Chile's Colbun delays Nehuenco generator restart

SANTIAGO, April 21 (Reuters) - Colbun, one of Chile's biggest electricity generators, said on Monday its Nehuenco 1 power plant would not come back on line until September rather than June as planned, raising the specter of energy rationing.

Chile's hydroelectric power generation has been hit by one of the worst droughts in decades and a reduction in gas imports from neighboring Argentina, while high diesel generator running costs are piling pressure on industry and the public alike ahead of the looming Southern Hemisphere winter.

Colbun COL.SN closed its Nehuenco 1 plant, a major electricity generator, in December because of a fire. The firm said it had shifted back the reopening date after German firm Siemens (SIEGn.DE: Quote, Profile, Research, Stock Buzz), which supplies the plant's turbines and replacement parts, consulted its own suppliers.

"The new estimated date for the plant to resume service, will be Sept. 10, 2008," Colbun said in an e-mailed statement. It added the new date could be subject to further change because the repair was so complex.

Chilean electricity companies' generating costs are rising as they face a shortage of natural gas, used to fire plants, higher diesel prices, and lower hydro dam levels due to a severe drought.

Chile's thermoelectric generators have also seen increased maintenance problems due to higher demand and because they have had to switch from natural gas to dirtier fuels such as diesel.

The government and private firms are forging ahead with a series of projects in a bid to diversify the country's energy supply that is dependent on natural gas supplies from Argentina -- which last year made the deepest supply cuts since 2004. (Reporting by Monica Vargas, Writing by Simon Gardner, Editing by Sandra Maler)