AN ADJUSTMENT DEVICE FOR OBTAINING THE MAXIMUM EFFICIENCY FOR WATER TURBINES

Abstract: An adjustment device for obtaining the maximum efficiency for water turbines having adjustable runner blades and guide rails and test probes provided in the draft tube after the turbine. The purpose of the present invention is to provide an adjusting device having a very simple design, a very high sensibility and which can distinguish inclined flow against the measuring position or the transmitter from rotation. These tasks have been solved in that the test probes (16) are provided in pairs at some distance from each other and substantially radially from the centre axis (22) of the draft tube (15) and mainly at the same level, that the test probes (16) are disc-formed with mainly symmetrical wing profile and on each flat side being equipped with at least one measurement spot (17a, 17b), that the measurement spots (17a, 17b) belonging to each probe are connected to one side each of a pressure difference transmitter (19, 20), and that the pressure difference transmitters (19, 20) are arranged to emit signals, which are proportional to the horizontal speed component of the recorded rotational speed of the water and which signals are used for adjusting the pitch of the guide rails.

Description: AN ADJUSTMENT DEVICE FOR OBTAINING THE MAXIMUM EFFICIENCY FOR WATER TURBINES The present invention refers to an adjustment device for obtaining the maximum efficiency for water turbines having adjustable runner blades and guide rails and test probes provided in the draft tube after the turbine. Background of the invention Water turbines referred to as being of the "full Kaplan"-type have adjustable guide rails as well as adjustable runner blades. By a correct adaption of the pitch thereof it is possible to obtain a rotation free flow after the turbine for different flows and drops. Absence of rotational energy in the turbine draft tube is synonymous with a maximum efficiency under given load conditions. The guide rails fulfill the double task of acting as starting device (effect adjustment) and for giving the water a pre-rotation before the runner wheel. For obtaining a correct runner blade pitch for every current regulation (guide rail pitch) the turbine is equipped with a so called combinator, which via a system of cams or electronically governs the adjustment in a predetermined manner. This governing function may be based on systematic tests of series of standard runner wheels, in model tests of the turbine in question or in full scale measurements of the efficiency in connection to putting into service. No direct measurement of the rotational energy is made in neither case. At several turbines it has not been possible fully to balance out rotational energy and here is consequently a big energy source, which can be utilized. There may be various reasons for not having optimum conditions. At several small turbines it might be that no careful adjustment has never been made, but it has been relied on standard series. Other turbines may have been in operation for maybe half a century, and beside the fact that they might have been incorrect at the beginning, it is also possible that changes have occured during the operation life in water paths and also in the turbine itself. There is furthermore always always the risk for scaling effects in cases where the adjustment is based on model tests. In cases where full scale efficiency measurements have been made, which appear to be the most accurate method, there is finally a certain unreliability as to the results. It is considered that an accuracy of 0,5 - 0,7 % is realistic with up-to-date ultrasonic technique and during good conditions. For certain types or age categories of machines, it is therefore possible to gain in efficiency of a sufficiently to motivate a system economically, which eliminates the last remnants of rotation downstream of the turbine. From US-A-1.931158 it is earlier known to detect the flow of water downstream of the turbine by means of a propeller-like detecting member, whereby any rotational motion thereof is used for effecting the desired adjustment of the pitch setting of the runner blades. The wings of the propeller extend over a substantial portion of the internal circumference of the draft tube and as rather big forces are required for the adjustment movement, this known adjustment device is very unsensitive and quite impossible to use for detecting the small rotation, which might remain behind the turbine. Purpose and most important features of the invention The purpose of the present invention is to provide an adjusting device having a very simple design, a very high sensibility and which can distinguish inclined flow against the measuring position or against the detector from rotation. These tasks have been solved in that the test probes are provided in pairs at some distance from each other and substantially radially from the centre axis of the draft tube and mainly at the same level, that the test probes are disc-formed with mainly symmetrical wing profile and on each flat side being equipped with at least one measurement spot, that the measurement spots belonging to each probe are connected to one side each of a pressure difference transmitter, and that the pressure difference transmitters are arranged to emit signals, which are proportional to the the water and which signals are used for adjusting the pitch of the guide rails. Description of the drawings The invention hereinafter will be further described with reference to the accompanying drawings, which show an embodiment. Fig. 1 shows a section through a Kaplan-type turbine equipped with the test probes according to the invention. Fig. 2 shows the test probe according to Fig. 1 in bigger scale in a front view. Fig. 3 is a section along line III-III in Fig. 2. Fig. 4 is a section along line IV-IV in Fig. 1. Fig. 5 shows a block diagram of the governing system for the adjustment device. Description of embodiment In the drawing 11 designates a water turbine e.g. of the Kaplan- type, having a turbine wheel 12 equipped with adjustable runner blades. 13 designates the intake tube of the turbine and 14 are adjustable guide rails, which serve as starting device, but which also impart a pre-rotation upon the water. Downstream of the turbine wheel 12 is provided a draft tube 15, in which are provided two test probes 16 in positions spaced from the wall of the tube. These probes are preferably located substantially on the same level and mainly at the same distance from the centre of the draft tube. The test probes 16 are disc formed and consist of a symmetrical wing profile with two measuring spots 17 in the form of two milled chambers on each side of the profile adjacent its leading edge. These chambers are via channels 18 connected to thin plastic tubes, which are led out of the draft tube 15 to one differential pressure transmitter 19, 20 each, see Fig. 4. The chambers are preferably covered with screens or sieves for preventing particles from entering the measuring system. The test probes shown in Fig. 2 and 3 are schematical and their profile should in fact be more carefully designed to prevent unnecessary resistance and risk for flow induced vibrations. The suspension of the test probes 16 may be made in many different manners. The most simple manner is to attach the probes to a sword fitted in the wall of the draft tube. If it is difficult to come far enough into the flow in this manner an arrangement with wires 21 is a solution, which is shown in Fig. 1. In this embodiment two probes 16 have been arranged on each side of the centre line 22 of the draft tube. The purpose of this arrangement is that any inclined flow caused by misalignment of the probes or by the geometry of the flow channel, shall cause a deflection of the same direction in both measurement spots, whereas a rotation component has opposed flow directions on opposite sides of the centre line. If the velocity profile is irregular it may be required four or maybe six test probes for obtaining a sufficiently representative specification thereof. The buoyance arising at inclined flow against a symmetric profile has its point of attack a distance of 0.25 times the chordal length downstream of the leading edge. At inclined flow the profile therefore will be arranged angularly thus that the angle of attack increases. This problem can become embarrasing at a cranky suspension as in the embodiment with wires. A method of out-balanzing this effect may be to give the upper wire a cross- sectional area three times bigger than that of the lower wire, whereby inclined flow should give a translational deformation only. Such a distribution of the relative tensional rigidness of the suspension wires furthermore should reduce the risk for flutter in the structure. If it is possible directly to measure the rotation, then th exactness of this measurement may be much lower as compared t the case where the total efficiency is measured and the optimu positioning of the runner blades is determined from the small variations occuring in the total efficiency at changes in th settin of the itch. There is in fact no requirement fo measuring the rotational energy in absolute figures, but the essential is the ability of determining when a minimum occurs. Hereinafter is described how this rotation can be measured directly and how the measurement results are used for adjusting the pitch setting to an optimum efficiency. The test probe 16a emits its signals P^ and P^2 to a pressure difference transmitter 19, and the test probe 16b in the same manner emits its signals P21 and P 22 to a pressure difference transmitter 20. The pressure difference transmitters 19 and 20 emit signals, which are proportional to eachAPi ( 11- 12) an ~~~ ( p 21"* p 22)* τ * e multiplexor 25 is used as a multi-hand input for the analog/digital converter 24, which converts the different analog signals (Δ p ι,ΔP2 26) to digital signals useful for the micro-processor 23. The micro-processor evaluates the value, with which the actual value 26 of the guide rail shall be adjusted for obtaining a lower degree of rotation, which gives an improved efficiency, and emits this value as an adjustment signal 27, which in turn is added to the actual value 26. The sum of 26 and 27 is then transferred to the regulator for the pitch angle 28, which in turn emits a governing signal 29 to the servo mechanism for the propeller (not shown). The signal path is illustrated in Fig. 5 (equipment shown as boxes, signals being framed). The pressure difference trans¬ mitters 19, 20 emit signals, which are proportional to the horizontal velocity component in each measurement spot. These signals are digitalized and are stored in the micro-processor 23 for a short period of time (5 - 15 sec.) Thereupon the mean values are calculated and subsequently the difference between the pressure differences on each side of the centre line 22, whereupon a measure of the rotational velocity in the point of measuring is obtained after multiplication with a calibration constant, as a function of the axial flow velocity. For the sake of regulation there is realy no need for adjusting directly on the measurement signal. Generally spoken, e.g. for being able to evaluate the economic usefullness of the system, it is however desirable to calibrate the test probe at flow velocity. For rough estimations of the axial flow velocity in plants where the drop does not vary much, it is possible to estimate the volume flow from the guide rail angle, which is available in the micro¬ processor. In other cases it is also necessary to install and sample a pressure transmitter. The rotational speed recorded is after every measurement series compared to a given limit value. The adjusting function is activated if this value is exceeded. This function operates in two steps. A low disturbance signal is first given to the actual value from the position transmitter for the guide rails. By recording the variations in rotational speed for this disturbance signal it is possible to establish the transfer function for the rotational flow with reference to the runner wheel pitch in the current operation point. By means of this transfer function is thereupon calculated the adjustment signal, which is added to the actual value for the guide rails in order to give a minimum of rotation. If the adjustment gives a remaining rotation exceeding the limit value, then the procedure is repeated until the condition for remaining rotational energy is fulfilled. In order to exclude the risk for drastic adjusting impulses at possible malfunction the adjustment signal is limited thus that it can at most reach a certain percentage of the maximum voltage of the actual value signal of the guide rails. For making it possible afterwards to analyze the effect of an installation of an adjustment system according to the invention it is suggested that the adjustment signal is recorded in a sampling manner. With aid of this information it is possible to calculate what efficiency has been reached and if a permanent installation should be motivated.

Claims: CLAIMS 1. An adjustment device for obtaining the maximum efficiency for water turbines having adjustable runner blades and guide rails and test probes provided in the draft tube after the turbine, c h a r a c t e r i z e d t h e r e i n, that the test probes (16) are arranged in pairs at some distance from each other and substantially radially from the centre axis (22) of the draft tube (15) and mainly at the same level, that the test probes (16) are disc-shaped preferably with a symmetrical wing profile and on each side being provided with at least one measurement spot (17a, 17b), that the measurement spots (17a, 17b) associated with the different probes are connected to one side each of a pressure difference transmitter (19, 10), and that the pressure difference transmitters (19, 20) are arranged to emit signals, which are proportional to the horizontal speed component of the recorded rotational speed of the water and which signals are used for adjusting the pitch of the guide rails. 2. An adjustment device as claimed in claim 1, c h a r a c t e r i z e d t h e r e i n, that several pairs of test probes (16) are arranged on mutually different distances from the centre axis (22) of the draft tube (15) and on different relative levels. 3. An adjustment device as claimed in claim 1, c h a r a c t e r i z e d t h e r e i n, that the test probes (16) are suspendable by means of wires, which can be passed through holes provided in their upper and lower edges, and that the wires are fitted to the internal side of the draft tube (15).

Inventors: SUNNERSJOE STAFFAN, SUNNERSJOE, STAFFAN
Applicants: SSPA MARITIME CONSULTING AB
Application year: 1988
Main classification: F03B15
IPC codes: F03B15