The Kinlochleven scheme in Scotland first produced aluminium in 1907, with completion of plant construction in 1909. Eleven Pelton turbines each drove two 250V DC generators to provide power for the smelting process. Three 10MW Francis turbines have been installed at the plant to replace the motor generator sets.

Gilkes’ experience of low, specific speed Francis turbines was utilised by the client, Alcan Smelting and Power, to provide an effective power generation solution. The company’s contract included the design, manufacture, supply, installation, commissioning and performance testing of the:

• Gilkes Francis turbine.

• GEC alstom generator.

• Main inlet valve.

• Hydraulic controls.

• Turbine controller.

• Lube oil system.

• Special inlet pipework.

Francis turbines

The main 10MW turbines are low, specific speed Francis machines with their stainless steel runners mounted directly onto the extended generator shaft. This direct mounting arrangement gives a compact plant layout. All the turbine shaft loadings are taken by the generator bearings and so close liaison with the generator manufacturer was required.

Gilkes had previously installed the existing 10MW turbine, and the second and third turbines now generate an extra 20MW of power, each from a head of 278m at 1000rpm.

The initial phase one 10MW Francis turbine had a simple PLC speed control to ensure synchronisation with the grid. Phase two required the replacement of the PLC speed control with a Gilkes digital speed governor that controls all three Francis turbines.

The three 10MW turbines are now able to operate either synchronised with the grid or in ‘island’ mode, the benefit being that the nearby Lochaber smelter is protected should the grid fail, as it can operate in island mode. The synchronous generators can supply power factor correction into the grid system when required.

Penstock system

In addition to the turbine installation, Gilkes carried out a full hydraulic analysis of the existing penstock system to ensure that the penstock pressure rise under all operational conditions remained below the permissible design limitations. As a result substantial flywheels are incorporated on each generator set to limit the rate of speed rise and corresponding flow reduction in the penstock system. Tests carried out during the commissioning of the plant confirmed the accuracy of the design and validity of the design software.

Careful design of the new inlet pipework was essential to minimise the forces transmitted to the existing penstocks, which are supplied from the nearby Blackwater reservoir. Flow to each 10MW Francis turbine is from two existing penstocks, which are combined in a fully constrained Y-piece. Additionally a lateral compensator fitted downstream allows inlet pipework movement without subjecting the turbine to transmitted pipework forces.

Smooth operation

The whole project has run smoothly from conception to completion. Alcan Smelting & Power, the contractors and Gilkes have worked closely together as a team throughout all phases of the project. The project has consequently been executed ahead of time, to budget and to everyone’s satisfaction.