nf l owi nto secti on k duri ng i - th peri odN n h r f hours i n peri od consi dered (168h per week

or 672h per month)

I t i s possi bl e to fi nd the correct probabi l i tydi str i buti on for the rainf al l (& k ) f ran weatherrecords. Hawever, the n o d di stri buti onwas used i nthese studi es to represent t he amount of rai nf al l i nthe secti ons f or the speci f i ed peri ods of ti me. Theseperi ods can be ei ther weeks or months, a month bei ng aperi od of f our weeks and therefore one year i s di vi dedi nto thi rteen months. The values of i i k are senpledusi ng the Box and Mul l er method [SI ; the val ues of themean and standard devi ati on being gi ven as i npt data.Three types of year are conai dered; dry, wet and n o dyears. The type of year i s encountered randomy, w th apMbabi l i t y determned by a di screte di str i buti on.

A l i near rel at i onshi p, expressed by k and a, as

set between rai nfal l and water i nfl ows. These provideenough f l exi bi l i ty to rel ate the i nf l ows of water wththe rainf al l of the area, and make i t si mpl e to

correl ate val ues of rai nf al l f ran weather records wthhi stori cal records of past i nf l ows i n the r i ver. A n

advantage for usi ng thi s r el ati onshi p i s t hat thespati al correl ati on 1141 whi ch in practi ce exi stsbetween the i nf l ows located in the same hydrographi calarea can be represented i n the model . Thi s can beachi eved by usi ng the same val ue of f or everysecti on in the chai n and selecti ng appropri ate val uesf or Ak and Ek to adj ust t he f i nal i nf l ows of water i ntothe hydrochain. Al so, when no si de i nf l ows exi st, theval ues of L and & are set to zero.

Reservoi r I nf l ows

The reservoi r i nf l ows i ncl ude the si de i nf l owsdescr i bed above and the water rel eased f ran upstr eamreservoi rs. Thi s water w l l f l ow i nto the reservoi rsane t i me after being released ( t i me del ay), and partof i t w l l be l ost on i ts way downstream due toi rri gati on schemes, drai nage etc. The canplete wateri nf l owmodel for the reservoi r i s therefore:

T(h)r = I i k +R(h-d)r- 1 t S(h-d)r -1 - L(h)k ( 3)

where:

T(h)k: total i nf l owi nto reservoi r k i n h-th hourR(h4)k- l : water rel eased f rom secti on k-1, d hours

S(h4)k-x: water spi l l ed f rom secti on k- 1, d hours

L(h)k: water l osses i n secti on k duri ng h-th hour

before h- th hour ( d i s t i me del ay)

before h- th hour

(negl ected i n these studi es)

The vol uoe of water at the reservoi r i n secti onk,cal cul ated at the begi nni ng of each si mul ated hour h,i s:

Vh)k =V(h-l )k - R(h-l )k - S(h-l )k + T(h)k ( 4 )

Reservoi r Model

The storage capabi l i ty of reservoi rs l ocated onnatural si tes are normal l y determned fromtopographi cal studi es. These studi es provide elevati on

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curves and related expressi ons that can be used formodel l i ng purposes [15]. A l i near expressi on representsverti cal si des, a second order equati on r epresents atrapezoi dal cross-secti on, etc. As a compromse betweenaccuracy and si mpl i ci ty, a quadrati c mode was used i nt.hese st udi es:

v = c t bH t aHz (5)

where:

V: reservoi r water vol ume (Nu3 )

a, b, c: model coef f i ci entsH: net head ( m

Thi s expression i s exact for r eservoi rs wt htr apezoi dal cross-secti ons.

Turbi ne-Generator Model

Two assumpti ons were made to si mpl i f y thegenerator- turbi ne perf ormance; the head l osses i ncurredi n the water condui ts are negl i gi bl e and the tai l water

el evati on remai ns constant . A l i near model [151 usi ngbasic hydraul i c rul es represents the performance of thehydro set. Thi s model gi ves an acceptabl e approximati onof the conversi on between potenti al energy of the waterand electri c energy output and i s gi ven by:

P gaHQs/ 106 ( 6 )

Q = G( 2gH) 1 / Z ( 7 )

where:

P: avai l abl e out pt capaci ty (MW)

g : graVi t at l OM1 constant (ms-2 )

a : overal l eff i ci ency of t he turbi ne-generator (pu)

Q turbi ne di scharge rate (m3s- )

s: speci f i c weight of water (103 kg. ~u- ~G maximumopeni ng area of t he gui de f or each turbi ne

(mz

OPERATING WLI CY AND WATER I"AGBlFANT

Concepts

D f f erent operati ng and water management pol i ci escan be fol l owed i n a mxed hydro-thermal generati ng

system These w l l af f ect the rel i abi l i ty of the system

151 part i cul arl y f or hydro system wth l i mted energy.When and how thi s energy i s used w l l determne theabi l i ty of the system to reduce possi bl e defi ci enci esof energy. The operati ng pol i cy i dent i f i es when thewater must be used and what hydro pl ants and hydrouni ts shoul d be comni tted, whi l e the management of thewater determnes when and how the water i s avai l abl efor producti on of energy. The two concepts w l li nteract i n d i n g the f i nal deci si on of how to operatethe hydro system

Operati ng Pol i cy

The pri nci pl e f or operati ng an energy l i mtedsystemi s to use the avai l abl e energy to the bestpossibl e advantage duri ng the peri od i n whi ch i t i savai l abl e. A n operati ng pol i cy can be based [ 16, 41 onei ther a pure safety pol i cy when only the system

rel i abi l i ty i s eval uated or a mxed economy-saf etypol i cy when the systemrunning cost as wel l as systemrel i abi l i ty are consi dered. The pure safety pol i cy wasadopted i n these studi es as onl y r el i abi l i ty eval uati onwas of i nterest. Thi s pol i cy means that water w l l beused onl y to avoi d or reduce l oss-of- l oad, and i n some

cases to avoi d spi l l age of water. Even w th thi s pol i cythere are di f ferent ways of usi ng the water. Fori nstance, water may be used whenever i t i s avai l abl e to

avoi d l oss-of - l oad, i t may be used to deal wth some

def i ci enci es encountered by the systeml eavi ng some

reserves of water f or f uture needs, or a certai n l evelof water may be permanentl y mai ntai ned i n order toobtai n a hi gher val ue of potenti al energy for t he waterused f romabove that l evel .

Whether the hydro systemhas to produce energy ornot must f i rst be deci ded. To do thi s three di f ferentcases of l oad demand have been i denti f i ed:

Case 1. The l oad i s greater than the total avai l abl egenerati on ( thermal and hydro). Water woul d be used to

suppl y the load if the l evel of water at the reservoi ri s above the l ower l i mt set by the management-of-waterconstrai nts (see bel ow .

Case 2. The l oad i s greater than the avai l abl e thermalgenerati on, but l ower than the total avai l abl egenerati on. The fol l owng two subcases exi st . Thedi f f erence between the l oad and the avai l abl e thermalgenerati on, i . e. the l oad whi ch coul d be suppl i ed bythe hydro generat i on i s ei ther:

( a) greater than or(b) l ess than

a certain val ue speci f i ed by the operati ng pol i cy. Thi scri ti cal val ue i s speci f i ed as:

F * LCI

where F i s an operati ng pol i cy weighti ng factor and LCIi s the mean value of l oad curt ai l ed per i nterr upti on.Thi s cri teri on permts di scri mnati on between l arge andsmal l def i ci enci es. The value of LCI can be used as aborderl i ne between what def i ci enci es are consi deredl arge and smal l and F can be used to adj ust thi sborderl i ne to hi gher or l ower val ues.

Case 3. The l oad i s l ower than the avai l abl e thermalgenerati on i n whi ch case, no water need be used.

When water i s needed, the hydro pl an* i n thehydrochai n are cm t t ed i n thei r geographi cal order,i . e. the pl ant at the begi nni ng of t he hydrochain ( t opof the ri ver) i s commt ted f i rst , t hen the second, and

so on. The producti on from each hydro Pl ant i sdetermned by the pl ant const rai nts, the managementconst raints and the l oad to be suppl i ed.

Management of Water

Management-of-water pol i ci es are to regul ate thevol ume of water at the reservoi rs. Thi s regul ati onaff ects the producti on of el ectr i c energy andsubsequent l y the rel i abi l i ty of the system Theobj ecti ve i s to maintai n a certai n vol ume of water ateach reservoi r f or each week of the year. Thi s can beachi eved by setti ng mni muml i mts of vol ume of waterat each reservoi r. No water i s used bel ow these l i mts.The al l owthe energy l evel of the water at thereservoi rs and the forecast water i nf l ows to be takeni nto account. By sett i ng hi gh l i mt s, a hi gher l evel ofenergy wl l be maintai ned i n the stored water at thereservoi rs whi ch w l l strongl y af f ect t he outputcapaci ty of the hydro uni ts. Also, f orecast dry and wetperi ods may be taken i nto account by using di f ferentl i mts f or each week. For i nstance by al l owng hi gherreserves duri ng wet peri ods, water woul d be moreavai l abl e i n dry peri ods.

These l i mts or management-of-water constrai ntsare set by means of ut i l i sati on pol i cy vectors U. Thereare two di f f erent vectors U1 and U?. Each reservoi r hasi ts own pai r of vectors. Each vector has 52 el ements,one for every week of the year. Each element i s the peruni t val ue of vol ume of water at the reservoi r, belowwhich no water w l l be used. These range f rom0.0 P. u. ,which means that water may be used unti l the reservoi ri s empty, t o 1.0 P. u. , whi ch means that water may be

l imts

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used onl y i f the reservoi r l evel i s ful l . The magni tudeof the defi ci ency determnes whi ch vector i s used, U1f or l arge def i ci enci es and UZ for smal l ones, i . e. U1

i s used for Cases 1 and 2(a) descri bed in the previ oussecti on on Operati ng Pol i cy and U2 i s used for Case

The eff ects of these vectors i n the f i naloperati on of the system are i l l ustrated i n l atersect i ons i n whi ch several practi cal cases ar e anal ysed.

2(b)

I ND CES EVALUATED

The f ol l ow ng l i st summari ses the i ndi ces

cal cul ated i n these studi es usi ng the previousl ydescr i bed model s.

AWE: average water used t o produce el ectr i ci ty (W3 / y r )

AWS: average spi l l ed water (Etn3/Y r)EAWE: energy produced f romAWE (c;wh/yr)

EAWS: energy producti on l ost due to water spi l l age

AEHG average energy produced by al l the hydro plants

FWG: f racti on of total energy demand suppl i ed by hydro

FoI : f requency of i nterrupt i on ( i nt/ yr)LOEE: l oss of energy expectati on ( M t l h h )

LQLE: l oss of l oad expectati on (h/ yr)m: oad curtai l ed per year ( MW / y r )

EI R: energy i ndex of rel i abi l i ty

ENSI : energy not suppl i edper i nterr upti on (MWh/ i nt)DO : durati on of i nterr upt i on (h/ i nt)LCI : l oad curt ai l ed per i nterrupt i on (MWi nt)

( Gwh/ Yr)

( Gwh/ Yr )

generati on (%)

SYSTEM DATA

The system used i n these st udi es i s based on theI EEE Rel i abi l i ty Test System (RTS) [ 171. Thi s wasdef i ned to provi de a h i s or r ewr t i ng on anal ysi smethods for combi ned generati on- transmssi on system.Al though some restri ct i ons have been found [ 181 f orthi s system the RTS remai ns wdel y accepted as a testsystemf or rel i abi l i ty eval uati on methods. Thecontains si x hydro uni ts but onl y forced outages areconsi dered as a cause of capaci ty def i ci enci es.However, hydro uni ts can f ai l to generate not onl ybecause of f orced outages but al so because of l ack ofenergy, i . e. l ack of water at. the reservoi rs. Extr adata rel ati ng to the hydro pl ant characteri si t i cs, such

as i nf l ows of water, vol ume of the reservoi r, turbi nedi scharge rates etc are therefore requi red. Thi sextended system i s def i ned as the Hydr o- Them1Rel i abi l i ty Test System(HT-RTS). The basic generati onand l oad data i s that descri bed i n Reference 17. Onlythe addi ti onal hydro data i s defi ned i n thi s secti on.For si mpl i ci ty the same set of data are used f or al lthe hydro pl ants i n the system al though the model canwork w th pl ants of di f f erent characteri sti cs.

addi t i onal hydro pl ant data i s shown i n Table1. Tabl e 2 gives the mean value of monthl y rai nfal l f orthree types of rai nf al l years; dry, wet and normal . Aweekl y data basi s coul d al so be used. The standard

devi at i on i s 5% of the mean val ue f or al l condi t i ons.The val ues of i nf l owcorr el ati on coef f i ci ents were setto A1 = 1 and B1 = 0 f or the mai n i nf l owand& = l k =0 (k > 1) f or si de i nf l ows; i .e. a ri ver w th notri butari es. The ef fect of si de i nf l ows i s descri bedl ater.

The

SIMULATION ANALYSI S OF RTS

The operati on of each systemstudy was si mulatedover a peri od of 400 years. Each si mulated yearconsi sted of 8736 si mulated hours and every si mulatedhour w a s consi dered i n chronologi cal order. Al though

the model was devel oped to study the rel i abi l i ty of

hydro- thermal generati ng syst em, the model was

TABLE 1 Hydro pl ant Data

number of hydro uni t s = 6pl ant overal l ef f i c i ency = 0. 8 pumaxi mumwat er head = 180 mreservoi r coef f i c i ents: a = 0. 00241

b = 0. 111c = 2. 0

i ni t i al wat er vol ume = 6 Mm3m ni mumwat er vol ume = 5 Mm3

maxi mum wat er vol ume 100 Mm3

m ni mumdi scharge r ate = 10. 6 m 3 / smaxi mumdi scharge rate = 53 m 3 / s

1.10 m2axi mumf l ow area

TABLE 2 Rai nf al l Dat a

mont h

12345

67

89

101 1

1213

mean val ue of wat erwet dry

2 . 05 1 . 203. 40 1. 454. 60 2 . 355. 70 2. 903. 10 1.402. 4 0 1. 101. 80 0. 8 0

1. 20 0. 501. 20 0. 501. 20 0. 4 01. 80 0. 801. 80 1. 002. 80 1. 20

i nf l ow, Mm3nor mal

1. 251 .953 . 0 04 . 2 02.001. 601. 20

0 . 800. 80

0 . 7 01. 001 . 601 . 80

TABLE 3 Resul t s f or t he RTS

case A1mean st d f r om

dev Ref 18

FOI ( i nt / yr ) 1 . 83LOEE ( MWh/ yr ) 1182 3178 1176LOLE ( h/ yr ) 9. 212 16. 06 9. 394

LCY ( MW/ y r ) 151. 3 289. 8EI R 0. 999923 0. 999923

ENS1 ( MWh/ i nt ) 646 . 4 1103DO1 (h/ i nt ) 5 .03 3. 94LCI ( MW i nt ) 82. 66 78. 26

i ni ti al l y tested w th the basi c RTS. Thi s onl y provesthe val i di ty of the model for al l - thermal system buti t al so gi ves exampl es of the rel i abi l i ty andi nterrupti on i ndi ces i nt r odd. The resul ts obtainedfor the Rl'S (case Al ) are shown i n Tabl e 3, togetherw th the standard devi at i ons of some of t he i ndi cescal cul ated by anal yti cal methods w thout approximati onsand f ound i n Reference [18].

SI NGLE HYDRO PLANT ANALYSIS

Ef f ect of Li mt ed Energy

A si ngl e hydro pl ant was used to study the ef f ectsof l i mted energy sources. The si x hydro uni ts havi ngunl i mted water suppl y in the I LTS were subj ected tol i mted water suppl y usi ng the characteri st i cs gi ven i nTabl e 1.

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TABLE 4 HT- RTS w

r eser voi r noU1U2

EAWE ( GWh/ yr )AWE ( Mm / yr )EAWS ( GWh/ yr )

AWS ( Mm3/ yr )

FOI ( i nt / yr )LOEE (MWh/ yr )LOLE ( h/ yr )LCY ( MW yr )EI R

AEHGFEHG

ENS1DOLC

__

( GWh/ yr( % )

( MWh/ i nt)h/ i nt )MW nt

t h s

case

1

0. 00. 0

ngl e hydr o pl ant

B1 case B2 case B3

1 1

0. 4 0. 60. 4 0. 6

3. 1 6. 2 6. 922. 7 22. 1 20. 50. 0 0. 2 0. 8

0. 0 0. 6 2. 0

8. 26 5. 02 4. 407475 5152 464348. 54 29. 64 26. 17819. 5 566. 9 510. 50. 99951 0. 99966 0. 99970

3. 139 6. 215 6 . 8620. 021 0. 041 0. 045

904. 9 1027. 9 10545. 88 5. 91 5 .9499. 21 113. 1 116. 0

case B4

1

0. 80. 8

6. 316. 92. 2

5. 5

4. 68518728. 41566. 30. 99966

6. 2610. 041

11076. 06120. 9

case B5

1

0. 00. 2

3. 32 2. 70. 0

0. 1

10. 00726754. 12808. 90. 99953

3. 3310 02 2

726. 35. 4180. 85

case B6 case B7 case B8

1 1 1

0. 2 0. 6 0 . 80. 4 0 .8 1 .0

4. 9 6. 8 5. 922. 5 20. 2 16. 00. 1 0. 9 2. 6

0. 2 2. 4 6. 4

10. 75 9. 34 12. 265967 4459 517945. 09 33. 65 40. 76747. 6 604. 6 714. 00. 99961 0. 99971 0. 99966

4. 876 6. 815 5. 1900. 032 0. 045 0. 039

554. 8 477. 5 422. 54. 19 3. 60 3. 3269. 51 64. 74 58. 23

A sumnary of the esti mated i ndi ces are shown as

cases B1- B4 i n Tabl e 4, each case being a di f ferentoperati ng pol i cy. The same mmagement-of - waterconstrai nts are appl i ed t o every def i ci ency i n casesB1-EM i .e. U1 equal s UZ. The f i rst rowof the tabl esshows that the energy produced ( FAWE) f romthe usedwater (AWE) i ncreases as the val ues of U1 and UZ arei ncreased. The val ue of FAWE i s maximum when U and U2are about 0.6. Beyond this poi nt BAWE decreases becauseof the reducti on i n the amount of used water (AWE).

The f i rst trend can be expl ai ned as fol l ows. Byi ncreasi ng U1 and Uz' the level of stored water i n thereservoi r i s hi gher, therefore, when the water i s usedi ts potenti al energy and thus the producti on ofelectri c energy i s hi gher. However hi gh val ues of U(above 0. 6) mean hi gh volume of water reserves whi chcan easi l y reach the maxi mum val ue of the reservoi rl eadi ng to spi l l age of water (AWS). Thi s water w l l notbe avai l abl e at the ti me i t i s needed. As the excess

water (AWS) ncreases there i s a decrease in the water

used ( AWE) to produce energy, si nce the i nfl owof wateri nto the reservoi r i s l i mted. The reducti on i n theamount of generated energy (EAWE) i s l ess si gni f i cantthan the reducti on i n the amount of used water ( AWE)due to the potenti al energy effect i n the storedwater.As the potenti al energy of the water i ncreases, l esswater i s needed to produce the same amount of el ectri cenergy.

The rel i abi l i ty of the system( represented by thei ndi ces i n rows 5-9) i ncreases as the val ue ofgenerated energy ( EAWE) i ncreases: Thi s fact j usti f i esthe i mportance of produci ng the hydropl ant i ndices. Thei nterr upti on i ndi ces ( rows 12-14) fol l owa di f ferentpattern. They i ncrease as U1 and U2 i ncrease. Thi s i snot a contradi cti on si nce l ower values of waterreserves mean more avai l abi l i ty of the water f l owngi nto the reservoi r. Theref ore, w th t i me, moredef i ciencies w l l be reduced though not necessari l yel i mnated. By spreading the avai l abl e energy over more

defi ci enci es, t hei r mean val ues are reduced, al thoughthi s may l ead to a l arger nmber of def i ci enci esexpressed by higher val ues i n the f requency ofi nterrupti on i ndex (FO ).

n k mai n ef fect of energy l i mtati on i s the

general i ncrease i n the unrel i abi l i ty of the systemthe resul ts i n Tabl e 4 bei ng si gni f i cantl y worse thanthose i n Tabl e 3 when there was no energy restri cti ons.

Al so the ef fects of the operati ng pol i cies are

si gni f i cant on the rel i abi l i ty of the l i mted energysystem. The analysi s of CasesB1 t o B 4 shows t h t amore rel i abl e systemi s obtained by keepi ng a certainl evel of water i n the reservoi r. I t i s al so possibl e toreduce the magni tude of the def i ci enci es encountered bythe system by l oweri ng thi s l evel of water but thepri ce to be pai d i s a l arger nunber of def i ci enci esw th the fi nal resul t of a l ess rel i abl e ayatem

Ef fect of Manqgement-of-Water Pol i ci es

Tabl e 4 a l s o shows the resul ts of cases where U1and UZ have di f ferent val ues, (casesB5-B8). Thi s me~ul s

that l arge and smal l def i ci enci es are deal t wth bydi f ferent management-of- water canstraints. I n al l casesF w as set equal to 0.9. The hydro pl ant i ndi ces (-

1-4) f or cases B5- B8 show the same trend as thosei ndi ces f or cases B1- EM Cases B5- B8 have a l argerf requency of i nterrupti on (FO ) and l arger mLE than

cases Bl - B4. On the other hand IDEE and LCY aresmal l er. Therefore, the apparent measure of rel i abi l i tychanges i n opposi te di recti ons dependi ng on the indexchosen. Great care i s therefore needed i n consi deri ngand maki ng deci si ons on the basi s of these i ndi ces.

The most i mportant di f ferences between cases Bl - B4and B5- B8 are found i n the i nterrupti on i ndi ces (rows12- 14) . These indi ces are si gni f i cantl y smal l er i ncases B5- B8 than i n cases Bl - B4. By di f ferenti ati ngbetween -11 and l arge def i ci enci es, the mgni tudes ofthe i nterrupti ons encountered by the system arereduced. Therefore gmal l er peaki ng m t s can be used t odeal wth these def i ci enci es, or the amount of l oad tobe cut woul d be smal l er i f l oad sheddi ng i s used.

Two HYDRO PLANTS ANALYSIS

Several measures can be adopted i n order toi mprove the rel i abi l i ty of the system Increasi ng the

i nstal l ed capci t y i s the most obvious one. However, i ti s also possi bl e to re-arrange the conf i gurati on of thesystemduri ng the pl anni ng stage, mai ntaini ng the samenwrber of generati ng uni ts. Thi s possi bi l i ty uasstudi ed by i ntr oducing more t han one hydro pl ant i n thesystem I n thi s case, the si x hydro uni ts are spl i ti nto two groups of three uni ts, i nstal l i ng each groupi n di f ferent hydro pl ants. The val ues f or the pol i cy

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TABLE 5 HT-RTS w t h mul t i pl e hydr o pl ant s

case C 1 case D1 case D2 case E l

r eser voi r no 1 2 1 2F 0. 9 0. 9A

BU1 0. 6 0 . 4 0. 5 0. 5U2 0. 8 0. 6 0. 6 0. 6

EAWE ( GWh/ yr ) 5.3 5. 2 4 . 2 4. 1

EAWS ( GWh/ yr ) 2.8 3. 1 3. 5 3. 7AWS ( Mm3/ yr ) 7. 6 8. 6 10. 4 10. 7

FOI ( i nt / yr ) 2.43 0. 2 0

- - - -- - - -

AWE ( Mm3/ yr ) 14. 8 13. 5 11. 3 10. 5

LOEE ( MWh/ yr ) 1488 126. 3LOLE ( h/ yr ) 11. 62 0. 9649LCY ( MW yr ) 193 . 2 16. 6EI R 0. 999903 0. 999992

AEHG ( GWh/ yr ) 10. 47 11. 88FEHG (% ) 0. 068 0. 078

ENS1 ( MWh/ i nt ) 613 . 0 623. 5DO1 ( h/ i nt ) 4.79 4. 76LCI ( MW i nt ) 79. 58 82. 20

3 1 2 3 1 20. 0 0. 0

1. 0 0. 1- - - - 1. 5 1. 5

0 . 5 0. 5 0. 5 0. 5 0. 5 0. 5

0. 6 0. 6 0 . 6 0. 6 0. 6 a.6

3. 7 4. 2 4. 1 3. 6 4. 1 4. 19. 3 11. 4 10. 5 9. 3 10. 9 10. 44. 0 3. 5 3. 7 4 . 0 9. 7 18. 611.2 10. 4 10. 7 12. 2 22. 9 38. 6

- - - -

0. 1 5125. 00. 829915. 20. 999992

11. 880. 078

847 . 25 . 62103. 0

0. 0763. 490. 42757. 30. 999996

11. 900 . 078

875 . 75 . 90100. 7

3

0.11. 50. 50. 6

3. 89. 627. 967. 5

vectors U1 and U2 shown i n Tabl e 5 were chosen usi ngthe inf ormati on obtained f romcases Bl - B8. These valuesassured a hi gh l evel of potenti al energy i n the f i rstreservoi r, as wel l as di f ferent treatment for smal l andl arge defi ci enci es. They al so attempted to reducespi l l age of water f romthe second reservoi r.

The resul ts of thi s case (designatedC1) are showni n Tabl e 5. The i mprovement i n rel i abi l i ty of thesystem i s very si gni f i cant compared wth cases B1- B8.The producti on of hydro-el ectr i c energy (AEHG) has beeni ncreased, mainl y because the water r eleased f rom thef i rst pl ant i n the hydrochai n i s re-used i n the second

one. As a consequence of thi s i ncrease of energyproducti on, the unrel i abi l i ty of the system hasdecreased, measured by the decrease of the NI , LOEE,mm and LCY i ndi ces and the i ncrease of EI R. Thei nterrupti on i ndi ces ( l ast three rows) are siml ar tothose i n cases B1- EB. Thi s means that the type ofdefi ci enci es encountered by the system are si ml ar,explai ned by the f act that no extra hydro uni ts havebeen added to the system and therefore the peakingcapaci ty of the systemremai ns si ml ar.

THREEHYDm PLANTS ANALYSIS

Al though the d e l can si mul ate system w thseveral hydro pl ants, these studi es have been l i mtedto a maxi mumof three hydro pl ants. The reason is t hatthe HT-RTS maintai ns the same thermal generati ng uni tsand therefore, as more hydro plants are added, an overcapaci ty of the systemcan occur. The resul ts for thesethree hydro pl ants are al so shown i n Table 5 and aredesi gnated as Cases D and D2. These have a total of 12extra hydro uni ts over the base system The addi t i on ofthese extra uni ts improves si gni f i cantl y therel i abi l i ty of the system The system rarel y suf f ersany def i ci ency, expressed by the smal l val ue of MI

(0. 2 nt/ yr i n D1 and 0. 15 i nt/ yr in D2) . On the otherhand, the spi l l age of water i s very i mportant (l argeval ues of AWS), whi ch suggest that, i nstead of usi ng anextra hydro pl ant , i t may be bett er to i nstal l moreuni ts i n the hydro pl ants al ready exi st i ng i n thesystem

The eff ect of di f f erenti at i ng between l arge andsmal l def i ci enci es can be observed in the i nterrupti on

i ndi ces. Case D1 (wthF equal to 0.9) has smal l eri nterr upt i on i ndi ces than case D2 (w th F equal to0 . 0 ) . Thi s mans that the system suf f ers smal l erdef i ci enci es i n case D1 than i n case D2, a si tuati oni l l ustrated by the XI - hi st ograms of both cases i nFigure 1. Thi s conf i rm once more the i mportance ofchoosi ng a near- opti mun cri teri on to deci de whatdef i ci enci es have to be reduced i n order to regul atethei r magni tudes.

Fi nal l y case E l shows the ef fect of the model whensi de i nf l ows are consi dered. For thi s case the val uesfor the Ak coef f i ci ents were set equal t o 1.0 f or t hemain i nf l owand equal to 0. 1 f or the si de i nf l ows,whi l e the values for the Bk coeff i ci ents were set equalto 1. 5 f or al l the i nf l ows. The resul ts are al so showni n Tabl e 5. The si de i nf l ows represent more waterf l ow ng i nto the hydrochain and thus the producti on of

hydro-electri c energy (AEHG) can he i ncreased. However,most of the extra water i s spi l l ed as excess water

(AWS) swest i ng t hat fewer hydro pl ants w th moreuni ts i n each of the pl ants coul d make the system moreproducti ve. The producti on of hydro-el ectri c energy i s

L C I , M W I i n t

Figure 1 H stogram of l oad curtai l ed per i nterr upti on

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1080

act, ual l y i ncreased by 26 MWh/yr compared to case D2.Thi s amount. of energy i s enough to reduce the FD ,LOEE, LOLE and IX Y i ndi ces by 50%compared to those i ncase D2. Thi s energy represents a si gni f i canti mprovement of the rel i abi l i ty of the system

CONCLUSI ONS

Thi s paper has descr i bed some model s andtechni ques that have been devel oped to eval uate therel i abi l i ty of generati on system contai ni nghydro pl ants formng a mul t i pl e exploi tati on scheme of

a river. These techni ques have used si mul ati ontechniqurJ s whi ch, a1 though requiri ng more comput i ngti me l .han anal ,vti ca techni ques, are parti cul arl ysui ted to the hydro generati on probl em due to thec~onserpcrl ti alnature of water i nfl ows and subsequentusage. They have the added benef i t t hat probabi l i tydi str i buti ons can be easi l y evaluated as wel l asexpected va1 ues.

The t echni ques have been appl i ed to t he I EEE&iahi l i t, y Test Systemextended by the i ncl usi on ofaddi ti onal hydro data. The resul ts have shown thatsi gni f i cxm changes occur i n the rel i abi l i ty i ndi cesdue to vari ati ons i n t. he usage of the water, i . e. watermanagement, and due to the number of hydro pl ants al ongthe ri ver. These resul ts al so showt hat, dependi . ng onopratiorial pol i ci es and water management, somere l i abi l i t,y i ndi ces may i ncrease whi l st othersdecrease. Careful thought i s therefore requi red as tothe requi red benef i ts i n rel i abi l i ty when such

operati ng pol j ci es are bei ng deci ded.The outcome of these studi es i s an i mproved

understanding of the behavi our of mxed hydro- thermalsystems and, i n part i cul ar, of the I EEE RTS.

1.

2.

3.

4.

5.

6.

7.

RFFERENCES

Ri l l i nton, R. and Al l an, R. N. , "Rel i abi l i tyEval uati on of Fngineeri ng System: Concepts andTechniques". Longman, London/ Pl enum New York,1983Ri l l i nton, R. and Al l an, R. N. , "Rel i abi l i tyEval uat. i onof Power System". Pl enum Publ i shi ng,NewYork, 1984Al l an, R. N. , Bi l l i nton, R. and Shahi dehpour, S.Mand Si ngh, C. , "Bibl i ography on the Appl i cat i on ofProbabj . l i t, y Methods i n Power SystemRel i abi l i tyEval uat i on, 1982-1987". EI X Wnter Power Meet i ng,New York, February, 1988B l l j ntori, R. and Al l an, R.N. , "Rel i abi l i tyAssessment of Large Electr i c Power System". Kl uwerAcademc Publ i shers, Bost on, 1988Cunha, S. H. F. , h e s , F. B. M , O i vei ra, G. L. andPerei ra, M V. F. , "Rel i abi l i ty Eval uati on i nHydrothermal Generati ng System". IEEE Trans,

Ruhi nstei n, R. Y. , "Si mul ati on a d the Monte Carl obkthod". Wl ey, New Y ork, 1981Gordon, G. , "SystemSi mul at i on". Prent i ce- Hal l , New

PAS-101, 1982, pp 4665-4673

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

J ersey, 1969Hamni ersl ey, I .M and Handscomb, D. C. , "Monte Carl oMethods". Wl ey, New York, 1964Al l an, R. N. , J ebri l , Y. A. , Saboury, A. and Roman,J . , "Monte Carl o Si mul ati on Appl i ed to Power SystemRel i abi l i ty Eval uat i on". 10th Advances i nRel i abi l i ty Technology, El sevi er, London, 1988,

J ebri l , Y. A. , "Monte Carl o Si mul at i on i n PowerSystem Rel i abi l i ty Eval uati on". MSc D ssert ati on,UM ST, Mari chester, 1985Saboury, A. , "Monte Carl o Methods i n Rel i abi l i ty

Evaluat i on of Hydro-thermal Generati ng System".MSc D ssert ati on, LMIST, mches t er , 1986

Roman, J . , "Rel i abi l i ty Eval uati onof Hydro- thermalSyst em using Monte Carl o Simul ati on Methods". t%Sc

D ssertati on, UM ST, Manchester, 1987Bi l l i nton, R . and Ghaj ar, R. , "Uti l i sati onof MonteCarl o Si mulati on i n Generati ng Capaci ty AdequacyEval uati on". (2%Trans, Vol . 26, 1987Sherkat , V. R. , Campo, R. , Mosl ehi , K. and Lo, E. O ,"Stochasti c Long-termHydrothermal Opt i msati on fora Mu1 t i - reservoi r System. I EEE Trans, PAS-104,

Amr , B. H. , "Short - term Opti mal Operat i on of aHydro-el ectri c Power System. PN) Thesi s, UMST,Manchester, 1983Sal vaderi , L. and Bi l l i nton, R. , " A Compari sonbetween Two Fundamental l y D f ferent Approaches toComposi te System Rel i abi l i ty Eval uat i on". I EEETrans, PAS-104, 1985, pp 3486-3492

T E E E Conuni ttee Report , "I EEE Rel i abi l i ty TestSystem. I EEE Trans, PAS-98, 1979, pp 2047-2054A l l an , R. N , Bi l l i nton, R. and AWel - Gad, N. M K. ,"The I EEE Rel i abi l i ty Test System- Extensi ons toand Eval uat i on of the Generati ng System. I EEETrans, PWHS-1, No. 4, 1986, pp 1-7

pp 149-162

1985, pp 2040-2049

BI BLI OQZhPH ES

Ron Al l an (M78, SM 80, F' 88) was born i n -l and. Heobtained a D p Tech ( Eng) f rom Portsmouth Pol ytechni cand subsequentl y an Msc, a PhD and a DSc f romtheUni versi ty of Manchest er, England. He i s i n the PowerSyst em Research Group at UMST, Manchest er, Engl and.He i s the author or co-author of numerous technicalpapers and of three rel i abi l i ty books. He i s a Fel l owof the I EE, a Fel l owof t he I EEE, a Fel l ow of theSaf ety and Rel i abi l i ty Soci ety (UK) and a CharteredEngineer i n the UK .

J ai meRoman was born i n Spai n i n 1961. He obtai ned hi sEl ectr i cal m neer i ng degree f rom the Uni versi dadPol i tecni ca de Madri d. He subsequent l y obtai ned an MSc

f romthe Uni versi ty of Manchester, England duri ng whichti me hi s research project was concerned w th the topi cof t hi s paper. He i s now a Research Fel l ow at theI nsti tuto de I nvesti gzi cion Tecnol ogi ca i n Madri d wherehi s research i nterests span al l aspects of powersystem anal ysi s.

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