FIELD OF THE INVENTION

The present invention relates to a hydraulic installation where sediment concentration in the water flow circulating through the cited installation is monitored continuously, and to a method for operating such a hydraulic installation.

BACKGROUND

In a hydraulic installation, where a forced flow of water passes through a hydraulic machine (of the type rotating turbine, pump or pump-turbine), the monitor- ing of sediment concentration in this water flow is of vital importance, as it originates abrasion phenomena in the hydraulic machine. In particular, sediment concentration is a key factor for hydro power projects that are located in rivers with high content of abrasive silt. As an example, the silt (sediment) content in a river flow during the flood season can go up from 100 mg/l to 10 g/l or even more. In spite of massive construction of de-silting basins provided, silt is moving ahead in the water flow; such high content of silt enters in the underwater hydraulic machine parts at significant speed of 20 m/s to 150 m/s, leading to severe abrasion and erosive wear in the cited hydraulic machine parts. Due to continuous impingement of silt onto the hydraulic machine parts being under water, erosion damages and changes the hydraulic profile of these underwater parts.

In order to mitigate this damage, abrasion resistant protection is applied on the hydraulic machine parts located under water, in order to enhance service hours. Moreover, at most of the sites, power plant operators shut down the hydraulic machine when a specific threshold silt concentration is reached. Hence, meas- uring the concentration of silt or sediment plays a significant role in the operation of a hydraulic machine. At most of the hydraulic power plants, sediment concentration measurement in the flow is made by manual weighing of the flow passing through the machine comprising sediments, which is compared to a clean water sample used as reference. Although this method is reliable and accurate, it is also very cumbersome, time consuming, expensive, and the results are not available quickly, requiring very often weighing in order to provide a more continuous measurement of the sediment to establish a proper record.

It is known in the state of the art, as per US 6466318 B1 , for example, a device for measuring the diameter and area of particles in a given volume, by means of a submersible laser scattering instrument. A beam of laser light is directed across a void where a sample of water containing particles is admitted. After passing through the water, the light which is forward scattered out of the direct beam falls on two detectors at the same time, providing two measured outputs that, when electronically combined, give a mean diameter for the measured particles. Howev- er, such a system works on a sampling basis, which is not truly a continuous measurement. Moreover, this device can only work to a limit of 1000 mg/l: for higher concentration it may require dilution that may admit uncertainties in the measurement and a high pressure feeding of the system is not possible, as a local high water speed of erosive water would damage the system.

Therefore, it is highly desirable to develop a hydraulic installation where the measurement and monitoring of the sediment concentration in the water flow circulating through said hydraulic installation is done accurately and continuously.

The invention is oriented towards providing such a hydraulic installation, and also to a method for operating such a hydraulic installation.

SUMMARY OF THE INVENTION

The present invention relates to a hydraulic installation where sediment con- centration in the water flow circulating through the cited installation is monitored continuously. According to the invention, the hydraulic installation comprises a pressure- reducing device and a primary sensor: the pressure reducing device decreases the pressure and discharge of upstream water flow, comprising sediments, allowing that the primary sensor can operate continuously measuring sediment concentra- tion from the upstream water flow. The hydraulic installation also comprises a calibrating device, providing the primary sensor with a reference value to be used for comparison matters and for establishing the content of sediment in the water flow.

According to the invention, the hydraulic installation can also comprise at barrage or dam upstream river, a second sensor that also measures sediment concentration in the water flow at the barrage or dam, also comprising a pump or second pressure-reducing device for the purpose of feeding properly the second sensor and a second calibrating device, aimed at transmitting an alarm signal to the turbine operator, in case the sediment concentration in the water flow raises a pre-defined limiting threshold value, well in advance for the operator to shut down the turbine operation.

The hydraulic installation can also comprise a third sensor, a second pump and a third calibrating device, installed typically downstream, at the outlet of the turbine, for measuring the sediment content in the downstream water flow just passed across the turbine.

The present invention also relates to a method of operating any of the hydraulic installations described above.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing objects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein.

Figure 1 shows an overall view of the hydraulic installation for sediment concentration monitoring in the water flow according to the present invention. Figure 2 shows the configuration of the pressure-reducing device in the hydraulic installation for sediment concentration monitoring in the water flow according to the present invention.

Figure 3 shows the configuration of the upstream hydraulic installation for sediment concentration monitoring in the water flow according to the present invention.

Figure 4 shows a cross-section of the filter component of the pressure- reducing device in the hydraulic installation for sediment concentration monitoring in the water flow according to the present invention.

Figure 5 shows a cross-section of the high pressure fittings in the tubing of the pressure-reducing device in the hydraulic installation for sediment concentration monitoring in the water flow according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, the hydraulic installation 100 operating a hydraulic turbine 101 , that comprises a pressure-reducing device 10 and a primary sensor 20, as shown in Figure 1 : the pressure reducing device 10 creates significant hy- draulic resistance and therefore decreases the pressure and discharge of upstream water flow 1 1 , comprising sediments, allowing that the primary sensor 20 can operate continuously measuring sediment concentration in the upstream water flow 1 1 . Depending upon the head available at different sites where the hydraulic installation 100 is going to work, the cited pressure-reducing device 10 is designed in such a way that it is able to decrease the relative pressure below 1 bar and discharge of the water flow 1 1 between 2 l/min to 8 l/min so that the primary sensor 20 can operate. The location of the primary sensor 20 is preferably the one shown in Figure 1 , close to the main inlet valve 12 at the turbine axis where full potential head is available.

As shown in Figure 1 , the hydraulic installation 100 also comprises a primary calibrating device 40, providing the primary sensor 20 with the reference value (typically, from a sample of clean water) to be used for comparison matters and for establishing the content of sediment in the water flow 1 1 .

With the installation of the invention, continuous recording of sediment concentration in the water flow 1 1 is done, thanks to the pressure-reducing device 10 allowing that the primary sensor 20 can work safely for turbine 101 with 10 m and up-to 2000 m head. This has been made possible by maintaining a low silted water velocity at desired pressure and flow for the sensor operation. The most important benefit is that the hydraulic installation safeguards the sensor against severe abrasion normally begins with 30 m/s of water speed inclusive of 1 g/l abra- sive silt content and permits the sensor to operate continually at highly abrasive sites for longer service period.

Further according to the invention, the hydraulic installation 100 preferably also comprises at barrage or dam upstream river, a secondary sensor 21 that also measures sediment concentration in the water flow 1 1 at the barrage or dam, also comprising a pump 30 or second pressure reducing device 14 and a second calibrating device 41 (see Figure 1 or Figure 3). The selection for installation of second pressure reducing device 14 or pump 30 will be based on site conditions with the objective to impart required flow and pressure at inlet of second sensor 21 to operate continuously. The purpose of the second sensor 21 is to transmit an alarm sig- nal to the turbine operator, in case the sediment concentration in the water flow 1 1 raises a pre-defined limiting threshold value, well in advance for the operator to shut down the turbine operation.

In addition, the hydraulic installation 100 of the invention can also comprise a third sensor 22, a secondary pump 31 and a third calibrating device 42, installed typically downstream, at the outlet of the turbine 101 , for measuring the sediment content in the downstream water flow 13, just passed across the turbine 101 .

Figure 2 shows the components of the pressure-reducing device 10 and its installation connected to the primary sensor 20. A probe 1 10 is inserted to collect the water from the penstock line, typically through tapping. The probe 1 10 is de- signed in such a way that it will minimize the local transients and this is achieved by maintaining the probe entrance water speed close to the water flow speed in the penstock from 2 m/s to 15 m/s, thus collecting the water comprising sediments similar to which is moving towards the turbine 101 .

The pressure-reducing device 10 also comprises at least two valves first valve 120 and second valve 121 set just after the probe 1 10, having the following objectives:

i) to switch on the water flow to move forward in the pressure-reducing device 10;

ii) to provide emergency cut-off, and

iii) to conduct any maintenance work in the downstream line.

The pressure-reducing device 10 can also comprise more than two valves, and these would be used as spare valves for safety purpose in case of malfunctioning of the main valves first valve 120 and second valve 121 .

A filter component 140 is added in the pressure-reducing device 10 in order to restrict the entrance of unwanted residues of cloth, rubber, thin sticks of wood or any other extraneous matter. Filter internal design encompasses a good hydraulic cross-section for smooth flow of water with sediments, as shown in representative example design in Figure 4. The pore size 0.5 mm to 2 mm of the filter screen 141 is selected in such a way that it allows all the sediment particles to pass through except for big agglomerated matter as described above. For cleaning during major clogging of the filter component 140 and of the filter screen 141 over the period of time, separate spare filter screens 141 are provided for quick startup of the line. A high pressure flexible hydraulic hose 130 is used to connect the first and second valves 120, 121 to the filter component 140.

After the filter component 140, a tubing 150, preferably made of stainless steel, and preferably having a spiral shape, is fitted, which is key segment of the whole pressure-reducing device 10 that offers significant hydraulic resistance to create major head loss. Preliminary loss coefficients are derived from the literature, and compared with actual water test: on receipt of appropriate loss coefficient, it is applied to any new project to define the characteristics of the tubing 150, mainly length and internal diameter. A reference of the head loss values for a given discharge of 3.5 Ipm shown in Table 1 attached below.

Table 1

The tubing 150 is encircled in circular form like a spring, to occupy less space and to make it compact. The tubing 150 is supported by a suitable frame 160. Tubing ends 170 are affixed with special high pressure fittings 171 which ensure leak proof operation, as shown in Figure 5: these fittings 171 are really simple to fix and open and, in case of little modification of the tubing 150, any tube joint can be easily introduced.

In the example design, a third valve 122 is fixed at down-stream of the tubing 150. The purpose of this third valve 122 is to bypass the flow in case of any malfunctioning of downstream line and to save the sensor 20 from high pressure damage.

A pressure gauge 180 is affixed at the inlet of the primary sensor 20 to read the pressure of the water flowing through. The pressure gauge 180 is mounted with a T-section fitting where its internal diameter is similar to the inside diameter of the sensor tubing.

The water flow 1 1 at high pressure gets adequate head loss while passing through the spiral tubing 150, and enters in the primary sensor 20 at required level of pressure with required range of water flow 1 1 for safe and erosion free operation. The primary sensor 20 measures the concentration of sediment in the water flow 1 1 . The sensor can be based on either of working principle of ultrasound, time-of -flight, optics, laser, acoustic, conductivity, density, photo imaging, nuclear radiation or coriolis mass flow. Continual data of this sediment concentration is recorded and automatic post processing is made with software to register continuous sediment concentration readings. At the outlet of primary sensor 20, a sampling tube 190 is located, so that a water sample can be collected to cross-check the sediment concentration by manual sedimentation method, whenever needed.

Calibrating devices 40, 41 and 42 are used to verify the results of sensors 20, 21 & 22 as and when desired. This ensures the correct data with good level of accuracy all over the period. It is recommended to conduct in-situ verification of sensors at every three months after installation at project site.

Although the present invention has been fully described in connection with preferred embodiments, it is evident that modifications may be introduced within the scope thereof, not considering this as limited by these embodiments, but by the contents of the following claims.

100 Hydraulic installation

101 Hydraulic turbine

10 Pressure-reducing device

20 Primary sensor

1 1 Upstream water flow

12 Main inlet valve

13 Downstream water flow

14 Second Pressure-reducing device

40 Primary calibrating device

21 Second sensor

30 Pump

41 Second calibrating device

22 Third sensor

31 Second pump

42 Third calibrating device 110 Probe of pressure-reducing device

120 First valve of pressure-reducing device

121 Second valve of pressure-reducing device

122 Third valve of pressure-reducing device

140 Filter component of pressure-reducing device

141 Filter screen in filter component of pressure-reducing device

142 Filter component upstream in the hydraulic installation

130 Hydraulic hose in pressure-reducing device

150 Tubing in pressure-reducing device

160 Frame for tubing in pressure-reducing device

170 Tubing ends in pressure-reducing device

171 High pressure fittings in tubing of pressure-reducing device

180 Pressure gauge in pressure-reducing device

181 Pressure gauge upstream in the hydraulic installation

190 Sampling tube in pressure-reducing device

191 Outlet line