17/04/2015

-          Unit for loading up.

-          Unit trip due hot reheat pressure measurement failure (turbine protection).

-          Unit restart

At 11:10 turbine 3000 rpm ready to synchronise

Close to 12:00

 Alstom advises that close to noon 17 April 2015, we experienced yet another blackout event with consequent abnormal run-down of the Unit 6 turboset.

At the time of the event, the excitation unit (AVR) was on and the power train unit was about to be synchronised.

The details of the incident as currently understood and with a focus on impact on the turboset, follow - these will be corroborated by the Sequence of Events logger when such information becomes available.

a. At about midday, an electrical board tripped in-turn tripping the turbine. at this stage the shaftline was running at 3,000 rpm with excitation on and synchronisation about to start.

b. At a shaftline speed of +800 rpm the main electrical board/main HV breaker tripped resulting in a total blackout.

c. The backup diesel generators failed to kick-in at this point and the shaftline continued to run-down on emergency (DC) lube oil supply.

d. At +150 rpm the diesel generators kicked-in and as experienced with the blackout event of 21 March '15, the controls/DCS showed the lube oil pump 'ON' but inspection proved that it was actually 'OFF' and non-operational.

e. Thus, shaftline had to be hand-barred on emergency lube oil, with jacking oil running off the generators, for some time.

f. The shaftline was eventually returned on to turning gear on emergency lube oil, and jacking oil.

Status : 17/04/2015 at 18:15 :

-          Unit ready for turbine start (1 mill in service – unit in by-pass operation)

-          Diesel generator 2 is working correctly  

-          Diesel generator 3 is not working correctly

-          ESKOM Engineering decided to stop the unit and to re-commission the Diesel generators before next start-up