One of the oldest sources of renewable energy, hydropower, is based on a simple principle: flowing water spins a wheel or a turbine which generates electricity. Hydropower stations vary in scale, but the ones on the larger end of the spectrum are a sight to behold. The parts are massive. A Francis turbine, the most common type found today, can weigh 200 tons and measure nearly eight meters in diameter.
Hydropower stations feature sizeable parts, like this turbine
The sheer size of hydro parts complicates maintenance. It’s not easy to find a stock replacement. When a part breaks, you need to repair existing parts to keep the stations up and running. This process demands skill and time. Regularly checking for wear, reverse engineering replacement sections, ensuring correct welding, machining parts into the intended shape… It’s no small feat.
Forward-thinking companies out there have discovered that new technologies can allow them to enhance the efficiency and precision of this process. Their secret weapon? 3D scanning.
Matthew Percival, a scanning service provider based in Canada, has witnessed this trend first-hand. Over the last decade, his business 3DRE has become the go-to scanning specialist for many hydroelectric facilities in British Columbia, and Percival himself has processed hundreds of hydro parts.
Recently he lent his skills to a hydro where pumice has been causing significant damage. The facility has been leveraging 3D scanning workflows for two different steps: checking the wear and repair of a certain part, and digitizing the existing part for future replacements.
Pumice are abrasive particles formed when super-heated, highly pressurized rock is rapidly ejected from a volcano. “The pumice in the water is wearing out all of the wicket gates, the runners, and other parts. It even makes holes right in the runners. The plant needed to take out the damaged parts of the turbine, weld on them or put in a new plate, and then machine the weld to the right thickness,” Percival explains.
A scanner and Geomagic Control X were used to inspect a draft tube, a large element fitted at the discharge of a turbine that decreases water’s exit velocity, and wicket gates, wing-like plates on the front of a generator that allow or stop the water flow into the turbine’s runner.
3DRE’s scanner of choice was Scantech’s TrackScan System, which has an optical tracker that allows large parts to be measured with or without targets. 3DRE needed to lift the part to capture its underside, and targets allowed them to move and scan the part at the same time. Two people completed the scan in three hours at a point spacing of 2 mm and a total of 11 million points of data.
3D scanning a draft tube to check for signs of wear
To identify signs of wear on the tube, Percival created a deviation map. He loaded the scan data into Control X, used the Plot command, and used a minimum thickness of -1mm and a maximum thickness of 15mm to generate the color map below.
“I knew the part was designed with a 10 mm wall thickness and that information was the basis for the inspection. I found some coating on the interior, which is reflected in the wall thickness of 11.5 mm. From this data, we were able to determine that there was no significant wear on the draft tube itself,” Percival says.
In addition to inspecting the tube, the hydrostation wanted to create its as-built model, which would show the part exactly as it exists in use. This type of model could be used in the future to replicate the draft tube once repair is no longer viable.
“When parts of a draft tube get worn, you cannot simply order a new one from a manufacturer, is because each part of a draft tube varies and its ends are cast in place within the facility it is used in. You need to 3D scan a worn part and remake an as-build part,” Percival explains.
To create the as-built CAD, Percival used Geomagic Design X, Oqton software for easy 3D reverse engineering. Using the drawing as reference he modelled the body using the Design Intent feature, then modelled the ends as-built since the mating ends are fixed into concrete and do not move.
Finally, he exported the file with the Live Transfer option and made the fabrication drawings. The model will be useful in creating and machining replacement parts.
3D scan of a runner shows the amount of weld build-up
While the 3D scan of the draft tube didn’t show any signs of wear, the wicket gates were a different story. “Wicket gates were wearing out because of the pumice in the water. They had been repaired, and we scanned to inspect that repair and see if it was machined correctly,” Percival says.
Welding is used to repair these large parts, but it often results in excess material around the welded area. This is machined to achieve a final shape that corresponds to the CAD model. 3D scanning is used to check if the process resulted in the right shape.
An analysis of the wicket gate wear conducted with Geomagic Control X
Geomagic software plays a part in making the entire process simpler. “I find Design X very easy to use. It’s just like any CAD and the compatibility with SolidWorks is perfect,” Percival enthuses.
The evolution of scanners and advanced 3D scanning software are offering greater cost-effectiveness and expanded capabilities for hydropower stations. As these technologies become more refined, a wider spectrum of users will be empowered to tackle grand manufacturing challenges, no matter how complex.