A seven metre diameter butterfly valve

I can’t be kept away from work. I don’t know if that’s a pity or I’m just weird. Then again, it’s not everyday that you get to see a hydroelectric power station in a drought-ridden country. It also awakened that technical side of my brain which has been lying dormant for a few days.

Built along with the dam is the Gariep Power Station. This is one of two major hydro stations in the country and on the Gariep River. There are four micro-hydro stations that do exist in the Eastern Cape – namely Collywobbles, Ncora, First Falls and Second Falls, but these are used for grid-stabilisation and are not under the control of Eskom Generation but rather under Eskom Distribution.

At present, the Gariep Power Station uses four generators rated at 90MW each to produce 360MW of power with the head of around 55m. The generators are presently being refurbished and by next year, this station will be generating 440MW. The Vandekloof generators will still be larger, but there are only two there. This value is impressive when one sees the dimensions of the dam wall. We won’t compare it to the 22000MW of Three Gorges…Getting into the station was pretty easy – well for me at least! With prior arrangement, the staff will happily take you around the station. No photographs are allowed though.

I get to the dam slightly early and attempt to get into the power station. This proves a problem seeing that there are two gated entrances. I’m a bit puzzled but I choose the gate on my right. Actually, I know that this entrance is the wrong one but I take it anyway. I obviously haven’t learnt my lesson after encountering the shooting range a few days earlier. Luckily, I don’t end up in some experimental farm but I do get a great view of the dam wall. Viewing it from a platform hundreds of metres away takes away the beauty of the scale of this wall. Coupled with the colossus of water it holds back, the wall looks pitifully small. That is until you see it up close! This wall is not solid but has a series of tunnels embedded in it. One such tunnel is so huge that there is an annual church service that is held within it. One can arrange tours of such tunnels if one wants.

At around 12h00, I meet a distinguished gentleman named Lucas Van Heerden. He has been working at this plant for many years and stays in the nearby hamlet of Gariep Dam (a town!). The town reminds me of a minor holiday town on the KwaZulu-Natal South Coast – albeit, a MUCH more laidback version of it. The station is pretty small and has the dimensions of maybe a single generator-set in a coal-fired station. On the ground level are huge circles painted onto the floor. Underneath each lies a vertically-mounted 90MW beast. The diameter of each is roughly 10m. That’s five of the tallest people you know stacked on top of each other. Pretty huge I tell you…

Taking the stairs down, I encounter the turbine. The hydro plants in South Africa, due to the small size of these plants, are used for peaking power. Simply, this means that when South Africa requires vast amounts of electricity, these stations run. When the load requirements drop, the station is switched off. Hydro stations are built for this purpose because of their very nature – liquid water turns the turbines. Without water, the turbines don’t turn. If these don’t turn, no electricity can be generated. This principle is built into the mechanics of the system so the absence of water does not cause damage to the system. Compare this to a coal-fired station – steam is used to turn the turbines. Steam must be generated by burning coal to heat up water to the required temperature. Water takes a while to heat up hence; coal needs to be burnt for quite a while before optimal conditions are reached. Cooling is then needed to extract the most energy out of this steam. Even with this simplification, one can see that this process is rather complex. Compare this to: Open sluice gate; run water through turbine; make power. One can see that hydro plants are much more suited to the peaking criteria!

As I walk into the room leading to the turbine (the power station was off), I encounter the tailrace pipes that transport the water to the turbine. At this point, Lucas explains to me what I see. When the station is not being used, water must not be let through to the turbine. This is controlled by a valve – a seven metre diameter butterfly valve at that. I look at shocked. I’m in shock and awe and my mouth can’t close because, well, it’s so freaking huge! Lucas sees me and gives the knowing look of, “Ja, I know.” I love being an engineer.

The station also has no control room. All controls of the station are handled via National Control. All alarms are, likewise, sent directly to National Control. If there are any faults, an operator sitting at national control calls up an engineer or technician and the fault is sorted out. Then again, this station maybe gets two alarms per week – something that should trickle through to coal stations. Okay, enough with the words, this is just awesome!

Lucas and I chat for a while about peaking, the new refurbishments of the generators, the new coal-fired stations and the role of renewables and the current financial situation of Eskom and the world in general. We also talk about a pending C&I upgrade to the plant which would render all the employees, which have been working there since the plant was commissioned, useless. The joys of technology…I bid Lucas farewell and leave the station extremely impressed by this great technology.

Hydroelectricity is loved and loathed by various green energy aficionados. The one school of thought sees the damage that dams do when built. Whole ecosystems are wiped out by building a simple dam. The Narmada Valley in India is a prime example (so are all the new dams in China.) The other harps on about the carbon-free energy that we get from this type of power generation. I guess the Gariep is special in this case – the ecosystem around the Gariep is thriving and provides a haven for many endangered species. Then again, most local Nature and Game reserves are built around artificial bodies of water. Without these, most of our flora and fauna would be decimated. Whilst doing this, the station provides the non-industrial electricity needs of several provinces without doing any harm. I wonder if the damage done whilst constructing this dam is offset by the role it’s played in conserving our natural resources…

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