Renewable Energy 71 (2014) 433e 433 e441
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Renewable Energy journal homepage: www.elsevier.com/locate/renene
Hydro turbine prototype testing and generation of performance curves: Fully automated approach George A. Aggidis*, Audrius Zidonis
Lancaster University Renewable Energy Group and Fluid Machinery Group, Engineering Department, Lancaster LA1 4YR, UK
a r t i c l e
i n f o
Article history: Received 1 August 2012 Accepted 20 May 2014 Available online 18 June 2014 Keywords: Renewable energy Hydropower Turbines Turbine testing Hill charts Automation
a b s t r a c t
This paper presents a technology that can accelerate the development of hydro turbines by fully automating the initial testing process of prototype turbine models and automatically converting the acquired data into ef �ciency hill charts that allow straight forward comparison of prototypes ' performance. The testing procedure of both reaction and impulse turbines is illustrated using models of Francis and Pelton turbines respectively. For the development of an appropriate hill chart containing no less than 780 points the average duration of the fully automated test is 4 h while the acquired data � les can be processed into descriptive standard ef �ciency hill charts within less than a minute. These hill charts can then be used in research and development to quickly evaluate and compare the performance of initial turbine prototype designs before proceeding to much lengthier and more expensive development stage of the chosen design. © 2014 Elsevier Ltd. All rights reserved.
1. Introduction In a number number of count countrie riess around around the world world includ including ing the UK, the constant increase in fossil fuel energy prices together with a need to improve their energy security by reducing the dependency on imported fuel supplies is boosting the development of renewable energy technologies [1e3] 3].. The UK has an estima estimated ted untapped untapped green-�eld small scale (capped to 10 MW) hydropower capacity of 1.5 GWs [4] GWs [4].. This paper describes the automation of a manual turbine prototype prototype testing facility (Fig. 1) 1) manufactu manufactured red by Gilbert Gilbert Gilkes & Gordon Ltd to enable very fast data acquisition and processing into turbine ef �ciency hill charts. Ability to quickly assess the performance of a prototype turbine at the initial stage of development is very important before moving towar towards ds more more accura accurate te but much much more more time time consu consumin ming g and expensive development phase. Depending on the conditions of a particular application, different types of turbines are used [5] and therefor therefore e different different issues are to be addresse addressed. d. Even though for modelling of reaction turbines Computational Fluid Dynamics has reached a feasible stage [6] [6],, numerical modelling of impulse turbines (like Pelton Pelton [7] or Turgo Turgo [8] [8])) is still still a chall challen enge ge.. When When model modellin ling g a full full geomet geometry ry,, time time durat duration ionss of up to 5 days days per simulation of one data point are reported [9,10]. [9,10]. Alternatively to
reduce reduce the time time durat duration ion severe severe simpli simpli�cation cationss of geomet geometry ry [11 [1 1e15] 15] or or turbine working principle [16e19] 19] are are implied. On the other hand, experimental model tests that use runner dimensions and � ow conditions that allow full scalability and ensure very high accuracy are usually performed only as the last stage of development because of its complexity and cost. That is why quickly pretesting of prototype turbine models might aid the research and development process overall. 2. Backgrou Background nd The guaranteed ef �ciency of a turbine (Eq. (1) (1))) as de�ned by the International Code for Model Acceptance Tests IEC 60193:1999 [20] is [20] is the ratio of the mechanical power provided by a shaft of a turbine (Eq. (2) (2))) to the power generator divided by the hydraulic power (Eq. (3) (Eq. (3)): ):
¼ P P m h
where h is the guaranteed ef �ciency of a turbine, P m is the mechanical power [J], P [J], P h is the hydraulic power [J],
P m
¼
* Corresponding
author. E-mail address: address:
[email protected] (G.A. Aggidis).
http://dx.doi.org/10.1016/j.renene.2014.05.043 0960-1481/ © 2014 Elsevier Ltd. All rights reserved.
(1)
h
u
$T
(2)
where u is the rotational speed of a turbine shaft [rad/s], T [rad/s], T is is the torque provided by the turbine shaft [Nm],
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Velocity pressure head is used only when calculating the net pressure head on reaction turbines as the downstream water �ow does not affect the performance of the impulse turbines. Physically the velocity head and the friction loss head are not distances measured from water levels; however they can be converted into adequate quantities expressed in metres (Eq. (6)) and then for the sake of convenience sketched on the diagram as shown in Fig. 2. 2
v
H V
(6)
¼ 2 g
where v is the mean velocity of downstream water � ow [m/s].
3. Af �nity laws Fig. 1. Fully automated turbine prototype tester.
P h
¼
r Q g DH
(3)
$
where r is the density of water [kg/m3], Q is the volumetric �ow rate [m3/s], g is the gravitational acceleration constant taken as 9.81 m/s2, D H is the net pressure head [m]. Calculating the mechanical power provided by the shaft is trivial, however �nding the hydraulic poweris more complicated as the net pressure head DH consists of more than one component [21], i.e. the gross pressure head, the head of pressure loss in a penstock and the velocity head. Moreover, the components differ when calculating the net head for impulse or reaction type turbines. Fig. 2 presents general schematics of a hydropower plant. First of all, it is important to understand how the gross pressure head is measured in each case. The gross pressure head for reaction turbines is simply the difference between the upstream and the downstream water levels. However, for impulse turbines the gross pressure head is measured as the distance between the upstream water level and the level of a jet impact point which is always higher than the downstream water level. Equations (4) and (5) show how the net pressure head is calculated for impulse and reaction turbines respectively and what terms are important for each of them:
Impulse turbines DH H G
¼ H L
Reaction turbines DH H G
¼ H L H V
(4) (5)
where H G is the gross pressure head [m], H L is the friction loss head [m] and H V is the velocity head [m].
When designing a hydropower station it is possible to calculate the performance of a known turbine design if the performance of its model is known. Performance scaling can be done by using the af �nity or so called similarity laws [22e24]. The af �nity laws mathematically relate the same turbine at different speeds or geometrically similar turbines at the same speed. Equations (7)e(9) show the relationships when the diameter of the runner is kept constant, whereas Equations (10)e(12) are used when the rotational speed is constant:
if D
n 1 1 ¼ const: Q ¼ Q n 2
DH 1
n 1
DH 2
¼
P 1 P 2
n
¼
(7)
2
2
(8)
n2
1
3
(9)
n2
where n is the rotational speed [rpm],
if n
1 ¼ const: Q ¼ DD1 Q 2
DH 1
2
D 1
DH 2
¼
P 1 P 2
D
¼
(10)
2
(11)
D2
1
3
(12)
D2
where D is the runner diameter [m]. In general, these laws are expressed as:
Q t Q m nt nm
p ffiffi ffiH ffi ffi D2 ¼ p ffiffi ffiH ffi ffitffi $D2t D
D
m
(13)
m
p ffiffi ffiH ffi ffi D ¼ p ffiffi ffiH ffi ffitffi $ Dm D
D
m
(14)
t
where indexes t correspond to the industrial turbine and m to the laboratory model. Therefore by choosing D H t 1 m and D t 1 m and rearranging Equations (13) and (14) to express Q m and nm, the formulae to calculate quantities known as the unit speed n11 [rpm] and the unit (speci �c) discharge Q 11 [m3/s] are derived:
¼
Fig. 2. Schematics of a hydropower station.
¼
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435
Fig. 5. Projections of a 3D ef �ciency curve: turbine ef �ciency vs n11 (left) and Q 11 vs n11 (right).
4.1. Impulse turbines Fig. 3. Schematics of the turbine tester (impulse turbines).
n$D ffiffi ffiH ffi ¼ p
n11
D
ffiffi ffiH ffi ¼ D2 $Q p
Q 11
D
(15)
(16)
Combinations of n11 and Q 11 providing constant ef �ciency h form iso-ef �ciency curve. Set of such iso-ef �ciency curves form a hill chart (example shown in Fig. 15). For scaling to be possible, care must be taken to ensure that the model dimensions and test conditions meet the criteria provided in the IEC 60193:1999 testing standards [20].
4. Methodology The Gilkes turbinetester can be treated as a small scale model of a real hydropower station which has all the corresponding features as the real power plant would have. Fig. 3 shows a schematic diagram of the tester with an impulse turbine mounted on. A centrifugal pump powered by a motor provides the �ow and the pressure, which can be converted into the pressure head, and therefore they can be treated as the gross pressure head and the river �ow in the real powerstation which was describedin previous section. The tester has a turbine which is coupled to a load to simulate the load applied by the generator.
To calculate the range of ef �ciencies of an impulse turbine model the quantities shown in the diagram (Fig. 3) are measured. The readings for both u and T can be taken directly off the shaft [25] of a turbine as it would be in a real power station (the rotational speed and the torque supplied to the generator). However, to be able to use the hydraulic power formula (Eq. (3)), indirect readings are taken and then converted into Q and DH . The � ow is measured by using a triangular pro�le weir [26,27], measuring the head on the weir, Z :
90 triangular profile weir Q
¼
8 C 15 d
p ffi2ffi g ffiffitan90 Z
2:5
2
(17)
where C d is a coef �cient of discharge and equals to 0.6. The conventional way of measuring the net pressure head DH for impulse turbines and reaction turbines is explained in Section 2 Background. Therefore, for impulse turbines mounted on the tester (Fig. 3), the gross head can be calculated from the pressure drop between the nozzle inlet pressure and the atmospheric pressure:
H GI
¼
p Z I r$ g
(18)
where H GI is the gross head of an impulse turbine [m], Z I is the distance of a pressure measurement point below the level of jet impact [m] as shown in the diagram (Fig. 3). Since p is measured below the point of the jet impact, the head seen by the nozzle is lower and has to be corrected by subtracting Z I. For simplicity pipe friction loss head is neglected in this tester as it is expected that the prototype designs would be compared at identical operating conditions (or performance envelopes) therefore the losses in the pipeline would cancel out. Then DH H GI and the equation for impulse turbines mounted on the tester (Eq. (19)) can be derived from Eq. (4):
¼
DH I
¼
Fig. 4. Schematics of the turbine tester (reaction turbines).
p Z I r$ g
(19)
Fig. 6. Projections of 3D ef �ciency curves: turbine ef �ciency vs n11 (left) and Q 11 vs n11 (right).
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Fig. 8. Stepper motor coupled to the inlet nozzle spear of the Pelton turbine model.
Fig. 7. 3D data covered with a mesh of tetragon elements.
Temperature � uctuations can induce unwanted errors therefore it is suggested to monitor the temperature during the testing so that the density value can be corrected.
neglected because of analogous reasons to the explained before that these losses would cancel out if the prototype turbine models are compared at identical operating conditions. Therefore, by substituting the assumptions listed above and the reaction turbine gross head expression (Eq. (20)) into Eq. (5), formula for the net pressure head seen by a reaction turbine mounted on the tester is derived: DH R
¼
4.2. Reaction turbines A method to calculate the net pressure head on reaction turbines is slightly different because of the gross head being measured as the total distance from the upstream level to the downstream level. Again, the pressure sensor p is lower than the downstream level and has to be accounted for in a similar fashion as with the impulse turbine. However, this time the level difference between the pressure sensor and the downstream level is combined of two components (Fig. 4) Z R and Z . Z R is the distance from the level of the pressure sensor to the level of a tip of the triangular pro �le weir, i.e. the distance to the downstream level when no � ow is present. The component Z R is a constant �gure once the pressure sensor is mounted. However, there is a varying component Z , which is varying with the �ow. Therefore, the gross head on reaction turbine mounted on the tester as shown in the schematics can be expressed as:
H GR
¼
p r$ g
ð Z R þ Z Þ
(20)
p $ g
r
ð Z R þ Z Þ
(21)
Again, monitoring the temperature throughout the testing to correct the density is suggested. Since all the quantities required for calculating n11, Q 11 and h are measured or calculated, it is possible to process the acquired data into a three-dimensional ef �ciency hill chart. 4.3. Test control The formulae provided above describe methodology of measuring turbines' performance under various conditions. However, to be able to acquire all the ef �ciencies in the range of n11 and Q 11 available by the turbine prototype model the inlet � ow and the load on the turbine have to be controlled. By increasing the load on the turbine output shaft a rotational speed is decreased. By varying the rotational speed, the unit speed n 11 is varied proportionally if DH and D are constant (Eq. (15)). Therefore, by varying load, ef �ciency vs. n11 curve can be acquired. However this is not entirely true for reaction turbines as DH is slightly varying because of variation in Z . Moreover, in the setting of the tester as described
As explained in Section 2 Background, the velocity head is to be subtracted from the gross head for the reaction turbines. However, for simplicity the velocity head and pipe friction losses are
Table 1 List of sensors used in the automation of the turbine tester. Sensor
Manufacturer (model)
Pressure sensor Optical speed sensor
Keller (Series 21 SR/MR) Compact Instruments (VLS/DA1) Pepper Fuchs (UB500F42S-I-V15) Tedea-Huntleigh (1042 e3 kg)
Ultrasonic sensor Single point load cell
þ
Total error
Variable
±0.50% ±0.75%
P n, u a
±1.00%
Z , Q b
±0.05%
T c
a
n is acquired in rpm, whereas u has to be in rad/s so that it could be used in Eq. (2). Therefore unit conversion takes place. b The ultrasonic sensor is measuring the water head Z on the triangular pro �le weir, which is then converted to the � ow Q (Eq. (17)). c Applied brake torque T on the turbine shaft is calculated by multiplying the brake arm radius times the load force measured by the Single Point Load Cell.
Fig. 9. Stepper motor coupled to a guide vane control of the Francis turbine model.
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Table 2 Test plan for the Francis turbine model. Angular velocity of the stepper motors Total revolutions on the � ow valve Number of the � ow rate samples Diameter of the turbine runner Total revolutions on the load control nut Number of the load samples Extra revolutions on the load control nut (to reach a complete stop) Number of samples per channel Delay time before taking readings Brake (load) arm radius Z R
Fig. 10. Schematics of the turbine shaft torque applying arm.
above, for a reaction turbine there is a relation of head and load on the turbine because higher load means more resistance to the � ow and provided that the pump is working at constant power, the pressure head increases with the load being applied to the turbine shaft. This is where the af �nity laws become extremely useful and allow the control of the test conditions to be simpli�ed and the test duration reduced. Moreover, it corrects any unwanted instabilities if all the readings are taken at the same time because the data is collected in 3D, i.e. x’, 'y' and 'z ' axes being n11, Q 11 and turbine ef �ciency respectively. This way a result of variation in the load with a �ow control position being constant (i.e. angle of guide vanes, nozzle opening distance, etc. is not moved) is a turbine ef�ciency curve ranging from n 11 min to n 11 max and being slightly inclined in a direction of Q 11 (Fig. 5). To be able to acquire more of such ef �ciency curves, preferably parallel or close to parallel ones, so that a surface of turbine 's performance is completely covered and then standard 2D hill charts can be produced, inlet �ow has to be controlled. Q 11 is varied proportionally by varying the inlet �ow Q , provided that DH is constant (Eq. (16)). Again, DH is varying with restrictions being applied to the � ow but this is not a problem as the 3D curve does keep all the information of the variations. In general, even if the lines would be not parallel but intersecting, they would be still lying on the surface of the performance hill, which is the data that is essential. Therefore changing the inlet � ow after a range of loads (free spin to a complete halt) has been tested, allows acquisition of ‘
5 rpm 3.5 15 0.08 m 1.5 50 3 500 5s 0.17 m 0.175 m
another ef �ciencycurvethat has been moved in the direction of Q 11. By repeating the acquisition of ef �ciency curves at different �ow rates varying from the maximum �owrateto 0 �ow rate a complete set of ef �ciency curves is acquired (Fig. 6). When the data is acquired in the form of multiple curves lying on the surface of a turbine ef �ciency hill, data processing to standard 2D hill charts takes place. Firstly, 5th order polynomials are �tted on every single ef �ciency curve [28]. Then data points are evenly spaced by interpolating the ef �ciency and Q 11 within the curves in equally spaced steps of n11. When every ef �ciency curve is processed to have the same amount of evenly spaced data points, the points are connected to the same index data point of the neighbouring curve. This procedure provides a surface mesh of tetragon elements (Fig. 7). Finally, when the surface is meshed, it can be sliced’ at chosen heights’ like in an isobaric map by interpolating the borders of the quadrants that intersect with chosen ef �ciencyplane. The intersectpoints arethen connectedby a closed curve (in some cases open, if the area within that curve is outside the tested range of the turbine model) and represents single ef �ciency in the hill chart, i.e. Q 11 vs. n 11 graph. ‘
‘
5. Implementation The methodology described in the previous section was implemented by fully automating the turbine tester which was originally designed and manufactured by Gilbert Gilkesand Gordon Ltd. Both functions: data acquisition and test control is automated and operated by a Virtual Instrument (V.I.) that is programmed in LabVIEW. A separate V.I. is programmed to process acquired data
Table 3 Example of Francis turbine results. Flow index
Load index
P [bar]
N [rpm]
Z [mm]
F 0 [g]
0 0 0 0 0 0 0
0 1 2 3 4 5 6
2.34 2.37 2.35 2.36 2.34 2.33 2.34
4657 4678 4670 4686 4660 4657 4656
80 81 81 80 81 81 81
68 70 70 73 65 72 69
49 50 51 0 1 2 3 4 5 6
1.35 1.35 1.37 2.36 2.35 2.36 2.36 2.37 2.36 2.36
1742 1713 0 4694 4677 4667 4685 4682 4683 4679
100 100 100 81 81 82 81 81 81 81
1334 1338 1396 57 67 66 68 69 72 72
…
0 0 0 1 1 1 1 1 1 1 Fig. 11. Francis turbine prototype model.
…
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438
Fig. 12. Raw results of the Francis turbine prototype model test in 3D. Fig. 14. Francis turbine ef �ciency hill chart with the mesh.
into graphs and ef �ciency hill charts shown in Figs. 5e7. Four electronic sensors are installed on the turbine tester and connected to a data acquisition card made by National Instruments (NI USB6008) to allow instant acquisition of all readings required. Table 1 presents all the sensors installed and links them with a variable that is measured by that sensor.
n 2P 60
¼
u
,
brake force is adjusted by tightening the control nut which is directly coupled to the stepper motor and hence driven by it. The Single Point Load Cell is measuring the load F applied by the brake arm which multiplied by the brake arm radius r gives the torque T applied to the turbine shaft:
T F $r
(22)
By using all the sensors provided in Table 1, a single data point is acquired, provided that the testing facility is at a steady state (i.e. turbine shaft brake torque T and �ow Q are kept constant). However, as explained in Methodology section, T and Q have tobe varied to test the entire performance range of a turbine and construct the complete ef �ciency hill chart. The control of the �ow valves andthe torque applying brake arm is automated by installing two unipolar stepper motors with an internal step down gearing ratio of 25:1, providing 1 Nm holding torque and 0.3 step angle. The motors are connected to the standalone PC driver boards controlled by the LabVIEW V.I. via the data acquisition card. Figs. 8 and 9 present photographs of the �ow controlling stepper motor coupled to the Pelton and Francis �ow valves respectively. The schematics of the brake arm used to apply the torque load on the turbine shaft and measure it is shown in Fig. 10. A rotating disc is mounted on the shaft to increase the diameter of the shaft at the place where the load is applied. The brake arm is causing friction on the surface of the rotating disc. It is done by pushing two self-lubricating pads mounted on the brake arm to the disc. The
Fig. 13. Processed results of the Francis turbine prototype model test in 3D: turbine ef �ciency hill surface meshed with tetragonal elements.
¼
(23)
where F is the force [N] applied tothe load cell by the brake arm, r is the brake arm radius [m]. 6. Test results Results of the automated tests performed on the horizontal axis Francis and Pelton turbine prototype models are provided in this section. 6.1. Francis turbine (reaction) A photograph of the horizontal axis Francis turbine model that was tested is shown in Fig. 11. The transparent pipe seen in the picture is the draft tube. Six guide vanes that control the � ow rate and the feed angle tothe runnercan be seen behind the transparent wall. The guide vanes are controlled by the �ow controlling stepper motor as described in Section 5 Implementation. Table 2 contains the information about the chosen test plan and important runner dimensions. A large volume of numerical data (780 rows containing 6 readings) is collected. An example of the format of the acquired numerical data is shown in Table 3.
Fig. 15. Normalised to 100% 2D ef �ciency hill chart of the Francis turbine model.
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Table 5 Example of Pelton turbine results. Flow index
Load index
p [bar]
n [rpm]
Z [mm]
F 0 [g]
0 0 0 0 0 0 0
0 1 2 3 4 5 6
1.71 1.71 1.71 1.71 1.71 1.71 1.70
2438 2445 2435 2444 2380 2435 2431
93 95 93 92 92 92 93
32 28 30 30 38 33 29
48 49 50 51 0 1 2 3 4
1.71 1.71 1.72 1.72 1.73 1.74 1.72 1.72 1.73
469 398 333 0 2525 2536 2537 2530 2526
94 93 93 93 91 90 93 90 92
2655 2683 2694 2838 39 35 31 42 45
…
0 0 0 0 1 1 1 1 1 Fig. 16. Pelton turbine prototype model.
…
These numerical results are automatically processed into graphs by the V.I. programmed in LabVIEW and mentioned in Section 5 Implementation. The formulae used for data processing are given in Sections 2, 3 and 4. The 3D graphs of the raw generic results plotted by the V.I. are shown in Fig. 12. The raw results are automatically meshed as described in Section 4 Methodology. The 3D graph of the processed results is shown in Fig. 13. The 2D ef �ciency hill chart is automatically constructed by interpolating the mesh at chosen ef �ciencies and then plotting the acquired iso-ef �ciency curves on the n11eQ 11 plane. More detailed description of this technique is provided in Section 4 Methodology. Fig. 14 presents the ef �ciency curves together with the top pro jection of the mesh. The absolute best ef �ciency of the automatically tested Francis prototype model was calculated and the �nal generic ef �ciency hill chart normalised to 100% is shown in Fig. 15. 6.2. Pelton turbine (impulse) A photograph of the horizontal axis Pelton turbine prototype model that was tested is shown in Fig.16. The runner with a total of 16 buckets can be seen in the centrethrough a transparent wall. The inlet nozzle can be seen in the bottom right corner mounted horizontally. The � ow control spear is directly coupled to the stepper motor as described in Section 5 Implementation. Table 4 contains the information about the chosen test plan and important rig dimensions. A large volume of numerical data (936 rows containing 6 readings) is collected. An example of the numerical data acquired is shown in Table 5.
Following the same steps as for the Francis results, the numerical Pelton results are automatically processed into the graphical format. The 3D graphs of the raw results plotted by the V.I. are shown in Fig. 17. Again, the surface of the raw results is automatically meshed. The 3D graph of the processed results is shown in Fig. 18. Same as with the Francis turbine results, the 2D ef �ciency hill chart is automatically constructed by interpolating the mesh at chosen ef �ciencies and then plotting the acquired iso-ef �ciency curves on the n 11eQ 11 plane. Fig. 19 presents the ef �ciency curves together with the top projection of the mesh. The absolute best ef �ciency of the automatically tested Pelton prototype model was calculated and the �nal generic ef �ciency hill chart normalised to 100% is shown in Fig. 20. 6.3. Comparison of the data The automatically obtained results are compared to the original results provided in the operating manual of the Gilkes Tutor GH5 1967 [29]. However, since the Gilkes turbine tester and the prototype turbine runners were manufactured in 1960s as an academic teaching tool rather than an industrial turbine testing facility the runners used for the results provided in the manual are not the same ones as used in this project. Even though it is expected that they are of the same design and dimensions the manufacturing quality of the prototype runners is quite poor compared to the real industrial turbines. Hence, two different runners of the same
Table 4 Test plan for the Pelton turbine model. Angular velocity of the stepper motors Total revolutions on the � ow valve Number of the � ow rate samples Diameter of the turbine runner Total revolutions on the load control nut Number of the load samples Extra revolutions on the load control nut (to reach a complete stop) Number of samples per channel Delay time before taking readings Brake (load) arm radius Z I
10 rpm 12 18 0.09 m 5 50 5 500 5s 0.17 m 0.175 m
Fig. 17. Raw results of the Pelton turbine prototype model test in 3D.
440
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Fig. 18. Processed results of the Pelton turbine prototype model test in 3D: turbine ef �ciency hill surface meshed with tetragonal elements. Fig. 21. Manufacturing quality of the academic Pelton prototype runner.
Fig. 19. Pelton turbine ef �ciency hill chart with the mesh.
design are expected to have different ef �ciencies or produce different shape iso-ef �ciency curves. Fig. 21 shows a photograph of the Pelton turbine prototype model surface quality to illustrate the problem. However, despite the limitations listedabove the results can still be compared and close resemblance can be seen. Fig. 22 presents the original results of the Francis turbine prototype model normalised to 100%. The absolute best ef �ciency of the model tested originally was 3% lower than the ef �ciency of the model used for automatic testing. It can be seen that the original results match the results acquired automatically (Fig. 15) very closely in terms of the operational range and the location of the best ef �ciency point.
Fig. 20. Normalised to 100% 2D ef �ciency hill chart of the Pelton turbine prototype model.
Fig. 22. The original normalised hill chart of the Francis turbine model.
Fig. 23 presents the original results of the Pelton turbine prototype model normalised to 100%. The absolute best ef �ciency of the model tested originally was 10% lower than the ef �ciency of the model used for automatic testing. Again, the original results match the automatically acquired results (Fig. 20) very closely in terms of the operational range and the location of the best ef �ciency point. Moreover, the automated test has tested the turbine at wider conditions (i.e. the maximum tested unit �ow of the original test was ~0.09 m3/s whereas the maximum tested unit �ow of the automated test was ~0.11 m 3/s). To conclude the comparison of data, the chosen algorithms for automated control of the testing conditions and the chosen data
Fig. 23. The original normalised hill chart of the Pelton turbine model.
G.A. Aggidis, A. Zidonis / Renewable Energy 71 (2014) 433e441
acquisition technique are proved to be valid. The only possible problem might be in the implementation of the turbine output torque reading technique as it is based on the mechanical brake. The weakness of the mechanical brake is its instability at low loads. The brake arm starts to vibrate when it is griping the rotating disc with low force and these unwanted vibrations are disturbing the readings. The reading quality of the output torque is acceptable for the prototype models used to date, however when testing models with accurate and �ne surface �nishes it is suggested to replace the mechanical brake with hydraulic or electromagnetic brakes. 7. Conclusions The technology for fast fully automated initial testing of hydro turbines was developed and implemented on the originally manual turbine testing facility manufactured by Gilbert Gilkes and Gordon Ltd. The testing facility was upgraded to a stage where test control, data acquisition and processing are fully automated. The operatoris only required to mount the prototype model to be tested, calibrate the sensors and specify the test plan. After the test is started, the facility can work for a number of hours and acquire hundreds of data points without any external action required. A typical test would acquire approximately 800 data points in 4 h. After completion of a test, the data � le can be loaded on the processing software and a hill chart characterising the performance of the tested turbine design can be produced within less than one minute. The implemented technology was illustrated by successfully performing tests on both reaction (Francis) and impulse (Pelton) turbine models and processing the acquired data into meaningful results of the standard form. Moreover, if the care is taken to ensure that the model dimensions and the test conditions are in agreement with the limits provided in the testing standard [20] the af�nity laws provided in this paper allow scaling and modelling of the turbine's performance by using the formulae (Eq. (15), Eq. (16)). Scaling is very important for the industry when hydropower plant is designed. Finally, the described technique for fully automated turbine testing can be very useful in further developing hydropower technologies. It can reduce the duration of initial research and development phase drastically by enabling quick testing of new prototype designs. Acknowledgements The authors would like to thank the Lancaster University Renewable Energy Group and Fluid Machinery Group, Dr. Antonios Tourlidakis, Andrew Gavriluk, Barry Noble and Ian Nickson for their comments, suggestions and technical support. The authors gratefully acknowledge the contribution of the turbine manufacturing company Gilbert Gilkes and Gordon Ltd. which supplied the manual turbine testing facility. References [1] European Renewable Energy Council (EREC). Renewable energy in Europe: markets, trends and technologies. 2nd ed. London: Earthscan; 2010 .
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