This is what: “Unforeseen maintenance” at one of the state run Eskom units looks like. Duvha is required it to remain shut down for 18 months for... “Unforeseen maintenance” .... So this is what we have discovered happened at Duhva power station... They were doing a test of the turbine over-speed protection system, and the protection did not kick in. Conventional wisdom would be that there should be a better way to test a protection system than to try and destroy the turbine and see if it protects itself, but that is basically what Eeeeeshkom did. The turbine has a governor valve which controls the amount of steam coming into the turbine in order to keep it running at the right speed (3000 rpm for our grid frequency). Then it has a main isolation valve to shut the steam off completely. The protection systems (of which there are 3 independent systems, and an operator with his finger on the emergency STOP button) are supposed to close this main isolation valve in a fraction of a second when the turbine over-speeds. So for the test, they dumped a massive amount of steam onto the turbine. It went from 3000 RPM to 4500 RMP in ten seconds (they are generally only designed for 10 to 15% over-speed. All three protection systems should have kicked in before 110%). All three systems failed, and the operator with his finger on the manual STOP button was not at his post. So the result was a huge explosion, some fire and a lot of steam. Duvha has a shared turbine hall. All six units are placed in one long straight line, with no missile shield between them. They are very fortunate they did not lose the entire station. This is the result of two decades of mis-management, Affirmative Action, Black Economic Empowerment, corruption & incompetence...Ineptocracy in a word.
Posted on: Sat, 06 Dec 2014 15:39:34 +0000
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