Keep on running

Refurbishment is giving hydro stations in the Scottish Highlands a new 30-year lease of life. Andrew Cavenagh reports

Some of the oldest power stations in the UK are coming to the end of their natural lives north of the Scottish border. However, this milestone will not produce the traumas that inevitably seem to arise when coal-fired or nuclear plants reach such a point.

This is because most of the 54 hydro stations that keep the lights on in the Highlands are to be given a new 30-year lease of life.

Hydro-Electric, which operates the system, will spend £150m on a refurbishment programme over the next 15 years. The programme will embrace the company’s 30 largest stations, which account for about 80% of its total installed hydro capacity of 1064MW.

The overhaul of each station will entail replacing its turbine runners (the annular steel constructions that weigh up to 12 tonnes and are sent spinning at 240 revolutions a minute by water pressure); rebuilding the cores of the generators that sit on top of the turbines; and replacing the switchgear, cabling and controls.

Advances in technology since the stations were built from the 1930s onwards – especially more efficient designs of turbine runner and self-lubricating materials that reduce maintenance – should mean the revitalised plants are more productive than before.

‘We are hoping at the end of it we can increase the annual output by 5% overall,’ says Jim Smith, Hydro’s engineer in charge of the refurbishment programme.

After 18 months, Hydro is half-way through the second refurbishment in the programme at the 66MW Fasnakyle station, about 40km west of Inverness. Renewal of the last of four turbine/generator units at the company’s largest hydro station – the 130MW plant at Sloy, about 125km to the south – is nearing completion, four years after the project began.

The reason the Sloy and Fasnakyle projects have taken so long is that Hydro continued to operate the plants throughout the operation, refurbishing a single turbine/generator unit at a time.

Now the company has established that the procedure is viable, it is looking to accelerate the programme, largely through farming out future work to turnkey contractors – Fasnakyle will be the last project Hydro itself manages.

Smith says that by handing the responsibility over to competent contractors, usually the designers and manufacturers of either the turbines or the generators, Hydro can make huge savings on the staff it has to devote to the programme.

The contractors will also be able to press ahead without the distraction of having to maintain generating operations, which will slash the time spent on each refurbishment.

Hydro recently awarded GEC-Alsthom an £8m contract for the next refurbishment, that of the 36MW Glenmoriston station just to the west of Loch Ness. The contractor will start on site in February and is scheduled to be finished in October, with the station closed for the duration. However, Smith says: ‘We won’t always close a station down.’

Hydro is assessing the four suitable tenders it received for the refurbishment of the Rannoch power station, which was built in 1930 and the oldest in the company’s portfolio.

As Hydro overhauls the means to provide perhaps the most readily renewable of all natural resources, it is ironic that the continued use of hydro power in Scotland – at least at current levels – is under threat from two ostensibly environmentally conscious sources.

The first is the river lobby. It was always recognised that damming rivers to create the pressure required for hydro plants would disrupt the natural water courses, and the stations – apart from some of the very earliest – are required to release a certain volume of water directly downstream from the reservoirs.

These water compensation agreements are specified in the indi-vidual statutes that authorise the plants, and can require a station to release up to 20% of the river flow.

Elements in the Scottish Environmental Protection Agency (Sepa), backed by the fishing lobby, have indicated they would like to see these release figures revised upwards.

But Hydro points out that any reduction in the amount of electricity from hydro power will mean more comes from fossil-fuel sources, increasing carbon dioxide emissions. This argument also has its supporters in Sepa.

Any change to the compensation agreements would require parliamentary action. Hydro is concerned that the issue might fall within the remit of the recently approved Scottish Parliament, which could prove more susceptible to parochial interests than Westminster is.

The other threat to hydro comes from wind. Paradoxically, the existing hydro plants are not included in the Scottish Renewables Order, which obliges power companies to purchase a certain amount of their requirements from ‘renewable sources’. As the most suitable sites for wind farms in Scotland tend to be in the same regions as Hydro’s plants and there is no spare capacity on the local grids, wind can only come on line at hydro’s expense.

As a power distributor itself, Hydro could be obliged to buy relatively expensive wind-generated electricity from a third party instead of its own, cheaper hydro power.