Note: Descriptions are shown in the official language in which they were submitted.
CA 02228145 1998-01-28
PROCESS FOR DE-ICING THE ROTOR BLADES
OF A WIND DRIVEN POWER STATION
The invention rolate~ to a method for de-icin~ a ~Ivind turbine rotor blade having
inter-conne!cted cavities. The invention relates also to a rotor blade that is
favourably suiTablR for implemen~ing The method.
A wind turbine feaTuring rotor blades Tha~ are ei~ a7 'Iy pr~necled e~ain~t the
formation of ice 8r the rotor blade ~ip8 iS known from DE-PS-842 330. In Ihis case,
the roTor blade has cavities on the inside of the leading ed~e that are connected
wilh each o~her, in terms of fluid dynamics. paralle~ to the longitudinal axis of the
roTor blade vla openinS~s in the reinfo~Le"lel~t rlbs. Warmed air is thus able to move
frorn the rotor blade hub roughly parallel to the lon5~itudinal axis of the roTor blade
via thc flow channels ~o the tip area of the rotor blade and is then expelled ou~ of
the inner blade via cG,llr~ t le vems. Hence. the wurmed air is channelled radielly
from the cen~ral part of The wind turbine to the outer parts of a rotor blade tip,
where ~he he~ ~ransfer medium transfen its thermal energy and warms the leadinç~edge of the rotor blade, the means by ~vhich it i5 attemptçd to prevent ice forming.
The ice formed on the surfaces of the rotor blades of a wind turbine may lead tounwan~ed unbalanced masses and concomitant mechanical loads on the wind
energy corlverter, ~s well a$ ~erodynami~ distL~rbances with potontially adverseeffects on the power output of the turbine. fu.TI,on,.ore, the formation of ice on a
wind turbine whilo in oper~tion ~oneratos the risk of accidents, because tho ice may
brlsak off and ice r~" .e. .ls be thrown considerable distances into the area
surroundinl~ the wind turbine.
Wind ~urbines should be manufactured at lowesl possible cost and be operaled forhigh yields. Although additional measures for preven~ing ice formation should have
no udverse effects as far as pss_" ~e either on manufactur;ng cost or on yields, it
is virrually impossible to prevent en impact on the manufacturing cost due to the
design and construction effor~ tha~ is necess~ily involved. Special desi~n problems
are generated In this connec~ion by rotor blades, which tend to ice up because they
move, unlike fixod components of the wind turbine, and for this reason the
transitions between fixed and movin~ parts of ~hc wind turbine must, as a matterof necessi ty, be given consideration durinçl the design phase with sufficient
eXperTise and attention to safety a~pecTs.
The purpo~~e of Ihe present invention is to provide a me~hod for preventing the
adverse ef1'ec~s resulting from ice forma~ion on ro~or blades, by means of a design
That is as simple a6 possible, and thus cost-efficient, while et the same tirne
effective, Zl5 well as to create a s~iTable rotor blade implementin~ the invention.
CA 02228145 1998-01-28
This purpoE:e i~ achleved by the invention in a rotor blade of the a~orementioned
typH by channelling ~hrou51h ~he cavities o heat t~_ .s~..r medium that has previously
been heated up a litlle~ specifically to appro~ etely + 1~ C to ~ 5~ C.
Ice can form at external temperatures arou nd r- ae~i. na point, e . 9 . between + 2 ~ and
-50 C, but only when ~he concer..r~ion of water va~our in the air is
corre~pondin~ly high. The ~ tl ,od of the present i..~arition advantageously exploits
the fac~ ~hat ice deposited on the rotor blade forms an insula~inçl layer beTween the
surface of Ihe blade and the surrounding air. It is therefore poOsible, with relatively
littl~ thermal inpu~, ~o warm the iced surface of the relevant blade to such an extent
that the ice thaws and falls off ~he rotor blade by itself. The de-icing method of the
invention dloes no~ Involve the rotor blade bein~ heated in order TO prevent iceforminla from ~he very ou~set, as descriL.ed in the aforementioned OE-PS-842 330,
but in~eadl any ice which has alreadv formed i6 ra...o~ed
Ice is forrned on a rotor blade above all at the leadin~ edge, which taces the
direcTion ol sweep, and at the outermost blade tip. Thia is why, in the emb~i..le.ll
ot the invention, the warmed heat transfcr medium i~ channelled, af~er flowing
throu~h a caviTy behind the leadin~ edge and transfer~ thermel ener~ay to the
blade walls,. into a nei.Jl.booring cavity, preferen~ially a cavi~y on the trailing edge
~ide of The blade. from whence it is than extracTsd.
If the rotor blades have reinforL~...en~ rib~ running parallel to the longitudinal axis
of The blade, thes~ can be utllised especi311y well in order to form channels throu~3h
which ~he heat transfer medium can flow, firstly through the leadin~ ed~e eavity,
~here i~ tnansfers its Iherl..al ener~y ro The blade wall and especially thH leadin~
ed~e In order to thaw out any ice which may h~ve formed there. The heat transfermedi~m ~nay s!~bseq!Jently flow th-ough a succ-%sion of other cavities as ~vell
before being expolled Of course, inter con. ,ec~ed cavities may also be es~ablished,
for example by means of embedded or integrated pipos, connector pipes and
similar.
It is particularly advan~ageous to channel ~he hea~ transfer medium firstly into a
section of the blade roo~ ~ha~ is connected to a rotor hub, and a~ the rotor blade tip
to divert it into the rel~van~ cavlty, namel~,r a chamber on the trailin~ ed~e aide, and
back aS~ain to the blade root. This is a vcry simple meshod for e~nsuring cTrculation
of the heaI uan~ter medium within the rotor blade. The air wi~hin ~he rotor blade
rnay be usl3d as a heat transfer medium. ~owever, it is also conceivablo to have
CA 02228145 1998-01-28
rotor blades containin~ 5pecial ga~e~ or vapours with ~,ociric proF~ . ~s ths~ are
more apt for this putpose than air, for example which can rslea~e condensation
hea~ in temperature rangos in which there is a risk of ice fo..,.alion, in ordor to
reduce the ener~y requlfL..,ent for a necessary warming of the hea~ ~ran~fer
medium circulating in the rotor blade. A nc~n-electrically conductive hea~ ~ransfer
medium such as air has a~di~iGual benefits with ra~ecl to li5~hTning prolec~ion for
Ihe wind ~urbine, as opposed to ele~ l heaTin~ u5in9 resi~tance wires, for
example.
In order to warm up the hea~ far medium aS~ain after it has exited the final
cavity, the chamber behind the trailing ed9e of the rotor blade, and to re-channel
it back into ths fir~ cavi~y, ~he chamber behind the leadin~ ed~e, eloctric~l fans as
well as he~cin~ element~ ~r,_n~aad in the flow path of the heat transfer medium may
be used to ;3~ner~-te and m~in~-in the circulation of the heat transfer medium withi
the rotor blade.
Since the fana and any heating elements int~l3rated into the fans a-o loca~ed a~ ~he
root end of the ro~or blade, thev are advanta~ou~lly positioned close ~o Ihe axia of
rotation and therefore ro~ate at a lower sv~ept speed, wi~h the re~ul~ tha~ s~allc and
dynan~ic irnpair",cnt arising fro m the in~tallation of the fans and ~he heatingelements are practically negli_-L 1~. In particulat, this produces ~he advan~age ~ha~
rotor blade~ already designed and constructeo and which heve been ~ried snd
tested in the field do no~ have to be adapted si~nificanlly in terms of their deaign
in order ~o make use of th~ de-icing method of the r~re~enl invention. Cloctrical fans
and healing elements with suitably low power requlrements, and which are fully
adequate for maintaining the eirculAtion of ~he wermsd air through the cav;ties or
chambers within the rotor blado. are small in size end are avalleble es geries-
produced parts.
Similarly, the electrical wirin~ for the cle~l,;cal fans and heating elements installed
in the ro~or blade are simple to impl~m~nr. The amount of elecrrical oner~y required
is relatively small.
In order that de-icing occur au~omaticall~r when ice forms on the rotor blade~ of the
~ind ~urbine. a develGr,~,~,e.,- of ~he ms~hod of the present invention enables
vibra~ions ,du~ to unbalanced massos arlsing from Ice formation on ~he ro~or blades
during wind turbine operelion ~o be detected by measurin~ equipment and
converted into a ~wi~ching signal to stop the ro~or of Ihe wind turbine and to start
CA 02228145 1998-01-28
up the circ~llation of the heat transfer medium in the rotor blad0s and ~he relevant
heatin~ elem~nts where ~FF~Ic~ble, such that after clrculation and ~he l.aatil.~elernents hiave o~,or~t-,~ for a certain predLt~,r... ~ed period, ~he wind tutbine i5
restarted and ~hat these staps ar~ repeated as often as necessPry until Ihe windturbino is able, as a result of de-icinEI, to o~t~c~alu without viLr.-tions.
Measures may be taken so that 1he outside temperature, the temperature of ~he
heat transfor medium, the rotor speed, the wind spood and vibrations are rneasured
and d~tect~d usin~ appropriate sensor~ and proc~sse' in a pro9ram-con~rolls~
automatic ~;ystem to ~onorat~ switchin~ si~nals that initiato and control a de-icing
process .
A rotor blacie sui~able for ;mple .,~ ll;ny the ...etl-od of ~he present invention, for
which sa"a,d~e patent pro~e_~lGn It~ clai.,.ed and whlch has inter-connoc~ed cavi~ies,
is char~ elissd by havinl3 a means for introducin~3 a hea~ uansfer medium inTo a~
leas~ one cavi~y on The leading edge side of the rotor blade cont~i..ed in the blade
root sec~iom, which may be connected to a rotor hub, and that there are flow
channels irl ~he tinal part of the chambers at the rotor tip side which connect
nei~hbouring cavititts and through which the heat transfer medium can flow.
In a ro~or blade embodying the invention, the cavities may be so formed that a
space insicle the rotor blade and enclosed by the blade walls is divided into
ch~rnbers by e~ least one reintorcement rlb running parallel to the longitudinal axis
of ~he blade. with at least one chamber on the leodin~ ed~e sido and one chamberon The ~ralling edge side.
The connecting flow channele may be simple openin~s in the reinforcement ribs
separating the cavities and/or chambers. If the heat~ransfer medium is In~roducs~
In~o ~he chamber on the leadin~ edl3s ~ide of ~h- root sec~ion of the rotor blade, the
medium flows throuçlh ~ho leadin~ edlae che."bcr towerds the end section at the
ro~or ~Ip, from whence it cross~s over into ~he nei~hbouring chamber",. ~,ferentially
~h~s chamber on the trailinE1 edS~e ~ide, in which it can then flow ba~k, for example,
to the root section of the ro~or blade.
1~ jS alBO possible, of course, to form the ~low chennels in the rotor bl~de in the
blade tip area in such a way that the heat transfer rnodium circulaTe~ Throu~hou~
~he entire ~~nd soction of the rotor blede interior at the rotor tip.
CA 02228145 1998-01-28
The means for introducing a heaT transfer medium comprise at least an electricalfan with imr-~int~d heatin~3 ~le...ents, whereby the suction side of e0ch fan adjoins
a final cavilty in the circulation flow, the trailin5~ edpe chamber, and the presRure
side of each fan adJoins the first caviTy, namely ~he leadinla ed~e chamber.
Electric;al fans with inteSIrated heatin~ elem~nt5 c3n be advant~3eously of suchsmall size that They can be mounted without problerns, also In a multiple
altLn~e...ent, in ths inTsrior of a ro~or blade, nsmely in ~he root section. The output
of e~ven thel smallesl ~lec~-ical fJn~ should be sur1.eien~ to iniTiaTe and maintain a
circulation of air throu~h the caYities in the rotor blade. Simple resistance heaters
with heating coils or similar tnay be used as healin~ ol~s.oorit5 intoEIrated in each
fan. Shouldl it transpire that the o~Jtput of an ele_~.ical fan with heatin~ elemenes
is not suffici~nt, s~vefal suitably low-sized fan6, oach with into~ral~sd hoating
elements, rnay be con~bined in a sin~le assembly unit so that the ousput levels of
the fans so~FI~ nant each other.
In order to l~nsuro op~lmsl circ~'etion throughout the interior of the rotor blade, the
end of the leadin~ ed~e cavi~y ei~ua~ed al the root end of the rotor blade can be
sealed off by means of a sealing cover from the inslde space that o~en6 into thetrailin6 ed~e cavi~.
The sealin~l cover may be used to special advanta~e as a rnount fot the electrical
fans with heatinl3 elements, o~/ havin~ at least opening into which ~ shaft section
with integratod f~n is fitted.
Each shafT ~ec~ion i- fitted into a hole in the sealin9 cover in such 8 wsy thst it is
sloped towards the leading edge and protr-ldes inTo the leadln5~ edge chsmber. The
air flo~lv ~cner~ed when the fan is op~retinç,~ is ~hus directed towards the leading
ed~e and ia located at an advan~3~eous distance from the root section of the rotor
blad~, Thu~, proventing unwanted ~,varmin~ during de-icing. Tubing, for example,could be u~ed a~ shaft elements.
I lea~ losses can be furth~r reduced by fittin~ insulating material betweon tho inside
of the blade root and the blad~ adapter for cGr".eclin~ the blade to the rotor hub.
~his in~erior cladding may be, for e~ample, a foam sheet specially moulded to fit
into ~he root end of the rotor blade and whieh ~t~nds roughly parallel to the sealin~
cover.
If ~he sealing cover is ~imilsrly constructed of insulating ma~erisl, Ihe inside space
on the suction side of the fan is insulated to a considerable e~tent.
CA 02228145 1998-01-28
An embodilment of the ;..~.,.li...- illustrating additiGnsl features of th~ invention is
shown in the drawin~s. These show:
Fig. 1 a lon~itudinal ~ec~ion of ths root area of The rotor blade
Fig. 2 a cross s6_tional view of a rotor blade along the line ll-ll in Figure 1
Fjg, 3 a cross-sectional vie~v of the rolor blado alon~ the line 111-111 in fi~ure
1 and
FiEI. 4 a circ~it diagram fot an automa~ic system to control the de-icinl3
~,rocass.
Figure 1 shows the lo ~ver part of a rotor blade, i~8 root soction, in a schematic
longi~udinal ssction. ~rrow I i..r 9t4~ the incid~ wind J;,~-tion, and thus points
to the leading ed~e 2 of the rotor blade. The tralling edSIe is marked with the
numeral 3.
The roTor blade is connected to a rotor hub (not shown in the diagram) by means
of a blade adapter 4, to which the blade root is attached A foam sheet 5 is
insert~d between the blade root and the blade adapter 4.
The rotor bl~de is hollow, and tho inside space 7 cnclo~s1 by tho outer blade
walls ~3 is divided by at lea6t one rdinforce.,.ent rib 8 (plus 8a, 8b where relevant~
runninE~ parallel to the longitudinal axis of The blade into chambers, compri~in~ at
least one :hamber 9 situated behind ~he loadin~3 ed~e of the blade and one
chamber 10 situated behind the trailin~ edl3e of the blade. The reinforcement rlb 8a
ends shortl~r before tho rotor blado tip 1 1. Arrow 12 Indica~e6 th~ presence of a
connectOr channel located near the blade tip 11, loadin~ from the leading edgs
chamber 9 to the trailing edge chamber 10.
The end of the leadin~3 ed~3e chambHr 9 situated Tn the root section ot the rotor
blado, as well as, in this embodiment, the ncigl .Louring chamber situatod betwoen
the reinforcement ribs 8 and 8a ~which chamber pe, rGr,.,~ no function~, ate sealed
off by means of a sealin~ cover 13 from the inside spece 7 open to the trailing edge
chamber 1 0 .
The sealin~ cover ~orves a~ fl mount fot shaft soctions 14, 15, which ~lope
~oward~ ~he leading edge 2 and which protrude into the leadin~ edge chamber 9.
CA 02228145 1998-01-28
Each shatt ~ection contains a fan 1~ and 1 ~i' with an integrated heating olemem.
Numeral 1 J referQ ~che.l.atically to the wiring for supplying the fan and the heaTin9
elHments ~~Jith sle .,ici.~,n
Fi~ure 3 shows a cro~is-sectional view of the root section of the rotor blade along
the line 111-1111 in Figure 1. Tho same components are marked again with the same
numerals.
Fi~ure 2 ~hows a cross-sectional view of tllo rotor blade ~lon~ the line 11-11 in
Fi~ure 1 . The same compc...ents are mariced with the san e nu~ner~ls as in Figure 1.
Figure 3 shows clearly that the sesling cover 13 ~erves as the moun~ for a total of
four shaft olen.~nl~ 14, 15 ~and 1~', 15' where relevan~. The shafT elemenrs 14,15 end 14', 15' containing the fms are fitted into a mount inQert 18, which in turn
can be flush-fitted as a unit into a corres~,ondin~3 oponinEI 19 in the sealing
cover 13, which serves as a holder for the mount insert 18.
Figure 4 shows a schematic circuit dia~ram for an embodiment of e control systemfor controlling the de iciny of three rotor blades of a wind turbine. E~ch rotor blade
19, 20 ancl 21 ib repres~n~ed by a rectan~ular field bordered by broken lines and
co-responcls in its embodimen~ to a rotor blade pursuant to Figures 1 to 3. Eachrotor ~l~de cont~ins s~ns~rs 22, 23 and 24, where relevant, for rneasuring the
~e,.,p~ tule of a heat transfer medium. Similarly, each rotor blade 19, 20 and 21
contains electrical fans 25, 26 and 27 (corrHspondin~ to f~n5 1 ff ~nd 1 fi' in Fig. 1),
each of v~l~hich contains the associeted heatin~ element 28, 29 and 30 in a
combined unit, wheroby the unitb form a meanb for introducin~ a heat transfer
medium into the leadin~ edge chamber of the respective rotor blade, the
te" ,p~r~ture of which medium Ib meaeured wi~h ~snser~ 2Z, 23 and Z4
respectively. Measurement of the ~emperature of the hea~ ~ransfer msdium usin~
sensors 22, 23 and ;24 se~vOs ~o monitor the functional o~er~liGn of fanb 25, 26,
27, of healting elements 28, 29 and 30, a~ well es to protect the rotor blades
against overheatinE~-
Temperatures areenquired byme~snsof apro~ coi,~,ol'ed automa~ic system 31.rhe progralm-controlled automaric sysrem al~o measures ~he ou~side ~emperature
with sensor 32, the wind speed wirh sensor 33, the rotor speed with sensor 34 and
vibrations buch as ~owsr oscillations with sensor 35.
As soon a!s the wind speed is sufficicnt for operating the turbine and the outside
tempera~ure is within e range where Ice may form on the roTor bladeb, ~he unir
CA 02228145 1998-01-28
comprislns~ the heatin~ elcments ~nd fans in eaCh rotor blade are activated by the
autom0lic control system. After a cer~aln interval, the ~,vind turbine is started. If
there is an iimbalance in the rotor due lo uneven ice formation on the rotor bl~ad~s,
~he resultant vibration i5 detected when the rotor is turnin~ by measuring th~ tower
oscillations, at which the turbine i~ switched off and the cie-icin~ o~ the ro~or blsdes
is repeated when the rotor has ~t~FF~Fi-
