SCOTTISH Hydro-Electric

yesterday announced a deal to fit new, more efficient turbines to its troubled Keadby power station in

Lincolnshire.

This gas-fired power station has suffered repeated problems with its turbines, made by General Electric of the US, since they were installed nearly four years ago.

Both sets will now be replaced with upgraded compressors that will increase the generating

efficiency of the 680-megawatt plant by 6% and will hopefully work more smoothly.

General Electric is already replacing one turbine, which has been off-line since August last year, free of charge.

A Hydro-Electric spokeswoman said the American company has now agreed to replace the other at an ''exceptionally good'' price.

This was not officially disclosed, but industry sources said Hydro-Electric would only pay half the #30m which General Electric usually charges for such turbines.

Both new compressors should be up and running in time for Keadby to meet peak electricity demand this winter.

The upgrade will allow the plant to convert nearly 58% of its heat into electricity, up from 54% at present.

Trouble with the original turbines caused a 12-month delay in commissioning Keadby, which was finally handed over in January 1996. Hydro-Electric and Norweb, which initially had a half-share in the power station, received an unspecified sum in compensation for this setback. But the turbines have been plagued by operational problems ever since.

Hydro-Electric said it was ''absolutely normal'' for new power stations to experience such teething problems for the first four or five years of their life, but Keadby has suffered more than most.

The Perth-based electricity company must now be praying that similar problems do not crop up at its Seabank combined cycle gas turbine power plant near

Bristol, which is due to start

commissioning trials shortly.

This 750mw plant is being built as a joint venture with BG, which will supply the natural gas to burn as fuel. Hydro-Electric will operate the power station and market its entire output.

The Scottish company has doubled its share of the UK generation market over the last five years. By the time Seabank opens and Keadby is running smoothly it will account for 9% of Britain's entire electricity output.

Hydro-Electric has further boosted its ability to sell electricity South of the Border by concluding a long-term agreement to buy 400mw of electricity from the Rocksavage gas-fired power station near Runcorn in Cheshire. This was built as a stand-alone power plant by Intergen, a partnership between Shell and a US generator. Hydro-Electric has put tentative plans to build further generating capacity in England on ice until the Government publishes its review of energy at the end of June.

At that point the Department of Energy will reconsider its moratorium on building any more gas-fired power stations.

The ban was imposed last year to give the remnants of Britain's coal-mining industry a breather.

If it is lifted, Hydro-Electric may well decide to expand the generating capacity of Keadby and eventually Seabank too. The company already has Section 36 planning consent to double the capacity of both power stations.

Meanwhile, Northern Ireland Electricity yesterday denied press reports that it might scrap plans to lay a 250mw undersea electricity cable to Scotland to gain access to cheaper electricity generated by ScottishPower and Hydro-Electric.

The company said it remains ''fully committed to interconnection with Scotland since it is convinced that this is in the long-term interests of electricity customers in Northern Ireland''.

ScottishPower is particularly keen on the interconnector going ahead since it would open up a new market in Northern Ireland and allow the company to burn more coal at its under-utilised Longannet power station in Fife.

Northern Ireland Electricity hopes the Government will give its final approval for the project by the autumn.