Power Stations, Process Control, Computers and cock ups.

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Power Stations, Process Control, Computers and cock ups.

Postby Million Horsepower » Sun Feb 17, 2019 8:08 pm

As I went through my career I saw technologies come, reach their zenith and die. I started out seeing cascaded control system utilising 3 to 15 psi air signals that controlled 60 MW units to PLCs and SCADA systems on 685 MW units. At some point in the middle the 741 op amps by the thousand controlled everything from steam turbine governing systems to boiler controls. I personally really liked the op amp technology because it was so easy to follow the signal path and fault find using just a DVM. If you wanted to change how it worked you got a soldering iron out.
The very first commercial Advanced Gas Cooled reactors (AGR) had Ferranti Argus 500 computers. They had magnetic drum storage as I recall. The operator used it to control the reactor and it had the potential to tweak the auto rods to even out the neutron flux density and also control the channel gas outlet gags to even out the temperatures. Plenty of scope to uneven everything as well. I spent many hours routinely checking the calibration of a myriad of trip units and also proving that every single one was capable of tripping the reactor if called upon. You could join the 660 MW club if you got it wrong. I was told by my boss, every time before we started testing “Don’t ***** trip it”
I can honestly say I never did trip a unit but I have seen quite a few people do it over the years. A colleague of mine managed to switch both channels of a dual channel automatic voltage regulator off at the same time. I watched the lights bounce up and down, the vector meter swung from one side to the other and then down rapidly after the machine pole slipped a few times, the loss of excitation trip had kicked in and everyone looked a bit deflated. We had also managed to do it just before the evening peak so you could watch the frequency meter dive as the deficit in generation woke up the loading desk engineer at Grid Control.
These events were actually few and far between, so they stick in your mind. On one occasion an operator got bored running at steady state full load. He decided he would lamp test the whole panel and change any faulty lamps. He proceeded to work his way around the panel until he got to the main boiler feed pump discharge valve. He used the lamp extractor but he accidentally operated the close button. The actuator started running shut and there was no way to stop it! If he had realised soon enough he could have taken the pump off auto and after starting the electric pumps he may have caught it. But what actually happened was the steam turbine turning the pump kept increasing power to try and feed the boiler. Eventually as the discharge valve was almost closed completely the poor pump gave up as it was destroyed. This was then used as a worked example of a 15 pence lamp fault costing £500 000 in maintenance and contract default payments.

During the storm in October 1987 the south east of England got cut off from the rest of the country. The stations had a black start plan to re-energise the local grid using gas turbines to start up from a dead system. And so it was after struggling to get to work the station was in the middle of a “Black Start”. It was the first and last time we had ever seen it for real. We had gas turbine powered tea and then I went up to the control room to see what was happening. As soon as I was there they said there were a few problems on the steam temperature controls and could I look at them. I went out the back to the equipment room and started resetting the faulty channels. Just as I reset the last one the whole place was plunged into darkness. My heart sunk and I started thinking “It can’t do that surely? Can it?” I went back into the control room and there was a very red faced control engineer who had just opened a breaker that should have remained closed! I was relieved.
I was going to talk about mini and microcomputers but I shall leave that to another day if anyone is interested enough to ask.
Million Horsepower
Posts: 3
Joined: Wed Apr 22, 2015 7:21 pm

Re: Power Stations, Process Control, Computers and cock ups.

Postby Lucien Nunes » Tue Feb 26, 2019 9:14 am

Fascinating tales. It would be interesting to compare the 'worst nightmares' of engineers at stations through the decades with different technologies under their command. What was the most fickle system or component, which human error was likely to wreak the most havoc etc. It's amazing how something that has been the bain of engineers' lives on a daily basis can suddenly drop off the radar during a refit, then ten years later it's nothing more than an amusing topic of conversation over a cup of tea.

Do tell more about the minicomputers...
Black was always meant to be a phase. The neutral phase.
Lucien Nunes
Posts: 329
Joined: Fri Apr 18, 2008 12:26 am

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