JOHANNESBURG, July 30 (Reuters) - South African power utility Eskom launched a $1 billion, 10-year bond at a yield of 6.875 percent on Tuesday, Chief Executive Brian Dames told Reuters.

The bond was four times subscribed, with the order book coming in around $4.3 billion.

'It's an expression of international investor confidence in Eskom and South Africa,' Dames said.

Eskom, which provides 95 percent of the power to Africa's biggest economy, needs 300 billion rand ($30.6 billion) for capacity expansion, 83 percent of which had been secured, the company said at a results presentation this month.

Eskom was also looking at obtaining funds from alternative sources such as the Islamic market.

The utility has been walking a tightrope for five years as it tries to bring long-overdue power plants online after a power crisis in 2008 caused factories and smelters to shut, costing the economy billions of dollars in lost output.

Power from Eskom's new Medupi plant, currently under construction, was planned to hit the grid in the second half of next year. But frequent construction delays have led analysts to think it may come on-line even later than that.

The South African Reserve Bank has raised concerns about electricity supply constraints, which it says are key risks to economic growth. ($1 = 9.8067 South African rand)

(Reporting by Xola Potelwa and Sherilee Lakmidas; Editing by Jon Herskovitz) Keywords: SAFRICA ESKOM/BOND

(xola.potelwa@thomsonreuters.com)(+27 11 775 3098)(Reuters Messaging: xola.potelwa.thomsonreuters.com@reuters.net)

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