Au oma ed Wind Tu bine Main enance Scheduling
Nu seda Y. Y¨u ¨u¸sena, Paul N. Rowleyb, Simon J. Wa sonc, Julio Mele oa,∗
aIns i u o Uni e si a io de In es igaci´on CIRCE
(Uni e sidad de Za agoza - Fundaci´on CIRCE),
C/ Ma iano Esquillo 15, 50018, Za agoza, Spain
bCREST, Loughbo ough Uni e si y, Holywell Pa k, Loughbo ough, LE113TU, UK
cDUWIND, Del Uni e si y o Technology, Kluy e weg 1, 2629 HS Del , Ne he lands
Abs ac
While many ope a ion and main enance (O&M) decision suppo sys ems
(DSS) ha e been al eady p oposed, a se ious esea ch need s ill exis s o wind
a m O&M scheduling. O&M planning is a challenging ask, as main enance
eams mus ollow speci ic p ocedu es when pe o ming hei se ice, which
equi es wo king a heigh in ad e se wea he condi ions. He e, an au oma ed
main enance p og amming amewo k is p oposed based on eal case s udies
conside ing a ailable wind speed and wind gus da a. The me hodology
p oposed consis s on inding he op imal in e en ion ime and he mos
e ec i e execu ion o de o main enance asks and was buil on in o ma ion
om egula main enance isi asks and a co ec i e main enance isi . The
objec i e is o ind possible schedules whe e all wo k o de s can be pe o med
wi hou b eaks, and o ind ou when o s a in o de o minimise e enue
losses (i.e. doing main enance when he e is leas wind). Fo he DSS, ou ine
main enance asks a e g ouped using he indings o an agglome a i e nes ing
analysis. Then, he ask execu ion windows a e sea ched wi hin p e-planned
main enance day.
Keywo ds:Wind Tu bine, O&M, Main enance, Scheduling
1. In oduc ion
The cos o main enance is a majo con ibu o o he o al le elized
cos o ene gy (LCOE) om wind a ms accoun ing o a sha e o a ound
∗Co esponding au ho : [email p o ec ed]
P ep in submi ed o Reliabili y Enginee ing & Sys em Sa e y Ma ch 20, 2020
20%-25% [1]. Minimisa ion o he main enance cos s equi es as p ecise as
possible main enance scheduling. Ex ended down ime, which can occu when
main enance in e en ions a e delayed du ing poo wea he , incu s inancial
cos s o wind a m owne s.
Wind a m ope a ional scheduling has been ound in he li e a u e o be
a unc ion o a ange o ac o s such as he ene gy demand [2], elec ici y
ma ke p ice and wind speed [3]. When he cons ain s a e in es iga ed,
wind a m accessibili y no mally comes in i s place in e ms o impo ance.
Fa m accessibili y depends on he a iabili y o he wind speed and he as-
socia ed heal h-sa e y and en i onmen egula ions (HSE) [4–9]. In o he
wo ds, inding an app op ia e wea he window is a majo c i e ion o any
ype o in e en ion o wind u bines and he e is a esea ch need closing
he gap be ween academic models and applica ion in p ac ice [10]. Acco ding
o he li e a u e, main enance wea he windows a e dependen on he wind
speed o an onsho e wind a m, while he wa e heigh is also a decisi e ac o
o o sho e wind a ms whe e accessibili y depends on he ype o main e-
nance essel u ilized [11–14]. Fo o sho e wind a m ope a ions, he loca ion
(dis ance o sho e and wa e dep h), me eo ological and oceanog aphic a i-
ables in luence he si e accessibili y, i is highligh ed in he li e a u e ha
he e is a end o mo ing om nea -sho e o deep wa e o o sho e wind
a m ins alla ions, which esul s in lowe si e accessibili y and highe cos s
o he execu ions o co ec i e main enance ac ions [15].
In addi ion o he measu ed mean wind speed, indus y p ac ice high-
ligh s wind gus as an impo an pa ame e when conside ing access o a
wind u bine [16]1. Howe e , hus a , his has no been e e ed o in he
li e a u e conce ning scheduling s udies as a cons ain which a ec s ei he
ope a ional scheduling o down ime. P e ious academic wo k in his ield
has conside ed only wind speed and ou pu powe as he decisi e pa ame e s
when gene a ing a easible main enance plan in onsho e [18, 19] and signi i-
can wa e heigh , wa e peak pe iod and wind speed in o sho e [7, 15]. I is
al eady no ed in bo h onsho e and o sho e c ane manuals and sa e wo king
guides ha wo king heigh and wind gus speed in luence execu ions o c ane
ope a ions [20, 21]. When a c ane ope a ion canno be pe o med, he co -
1In his s udy, wo majo wind u bine manu ac u e s’ O&M guidelines a e used. These
wo companies a e also leading o iginal equipmen manu ac u e s in he wind sec o . Ac-
co ding o 2017 s a is ics, he o iginal equipmen manu ac u e s o wind u bine ha e he
highes ma ke sha e among he wind a m O&M se ice p o ide s [17].
2
esponding wind u bine main enance ac ion can also no be pe o med as
well and esul s in delay o O&M ac ions. This delay con ibu es o wea he
ela ed down ime, which is esul ing om coa se main enance planning and
insu icien accessibili y o bo h wind a m si e and wind u bine componen .
In he p esen s udy, he au ho s conside bo h mean wind speed and
wind gus as limi ing ac o s o accessibili y o an onsho e wind u bine and
demons a e he applica ions o wind speed measu emen s in de e mining
ask execu ion sequence whils minimising down ime due o ad e se wea he
condi ions du ing pe iods o in ended main enance. The goal is au oma ed
scheduling o asks o be pe o med wi hin a wo kday, such ha asks wi h
s ic equi emen s a e scheduled when condi ions a e mos benign. The no -
mal p ac ice depends on wo weeks ahead main enance se ice eam booking
wi h a single call en ailing which ala m is ac i a ed o which u bine. These
wo k o de s a e lacking de ailed planning o he main enance day and he
asks o be pe o med. The e o e, he e a e coa se planning and wea he
ela ed wai ing pe iods in he wind a m si e.
The s uc u e o his pape is as ollows: in he ollowing sec ion, an
o e iew o a ypical wind a m main enance policy is desc ibed. Gene al
cha ac e is ics o mean wind speed, wind gus , main enance log books and
ask comple ion du a ion da a a e p esen ed in Sec ion 3. The nex sec-
ion desc ibes he me hodology, and he p oposed amewo k. Case-s udies
a e hen p esen ed o show he alue o a p oposed main enance planning
me hodology, which demons a es how an op imal sequence o main enance
in e en ions can be de ised. Then, in Sec ion 6, p ac ical explana ion o
he indings, he limi a ions and he assump ions a e p esen ed. The inal
sec ion summa ises he main ou comes o his s udy.
2. Main enance plans & p oblem s a emen
Wind u bine main enance can consis o bo h co ec i e and p e en i e
ac ions. Long e m main enance policies mus co e bo h o hese. Co ec i e
main enance is no mally ca ied ou once a aul has been de ec ed, whe eas,
p e en i e main enance is gene ally pe o med acco ding o calenda -based
p e-de e mined in e als such as biannual, annual, biennial and quinquennial
pe iods [4, 5, 22–24]. The numbe o asks and he du a ion o a scheduled
main enance ac ion a e di e en om one case o ano he and depend on
speci ic sub-assembly, componen s, manu ac u e , model and capaci y o he
wind u bine. Scien i ic li e a u e and manu ac u e s’ main enance guides
3
gi e igu es o he equi ed du a ion o a ange o main enance asks ha
a y om lub ica ion which ypically akes ew hou s o o he mo e leng hy
which las up o 18 hou s [23, 24] du ing a biannual main enance isi . In
addi ion, wo king p ac ices may di e om one ope a o o ano he . These
ac o s mus be aken in o accoun in e ms o de ining a comp ehensi e
main enance s a egy and p o ide a challenge when de eloping a model o
main enance op imisa ion.
(a)
4
(b)
Figu e 1: Main enance scheduling p ocedu e (a) p e en a i e policy and (b) co -
ec i e in e en ion.
P e en a i e main enance is usually planned a yea in ad ance on an
annual basis o onsho e wind a ms [25]. A ypical low diag am o his
ype o ad anced planning is shown in Figu e 1a whe e accoun needs o be
aken o he wea he and elec ici y ma ke p ices as well as he a ailabili y
o a main enance eam [16]. Requi emen s o p e en a i e main enance can
also be seen e en when planning co ec i e ac ions as shown in Figu e 1b.
Bo h, egula and co ec i e main enance in ol e unce ain ies, pa icula ly
conce ning he wea he ela ed limi a ions. The ypical limi ing ac o o
execu ing main enance ac ions is he wind speed. Regula ions and manu ac-
u e s’ good p ac ices se he maximum alues o he wind speed which allow
wo k a di e en loca ions on he u bine. This in o ma ion has been used in
p e ious esea ch wo ks o de elop main enance amewo ks. Fo example,
one s udy ixed he wind speed limi as 10 m/s o accessing he whole u -
bine [5], while ano he based he sa e wo king limi on cu in wind speed, i.e.,
he u bine was only conside ed main ainable when he wind speed was lowe
han cu -in [6]. Fu he mo e, cu en egula ions and main enance guides in-
clude dynamic sa e y limi s aking in o accoun no only he mean 10-minu e
wind speed alue bu also he gus alue, when a c ane usage is equi ed o
such a case like majo componen eplacemen . The de ini ion o gus is a
sho -du a ion (seconds) maximum o he luc ua ing wind speed [26].
The maximum pe missible wind gus speed o c ane usage depends on
5

a ious ac o s such as mean wind speed, in e en ion heigh and weigh o
he load [20]. The e o e, co esponding wind gus es ic ion o any in e -
en ion equi es imely and case based con ols. Mo eo e , high gus alues
cause mo e es ic i e wind u bine componen speci ic accessibili y ules e-
ducing he highes allowed mean wind speed.
Taking in o accoun only wind speed limi s, he sa e wo king ules a e
also di e en depending on u bine model and size. Fo example, in he case
o MADE AE 46 u bines, p e en a i e main enance equi es wind speeds
below 20 m/s a he nacelle, howe e changing he whole nacelle equi es he
wind speed o be no mo e han 5 m/s. I we check he equi emen s o NEG
Micon NM 52 u bines, wo king in he hub equi es wind speeds below 15
m/s while wo king in he nacelle oo is allowable un il 12 m/s and gene a o
alignmen should no be pe o med o wind speeds abo e 10 m/s. Finally,
o he Ves as V 90 3.0 MW model, gene a o alignmen in e en ion can’
be done o wind speeds abo e 8 m/s, changing pi ch angle equi es wind
speed alues smalle han 6 m/s and wo king in he d i e ain is allowed up
o 7 m/s [16].
Wi hin a wo k shi , a ious asks mus be comple ed on a wind u bine
acco ding o he p e ailing ime and labou o ce es ic ions. As s a ed in
[11], i is almos impossible o gene a e a lawless main enance plan in e ms
o a oiding p oduc ion loss, since i is di icul o ind a pe iod whe e he
u bine is no p oducing due o low wind speeds. Wha can be done in his
sense is o schedule he main enance wi h an accep able unce ain y [27, 28].
3. Da a sou ce, wind a m main enance p ocedu e and da a
Main enance logs, se ice wo k o de s and SCADA da a we e ob ained
om a Spanish wind a m. In his analysis, O&M se ice epo s, which
co e a 3 yea s window, a e used o de ine he lis o ac ions and he needed
du a ion o each ype o in e en ion and ac i i y in he s udied wind a m.
Rega ding he me eo ological da a, 10-minu e wind speed and wind gus da a
a e collec ed o yea 2019. In he inal analysis, accessibili y in es iga ions
o 24 hou s windows a e p o ided o he example cases. Acco ding o he
in o ma ion ga he ed, he a e age du a ion o he biannual, annual, biennial
and quinquennial isi s a e app oxima ely 21, 26, 15 and 18 hou s espec-
i ely. The o al numbe o di e en asks o be pe o med in main enance
isi s is 169. Mos o hem, 117, a e included in he biannual isi ac ions
while he o he s a e dis ibu ed o e he o he isi s. Howe e , no all main-
6
enance ac ions a e ca ied ou du ing each planned isi as some o hem
ha e p io i y based on he indings o p e ious se ice isi s and he needs
o he wind u bine.
Table 1: Execu ed asks o he scheduled isi
Tu b. Wo k Zone Sub Sys em Task Numbe s
A-G ound Towe 1 o 2
A-G ound Elec ical Pa s 3
A-G ound Ro o -Blades 4
B-Pla o m Elec ical Pa s 5 o 7
C-Towe Yaw Sys em 8 o 14
D-Nacelle Main Sha and Bea ing 15 o 17
D-Nacelle Gea box 18 o 27
D-Nacelle Gene a o 28
D-Nacelle Base S uc u e and Co e 29 o 31
D-Nacelle Elec ical Pa s 32
E-Hub Ro o 33 o 34
F-Ou side o Nacelle Senso s 35 o 36
Figu e 2: Example o u bine wo king zones
Figu e 2 shows he conside ed u bine wo king zones, while he ask num-
be s associa ed o hese zones a e lis ed in Table 1. In his wo k, o he sake
7
o simplici y, only he asks numbe s lis ed in Table 1 a e used o de ine a
case s udy conside ing a egula se ice isi . A second case s udy is based
on a majo in e en ion, which equi es a c ane usage. Mo e speci ically, a
gene a o eplacemen is s udied and mo e in o ma ion will be p o ided e-
ga ding he co esponding ask. To explain he wo king en i onmen o he
se ice pe sonal o pe o ming ei he a egula se ice o a majo in e en-
ion, he seasonal and gene al cha ac e is ics o he subjec wind a m a e
shown in Figu es 3 and 4.
In Figu e 3, he wind speed seasonal his og ams om he case Spanish
wind a m a e p esen ed. The annual his og am is included in each g aphic
o highligh he seasonal con ibu ion. I can be seen ha he majo i y o
wind speed obse a ions lie be ween 0 and 10 m/s in summe mon hs. Then,
summe looks he bes season o main enance ac ions, bu he e a e s ill
a signi ican numbe o wind speed obse a ions wi h alues highe han 15
m/s.
Figu e 3: Annual e sus seasonal wind speed his og ams using 10-minu e a e aged
mean wind speeds
Figu e 3 shows he seasonal cha ac e is ics o he nacelle wind speed
ob ained om he analysed wind a m. I is known ha he seasonal wind
8
speed beha iou is dependen on he loca ion o he wind a m. The annual
main enance plan mus be p epa ed conside ing he seasonal wind beha iou
and he elec ici y ma ke p ices o he coun y whe e he analysed wind a m
is loca ed. Then, he seasonal wind beha iou is an impo an ac o o long
e m scheduling, which is no he aim o his s udy. The esul ing p og am
om he annual main enance plan is an inpu o decision making suppo
ool. The e o e, his inpu mus be modi ied, when he analysed wind a m
is changed.
Figu e 4 illus a es he diu nal beha iou o he wind speed o each
season du ing 2019 compa ing he maximums eco ded in hou ly da a pe
seasons. I can be seen ha he day shi (08:00 o 18:00) in summe , wi h
wind speed maximums lowe han 20 m/s, indica es ela i ely easonable
wind a m accessibili y o pe o m a main enance isi .
Figu e 4: Seasonal wind speed ends as hou ly maximums. This igu e is ob ained
calcula ing he maximums pe hou o each day o e a season in 2019. The window,
which is shaded in yellow ep esen s he day shi om 08:00 o 18:00.
The majo i y o scheduled main enance in e en ions a e planned in sum-
me and au umn mon hs in he case s udy main enance log. Fo his eason,
9
In dend og am isualisa ion, heigh ep esen s he alue o he Euclidean
dis ance be ween clus e s. To es ima e his dis ance, inpu da a mus be
scaled. As an example, o an inpu consis ing o 100 ows and 2 columns,
he i s column indica es he wo king zone and he second one s ands o
he co esponding wind speed es ic ion. A e scaling he inpu da a each
obse a ion is i s ly assigned o a empo a y clus e . Following his p oce-
du e, in he i s s ep he e exis 100 clus e s (100 asks) and, o ins ance,
he Euclidean dis ance be ween Clus e 1 and Clus e 2 can be ob ained as;
Eucdis =q(HSE C1−HSE C2)2+ (WZC1−WZC2)2(5)
whe e HSE ep esen s he wind speed es ic ion and W Z ep esen s he
wo king zone. The same calcula ion is epea ed o all 100 clus e s. A e -
wa ds, he Wa d algo i hm g oups hese clus e s acco ding o he minimisa-
ion p inciple o Euclidean dis ances.
4.4. P oposed amewo k
The p oposed me hodology is g aphically explained in Figu e 7. The
ini ial s ep is o p o ide in o ma ion on he ype o he in e en ion, ini ial
sa e wo king ules and wind o ecas s. Then, i is equi ed o decide i wind
gus measu emen s and es ima ions a e needed as decision a iables. The
co esponding answe depends on he speci ic equi emen s o he planned
in e en ion, such ha in e en ion may equi e a c ane usage.
16

Figu e 7: Flowcha o p oposed solu ion, HSE: Heal h-Sa e y and En i onmen
egula ions
In he p oposed me hodology iis he use de ined limi o ini ia ing he
agglome a i e nes ing p ocess, as shown in Figu e 7. He e, we assumed ha
a main enance ask can be done wi hin a minimum o ou s ages such as:
17
access o wo king a ea, access o ailed componen , emo e ailed componen
and placemen o he new componen . Then, o a case ha each s age e-
qui es a unique sa e wo king ule, he minimum o al numbe o sa e wo king
ules is 4. The e o e, p ede e mined compa ison alue, i, is se o 4 .
Fo an in e en ion consis ing o mo e han ou asks o equi ing he
ul ilmen o mo e han ou sa e y ules ela ed o wind speed, o ecas s
mus be used along wi h he ou comes o he agglome a i e nes ing as inpu
in he sea ch p ocess. The gus o ecas s a e necessa y i he in e en ion is
pe o med using a c ane, which equi es educ ion o he wind speed limi s
due o he high gus alues. Las ly, he sea ch p ocess scans he a ailable
ime windows du ing he in ended main enance day o ind he op imal ime
window o he wo k o ake place. I he main enance in e en ion can be
execu ed du ing he p e-planned day, op imal execu ion ime and o de o he
asks a e de e mined. I no , a change in he p e-planned day is sugges ed.
This me hodology can also be used o o sho e applica ions, bu i is
e y impo an o upda e HSE equi emen s conside ing wa e heigh and
o sho e ope a ions speci ic ules. Mo eo e , in e en ion ype, equi ed du-
a ion, ou pu s o annual main enance, e c. mus be upda ed conside ing he
echnology ype and he wo king en i onmen .
5. Resul s
The ials wi h he p oposed app oach o wo dis inc main enance isi s
a e epo ed in his sec ion. Case 1 is an applica ion es o a ou ine main-
enance isi , whe eas Case 2 ocuses on a majo componen eplacemen .
5.1. Case 1: Rou ine Main enance
5.1.1. Clus e ing
The p oblem o planning a high numbe o asks is simpli ied by applying
he agglome a i e nes ing me hodology o he pool o 36 asks. Clus e ing
was pe o med using he Euclidean dis ance as simila i y c i e ion. I was
calcula ed using he wind speed limi and he co esponding u bine wo king
zone o each ope a ion. Figu e 8 shows how he asks a e g ouped o ming
a o al numbe o 4 clus e s ( ep esen ed wi h di e en colo s) as a unc ion
o he es ic ions, wind u bine wo king zone and wind speed.
18
Figu e 8: G aphical ep esen a ion o he clus e ing p ocess. Di e en colou s
ep esen he di e en clus e s o asks. (The dend og am needs o be egene a ed
o di e en echnologies conside ing main enance in e en ion lis s.).
A summa y o he clus e ing esul s is gi en in Table 2 whe e he clus e
du a ion and i s wind speed limi a e shown. As main enance asks a e
usually accomplished by wo echnicians, which will equi e hal he ime,
and he equi ed esolu ion o he planning schedule is based on 10-minu e
s eps, he ounded du a ion pe pe son on a 10-minu e scale is also p o ided.
Table 2: Clus e ing esul s
Clus e Du a ion (min) Pe pe son (10 mins) lim (m/s)
1 66 4 20
2 106 6 15
3 491 25 12
4 50 3 10
5.1.2. 24 hou s e alua ion o execu able/no execu able windows
Now by applying he p ocedu e, explained in Sec ion 4.2, wi h measu ed
wind speed da a o es days ( he summe day was 27 h June 2019 and he
au umn day, 08 h No embe 2019) execu able and no execu able pe iods
o he main enance clus e s a e de e mined. Figu e 9 and Figu e 10 show
he allowed in e en ion s a ing imes o each o he clus e s ound in he
p e ious sec ion.
19
Execu ion o he main enance se ice is only possible, i he s a ing ime
o he in e en ion is wi hin he g een do s. He e g een do s ep esen alid
pe iods o bo h wind speed sa e wo king limi and he a ailabili y o a win-
dow o accomplish he ask wi hin i s minimum equi ed comple ion du a-
ion. In hese igu es, lim ep esen s wind speed limi and Du s ands o
he equi ed du a ion o he execu ion o he co esponding clus e .
Figu es 9 and 10 a e gi en in o de o display he complexi y o p og am-
ming wi h dynamic wea he es ic ions. The decision make mus conside
all he in e en ion speci ic accessibili y windows and gene a e a main enance
p og am combining hem.
Figu e 9: Rou ine main enance e alua ion wi h ac ual inpu da a o he summe
day (a) clus e 1, (b) clus e 2 (c) clus e 3 (d) clus e 4
20
Figu e 10: Rou ine main enance e alua ion wi h ac ual inpu da a o he au umn
day (a) clus e 1, (b) clus e 2 (c) clus e 3 (d) clus e 4
The esul s o each o he clus e s we e:
Clus e 1: Tasks a e execu able du ing bo h analysed days, since he
co esponding wind speed es ic ion is e y lexible and i s du a ion is ela-
i ely low, see Figu es 9a and 10a.
Clus e 2: Tasks a e mos ly execu able o bo h days, see Figu es 9b
and 10b. Al hough, he e a e sho non-execu able windows in he au umn
day, see Figu e 9b.
Clus e 3: Tasks a e execu able o he calme summe day and asks a e
non-execu able o he windie au umn day, see Figu es 9c and 10c. Clus e
3 asks a e he mos challenging g oup, because hey equi e a longe ime
wi h majo wind speed es ic ions.
Clus e 4: The execu ion o Clus e 4 asks depends mos ly on he mos
es ic i e wind speed limi . Ne e heless, i can be seen ha he e exis
some execu able windows, since he execu ion o his clus e equi es he
lowes du a ion, see Figu es 9d and 10d.
These p elimina y analysis shows ha in he summe day all asks can
be pe o med, whe eas in he au umn day he e is no sui able ime window
o pe o m Clus e 3 asks. The e o e, in he nex analysis only he esul s
ob ained om he summe day a e p esen ed.
Conside ing he hou ly elec ici y ma ke p ice, i is possible o combine
21

i wi h he ene gy losses o each plan, es ima ed om measu ed wind speed
alues and manu ac u e ’s powe cu e, o ob ain he e enue p io i ised
decision pools. Figu e 11 shows he day-ahead elec ici y ma ke p ices o
27 h June 2019 and 08 h No embe 2019 [35]. I can be clea ly seen ha
in Summe , 27 h June 2019, he elec ici y ma ke p ices highe han 50
EUR/MWh, while in Au um, 08 h No embe 2019, mos o he p ices a e
be ween 30 and 40 EUR/MWh, ollowing he common end obse ed in he
spanish ma ke [35].
Figu e 11: Day-ahead hou ly elec ici y ma ke p ice
Figu e 12 shows he co esponding e enue losses o he p io i ised main-
enance plans, labelled as “low” when hey a e below he mean o he e enue
losses es ima ed o he day unde conside a ion. When hey a e lesse han
he hi d qua ile and g ea e han he mean, he label is “medium”. Las ly,
o he plans wi h he e enue losses g ea e han he hi d qua ile, he label
is “high”.
This DSS is p epa ed as a compu a ional ool and he isualisa ion o he
epo ing module is gi en in he Appendix 1, whe e he al e na i e plans and
he e enue e alua ion p ocedu e a e exempli ied.
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Figu e 12: Decision pool o ou ine main enance isi scheduling o he summe
day, he second y axis s ands o he g ouping acco ding o he e enue losses,
yellow shaded window shows he day shi .
In Figu e 12, only selec ed al e na i e main enance plans a e plo ed when
a cos -wise clea sepa a ion can be obse ed among he 1093 al e na i es (14
o 1093) o he analysed summe day. Each al e na i e ep esen s a p og am,
which con i ms ha wea he ela ed down ime is minimised. Acco ding o
Figu e 12, he ea ly hou s o he day a e mo e p e e able in o de o pe o m
p e en a i e in e en ion conside ing he e enue losses. Al hough elec ici y
ma ke p ices a e high du ing hese hou s, he limi ed wind esou ce a ail-
abili y, educes powe p oduc ion losses and co esponding e enue losses.
5.2. Case 2: Gene a o eplacemen
5.2.1. 24 hou s e alua ion o execu able/no execu able windows
In his case s udy, he gene a o eplacemen is in es iga ed o he p o-
posed scheduling p ocess. To eplace he gene a o , a c ane mus be used.
23
Fi s ly, he nacelle co e mus be emo ed and hen he ailed gene a o mus
be aken ou . These emo als a e ollowed by ins alla ion o he new gen-
e a o and e-ins alla ion o he o iginal nacelle co e . In o he wo ds, his
in e en ion equi es wo ypes o li ing /unloading asks. Sa e y equi e-
men s wi h ega ds o wind speed a y due o he gus alues. The mean
wind speed limi o sa e wo king has o be dec eased by 2 m/s when he
wind speed gus is abo e 5 m/s o ope a ion equi ing a c ane usage [16],
om 10 m/s, o a gus lowe han 5 m/s, o 8 m/s o a gus highe han 5
m/s in he case o nacelle co e and om 8 m/s o 6 m/s, o he same gus
alues, in he case o he gene a o . I is wo h men ioning he e ha he
gus limi , o he au ho s knowledge, has ne e been conside ed in p e ious
scien i ic s udies. Ano he di e ence, ega ding ou ine main enance plan,
is he equi emen o ollow a ixed ask o de , as ob iously, i would no
be possible o pe o m emo al o old gene a o be o e emo ing he nacelle
co e . The e o e, he main enance execu ion o de is ixed o his p oblem.
The ob ained esul s o a co ec i e main enance isi in he p e iously
selec ed Summe day a e shown in Figu e 13. Execu able (g een) and no
execu able ( ed) ime windows a e shown o he ou main asks o a co ec-
i e in e en ion. He e, a 120 minu es window is sea ched o he emo al o
he old gene a o and ano he 120 minu es window o placemen o he new
one. In hese sea ches, he pe missible wind speed educes om 8 m/s o 6
m/s, when he wind gus alue exceeds 5 m/s. The emaining asks equi e
a 90 minu es window sea ch o he emo al o he nacelle co e and ano he
90 minu es o he placemen . In hese sea ches, he pe missible wind speed
educes om 10 m/s o 8 m/s, when he wind gus alue exceeds 5 m/s.
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Figu e 13: E alua ion o gene a o eplacemen when conside ing dynamic sa e
wo king limi s due o gus (Summe day).
I is a he easy o highligh he impac o he gus a iable wi h a simple
compa ison be ween Figu e 13 and Figu e 10. Due o he gus ela ed es ic-
ions, a co ec i e in e en ion canno be pe o med in his case, al hough i
was possible o pe o m a p e en a i e main enance in e en ion.
6. Discussion and Limi a ions
When a decision make uses only he mean wind speed cha ac e is ics,
any day om he summe season is a good candida e in o de o p epa e
he main enance plans. This s udy p esen ed ha each candida e day mus
be analysed p o oundly. Because, while he powe losses esul ing om he
main enance in e en ions could be limi ed, he e enue losses could be se-
e e due o he elec ici y ma ke p ices and ice e sa. As i is shown in
his s udy, no only he mean wind speeds, bu also he wind gus s a e he
limi ing ac o s o pe o ming some majo main enance ac i i ies. The im-
plemen a ion o o he en i onmen al limi ing ac o s ( og, ain, e c.) was no
possible due o da a una ailabili y.
The p ac icali y o such a DSS highly depends on he inpu da a. Unce -
ain ies in ega ds o du a ion o asks and in ela ion o wea he o ecas s
a e no conside ed in he p esen s udy. I mus be no ed ha in o de o
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