Penstock replacement in the Scottish Highlands

The location some 1,000 ft above sea level, extreme weather and tight manufacturing timescales made Kinlochleven a challenging and exciting replacement project

Challenging conditions

Access and potential exposure to extreme weather events were two of the key challenges facing the customer and Glenfield Invicta on the Kinlochleven project. The penstocks themselves are located almost 1,000 feet above sea level and, during the original construction of the scheme almost 142mm (5.6 inches) of rain fell in one 24-hour period.

Given the location and weather the customer was keen for the work to be undertaken in one visit. This in itself was a challenge with the penstocks in three separate locations and a short manufacturing time from drawing approval to start on site. Compounding all of these hurdles was the Covid-19 lockdown. The project was awarded, manufactured and installed during national lockdown.

Hydropower: an international perspective

The UK has 4,700 MW of installed hydropower capacity; a massive amount of energy, when you consider that with just 1 MW, it is possible to power an average home for over a month. The vast majority of this capacity is located in North Wales and The Highlands of Scotland.

Interestingly, electricity was first generated from hydropower in Scotland in 1879, two years before the first public electricity generator.

To provide an international perspective, China has almost one hundred times more installed hydropower capacity than the UK. According to the International Hydropower Association, Denmark has only 9 MW, the smallest installed capacity of any major European country with the exception of Estonia.

Almost 100 years old and still in operation

Glenfield Invicta visited the site and discussed the challenges to be addressed. Glenfield Invicta had worked on the Kinlochleven in the past, and the current penstocks dating back to the 1930s were manufactured by Glenfield. This pedigree, reinforced by a rapid response and a scheme of works that required only one visit to site, led to Glenfield Invicta being awarded the works. The general arrangement (GA) drawings quickly followed, and customer approval enabled the manufacturing process to begin.

From manual to remote operation

The penstocks were manufactured from stainless steel and were fitted with electric actuators to enable remote operation; a major benefit compared to the manual operation of the legacy penstocks.

The scheme’s history

The Alvance Aluminium smelting works based at Fort William is the last one of its kind in the UK. Aluminium smelting is energy intensive as the process requires alumina (aluminium oxide) to be dissolved in synthetic cryolite at 1,000ËšC. The only commercial deposit of the mineral cryolite was in Greenland, but this has now been exhausted.

The Fort William smelting works draws the majority of its power from two hydroelectric schemes: the Lochaber hydroelectric scheme commissioned in 1929 and built specifically for the works, and the Kinlochleven hydroelectric scheme, originally built to supply power to a now non-existing smelting works. Both schemes are now operated by Alvance’s sister company, SIMEC, and in their day were major civil engineering projects.

The Kinlochleven scheme is fed by the Blackwater river’s chain of creeks. The Blackwater dam, the longest dam in the Highlands at 948.5m, was constructed in the first decade of the 1900s to create a reservoir.

Water from the reservoir is transported via a 5.6km long concrete conduit and subsequently into steel pipes that feed the water into the power station turbines. The flow of water into the conduit and pipes is controlled by three DN1000 penstocks. These were originally manually operated.

Made by hand

The Blackwater dam is located in almost inaccessible terrain. Amazingly, the dam was constructed using hand tools by over 2,000 manual workers, without the benefit of mechanical earth moving machinery. Materials were transported to the site from the wharf at Loch Leven via a 10.5km cableway.

Great team effort

The installation was undertaken by Glenfield Invicta’s full-time penstock installation team, which made it through on time despite significant flooding during the week of the installation.
The works themselves were quite challenging as cofferdams had to be created and water pumps used, to divert the flow of water. A cofferdam is an enclosure built within a body of water to allow the area to be pumped out. This creates a dry working environment so the work can be carried out safely.

Peter Dodds (Mechanical Engineer at SIMEC) was delighted with the attitude of the team and their drive to get the job done without a need for a second visit:
“The installation team were great to deal with and helped overcome all problems such as the unexpected rainfall which tested the pumps and cofferdams. The newly installed penstocks have been a great improvement in terms of operation, leakage, and improved safety for our operators.”

Wilson McPhail and Jim McAllister, Glenfield Invicta’s leads on the project, add:
“The success of the project can be put down to three key factors. Firstly, the customer trusted our expertise and allowed us to get on with the job. Secondly, open communications and teamwork helped smooth project delivery. Finally, the positive attitude of the Glenfield Invicta workshop and installation teams meant we were able to absorb everything that the weather had to throw at us – and it was very wet! – and still complete the works within the narrow time window available to us.”


109-year-old Glenfield pressure reducing valves refurbished

Glenfield was asked to conduct an inspection of the valves installed in the Kinlochleven hydropower plant during its original construction, to diagnose the problem and report on the feasibility of a refurbishment program to return the valves to their original condition.