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Flow rate measurements in hydropower plants by means of radioisotopes
International Journal of Applied Radiation and Isotopes, 1967, Vol. 18, pp. 101-I09. Pergamon Press Ltd. Printed in Northern Ireland
Flow Rate Measurements in Hydropower Plants by Means of Radioisotopes M.
K N A P P , S. R E g T A R O V I I 2 1 a n d J. L O N ~ A R I ~ Institut za Naftu Zagreb, Zagreb, Yugoslavia
(Received 15 May
1966)
T h e paper describes how radioisotopes have been utilized to measure flow rates at two large Yugoslav hydroelectric power plants. Measurements taken have provided valuable information about the turbine efficiency and water power value of the plants. T h e advantages of the method, results obtained and hazards involved are discussed.
M E S U R E DES V I T E S S E S D ' E C O U L E M E N T D A N S LES C E N T R A L E S H Y D R O E L E C T R I Q U E S A U M O Y E N DES R A D I O I S O T O P E S La communication ddcrit comment on a utilis6 les radioisotopes pour mesurer les vitesse d'6coulement ~ deux grandes centrales hydrodlectriques jugoslaves. Les mesures achevfes ont rendu des renseignements de grande valeur sur l'efficacit6 des turbines et sur les valeurs de puissance d'eau de ces centrales. O n discute les avantages de la mdthode, les r6sultats obtenus et les hazards qui s'y trouvent.
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STROMUNGSMESSUNGEN
IN WASSERKRAFTANLAGEN
MIT RADISOTOPEN
Der Artikel beschreibt, wie Radioisotopen ftir StrSmungsmessungen in zwei grossen jugoslawischen Wasserkraftanlagen eingesetzt wurden. Die durchgeffihrten Messungen haben wertvolle Angaben fiber den Turbinenwirkungsgrad und die Wasserkraftwerte der Anlagen ergeben. Es werden die Vorteile der Methode, die erzielten Resultate und die auftretenden Gefahren er6rtert. 101
102
M. Knapp, S. Rdtarovid and J. Lon{arid
IN THIS contribution we wish to report on the flow-rate measurement work which consisted of: a. determination of water-power value for a given work regime; b. determination of the turbine efficiency; c. provision of data referring to the loss in water energy within the tunnel conduit system and pipes between storage and turbines, and d. comparison between the degree of efficiency of different turbines. During the symposium on the application of radioisotopes in hydrology--held in Tokio in 1963--it was reported that radioisotopes were applied by a group of French experts in order to measure the flow-rate in hydropower plants, but by using the total count method.
MEASUREMENTS OF T U R B I N E EFFICIENCY AND WATER POWER VALUE IN HYDROPOWER PLANTS I n Yugoslav hydroelectric power production, unofficial acceptance has been made of the rules issued by the Swiss Electotechnieal Society (Schweizerisches Elektrotechnische Verein) which define exactly the methods of measurements and computations of the above mentioned data, mode of results presentation and correction. Turbine efficiency is represented as the ratio between the water power Pw at the turbine ? og 08 07 06 05 0403020.1O-
+
I
20
sb
inlet and the turbine power P,.
The generated power Pa is measured at the turbine outlet. Water power Pw is computed from the equation: Pw --
QgTkw 102
where Q = turbine flow-rate in ma/sec; H = net head of water in m, and 7 = w a t e r sp. gr. = 1000kg/m 3, depending on water temperature and composition. Different types of turbines demand corresponding water net head definition; in principle however, it is obtained by reading the manometer pressure, this manometer being mounted just ahead of the turbine water inlet. Corrections are made of readings with regard to the position of manometer (pressure gauge), dynamic water pressure, and to the water level at the outlet behind the turbines. Flow-rate measurements will be discussed later. Turbine efficiency depends upon the turbine power and measurements have to be made at different turbine powers. The obtained results are expressed in the form r] = f ( P ) . In addition, the correlation of results obtained at individual points can be made correctly only in the case when power and flow-rate values have undergone necessary corrections. These corrections are made after the following
i----
5'o
i
eo
Po(MW) Fie.. 1. Diagram of turbine efficiency r]
=f(Paeorr) corrected,
HPP Nikola Tesla, Vinodol.
Flow rate measurementsin hydropowerplants by meansof radioisotopes
depend on the power and is presented in the diagram kWh/m a = f ( P ) . Here, the power and flow-rate corrections have to be made for each measuring point relative to the constant storage level, i.e. to the design net head. Such a diagram is shown in Fig. 2. It has been drawn according to the results of measurements made in the hydropower plant Vinodol. However, the most important data for both results is the flow-rate, the computation of which is faced with considerable difficulties. The most frequently applied flow-rate measurement method is the one with hydraulic screws (a method recommended by SEV standards ~2)). The hydraulic screw method consists of mounting these screws at a favourable place in the conduit, ahead of the turbine. How many screws will be mounted depends upon the pipeline dimensions. The screws are placed on two crossed bars. Moved by water flow the screws rotate and the flow-rate is determined by their rotation speed and the known conduit diameter at the place where the hydraulic screws are mounted. Screw rotation speed is checked by the known
equations : corrected flow-rate -- Qeorr = Q
r
corrected power = Peo,.,. = P , / ~ " The diagram of dependence between the turbine efficiency and power is shown in Fig. 1. This diagram is based upon measurements made in the Gojak hydropower plant. The power value of water is defined as the number of k w h produced by 1 m 3 of water at a given operation regime of the hydropower plant and a given water level (constant) in the storage. The power value is presented by the following expression :
Po
103
1
power value of water -- Q 3600 kWh/ma (P~ in kW, Q in m3/sec). The computation of the water power value requires the knowledge of the power produced by the turbine, the turbine flow rate and of the storage water level. The power value of water
# kwh_1 m J i
I I
kWh/m~=r(pj
1,500+
"r! "'+
+2
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I
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130o~ i
1,2001
1,100+ I
I
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20
I
30
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40
. . . . .
+
50
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60
-
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70
i:
- - - - H
MW
80 P
FIG. 2. Power value of water and flow-rate as a function of power, HPP Nikola Tesla, Vinodol.
104
A4. Knapp, S. Re~tarovigand J. Longarig
flow-rate before a n d a l t e r m e a s u r e m e n t . A t f a v o u r a b l e w o r k i n g conditions the error t h a t m i g h t occur t h r o u g h a p p l i c a t i o n o f this m e t h o d is 5 p e r cent. H o w e v e r , the o p e r a t i o n of the h y d r o p o w e r p l a n t has to be s t o p p e d a n d the c o n d u i t e m p t i e d before a n d after i n s e r t i n g the m e a s u r i n g screws. O n e o f the m e t h o d s specified a m o n g the S E V s t a n d a r d s is the well k n o w n m e t h o d of flow-rate m e a s u r e m e n t b y salting w a t e r in the conduit. This m e t h o d , however, p r o d u c e s difficulties a n d c a n n o t be r e c o m m e n d e d . I t is k n o w n as ALT.EN'S m e t h o d , (a) two points m e t h o d , or " p e a k " t i m i n g m e t h o d a n d is based u p o n the c o n d u c t i v i t y o f salted w a t e r as electrolyte, w h i c h is m u c h h i g h e r t h a n t h a t of the p u r e water. O n two places in the c o n d u i t , two electrodes are b u i l t in a n d the electrical resistivity is m e a s u r e d . T h e m o m e n t the salt w a t e r reaches the first two electrodes a decrease in electrical resistivity is registered. A c c o r d i n g l y , the time t h a t elapses from the m o m e n t the salt w a v e passes from the first p a i r of electrodes to the second one m a y be c o m p u t e d . I f the v o l u m e of the c o n d u i t b e t w e e n the two p a i r s o f e l e c t r o d e s is known, the flow-rate can be d e t e r m i n e d . O n e of the d i s a d v a n t a g e s of this m e t h o d is in the error i n t r o d u c e d b y the time r e q u i r e d for a d d i n g sufficient salt to the water, i.e. salt h a d to be a d d e d quickly in o r d e r to o b t a i n a clearly n o t i c e a b l e c h a n g e in electrical resistivity. A m o d i f i c a t i o n of this m e t h o d has b e e n c a r r i e d out b y our workers, consisting of the use of radioisotopes i n s t e a d of salt. N o electrodes
are necessary a n d radioisotopes c a n be i n j e c t e d quickly into the water. T h e effect of the now r a d i o a c t i v e wave was very intensive. T h e p a t t e r n a n d a r r a n g e m e n t of m e a s u r e m e n t is seen s c h e m a t i c a l l y in Fig. 3. A t p o i n t 5, radioisotopes are injected b y compressed air. I n j e c t i o n place is not necessarily the gate c h a m b e r as is shown in the figure, it m a y be also a w a t e r oscillations d a m p i n g c h a m b e r (water c h a m b e r ) , t u n n e l inlet or some o t h e r suitable o p e n i n g in the conduit. A t least 15 m below the injection p o i n t the f i r s t - - t h e " u p p e r " - - c h e c k p o i n t is p l a c e d for r a d i o a c t i v i t y m e a s u r e m e n t , a n d further d o w n at a suitable p l a c e is the s e c o n d - - t h e " l o w e r " - .... check point. T h e detectors m a y be l o w e r e d into the w a t e r in the c o n d u i t , or a t t a c h e d onto the c o n d u i t wall (in case m e a s u r e m e n t s are m a d e in a steel c o n d u i t ) , d e p e n d i n g on tile m e a n s of m e a s u r i n g . Detectors m a y be scintillation probes, or t h e y m a y consist of a set of G M - T u b c s . I n o u r case a scintillation p r o b e w i t h 1½- in. crystal a n d a set of five 1 × 15 in. G M - t u b e s were used. Both types o f detectors at the a b o v e - s t a t e d m e a s u r i n g conditions has y i e l d e d a sufficiently h i g h f r e q u e n c y of o u t p u t impulses. E a c h d e t e c t o r was fitted with the r a t e m c t e r . O u t p u t s of r a t e m e t e r s were c o n n e c t e d to a c o m m o n r e c o r d e r a n d the passages of the r a d i o a c t i v e w a v e a l o n g the detectors were registered on tim r e c o r d e r chart. T h e r e c o r d e r charts in Figs. 4 a n d 5 show the m e a s u r i n g d a t a for the big a n d small flow-rate.
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Fro. 3. Block diagram of measurement. 1. Upper check point. 4. Recorder. 2. Lower check point. 5. Gate chamber. 3. Set of instruments. 6. Steel conduit.
105
Flow rate measurements in hydropower plants by means of radioisotopes
20
23 22
18
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72 11
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0 RAI$ /hjected cver 21hr ,5rnm Measurement carried out 2 October/964
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RA/S Injected over Measurement carr/ed out ,5 October 1 9 ~
FIG. 4. Flow-rate measurement in HPP Nikola Tesla, Vinodol. Recorder chart of two 70 M'W measurements.
FIG. 5. Flow-rate measurements in HPP Nikola Tesla, Vinodol. Part of the recorder chart of one 7 MW measurement.
T h e passage time t of the radioactive wave from the u p p e r to the lower detector is c o m p u t e d from the k n o w n c h a r t speed of recorder B ( u n d e r a p e r m a n e n t control) a n d the m e a s u r e d l e n g t h D from the top to the b o t t o m of the radioactive wave registered o n the recorder chart.
tion of the power p l a n t m u s t be kept constant. W e have followed the principle according to which four e q u a l flow-rate m e a s u r e m e n t s are to be m a d e for each power separately, calculating t h e n a m e a n flow-rate v a l u e a n d a s t a n d a r d deviation. Errors in other values result from the total differential d e d u c e d from their f u n c t i o n a l relation. Deviations of i n d i v i d u a l variables i n equations are p r o b a b l y errors i n m e a s u r e d values. W a t t m e t e r s were not used for power measu r e m e n t , b u t readings were taken of g e n e r a t e d power o n k W h meters (tests, however, with wattmeters were made). Sometimes, one flowrate m e a s u r e m e n t took more t h a n 1 hr at small
D W a t e r passage time t = ~- sec. W i t h the k n o w n c o n d u i t v o l u m e V between the two detectors, the c o m p u t a t i o n of the flowrate is m a d e with the e q u a t i o n : Q-
V t -
VB D ma/sec"
D u r i n g the flow-rate m e a s u r e m e n t the opera-
106
~FI. Knapp, S. Rdtarovig and J. Lon~arig
powers. W h e n wattmeters were used, a series of readings had to be m a d e a n d the m e a n value c o m p u t e d . As to the i n s t r u m e n t itself, its size did not allow precise readings. O n the other h a n d , the k W h meters yielded the true average value of g e n e r a t e d power a n d since readings were m a d e in intervals of 15 m i n each, the average power value could have b e e n read j u s t within the time interval w i t h i n which flow-rate was measured. I t m u s t be u n d e r s t o o d that c a l i b r a t i o n a n d type of m e t e r should be given greatest a t t e n t i o n .
MEASUREMENTS MADE AND RESULTS OBTAINED 1. First m e a s u r e m e n t s were m a d e i n the H P P Split on the C e t i n a river. T h e H P P ' s n o m i n a l power is 432 M W a n d its flow-rate 200 m3/sec. I n 1962, however, w h e n the above m e a s u r e m e n t s were done, only 50 per cent of the total p l a n t h a d b e e n constructed. I n this h y d r o p o w e r plant, sixteen flow-rate m e a s u r e m e n t s were m a d e at four different powers, tbur equal m e a s u r e m e n t s for each power level. I n addition, two test m e a s u r e m e n t s were m a d e at the b e g i n n i n g , b u t u n t b r t u n a t e l y were unsuccessful. Nevertheless, they were of a n instructive character to the power p l a n t staff a n d were used to control a n d verify the a n t i c i p a t e d work output. (~) Isotopes were injected t h r o u g h the vent-hole b e h i n d the gate at the t u n n e l - i n l e t of the Praneevidi d a m on C e t i n a river. A special radioisotope injector was constructed for this purpose. So, w h e n the injector had been lowered, radioisotopes were injected into the t u n n e l c o n d u i t directly, b y m e a n s of compressed air. T h e pressure of 20 a t m was applied for isotopes injection which took 2 - 4 see, d e p e n d i n g on the a m o u n t of p r e p a r e d solution. T h e t u n n e l section from the Praneevidi d a m to the water c h a m b e r , some 9"652 m long, 6.10 m in d i a m e t e r a n d a vol. of 281.935 m a was the first m e a s u r i n g section. T h e second section e x t e n d e d from the d a m to the gate c h a m b e r a n d h a d a v o l u m e of 289.538 m a. T h e detection of the radioactive wave passage in the water c h a m b e r was performed, using a G e i g e r - M t i l l e r detector, placed in a special watertight casing a n d lowered into the t u n n e l . A set of such detectors was used i n the gate
c h a m b e r ; they were c o n n e c t e d in parallel a n d a t t a c h e d onto the external wall of the steel pipeline. For each m e a s u r e m e n t some 50 mc of radioisotope Br s2 were injected. Flow-rate m e a s u r e m e n t s in the H P P Split was done with a c o n s u m p t i o n of isotopes a m o u n t i n g to 1200 mc, i n total a n d the o b t a i n e d results are given in T a b l e 1. Flow-rate measurem c n t results c o n t a i n e d in the third c o l u m n are the average values c o m p u t e d out of the four equal measurements. T h e errors shown in the fourth c o l u m n i n d i c a t e a slight dissipation of results. TABLe 1. Flow-rate measurements in HPP Split
Nominal flow-rate (m3/sec)
Power measured in MW
40 86-00 ± 0.10 85 183.0 ± 0.3 100 216.5 ± 0.3 flow-rate max. 227.5 ± 0.3
Final flow-rate Mean measurement standard results deviation (m3/see) (~}~,) 37.8 ± 0.2 81.0 :L 0-4 97.15 ± 0-06
0.5 0-5 0.06
109.0 ± 0-1
0-1
2. Similar flow-rate m e a s u r e m e n t s had b e e n d o n e i n a u t u m n 1963 i n the H P P Nikola Tesla n e a r Rijeka, Yugoslav A d r i a t i c seaport, with a n o m i n a l power of 8 4 M W a n d 16mS/see flow-rate.(5) Forty flow-rate m e a s u r e m e n t s were m a d e for n i n e different powers. Radioisotopes were injected into the c o n d u i t t h r o u g h the water c h a m b e r . T h e l e n g t h of m e a s u r i n g section i n the pressure steel c o n d u i t was 1181.6 m with the v o l u m e of 2499 m a. Same m e t h o d was applied here as it was m a d e i n the H P P Split, b u t the m e t h o d of m e a s u r e m e n t u n d e r w e n t some alterations. I n this case the flow-rate m e a s u r e m e n t s were not started at the p o i n t a n d the m o m e n t the radioisotopes had been injected, as it was done i n the H P P Split; there was a n u p p e r m e a s u r i n g p o i n t for the radioactive wave detection. This p o i n t was some 50 m d o w n stream f r o m the radioisotopes injection point. F o r each flow-rate m e a s u r e m e n t some 20 m c of radioisotope Br s2 or 40 mc of I T M were injected into the pipeline. I n total, the measu r e m e n t s in the H P P Nikola Tesla c o n s u m e d
107
Flow rate measurements in hydropower plants by means of radioisotopes TABLE 2. Flow-rate Measurements in H P P Nikola Tesla, Vinodol
Nominal power (MW) 7 14 21 28 42 56 70 75 76
Flow-rate corrected (m3/sec) 1.402 2.635 3-939 5.36 8.013 11.10 13-97 15.47 16.48
Relative flow-rate error (%)
Total relative error of measurement (%)
0.28 0.45 0.23 0.37 0.06 0.36 0.43 0-19 0.12
0.85 0.74 0.42 0.55 0.20 0-50 0.60 0-35 0.30
-4- 0.004 -4- 0.012 -4- 0-009 ~ 0-02 ± 0.005 -4- 0.04 i 0.06 -4- 0-03 :~ 0.02
s o m e 1000 m c o f r a d i o i s o t o p e Br s2 a n d s o m e 300 m c o f I TM. R e s u l t s o f these m e a s u r e m e n t s a r e g i v e n i n T a b l e 2. T h e f l o w - r a t e v a l u e g i v e n for e a c h i n d i v i d u a l p o w e r is i n fact t h e m e a n ( a v e r a g e ) v a l u e computed out of the four equal measurements. 3. I n D e c e m b e r 1964 f l o w - r a t e m e a s u r e m e n t s were made in the HPP Gojak near Ogulin, h a v i n g t h e n o m i n a l p o w e r o f 50 M W a n d a 50 m3/sec f l o w - r a t e ) 6) H e r e , t h i r t y - t w o m e a s u r e m e n t s w e r e m a d e for n i n e d i f f e r e n t p o w e r s w i t h f r o m o n e to t h r e e t u r b i n e s in o p e r a t i o n . Isotopes were injected into thewater chamber. S e c t i o n u s e d for m e a s u r e m e n t s in t h e p i p e l i n e was 680 m l o n g , w i t h a v o l u m e o f 5441 m 3. Method of isotope injection and the pattern of m e a s u r i n g p o i n t s w e r e t h e s a m e as in t h e H P P Vinodol; however, at the upper measuring p o i n t t h e G e i g e r - M f i l l e r d e t e c t o r s w e r e used,
Power value of water in kWh/m 3 1-387 1.475 1.480 1.451 1.456 1.401 1.392 1.347 1.281
+ 0.012 -4- 0.011 :tz 0.006 -4- 0.008 + 0.003 -4- 0.007 -4- 0.008 -4- 0.005 =. 0.004
while at the lower one the scintillation probe was u t i l i z e d . F o r e a c h m e a s u r e m e n t 50 m c abs. o f r a d i o isotopes I TM w e r e i n j e c t e d . I n this case n o i s o t o p e Br se was u s e d d u e to a r a t h e r difficult c o m m u n i c a t i o n to t h e l o c a t i o n o f m e a s u r e m e n t s , a n d b e c a u s e o f a s p e e d y d e c o m p o s i t i o n o f these r a d i o i s o t o p e s . I n total, 1600 m c o f I TM isotopes w e r e u s e d for f l o w - r a t e m e a s u r e m e n t s in this hydropower plant. T h e results o b t a i n e d a r e s h o w n i n T a b l e 3. T h i s t a b l e c o n t a i n s also d a t a o b t a i n e d for w a t e r p o w e r , t u r b i n e efficiencies a n d w a t e r power value.
RADIATION
HAZARDS
T h e e x p e r i e n c e s has p r o v e d t h a t t h e d i l u t i o n o f r a d i o i s o t o p e s in w a t e r is i n d e p e n d e n t o f flow-rate value, and dependent upon the
TABLE 3. Flow-rate Measurements in H P P Gojak Average turbine power (MW) 0 1.60 5-07 12-0 16"8 23.2 30.4 40.8 48-2
-4- 0'05 ± 0'10 -4- 0.1 4- 0"1 + 0.2 4- 0.2 -4- 0.3 -4- 0'3
Net head 131.3 131.4 130.7 130.0 129.4 128.5 123.7 118.9 112.1
± 0.5 -4- 0-5 -4- 0-5 -t- 0.5 -4- 0"5 -4- 0.5 4- 0.5 -4- 0.5 ± 0.5
Flow-rate mean value (m3/sec) 1"759 2-908 5.84 11.44 15"02 22.05 29.48 40.6 50.1
± 0.009 ± 0.005 ± 0.01 -4- 0.05 -4- 0.04 -4- 0.04 -4- 0.09 4- 0.2 -4- 0.3
Water power (MW) 2.26 3.75 7.48 14.59 19.05 27.78 35.8 47.3 55.1
± 0'02 -4- 0.22 4- 0.04 -4- 0-13 -4- 0.13 -4- 0.16 -4- 0'2 -4- 0.4 -4- 0.5
Turbine efficiency 0 0.427 0.678 0-824 0-882 0.835 0.849 0.863 0.875
± 0.015 ± 0.017 -4- 0.014 -4- 0"011 4- 0.012 -4- 0.011 -4- 0.013 -4- 0-013
Power value of water (kWh/m 3) 0 0.153 0.241 0-291 0.310 0.292 0.286 0.279 0.267
± 0.005 ± 0.007 -4- 0.004 -4- 0.003 ± 0"003 ± 0.003 -4- 0'003 -4- 0-003
108
A,I. Knapp, S. Re~taroviiand d. Londarid
p i p e l i n e size a n d structure, a n d on t h e distance b e t w e e n the m e a s u r i n g a n d injection points. T h e r e f o r e , e q u a l radioisotopes a m o u n t s can be i n j e c t e d into the pipeline, regardless to the flow-rate values. A c c o r d i n g to the radioisotopes quantities t h a t were injected in h y d r o p o w e r plants, t h e n a c c o r d i n g to the o b t a i n e d r a d i o a c t i v e w a v e volumes a n d the p r e s c r i b e d m a x i m u m permissible radioisotopes c o n c e n t r a t i o n in water, it m a y be c o n c l u d e d t h a t an a v e r a g e radioisotope c o n c e n t r a t i o n in the r a d i o a c t i v e w a v e in the pipelines o f the H P P Split a n d Gojak, a l r e a d y was below the permissible, while in the H P P V i n o d o l it was twice as h i g h as m a x i m u m permissible. H o w e v e r , d u e to the fact t h a t d u r i n g the passage of w a t e r u p to the outlet structure of the h y d r o p o w e r p l a n t the r a d i o isotope c o n c e n t r a t i o n gets m o r e a n d m o r e diluted, the conclusion m a y be d r a w n t h a t no dangerous radioisotope concentration developed in a n y of our cases. T h e r a d i a t i o n the personnel of the h y d r o p o w e r plants were exposed to, was so small t h a t it m a y be considered harmless. H o w e v e r , the staff o f the I n s t i t u t e o f P e t r o l e u m t h a t were c h a r g e d w i t h the p r e p a r a t i o n a n d injection of radioisotopes were exposed to strong r a d i a t i o n , for the w o r k was c a r r i e d out b y using a n open radioisotope. Therefore, t h o r o u g h checking was m a d e of r a d i a t i o n o f bodies a n d care was taken not to keep the staff too long exposed to the a c t i o n o f radioisotopes, as well as to keep the r a d i a t i o n sources d u r i n g the w o r k a t a r e a s o n a b l e distance from the staff. O n average, r a d i o isotopes were injected twice a d a y a n d two m e n w o r k e d in a l t e r n a t i o n . CONCLUSION T h e o b t a i n e d results p r o v e the flow-rate measuring method--the peak timing method-to be a g o o d a n d r e l i a b l e as far as it is a p p l i e d in h y d r o p o w e r plants w i t h sufficiently l o n g pipelines o f k n o w n volumes. F u r t h e r m o r e , it has b e e n p r o v e d t h a t this m e t h o d is relatively easy to be a p p l i e d , y i e l d i n g reliable a n d accurate data. As it m a y be seen in the T a b l e s , m e a s u r e m e n t s were m a d e o f the flow-rates from 1-5 to 109 mS/see, a n d the s t a n d a r d d e v i a t i o n never r e a c h e d m o r e t h a n 0"7 p e r cent.
I t should be p o i n t e d out t h a t the p r o b a b l e errors given in the T a b l e s reflect the errors in the flow-rate m e a s u r e m e n t , whilst some f u r t h e r deviations from the real values m a y be introd u c e d b y a difference b e t w e e n a n o m i n a l a n d a c t u a l c o n d u i t volume. T h e v o l u m e of the p i p e l i n e is d e t e r m i n e d ti'om the construction designs of the p o w e r stations. As r e q u i r e d b y the designers, the civil e n g i n e e r ing s t a n d a r d s m u s t not tolerate a n error in two crossed p i p e d i a m e t e r s o f g r e a t e r t h a n 0-5-1 p e r cent w i t h r e g a r d to the respective design value. I f the total d e v i a t i o n w o u l d be due to the d i a m e t e r error, the m a x i m a l sectional or v o l u m e error could a m o u n t to 1-2 p e r cent. H o w e v e r , the d i s c r e p a n c y d u e to the ellipticity of pipes s h o u l d be i n c l u d e d into the m a x i m a l error o f crossed diameters. T h i s d i s c r e p a n c y is to be neglected w h e n the difference b e t w e e n the axes is as small as in this case, since it has p r a c t i c a l l y no effect on the c h a n g e in the p i p e volume. I f we take t h a t on a v e r a g e one h a l f of established deviations result from the scctional error a n d the second h a l f from the p i p e ellipticity, t h e n the m a x i m a l v o l u m e e r r o r for a given p i p e should not be g r e a t e r t h a n 0"5 1 p e r cent. Steel p i p e l i n e of h y d r o p o w e r plants usually consist of 6-10 m long pipes, so t h a t 100 or even m o r e pipes m a k e one m e a s u r i n g section. Since i n d i v i d u a l pipes d e v i a t e from the a c t u a l design value, m a n y positive a n d negative errors will cancel a n d the total error resulting is thus m u c h smaller. T h e r e is one o t h e r factor b y w h i c h the p i p e line v o l u m e can be affected, i.e. the expansion of the filled p i p e l i n e in relation to the e m p t y one. D u e to the w a t e r pressure, the m a g n i t u d e of e x p a n s i o n d e p e n d s u p o n the w a t e r level a b o v e the observed p o i n t of the pipeline, on the w a t e r flow-rate a n d w h e t h e r the p i p e l i n e is selfs u p p o r t e d , p l a c e d in concrete or in the rock. T h e difference in t e m p e r a t u r e b e t w e e n the full a n d the e m p t y pipeline m a y also be the cause of its e x p a n s i o n or shrinkage. W h e n a p p l y i n g this m e t h o d , the v o l u m e e r r o r is considered systematic w h e r e b y all results get shifted for the same relative value, so t h a t the relations b e t w e e n the results o b t a i n e d at given m e a s u r i n g points a r e not affected b y this error.
Flow rate measurements in hydropower plants by means of radioisotopes
T h e advantages this method will have in its future application lie in the fact that, should in the case of designing a hydropower plant, a provision be made for the measurement of turbine efficiency by means of radioisotopes, the volume error could be eliminated and the precision of flow-rate measurements would comply with the values given in Tables 1-3. For instance, by measuring the volume of pipes just prior to their placing, the volume of etnpty pipeline m a y be exactly determined. T h e expansion of the pipeline due to the stress m a y be determined and its value, during the test operation of the plant, m a y be found by means of Tensometer mounted onto the pipeline wall. This m a y be also used during the pressure tests when water is p u m p e d into the closed pipeline resulting in dependence of pressure upon the pumped-in quantity of water (respectively upon the change of pipeline volume). This method suits fully the prescribed way
109
of measuring the turbine efficiency in hydropower plants, whereby the correctness of the manufacturers' guarantees is verified. In addition, this method m a y be applied for the measurement of flow-rate in any pipeline where the volume of one of its sections is known. REFERENCES 1. SIA Normen fiir Wassermessungen bei Durchfi~hrung yon Abnahmeversuchen and Wasserkraftmaschinen. Auf-
gestellt yon SIA, Ztirich (1924). 2. Schweizerische Regeln fiir Wasserturbinen, Bull. SEV
48, No. 3 (1957). 3. ALLENG. M. and TAYLORE. A. Trans. Am. Soc. l~Iech. Eng. 14 (1923). 4. Report on Flow-Rate 3Ieasurements in HPP Split,
Institute of Petroleum, 7m~reb (1962). 5. Report on Flow-Rate ~le,l~wements in HPP ~Tnodol,
Institute of Petroleum, Zagreb (1963). 6. Report on Flow-Rate Measurements in HPP Gojak,
Institute of Petroleum, Zagreb (1964).
Flow Rate Measurements in Hydropower Plants by Means of Radioisotopes M.
K N A P P , S. R E g T A R O V I I 2 1 a n d J. L O N ~ A R I ~ Institut za Naftu Zagreb, Zagreb, Yugoslavia
(Received 15 May
1966)
T h e paper describes how radioisotopes have been utilized to measure flow rates at two large Yugoslav hydroelectric power plants. Measurements taken have provided valuable information about the turbine efficiency and water power value of the plants. T h e advantages of the method, results obtained and hazards involved are discussed.
M E S U R E DES V I T E S S E S D ' E C O U L E M E N T D A N S LES C E N T R A L E S H Y D R O E L E C T R I Q U E S A U M O Y E N DES R A D I O I S O T O P E S La communication ddcrit comment on a utilis6 les radioisotopes pour mesurer les vitesse d'6coulement ~ deux grandes centrales hydrodlectriques jugoslaves. Les mesures achevfes ont rendu des renseignements de grande valeur sur l'efficacit6 des turbines et sur les valeurs de puissance d'eau de ces centrales. O n discute les avantages de la mdthode, les r6sultats obtenus et les hazards qui s'y trouvent.
H 3 M E P E t t H H H A P A M E T P O B I I O T O H A I I P H IIOMOIIIH P A , / I H O A H T H B I I b l X H3OTOIIOB tIA FH,~PO33IEHTPHItECHHX CHJIOBblX ~:CTAItOBHAX ~IoHaaA OrI~tCMBaeT HaK IICIIOJlb3OBa~'IHCt, pa~ttOaHTIiBHMe II30TOHM ~JIYI laaMepeltHg impaMeTpoB IIOWOHaHa nByx 6oJI~mnx I O r o e a a n e ~ . x rnXpoaJIetCTp~iqecmlx CH~IOBbIXycvanOBl~ax. IIozIy~emu,m HaMepeHH~ ~aa~I aeHHyIO IIH(~OpMaILIIlO,KacaIomyIoc~ t~oa~)(~nlI~IeHwa IIOJI08HOFO ~OfICTBH/I T y p 6 H H b I H 8HaN0ttI4H MOUlHOCTtl BO,l~IoI OTtlX yCTaHOBOH.
06cymAaloTeH IIp0HMylIIeCTna ,~atIHOrO MeTO)la, HoJIyq0HHBI0 peuyJIbTaTH H BO3MO~HHt,Ie oIIaCHOCTH.
STROMUNGSMESSUNGEN
IN WASSERKRAFTANLAGEN
MIT RADISOTOPEN
Der Artikel beschreibt, wie Radioisotopen ftir StrSmungsmessungen in zwei grossen jugoslawischen Wasserkraftanlagen eingesetzt wurden. Die durchgeffihrten Messungen haben wertvolle Angaben fiber den Turbinenwirkungsgrad und die Wasserkraftwerte der Anlagen ergeben. Es werden die Vorteile der Methode, die erzielten Resultate und die auftretenden Gefahren er6rtert. 101
102
M. Knapp, S. Rdtarovid and J. Lon{arid
IN THIS contribution we wish to report on the flow-rate measurement work which consisted of: a. determination of water-power value for a given work regime; b. determination of the turbine efficiency; c. provision of data referring to the loss in water energy within the tunnel conduit system and pipes between storage and turbines, and d. comparison between the degree of efficiency of different turbines. During the symposium on the application of radioisotopes in hydrology--held in Tokio in 1963--it was reported that radioisotopes were applied by a group of French experts in order to measure the flow-rate in hydropower plants, but by using the total count method.
MEASUREMENTS OF T U R B I N E EFFICIENCY AND WATER POWER VALUE IN HYDROPOWER PLANTS I n Yugoslav hydroelectric power production, unofficial acceptance has been made of the rules issued by the Swiss Electotechnieal Society (Schweizerisches Elektrotechnische Verein) which define exactly the methods of measurements and computations of the above mentioned data, mode of results presentation and correction. Turbine efficiency is represented as the ratio between the water power Pw at the turbine ? og 08 07 06 05 0403020.1O-
+
I
20
sb
inlet and the turbine power P,.
The generated power Pa is measured at the turbine outlet. Water power Pw is computed from the equation: Pw --
QgTkw 102
where Q = turbine flow-rate in ma/sec; H = net head of water in m, and 7 = w a t e r sp. gr. = 1000kg/m 3, depending on water temperature and composition. Different types of turbines demand corresponding water net head definition; in principle however, it is obtained by reading the manometer pressure, this manometer being mounted just ahead of the turbine water inlet. Corrections are made of readings with regard to the position of manometer (pressure gauge), dynamic water pressure, and to the water level at the outlet behind the turbines. Flow-rate measurements will be discussed later. Turbine efficiency depends upon the turbine power and measurements have to be made at different turbine powers. The obtained results are expressed in the form r] = f ( P ) . In addition, the correlation of results obtained at individual points can be made correctly only in the case when power and flow-rate values have undergone necessary corrections. These corrections are made after the following
i----
5'o
i
eo
Po(MW) Fie.. 1. Diagram of turbine efficiency r]
=f(Paeorr) corrected,
HPP Nikola Tesla, Vinodol.
Flow rate measurementsin hydropowerplants by meansof radioisotopes
depend on the power and is presented in the diagram kWh/m a = f ( P ) . Here, the power and flow-rate corrections have to be made for each measuring point relative to the constant storage level, i.e. to the design net head. Such a diagram is shown in Fig. 2. It has been drawn according to the results of measurements made in the hydropower plant Vinodol. However, the most important data for both results is the flow-rate, the computation of which is faced with considerable difficulties. The most frequently applied flow-rate measurement method is the one with hydraulic screws (a method recommended by SEV standards ~2)). The hydraulic screw method consists of mounting these screws at a favourable place in the conduit, ahead of the turbine. How many screws will be mounted depends upon the pipeline dimensions. The screws are placed on two crossed bars. Moved by water flow the screws rotate and the flow-rate is determined by their rotation speed and the known conduit diameter at the place where the hydraulic screws are mounted. Screw rotation speed is checked by the known
equations : corrected flow-rate -- Qeorr = Q
r
corrected power = Peo,.,. = P , / ~ " The diagram of dependence between the turbine efficiency and power is shown in Fig. 1. This diagram is based upon measurements made in the Gojak hydropower plant. The power value of water is defined as the number of k w h produced by 1 m 3 of water at a given operation regime of the hydropower plant and a given water level (constant) in the storage. The power value is presented by the following expression :
Po
103
1
power value of water -- Q 3600 kWh/ma (P~ in kW, Q in m3/sec). The computation of the water power value requires the knowledge of the power produced by the turbine, the turbine flow rate and of the storage water level. The power value of water
# kwh_1 m J i
I I
kWh/m~=r(pj
1,500+
"r! "'+
+2
I
Vao-
~'N
I
+1o
130o~ i
1,2001
1,100+ I
I
/,0oo~
---
I
I0
I - -
20
I
30
I
40
. . . . .
+
50
I
60
-
I
70
i:
- - - - H
MW
80 P
FIG. 2. Power value of water and flow-rate as a function of power, HPP Nikola Tesla, Vinodol.
104
A4. Knapp, S. Re~tarovigand J. Longarig
flow-rate before a n d a l t e r m e a s u r e m e n t . A t f a v o u r a b l e w o r k i n g conditions the error t h a t m i g h t occur t h r o u g h a p p l i c a t i o n o f this m e t h o d is 5 p e r cent. H o w e v e r , the o p e r a t i o n of the h y d r o p o w e r p l a n t has to be s t o p p e d a n d the c o n d u i t e m p t i e d before a n d after i n s e r t i n g the m e a s u r i n g screws. O n e o f the m e t h o d s specified a m o n g the S E V s t a n d a r d s is the well k n o w n m e t h o d of flow-rate m e a s u r e m e n t b y salting w a t e r in the conduit. This m e t h o d , however, p r o d u c e s difficulties a n d c a n n o t be r e c o m m e n d e d . I t is k n o w n as ALT.EN'S m e t h o d , (a) two points m e t h o d , or " p e a k " t i m i n g m e t h o d a n d is based u p o n the c o n d u c t i v i t y o f salted w a t e r as electrolyte, w h i c h is m u c h h i g h e r t h a n t h a t of the p u r e water. O n two places in the c o n d u i t , two electrodes are b u i l t in a n d the electrical resistivity is m e a s u r e d . T h e m o m e n t the salt w a t e r reaches the first two electrodes a decrease in electrical resistivity is registered. A c c o r d i n g l y , the time t h a t elapses from the m o m e n t the salt w a v e passes from the first p a i r of electrodes to the second one m a y be c o m p u t e d . I f the v o l u m e of the c o n d u i t b e t w e e n the two p a i r s o f e l e c t r o d e s is known, the flow-rate can be d e t e r m i n e d . O n e of the d i s a d v a n t a g e s of this m e t h o d is in the error i n t r o d u c e d b y the time r e q u i r e d for a d d i n g sufficient salt to the water, i.e. salt h a d to be a d d e d quickly in o r d e r to o b t a i n a clearly n o t i c e a b l e c h a n g e in electrical resistivity. A m o d i f i c a t i o n of this m e t h o d has b e e n c a r r i e d out b y our workers, consisting of the use of radioisotopes i n s t e a d of salt. N o electrodes
are necessary a n d radioisotopes c a n be i n j e c t e d quickly into the water. T h e effect of the now r a d i o a c t i v e wave was very intensive. T h e p a t t e r n a n d a r r a n g e m e n t of m e a s u r e m e n t is seen s c h e m a t i c a l l y in Fig. 3. A t p o i n t 5, radioisotopes are injected b y compressed air. I n j e c t i o n place is not necessarily the gate c h a m b e r as is shown in the figure, it m a y be also a w a t e r oscillations d a m p i n g c h a m b e r (water c h a m b e r ) , t u n n e l inlet or some o t h e r suitable o p e n i n g in the conduit. A t least 15 m below the injection p o i n t the f i r s t - - t h e " u p p e r " - - c h e c k p o i n t is p l a c e d for r a d i o a c t i v i t y m e a s u r e m e n t , a n d further d o w n at a suitable p l a c e is the s e c o n d - - t h e " l o w e r " - .... check point. T h e detectors m a y be l o w e r e d into the w a t e r in the c o n d u i t , or a t t a c h e d onto the c o n d u i t wall (in case m e a s u r e m e n t s are m a d e in a steel c o n d u i t ) , d e p e n d i n g on tile m e a n s of m e a s u r i n g . Detectors m a y be scintillation probes, or t h e y m a y consist of a set of G M - T u b c s . I n o u r case a scintillation p r o b e w i t h 1½- in. crystal a n d a set of five 1 × 15 in. G M - t u b e s were used. Both types o f detectors at the a b o v e - s t a t e d m e a s u r i n g conditions has y i e l d e d a sufficiently h i g h f r e q u e n c y of o u t p u t impulses. E a c h d e t e c t o r was fitted with the r a t e m c t e r . O u t p u t s of r a t e m e t e r s were c o n n e c t e d to a c o m m o n r e c o r d e r a n d the passages of the r a d i o a c t i v e w a v e a l o n g the detectors were registered on tim r e c o r d e r chart. T h e r e c o r d e r charts in Figs. 4 a n d 5 show the m e a s u r i n g d a t a for the big a n d small flow-rate.
5 I'
-.._./ Epl
2r--n i
[
J
......
i
......
< 2
Fro. 3. Block diagram of measurement. 1. Upper check point. 4. Recorder. 2. Lower check point. 5. Gate chamber. 3. Set of instruments. 6. Steel conduit.
105
Flow rate measurements in hydropower plants by means of radioisotopes
20
23 22
18
21
17
2O
16
19 18
/4
17
/3
/6
72 11
/4
10
73
9
0 RAI$ /hjected cver 21hr ,5rnm Measurement carried out 2 October/964
I
2o
,o
I
j,oo
RA/S Injected over Measurement carr/ed out ,5 October 1 9 ~
FIG. 4. Flow-rate measurement in HPP Nikola Tesla, Vinodol. Recorder chart of two 70 M'W measurements.
FIG. 5. Flow-rate measurements in HPP Nikola Tesla, Vinodol. Part of the recorder chart of one 7 MW measurement.
T h e passage time t of the radioactive wave from the u p p e r to the lower detector is c o m p u t e d from the k n o w n c h a r t speed of recorder B ( u n d e r a p e r m a n e n t control) a n d the m e a s u r e d l e n g t h D from the top to the b o t t o m of the radioactive wave registered o n the recorder chart.
tion of the power p l a n t m u s t be kept constant. W e have followed the principle according to which four e q u a l flow-rate m e a s u r e m e n t s are to be m a d e for each power separately, calculating t h e n a m e a n flow-rate v a l u e a n d a s t a n d a r d deviation. Errors in other values result from the total differential d e d u c e d from their f u n c t i o n a l relation. Deviations of i n d i v i d u a l variables i n equations are p r o b a b l y errors i n m e a s u r e d values. W a t t m e t e r s were not used for power measu r e m e n t , b u t readings were taken of g e n e r a t e d power o n k W h meters (tests, however, with wattmeters were made). Sometimes, one flowrate m e a s u r e m e n t took more t h a n 1 hr at small
D W a t e r passage time t = ~- sec. W i t h the k n o w n c o n d u i t v o l u m e V between the two detectors, the c o m p u t a t i o n of the flowrate is m a d e with the e q u a t i o n : Q-
V t -
VB D ma/sec"
D u r i n g the flow-rate m e a s u r e m e n t the opera-
106
~FI. Knapp, S. Rdtarovig and J. Lon~arig
powers. W h e n wattmeters were used, a series of readings had to be m a d e a n d the m e a n value c o m p u t e d . As to the i n s t r u m e n t itself, its size did not allow precise readings. O n the other h a n d , the k W h meters yielded the true average value of g e n e r a t e d power a n d since readings were m a d e in intervals of 15 m i n each, the average power value could have b e e n read j u s t within the time interval w i t h i n which flow-rate was measured. I t m u s t be u n d e r s t o o d that c a l i b r a t i o n a n d type of m e t e r should be given greatest a t t e n t i o n .
MEASUREMENTS MADE AND RESULTS OBTAINED 1. First m e a s u r e m e n t s were m a d e i n the H P P Split on the C e t i n a river. T h e H P P ' s n o m i n a l power is 432 M W a n d its flow-rate 200 m3/sec. I n 1962, however, w h e n the above m e a s u r e m e n t s were done, only 50 per cent of the total p l a n t h a d b e e n constructed. I n this h y d r o p o w e r plant, sixteen flow-rate m e a s u r e m e n t s were m a d e at four different powers, tbur equal m e a s u r e m e n t s for each power level. I n addition, two test m e a s u r e m e n t s were m a d e at the b e g i n n i n g , b u t u n t b r t u n a t e l y were unsuccessful. Nevertheless, they were of a n instructive character to the power p l a n t staff a n d were used to control a n d verify the a n t i c i p a t e d work output. (~) Isotopes were injected t h r o u g h the vent-hole b e h i n d the gate at the t u n n e l - i n l e t of the Praneevidi d a m on C e t i n a river. A special radioisotope injector was constructed for this purpose. So, w h e n the injector had been lowered, radioisotopes were injected into the t u n n e l c o n d u i t directly, b y m e a n s of compressed air. T h e pressure of 20 a t m was applied for isotopes injection which took 2 - 4 see, d e p e n d i n g on the a m o u n t of p r e p a r e d solution. T h e t u n n e l section from the Praneevidi d a m to the water c h a m b e r , some 9"652 m long, 6.10 m in d i a m e t e r a n d a vol. of 281.935 m a was the first m e a s u r i n g section. T h e second section e x t e n d e d from the d a m to the gate c h a m b e r a n d h a d a v o l u m e of 289.538 m a. T h e detection of the radioactive wave passage in the water c h a m b e r was performed, using a G e i g e r - M t i l l e r detector, placed in a special watertight casing a n d lowered into the t u n n e l . A set of such detectors was used i n the gate
c h a m b e r ; they were c o n n e c t e d in parallel a n d a t t a c h e d onto the external wall of the steel pipeline. For each m e a s u r e m e n t some 50 mc of radioisotope Br s2 were injected. Flow-rate m e a s u r e m e n t s in the H P P Split was done with a c o n s u m p t i o n of isotopes a m o u n t i n g to 1200 mc, i n total a n d the o b t a i n e d results are given in T a b l e 1. Flow-rate measurem c n t results c o n t a i n e d in the third c o l u m n are the average values c o m p u t e d out of the four equal measurements. T h e errors shown in the fourth c o l u m n i n d i c a t e a slight dissipation of results. TABLe 1. Flow-rate measurements in HPP Split
Nominal flow-rate (m3/sec)
Power measured in MW
40 86-00 ± 0.10 85 183.0 ± 0.3 100 216.5 ± 0.3 flow-rate max. 227.5 ± 0.3
Final flow-rate Mean measurement standard results deviation (m3/see) (~}~,) 37.8 ± 0.2 81.0 :L 0-4 97.15 ± 0-06
0.5 0-5 0.06
109.0 ± 0-1
0-1
2. Similar flow-rate m e a s u r e m e n t s had b e e n d o n e i n a u t u m n 1963 i n the H P P Nikola Tesla n e a r Rijeka, Yugoslav A d r i a t i c seaport, with a n o m i n a l power of 8 4 M W a n d 16mS/see flow-rate.(5) Forty flow-rate m e a s u r e m e n t s were m a d e for n i n e different powers. Radioisotopes were injected into the c o n d u i t t h r o u g h the water c h a m b e r . T h e l e n g t h of m e a s u r i n g section i n the pressure steel c o n d u i t was 1181.6 m with the v o l u m e of 2499 m a. Same m e t h o d was applied here as it was m a d e i n the H P P Split, b u t the m e t h o d of m e a s u r e m e n t u n d e r w e n t some alterations. I n this case the flow-rate m e a s u r e m e n t s were not started at the p o i n t a n d the m o m e n t the radioisotopes had been injected, as it was done i n the H P P Split; there was a n u p p e r m e a s u r i n g p o i n t for the radioactive wave detection. This p o i n t was some 50 m d o w n stream f r o m the radioisotopes injection point. F o r each flow-rate m e a s u r e m e n t some 20 m c of radioisotope Br s2 or 40 mc of I T M were injected into the pipeline. I n total, the measu r e m e n t s in the H P P Nikola Tesla c o n s u m e d
107
Flow rate measurements in hydropower plants by means of radioisotopes TABLE 2. Flow-rate Measurements in H P P Nikola Tesla, Vinodol
Nominal power (MW) 7 14 21 28 42 56 70 75 76
Flow-rate corrected (m3/sec) 1.402 2.635 3-939 5.36 8.013 11.10 13-97 15.47 16.48
Relative flow-rate error (%)
Total relative error of measurement (%)
0.28 0.45 0.23 0.37 0.06 0.36 0.43 0-19 0.12
0.85 0.74 0.42 0.55 0.20 0-50 0.60 0-35 0.30
-4- 0.004 -4- 0.012 -4- 0-009 ~ 0-02 ± 0.005 -4- 0.04 i 0.06 -4- 0-03 :~ 0.02
s o m e 1000 m c o f r a d i o i s o t o p e Br s2 a n d s o m e 300 m c o f I TM. R e s u l t s o f these m e a s u r e m e n t s a r e g i v e n i n T a b l e 2. T h e f l o w - r a t e v a l u e g i v e n for e a c h i n d i v i d u a l p o w e r is i n fact t h e m e a n ( a v e r a g e ) v a l u e computed out of the four equal measurements. 3. I n D e c e m b e r 1964 f l o w - r a t e m e a s u r e m e n t s were made in the HPP Gojak near Ogulin, h a v i n g t h e n o m i n a l p o w e r o f 50 M W a n d a 50 m3/sec f l o w - r a t e ) 6) H e r e , t h i r t y - t w o m e a s u r e m e n t s w e r e m a d e for n i n e d i f f e r e n t p o w e r s w i t h f r o m o n e to t h r e e t u r b i n e s in o p e r a t i o n . Isotopes were injected into thewater chamber. S e c t i o n u s e d for m e a s u r e m e n t s in t h e p i p e l i n e was 680 m l o n g , w i t h a v o l u m e o f 5441 m 3. Method of isotope injection and the pattern of m e a s u r i n g p o i n t s w e r e t h e s a m e as in t h e H P P Vinodol; however, at the upper measuring p o i n t t h e G e i g e r - M f i l l e r d e t e c t o r s w e r e used,
Power value of water in kWh/m 3 1-387 1.475 1.480 1.451 1.456 1.401 1.392 1.347 1.281
+ 0.012 -4- 0.011 :tz 0.006 -4- 0.008 + 0.003 -4- 0.007 -4- 0.008 -4- 0.005 =. 0.004
while at the lower one the scintillation probe was u t i l i z e d . F o r e a c h m e a s u r e m e n t 50 m c abs. o f r a d i o isotopes I TM w e r e i n j e c t e d . I n this case n o i s o t o p e Br se was u s e d d u e to a r a t h e r difficult c o m m u n i c a t i o n to t h e l o c a t i o n o f m e a s u r e m e n t s , a n d b e c a u s e o f a s p e e d y d e c o m p o s i t i o n o f these r a d i o i s o t o p e s . I n total, 1600 m c o f I TM isotopes w e r e u s e d for f l o w - r a t e m e a s u r e m e n t s in this hydropower plant. T h e results o b t a i n e d a r e s h o w n i n T a b l e 3. T h i s t a b l e c o n t a i n s also d a t a o b t a i n e d for w a t e r p o w e r , t u r b i n e efficiencies a n d w a t e r power value.
RADIATION
HAZARDS
T h e e x p e r i e n c e s has p r o v e d t h a t t h e d i l u t i o n o f r a d i o i s o t o p e s in w a t e r is i n d e p e n d e n t o f flow-rate value, and dependent upon the
TABLE 3. Flow-rate Measurements in H P P Gojak Average turbine power (MW) 0 1.60 5-07 12-0 16"8 23.2 30.4 40.8 48-2
-4- 0'05 ± 0'10 -4- 0.1 4- 0"1 + 0.2 4- 0.2 -4- 0.3 -4- 0'3
Net head 131.3 131.4 130.7 130.0 129.4 128.5 123.7 118.9 112.1
± 0.5 -4- 0-5 -4- 0-5 -t- 0.5 -4- 0"5 -4- 0.5 4- 0.5 -4- 0.5 ± 0.5
Flow-rate mean value (m3/sec) 1"759 2-908 5.84 11.44 15"02 22.05 29.48 40.6 50.1
± 0.009 ± 0.005 ± 0.01 -4- 0.05 -4- 0.04 -4- 0.04 -4- 0.09 4- 0.2 -4- 0.3
Water power (MW) 2.26 3.75 7.48 14.59 19.05 27.78 35.8 47.3 55.1
± 0'02 -4- 0.22 4- 0.04 -4- 0-13 -4- 0.13 -4- 0.16 -4- 0'2 -4- 0.4 -4- 0.5
Turbine efficiency 0 0.427 0.678 0-824 0-882 0.835 0.849 0.863 0.875
± 0.015 ± 0.017 -4- 0.014 -4- 0"011 4- 0.012 -4- 0.011 -4- 0.013 -4- 0-013
Power value of water (kWh/m 3) 0 0.153 0.241 0-291 0.310 0.292 0.286 0.279 0.267
± 0.005 ± 0.007 -4- 0.004 -4- 0.003 ± 0"003 ± 0.003 -4- 0'003 -4- 0-003
108
A,I. Knapp, S. Re~taroviiand d. Londarid
p i p e l i n e size a n d structure, a n d on t h e distance b e t w e e n the m e a s u r i n g a n d injection points. T h e r e f o r e , e q u a l radioisotopes a m o u n t s can be i n j e c t e d into the pipeline, regardless to the flow-rate values. A c c o r d i n g to the radioisotopes quantities t h a t were injected in h y d r o p o w e r plants, t h e n a c c o r d i n g to the o b t a i n e d r a d i o a c t i v e w a v e volumes a n d the p r e s c r i b e d m a x i m u m permissible radioisotopes c o n c e n t r a t i o n in water, it m a y be c o n c l u d e d t h a t an a v e r a g e radioisotope c o n c e n t r a t i o n in the r a d i o a c t i v e w a v e in the pipelines o f the H P P Split a n d Gojak, a l r e a d y was below the permissible, while in the H P P V i n o d o l it was twice as h i g h as m a x i m u m permissible. H o w e v e r , d u e to the fact t h a t d u r i n g the passage of w a t e r u p to the outlet structure of the h y d r o p o w e r p l a n t the r a d i o isotope c o n c e n t r a t i o n gets m o r e a n d m o r e diluted, the conclusion m a y be d r a w n t h a t no dangerous radioisotope concentration developed in a n y of our cases. T h e r a d i a t i o n the personnel of the h y d r o p o w e r plants were exposed to, was so small t h a t it m a y be considered harmless. H o w e v e r , the staff o f the I n s t i t u t e o f P e t r o l e u m t h a t were c h a r g e d w i t h the p r e p a r a t i o n a n d injection of radioisotopes were exposed to strong r a d i a t i o n , for the w o r k was c a r r i e d out b y using a n open radioisotope. Therefore, t h o r o u g h checking was m a d e of r a d i a t i o n o f bodies a n d care was taken not to keep the staff too long exposed to the a c t i o n o f radioisotopes, as well as to keep the r a d i a t i o n sources d u r i n g the w o r k a t a r e a s o n a b l e distance from the staff. O n average, r a d i o isotopes were injected twice a d a y a n d two m e n w o r k e d in a l t e r n a t i o n . CONCLUSION T h e o b t a i n e d results p r o v e the flow-rate measuring method--the peak timing method-to be a g o o d a n d r e l i a b l e as far as it is a p p l i e d in h y d r o p o w e r plants w i t h sufficiently l o n g pipelines o f k n o w n volumes. F u r t h e r m o r e , it has b e e n p r o v e d t h a t this m e t h o d is relatively easy to be a p p l i e d , y i e l d i n g reliable a n d accurate data. As it m a y be seen in the T a b l e s , m e a s u r e m e n t s were m a d e o f the flow-rates from 1-5 to 109 mS/see, a n d the s t a n d a r d d e v i a t i o n never r e a c h e d m o r e t h a n 0"7 p e r cent.
I t should be p o i n t e d out t h a t the p r o b a b l e errors given in the T a b l e s reflect the errors in the flow-rate m e a s u r e m e n t , whilst some f u r t h e r deviations from the real values m a y be introd u c e d b y a difference b e t w e e n a n o m i n a l a n d a c t u a l c o n d u i t volume. T h e v o l u m e of the p i p e l i n e is d e t e r m i n e d ti'om the construction designs of the p o w e r stations. As r e q u i r e d b y the designers, the civil e n g i n e e r ing s t a n d a r d s m u s t not tolerate a n error in two crossed p i p e d i a m e t e r s o f g r e a t e r t h a n 0-5-1 p e r cent w i t h r e g a r d to the respective design value. I f the total d e v i a t i o n w o u l d be due to the d i a m e t e r error, the m a x i m a l sectional or v o l u m e error could a m o u n t to 1-2 p e r cent. H o w e v e r , the d i s c r e p a n c y d u e to the ellipticity of pipes s h o u l d be i n c l u d e d into the m a x i m a l error o f crossed diameters. T h i s d i s c r e p a n c y is to be neglected w h e n the difference b e t w e e n the axes is as small as in this case, since it has p r a c t i c a l l y no effect on the c h a n g e in the p i p e volume. I f we take t h a t on a v e r a g e one h a l f of established deviations result from the scctional error a n d the second h a l f from the p i p e ellipticity, t h e n the m a x i m a l v o l u m e e r r o r for a given p i p e should not be g r e a t e r t h a n 0"5 1 p e r cent. Steel p i p e l i n e of h y d r o p o w e r plants usually consist of 6-10 m long pipes, so t h a t 100 or even m o r e pipes m a k e one m e a s u r i n g section. Since i n d i v i d u a l pipes d e v i a t e from the a c t u a l design value, m a n y positive a n d negative errors will cancel a n d the total error resulting is thus m u c h smaller. T h e r e is one o t h e r factor b y w h i c h the p i p e line v o l u m e can be affected, i.e. the expansion of the filled p i p e l i n e in relation to the e m p t y one. D u e to the w a t e r pressure, the m a g n i t u d e of e x p a n s i o n d e p e n d s u p o n the w a t e r level a b o v e the observed p o i n t of the pipeline, on the w a t e r flow-rate a n d w h e t h e r the p i p e l i n e is selfs u p p o r t e d , p l a c e d in concrete or in the rock. T h e difference in t e m p e r a t u r e b e t w e e n the full a n d the e m p t y pipeline m a y also be the cause of its e x p a n s i o n or shrinkage. W h e n a p p l y i n g this m e t h o d , the v o l u m e e r r o r is considered systematic w h e r e b y all results get shifted for the same relative value, so t h a t the relations b e t w e e n the results o b t a i n e d at given m e a s u r i n g points a r e not affected b y this error.
Flow rate measurements in hydropower plants by means of radioisotopes
T h e advantages this method will have in its future application lie in the fact that, should in the case of designing a hydropower plant, a provision be made for the measurement of turbine efficiency by means of radioisotopes, the volume error could be eliminated and the precision of flow-rate measurements would comply with the values given in Tables 1-3. For instance, by measuring the volume of pipes just prior to their placing, the volume of etnpty pipeline m a y be exactly determined. T h e expansion of the pipeline due to the stress m a y be determined and its value, during the test operation of the plant, m a y be found by means of Tensometer mounted onto the pipeline wall. This m a y be also used during the pressure tests when water is p u m p e d into the closed pipeline resulting in dependence of pressure upon the pumped-in quantity of water (respectively upon the change of pipeline volume). This method suits fully the prescribed way
109
of measuring the turbine efficiency in hydropower plants, whereby the correctness of the manufacturers' guarantees is verified. In addition, this method m a y be applied for the measurement of flow-rate in any pipeline where the volume of one of its sections is known. REFERENCES 1. SIA Normen fiir Wassermessungen bei Durchfi~hrung yon Abnahmeversuchen and Wasserkraftmaschinen. Auf-
gestellt yon SIA, Ztirich (1924). 2. Schweizerische Regeln fiir Wasserturbinen, Bull. SEV
48, No. 3 (1957). 3. ALLENG. M. and TAYLORE. A. Trans. Am. Soc. l~Iech. Eng. 14 (1923). 4. Report on Flow-Rate 3Ieasurements in HPP Split,
Institute of Petroleum, 7m~reb (1962). 5. Report on Flow-Rate ~le,l~wements in HPP ~Tnodol,
Institute of Petroleum, Zagreb (1963). 6. Report on Flow-Rate Measurements in HPP Gojak,
Institute of Petroleum, Zagreb (1964).