Download - Guide Vane Assembly Mechanism & its Function
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Guide Vane Assembly-Mechanism& its Function
By
Er NC Goyal
Former Chief Engineer,PSEB
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Guide Vanes
Guide Vanes arc installed in the turbine to regulate the quantity of water to the runner with change in load.
These are operated by two servomotors through guide vane operating mechanism via links & levers.
The servomotors get signals from Governor. The guide vanes are of aero flow section, which allows the
flow of water without formation of eddies in all positions. Depending upon silt flow, the guide vanes may be made of
mild steel or stainless steel with integral machined stems, which are drilled for grease lubrication of bushes.
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Guide Vanes
In case of mild steel castings, stainless steel liner is provided on the mating surface.
The guide vanes rotate in three bush bearings. The top two are located in the head cover&the
bottom is in the pivot ring slot. These bushes were earlier made of gun
metal/bronze& lubricated externally with grease through grease passage in the guide vane itself.
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Guide Vanes
The present trend is to make upper bushes grease lubricated & the bottom of ferobestos material, which is self lubricated.
During renovation of Bhakra right bank powerhouse, M/s. T.P.E. Russia has supplied Teflon coated bushes, which do not require any greasing.
Ferobestos self-lubricated bushes have not been successful in some silt -effected power plants & have been replaced with grease lubricated bushes at Chhibro of U.P.S.E.B.& Dehar of BBMB.
Each guide vane is provided with a thrust collar to carry weight of the vane & resist any upward thrust.
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Guide Vanes
Arrangement is also made for adjustment of vertical clearance between the vane & top cover / pivot ring.
A stuffing box is provided at middle &. lower stem to prevent leakage of water through clearance between bush & stem.
These days, generally chevron packing are provided on the middle stem & rubber cup sealing on the lower stem.
The present trend is to provide middle seal replaceable with out dismantling guide apparatus.
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Operating –Ring
Pit-Liner
GV
By-pass valve
Spiral
DT Cone
DT
Servo-motors
Head cover
Exit
Links & Levers
FrancisBlades
Francis Turbine
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Stay Vane
Spiral Case
Francis Runner
Wicket gate
Shaft
Draft Tube
Servomotor
Head Cover
Bottom Ring
Operating Ring
Francis Turbine
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Head Cover
Operating Ring
Servomotor
Wicket Gate
Bottom Ring
Lever
Frances Turbine Distributor
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Maintenance Of Guide Vanes
The maintenance of guide vanes is clubbed with the rest of the machine.
Over hauling may have to be done after 1-3 years in case of silt effected power plants & 5-7 years in other cases.
There may be power plants where arrangement exists for taking out guide vanes without dismantling machine. In such silt effected power plants, over hauling may be done every year. For all silt effected new power plants, provision should be made for removal of guide vanes without dismantling turbine.
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Maintenance Of Guide Vanes
It can be done by lifting turbine cover & lowering the guide vanes with chain pulley blocks.
A good lathe & shaper machine for accurate machining of stem, face & mating surface of guide vanes is very necessary. Similarly a wooden / steel template made from a new guide vane profile is also very necessary for ensuring correct profile of vanes.
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Maintenance Of Guide Vanes
MONTHLY MAINTENANCE:Check for free flow of grease to bushes.Check leakage from guide vane stem packing. If
excessive,then press/replace the packing. It may have to be replaced biannually in silt-
effected power plants.
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12Diagram Of Guide Vane And Adjoining Turbine Parts
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Maintenance Of Guide Vanes
Annual Maintenance:i) GREASING: - Normally, greasing of guide vane bushes is done daily
with the help of centralized greasing system from the top stem of each vane.
The grease should reach whole areas of the three bushes. During routine inspection, check from pivot ring that
grease is actually reaching the middle&lowest bushing. If not then dismantle the grease nipple & clean the grease
hole in the guide vane with a thin wire brush/GSL
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Maintenance Of Guide Vanes
ii) MATING SURFACES: - First check mating surfaces with the help or straight
edge& carry out correction whenever due with the help of welding, grinding & polishing.
Check clearance between mating/bedding surfaces when in fully closed position without giving any pinch or servo motor oil pressure.
Normally there should be no gap.
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Maintenance Of Guide Vanes
Maximum permissible is 0.1mm. Weld repair the same in case it is more than 0.1 mm.
After grinding, check with straight edge.Leakages through guide vane not only
waste water & hence energy but also makes the stopping of machine difficult.
III) Weld repair other surfaces also.
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Maintenance Of Guide Vanes
IV) FREE MOVEMENT OF GUIDE VANES: -Measure upper& lower gaps(Fig).
These should be as per manufacturer's recommendations. Generally the minimum value is 0.1 mm & maximum value
is 0.4 mm. The values would increase due to erosion/corrosion. In silt-effected power plants, these would increase very much
but almost nothing can be done without taking these out. If vanes are not moving freely due to unequal upper & lower
gaps, adjust with adjusting bolts. It needs lot of care as other adjustments are also affected.
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Maintenance Of Guide Vanes
v)STEM PACKING: - Check guide vane stem packing. Replace annually in silt
effected power plants. In silt free plants, take action based on experience so that no shut down on this score has to be taken during the year.
An idea of condition of stem packing can be had from leakages. If it is very less say less than 100 c.c. per minute, then packing is very tightly pressed. If it is more than 700-800 c.c. per minute, then the packing needs retightening/replacement.
Check tightness of all bolts & nuts. Since these are not easily approachable during annual maintenance, check by hammering.
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Maintenance Of Guide Vanes
Vl) WEAROF STEMS AND BUSHES:- Check wear of stems&bushes by pushing some
guide vanes at random by a 5 ton jack in two directions & measure movement by dial indicator.
Though no remedial measure can be taken during annual maintenance, yet their condition would be known.
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Maintenance Of Guide Vanes
Capital Maintenance/Over Hauling:-
Carry out all checking as described under annual maintenance thoroughly at appropriate stage of over hauling.
Greasing: Clean all grease passage & pipes with brush and kerosene oil thoroughly& ensure that no dried grease flake is sticking. Fresh grease should flow freely to all require places.
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Maintenance Of Guide Vanes
Weld Repairs: Weld repair whole of guide vane. Machine, grind &
polish it to exact manufacturer's drawling. Check mating surfaces with a straight edge. The clearance between adjacent mating surfaces should
be nil. The profile should also be as per original. For this, check with template. Check up proper machining & dimensions of guide
vane stems.
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Maintenance Of Guide Vanes
IF THE STEMS ARE NOT EXACTLY STRAIGHT AND OF CORRECT DIMENSION, THEN LOT OF DIFFICULTY WOULD ARISE AT THE TIME OF ASSEMBLY.
If lathe machine is not accurate, then check deformation as per Fig
If provision for S.S. liners has been made, then replace the same as the opportunity for next replacement would come only on next capital maintenance
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Maintenance Of Guide Vanes
If provision does not exist, then for silt-effected power plants, consult manufacturers for making the provision at site.
At the time of final assembly, ensure that upper & bottom clearances are as per manufacturer's drawing/design.
If S.S.liners are provided then after replacement exact dimensions would be achieved.
Keep a record of damage to the guide vanes.
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Guide Vane Bushes
ANNUAL MAINTENANCE: Practically no annual maintenance is possible as these are in accessible without dismantlement of guide vanes. However ensure free flow of grease.
CAPITAL MAINTENANCE: - i) Check the play of guide vane stem in the bushes by
measuring outside dia. Of stem & inside dia. of bush. If the gap is more than permissible (Generally less
than0.2mm), replace bushes. Even if the gap is within limits & from experience it is
observed that by the next capital maintenance, it would exceed normal values,these should be replaced.
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Guide Vane Bushes
ENSURE ACCURATE DIMENSIONS AND CIRCULARITY 0F THE BUSHES OTHERWISE GREAT DIFFICULTY WOULD BE EXPERIENCED DURING REASSEMBLY.
A LOT OF GRINDING OF THE BUSHES ANDHOUSING HAVE TO BE DONE TO FIT THE BUSHES AND ENSURE FREE MOVEMENT OF GUIDE VANES.
IT IS BETTER TO SPEND SOME MORE TIME AT THIS STAGE THAN WASTE TIME LATTER ON DURING ASSEMBLY.
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Guide Vane Bushes
• ii) FITTING OF THE BUSHES: -The bushes are fitted in the bush housing provided in the head cover & pivot ring.
Different methods are adopted in different power plants& some of these are as follows:
a) At some places,these are shrunk by dipping them in liquid nitrogen & are then placed inside the housing. This process takes5-10 minutes.
b) At some places, these are shrunk by using dry ice. c) At some places these are press fitted with the help of
jacks screws,
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Guide Vane Bushes
While using method a & b exact dimensions may be ensured.
If outer dimensions are more, then due to shrinking, the bush would fit in the housing but great difficultly would be encountered while taking these out on next over hauling.
A very tight bush would unnecessarily cause high local stresses on housing & bush body.
In general ensure that proper interfacing is achieved.
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Guide Vane Mechanism
CONSTRUCTION IN BRIEF: The guide ring is fabricated or casted & is supported on
top cover. The rings, its links & levers are strong enough to
transmit power from servomotor to guide vane for normal & emergency closing without any distortion.
The simultaneous movement of all guide vanes during opening & closing is achieved with the help of guide vane operating mechanism.
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Guide Vane Mechanism
The top portion of each stem of guide vanes is coupled to regulating ring by means of links & levers.
The servomotor actuates the regulating ring, which in turn operates all the guide vanes through those links & levers.
The moving parts of the turning mechanism are grease lubricated.
The present day trend is to provide self lubricating PTFE bushes.
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Guide Vane Mechanism
Stops are provided to prevent movement of guide vanes beyond fully open & close position.
Shear pins are provided & designed to fail, if any foreign body gets entrapped between vanes during closing operation.
Stops are provided in the bush housing to limit angular movement of guide vane ,whose pin has broken to prevent its interference with other guide vanes.
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Guide Vane Mechanism
Similarly a lever stopper is fixed to the upper bush housing to prevent lifting of guide vane due to water pressure.
A cover is provided on guide vane lever through which vane is suspended.
This suspension enables accurate adjustment of guide vane top & bottom clearances.
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Guide Vane Mechanism
i) MONTHLY MAINTENANCE: Inspect for free flow of grease to all bushes, guide
rings, links & pins, etc.
ii) QUARTERLY MAINTENANCE: Examine the check nuts on guide vane connecting
links for tightness. Check the fixing keys of all the pins. Clean all links thoroughly.
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Guide Vane Mechanism
iii) CAPITAL MAINTENANCE: Disassemble all levers, bushes etc. & wash thoroughly. Check for any grooves or damage to journal surface of
levers. Repair by welding, grinding & polishing to nearest bore
dia. Check looseness of bushes, wear of pins etc. & set these
right. Finally clean & paint wherever required.
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Thanks for
Patient Hearing