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Wasserbaukolloquium 2009: Wasserkraft im Zeichendes Klimawandels

Dresdener Wasserbauliche Mitteilungen Hef t 39

In ta k e F lo w Prob lems a t L o w - H e a d Hydropower

Pet r Lichtneger

The questions o f intake flow conditions mostly associated with low-head run-off-river plants a re discussed in th e paper. A s an example a n intake flow non-

uniformity and the arising problem with shaft vibration is presented to documentth e flow influence. Finally the IFLOW project is introduced which is going to dealwith intake flow phenomena and possibilities o f their simulation an d optimisation.

Im Beitrag wird die Problematik de r Einlaufstfmung diskutiert, die am meistenm it Wasserkraftanlagen de r niedligeren Fallhehen verbunden ist. Am Beispielwerden e ine Anstr6mungsungleichmaBigkeit un d die entstehenden Probleme m itWellenvibrationen priisentiert, unt die Wirkung de r Str6mung zil dokumentieren.SchlieBlich wird das Projekt IFLOW vorgestellt, da s sich m it der Einstramungs-problematik und den M6glichkeiten de r Strdmungssimulation un d Optimierungbeschitigen wird.

1 I n t r o d u c t i o n

A n effect ive exploitation o f renewable resources has been increasinglyaccentuated in th e r ecen t years. Operators o f th e existing w a t e r p o w e r plantstherefore carry out overhauls in order to increase th e efficiency and output of amachine. Firs t of all, it is th e m o d e r n i z a t i o n o f th e turbine hydraulic profile, i. e .modernizat ion o f th e runner. However, the desired efficiency and turbine outputm a y be r educed by hydraulic losses in an incorrectly profiled intake part. Apartf r o m these, there are other character is t ics of impropriate hydraulic condit ions:

- Formation o f free surface vortex accompanied by a ir entering th e turbinew a t e r passage;

- Increase in vibra t ion caused by addit ional r a d i a l forces, as a result o f non-u n i f o r m inf lux on th e runner.

High-head w a t e r p o w e r plants usually h a v e their intakes designed in accordancewi th

well-provenmethods. However, with low-head run -o ff

p o w e r plants(usually equipped with a Kaplan turbine) w a t e r in take s t ructure geometry can

v a r y significantly from case to case.

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8/11/2019 Intake Flow Problems at Low-Head Hydropower

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In take F l o w Problems atLow.Head Hydropower

U n d e r optimal working condi t ions o f a w a t e r machine th e streamlines an d the

guide vanes surfaces should be parallel; otherwise an a d d it io n a l l o ca l loss occurs

on th eguide

vanes. Non-uni form inf lux causesirregular

load on th e turbine

runner producing addit ional radial forces acting on the ro to r. Inf lux swirlingstruchires also indicate an improper solution of th e intake configuration design.Strong su/face vortices m a y also suck a ir into th e turbine w a t e r passage, thus

adversely affecting th e turbine efficiency a nd vibrat ion.

2 A case ofirregular in take f low a t run-off-r iver power plant

A particular case o f irregularity o f intake f low a t a run-off w a t e r p o w e r plantwill be presented here. The ill-designed intake st ructure induces a non-uniform

loading o f th e turbine and it s increased leve l in shaft vibration. The objective

hydro p o w e r plant Vr a n e (1936) w i t h tw o ver t ica l units with Kaplan turbines

an d th e generating capacity o f 2 x9 M W is situated on a right bank o f VltavaR i v e r in Czech . T h e n e x t figure s h o w s th e H P P locat ion on a satellite picture.T h e c o nn e ctio n to th e m a i n r iver bed is i l lustrated there as wel l as th e wake zone

a t th e wei r pile which seems to be th e essential problem o f th e flow irregularityas will be demonstrated b e l o w.

Figure 1 The H PP Viane Situation

Af te r th e Unit N r. 2 (the left one a t th e wei r pile) was refurbished in 2007 th e

commissioning and field acceptance tests were d o n e to verify th e hydraulicm a c h i n e condit ion. Surprisingly a higher l eve l o f shaft vibrat ion occurred a t

t u rb ine r ad ia l bearing. A causal study brought an explanation in th e uneven flow

a t entrance section o f th e pressurized part o f th e turbine w a t e r passage.

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WasserbaukolIoquium 2 0 0 9 : Wa s se rk ra f t im Zaichen de s Klimawandels

Dresdener Wasserbauliche Mit[eilungen H e f t 39

2 .1 Fiow m e a s u r e m e n t

During the turbine efficiency m e a s u r e m e n t th e discharge was gauged w ith O T Tc u r r e n t meters . A hor izonta l frame wi th 12 current mete r s was slowly draggedd o w n an d up across th e cross-section in grooves o f inspection gate behind th e

fine rack. T h e f low measurement was done in accordance wi th th e direct

integration m e t h o d (refer to IS O 3354). Thus th e perpendicular mean velocit iesin 12 perpendiculars were measured fo r th e d o w n a n d up direction separately,which were then integrated across th e width to de te rmine th e total flow rate.B eca use th e intake structure was split into tw o channels to ach ieve smaller

inspection gate area, a ll m e a s u r e m e n t s were done twice, in th e left and in th e

right i nt ak e c h a n ne l. T h e result char ts showing th e distr ibution o f perpendicularmean velocity across th e intake w i d t h presents th e Fig. 2 . T h e re d shaded

regions an d arrows document th e influence o f th e running un i t no. 1 on th e un i t

no. 2 w h e n the f low distr ibution goes to the right slice ye t more. W h e n runningu n i t no. 2 only th e right to le f t s lic e f low rat io equals to 1.25 fo r a ll discharges(from 25 to 94 m /s), w h e n running both th e uni t no. 2 a nd no.1 th e ratioincreases to 1.35 (2x40 m /s).

1-136=7

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f1 0

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