Lochaber Hydro Scheme
Turbine Maintenance & the Importance of Records.
A turbine we were asked to provide service and maintenance support for was not producing power as expected. Inspection of the intake, transfer pipe, header tank and penstock identified anomalies with the construction:
The dam wingwalls were too low, meaning water was passing around the side of the screen before the design flow was met.
The long transfer pipe between the intake and header tank was choking. At higher flows, it could not pass enough water to the header tank. An internal inspection with a remote camera showed high points and air pockets. Analysis of the penstock length, diameter and type suggested there was the potential for losses at high flows.
A significant drop in dynamic head on the pipeline during periods of higher power output was noted. These were beyond what would be expected. An inspection of the upper penstock from the header tank showed a significant build-up of peat deposits on the inside surface of the penstock.
In 2020 we raised the dam by 200mm. This meant that the full design flow was available to the hydro scheme before water passed over the wider weir. This showed an improvement in output.
This summer we carried out major remedial works on the hydro scheme, over two two week periods.
We replaced the transfer pipe with a larger diameter pipe. Critical to this was that there was only 300mm drop over 150m between the intake and the header tank. This has yielded significant improvements in output, with the turbine reaching peak powers earlier, using less water, and sustaining those higher power outputs for longer.
Adding airvents to the newly installed transfer pipe.
Installing the new transfer pipe
We have now just completed the installation of a pigging chamber and infrastructure outside the turbine house. The original installation had no facility to allow for the penstock to be cleaned. The penstock originally ran directly into the turbine manifold, no removable sections or tees. Now the system has been fitted with a swept tee, isolation valve and pig catcher, meaning pigs can be launched from the header tank and managed safely through the penstock and retrieved. Pigging is to be carried out in the coming weeks.
The combination of these works is already showing a large increase in the generating capability of the hydro scheme. Designing the infrastructure into the system during construction would have been the best solution. However, where this is not obvious, monitoring the behaviour of your hydro scheme can help to identify issues and analysis will show you where these are.
To learn more about making hydro work for you, contact us and speak to one of our experienced engineers.
The area of blue on the top of the pipe shows where air pockets collect.
Replacing the intake screen once the dam has been raised.
Installing the pigging chamber