Hydro Quebéc


Laforge-2 Project
Plant size - 304 MW

In 1997, Hydro Quebec measured turbine discharge at the Laforge-2 low-head plant with both the current meters and the ASFM. Three frames were used, with 10 current meters mounted on each of four rows. The ASFM transducers were mounted near the top of only one of the frames. Measurements were taken simultaneously at various operating conditions using:
a) five fixed frame positions (using data from four rows of current meters and from the ASFM), and
b) frame profiling continuously (using data from the lowest row of current meters and from the ASFM).

In spite of trash racks having been removed, resulting in turbulence being lowered by 50%, the ASFM results were within 1.5% of the current meter results and confirmed that the ASFM is capable of the accuracy required to measure turbine discharge in low-head plants.

Publication presented at IGHEM98, HydroVision 2011

Les Cèdres
Plant size - 135 MW

Les Cèdres powerplant is situated on the St-Lawrence. The geometry of the water intake of each of its 17 units corresponds well to the typical shape for which the ASFM was developed: short and irregular.  The intake comprises three separate entrances, each of which are divided in two vertical sections by a two foot thick horizontal pier. 

In 2000, measurements were done using both the current meters and the ASFM.  The instruments were placed in the gate slots upstream of the trash racks. The current meter measurements were made using mobile frames, with ten current meters mounted on the lower horizontal support rod of each frame. The first set of measurements with the ASFM  was made in the same slots as the current meter frames, upstream of the trash racks.  As a result the current meter and ASFM measurements were not done simultaneously.

The second set of ASFM measurements was made with the transducers installed downstream of the trash racks in the lower headgate slots.  This was done as the measurements made upstream of the trash racks showed very low turbulence levels over a large part of the measurement section.

A comparison of the discharge measurements was made by using an index measurement as the reference since the current meter and ASFM measurements were not done at the same time. The index measurement was based on the pressure difference between the headrace level and the pressure in the scroll case and calibrated using the current meter discharge. The mean difference between current meter and the second ASFM results was 1.75 %, well within the measurement uncertainty of the current meter measurements.

Publication: presented at HydroVision 2008, HydroVision 2011

Coteau 1 spillway
Coteau 1 spillway

The Coteau 1 spillway is part of the Beauharnois development on the St-Lawrence river.  It is used to control the flow going to Les Cèdres powerplant situated slightly downstream. Model tests were performed to determine the spillway flow, however, a better accuracy was required for the plant operation.

The Coteau 1 spillway has twenty gates that are 12.8m wide and have an upstream water level of 5.4 m above the sill.  In 2000, Hydro-Quebec chose the ASFM method, after at first considering the use of the current meter method.  The latter was not retained as the water velocity was too high and the flow strongly inclined. 

The ASFM transducers were installed on rails specifically fabricated for the tests and could be positioned at any chosen height using two electronically synchronised hoists.  During the tests, the measurements were made while a continuous sweep of the gate section was performed with the transducers. 

The measurements were attempted at heights between the full opening and 0.55m above the sill. Beyond 0.75m above the sill, air was entrained in the flow and resulted in signal loss and a reduction in the quality index of the acoustic signal.   Only at the 0.55m position were the results satisfactory.  The measured flow of 47.0 m3/s compared well with the model test value of 46.0 m3/s (a 2.1% difference).

Publication: presented at HydroVision 2008

Plant size - 95 MW

Rapides-des-Quinze is not a typical low-head power plant because the two intake bays converge to a single penstock and a standard scroll case. As most of the Gibson pressure taps were blocked, the current meter method was used in the intake. In 2002, the  current meter frames were placed in the stop log slots, upstream of the trash racks. As the ASFM transducers were placed on top of the frames, they were also upstream of the trash racks.
As expected, poor results were obtained from the ASFM measurement. A very low quality index, or even no velocity were measured due to the absence of trash rack generated turbulence.

Publication: presented at HydroVision 2008

Click image to enlarge
La Grande-1
Plant size - 1436 MW
For the 2003 comparison between the current meter and ASFM discharge measurements at La Grande-1, the ASFM transducers were mounted at the top of the current meter frame, so the velocity profile was only partially sampled. The results showed a difference between the two methods of around 1.8 %, with the ASFM underestimating. By using filtering technique to account for vibration of the frame and by changing the number of samples for each individual velocity calculation, this difference was eliminated. CFD simulations of the flow in the intake showed significant velocity variation due to the wake of the main structural members of the trash racks. This was confirmed by both the ASFM and current meter methods.

Publication: presented at IGHEM 2004, HydroVision 2008, HydroVision 2011

More recently, a special version of the ASFM Monitor has been used with three paths installed vertically at the end of the spiral case, chosen because this location is the farthest from the intake and thus can limit the influence of velocity profile changes. The other methods tested were Acoustic Time of Flight, Acoustic Doppler and various pressure difference sensors on the stay vane.

The first series of tests has been performed to compare and calibrate the ASFM Monitor measurements with previous results obtained in 2005 with the Current Meter method. The second series of tests has been performed to verify the influence of the operation of adjacent units. The maximum
deviation was between ±1.5 and ± 2 %, equal or less than the deviations observed with other methods tested at the same time.

Publication: presented atHydro 2009, HydroVision 2011


Rocher-de Grand-Mère
Plant size - 220 MW

The Rocher-de-Grand-Mère is a newly commissioned power plant on the St-Maurice river. The intake has two bays and the layout is typical of a modern design with a relatively smooth converging form. The discharge measurement method used for the acceptance test in 2006 was the current meter method, with 28 current meters mounted on each movable frame. The ASFM transducers were mounted near the bottom upstream edge of each end plate, around 30 cm above the lower row of current meters.

Overall, the mean difference between the CM and ASFM discharge was very low. However, large differences were observed in the left and right bay. The analysis of the velocity profile from the current meter measurements showed evidence of asymmetry with more velocity on one side of these bays. This is due to flow in the forebay arriving at a 50° angle to the intake face.

Publication: presented at HydroVision 2008

Reprocessing of the data by using a low pass filter to remove the effect of current meters has shown a great improvement in the results from the ASFM methods even though this process has removed a large part of the spectral content of the acoustic signals; better results were found at high discharge where more of the signal was retained.

Although the installation of the ASFM transducers on the same frame as the current meters allows making a comparative measurement at low cost, this should never override the need to have the ASFM transducers farther from the current meters.

Publication: presented at WaterPower 2009, HydroVision 2011

Rupert Control Structure
Plant size - 220 MW

The Rupert Control Structure is part of the river partial diversion project  that will bring water to three existing power plants as well as to a new plant (La Sarcelle). Maintaining a minimum flow of water in the river bed for environmental purposes is so important that Hydro-Québec decided to monitor the discharge with two methods: the Acoustic Time of Flight and the ASFM Monitor.

The two flow meters are installed in the central control spillway, with the transducers embedded in the concrete so that they are completely out of the flow. For the ASFM Monitor, eight paths have been installed about 9 m upstream from the gate. This position has been chosen as a compromise between the need to be as far as possible from the forebay in order to get enough turbulence and flow uniformity as well as avoiding flow recirculation close to the partially opened gate. The measurement took place in December 2009 and covered the full gate opening.

Publication: presented at Hydro 2009