This is only the latest in a series of serious incidents at Duvha – the worst being a two-year outage of Unit 4 – which raises questions about the quality of management at the power station.
The incident has increased the utility’s unplanned outages by 600MW to 4665MW and has reduced an already slim reserve margin to 1 688MW.
A further 5 624MW of generation capacity has been taken out of the system for planned maintenance.
The utility said on Monday night there was no immediate threat of load shedding.
It said: “After a boiler tube leak alarm, the boiler tripped on a high pressure alarm. Upon inspection, damage was observed in the boiler and surrounding equipment.
“The reason for the boiler over pressurisation is being investigated. Eskom engineers have been on site today and have undertaken a preliminary assessment while the boiler cools down enough for a full assessment to be undertaken. The results of this assessment and the implications of this incident will be reported once available.”
Duvha Unit 4 was extensively damaged in February 2011, reportedly due to “operator error”. It was offline for two years until January 2013, reducing available generating capacity by 600MW.
In February this year former Eskom CEO Brian Dames disclosed that the coal conveyor belt that transports coal from the adjacent mine to Duvha was damaged in December, resulting in significant coal-supply challenges for the station, a reduction in output and coal being transported by truck as a temporary measure.
Business recently reported that the National Energy Regulator (Nersa) was very concerned about Eskom’s maintenance regime.
Thembani Bukula, Nersa member for electricity, said the regulator was concerned about units taken out of service for major maintenance that often break down again shortly thereafter.
Bukula criticised Eskom for doing extensive maintenance at all cost, but not doing it properly. The result is excessive unplanned outages that coincide with huge amounts of planned maintenance and insufficient generation capacity left to keep the lights on.
Shaun Nel, spokesperson of the Intensive Energy Users that represents Eskom’s biggest industrial customers says the organisation shares Nersa’s concern and there is clearly something wrong at Duvha.
“Last year Duvah was shut down for ten days for maintenance, but it took much longer to bring it back to service again.”
He said unplanned outages were significant and it was clear Eskom’s maintenance was not done properly or something was going wrong when it was brought back to service again.
The information Eskom supplied was usually at an aggregate level and the data for individual plants was not available.
“The problems are at a level where it cannot be interrogated,” he said, calling for more transparency and disclosure.