Everything you ever wanted to know about Guri but were afraid to ask

The lower the water level at Guri goes, the more water you need to produce the same amount of power, and the more you risk damaging the actual turbines.

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“The other day I was at the dentist and he is getting ready with his electric drill to make holes, and I thought I better think of something fast or else it is gonna hurt. Then I thought about this little motor going around and what was it that made it turn. And what was going on, and what’s going on is that there is a dam some distance away, and water going over the dam turns a great big wheel, alright. And this wheel is connected with long thin pieces of copper, which split up into other pieces of copper, which split up into other pieces of copper and spread all over the city. And they they are connected back thru another little gadget and makes the wheel turn. All the wheels in the city are turning because this other wheel turns. If this wheel stops all the wheels stop…”

Richard Feynman

Feynman had a knack for explaining things simply and beautifully. He paints a dramatic picture of what will happen when water tumbling over Guri’s great wheels no longer flows and motion stops. Every wheel in every city, every light bulb, every compressor, pump, radio, TV, everything will stop.

Guri is by far the biggest power generating wheel we have. Chavez demonized hydropower and our dependance on it and shelled out cash to nearly double the country’s thermoelectic generation capacity. The plan was to go from 19,000 MW in 1998 to 34,500 MW in 2015.

 
Right now, Guri is just three meters from the lowest point ever recorded.

After all was said and done, today we have today less generating capacity than in 1998 with 17,000 MW available. That’s some 1,700 MW less than the actual demand. We’ve proven utterly incapable to get thermoelectric plants old and new in operation. Hydropower continues to be our most reliable source of energy.

Hydropower is simple. You dump buckets of water from a certain height onto a wheel. Power is proportional to the size of the bucket you drop per unit of time (flow) and the elevation (known as head). Bigger buckets dropped from higher up yield more power. In a hydropower plant, the effective drop is the difference in elevation from the upstream reservoir level to the downstream reservoir level.

This week the upstream water level at gury fell to just 247 meters above sea-level, from a maximum level of 271 meters.

Why is this a big deal?

For a few reasons. Our water buckets are falling from a lower elevation, which means that we have to consume more water to generate the same amount of power. So reservoirs have to be depleted faster and faster just to stand still, in terms of the power availale.

 
At this rate, we are going to reach the historic minimum this month and fall all the way to the critical 240 m mark, where half the plant has to shut down, sometime in late April.

But it’s not just that. You can think of the reservoir as a martini glass. Water available is proportional to the square of elevation. Up higher to the rim, there’s a lot more liquid per cm. elevation than down towards the bottom.

Another key point is that you need to keep a certain minimum pressure to keep the turbines working properly. Without it, you get cavitation. And that’s bad news.

Cavitation is what happens when water goes so fast around the turbine blades that local drops in pressure turn it into vapor globules. When it slows down again, pressure rises again and the vapor bubble becomes water again in a process that creating tiny implosions. Those implosions chip the metal away. This slowly damages the turbines, which undermines their efficiency.

Of course, when the reservoir is low, the last thing you need is anything that requires you to use still more water to generate the same amount of power…but that’s just what cavitation does.

We’ve heard reports that the turbines already suffered some cavitation damage after the last dry spell in 2010, and they were never repaired.

The bigger deal about this 247 meters above sea level number is that, at 240 meters the inlet to nearly half the turbines starts to get exposed, and that forces you to shut them down altogether. That’s 5,000 MW off, what it takes to power maybe 20 mid-size venezuelan cities. It’s about 30% of the total power generation capacity in the whole country: hitting 240 meters would be a proper disaster.

Is that in the cards, really?

Oh yes.

Right now, Guri is just three meters from the lowest point ever recorded. At the moment, the reservoir is dropping at around one meter per week. At this rate, we are going to reach the historic minimum this month and fall all the way to the critical 240 m mark 49 days from now. By then, we’ll have damaged the turbines further through cavitation.

And remember, because of the Martini-glass effect, we shouldn’t expect the rate-of-decline to be quite linear: at least, if the water continues to drop at a linear rate, Guri will be producing less and less power every day. Even so, we have enough water until the end of April, more or less.

The rainy season usually start in May…but not always. Sometimes the rains start a bit earlier, sometimes later. It’s an El Niño year, when the normal patterns are upended.

What can we done today? Brace yourself, buy candles and pray for rain.

 

39 COMMENTS

  1. Who will make the decision to shut-down Guri in April? Maduro? At 241? or wait till 239? When? If they wait too long, and those turbines are subsequently damaged, how many months/years would it take to repair the damage, all the while leaving the entire country in a permanent state of blackout? (pause here) And what amount of foreign reserves would it cost the government to fix this catastrophe, especially with very limited lines-of-credit from anyone or any source? What’s coming is breathtaking. .

    • At 240 meters there is no choice. At 240 meters air starts entering thru the inlet. It will simply make the turbines stop.

      Do you choose to keep your engine running when you are out of gas?

    • “If they wait too long, and those turbines are subsequently damaged, how many months/years would it take to repair the damage, all the while leaving the entire country in a permanent state of blackout?”

      If you take it from Tocoma’s experience it will take years and years, apparently for these guys anything with a minimal intelectual effort is impossible.

      This made me remind the Guaira’s Viaduct that simply fell, they just let it fell. Same thing is happening with the Cabrera’s Viaduct.

      They just let bad things to happen.

  2. Rodrigo,

    Good explanation about what is cavitation, simple and clear.
    I will disagree with the turbine cavitation statement and water elevation at Guri, Although they are directly related, a basic design factor is to prevent cavitation during operation even during the lowest elevation level. At least that’s the way i design and how it should be done,
    If cavitation is happening, probable is caused by maintenance problems than elevation. If suction strainers are not clean it could reduce water flow into the turbine. Don’t get me wrong, it could take an easy decade to clog a dam strainer but knowing the current administration and the maintenance history of our country this could be the main cause.
    Also, Guri was design during times that computers were not available so huge safety factors were added into the calculations.
    If Guri gets below the line we have bigger problems to address than turbine cavitation. Lets only start with sediment and other operational factors that will take a few years to fix.

    • Clogged trash racks (strainers) do cause greater head losses.

      Cavitation levels are known from the design stage and the turbine is installed at a certain depth to prevent it from occurring at a certain head. But there is always a compromise since installing the turbines deeper increases the cost exponentially. They are usually set as high as possible to keep them from cavitating at normal operating conditions.

  3. Cómo se puede tener esperanza?! Cómo vivir en el país más hermoso del mundo, gobernado por los peores gobernantes que existen? Cómo sobrevivir esta desgracia?…

  4. Excellent explanation!

    Building on top of the cavitation issue, I would also like to add the fact that at lower reservoir levels the turbine’s submergence might get compromised, raising the potential of vortex formation and allowing air to get into the turbine itself, creating vibrations that might become critical to the whole powerhouse.

  5. Rodrigo, excellent explanation. Two questions: 1) Is that a Cruz Diez design on the massive walls supposedly somewhere inside the Guri Dam?; 2) At 240 level we lose half the turbines/30% of the Country’s electricity; at what level do we lose the other half of the turbines/another 30% of the Country’s electricity?

      • Rodrigo,

        Just to be clear; the “sala de maquinas 2” is the one with the intakes at 240 masl, and there are the bigger generators. All “sala de maquinas 2” has installed capacity higher than 7000 MW (more than 70% of total installed capacity of Gury).
        So if the reservoir reaches the 240 masl, we will be loosing 80% of “sala the maquinas 2” (that considering that the other 2 turbines at 223masl are up and running), which will be more than simply 5000MW.

  6. We are not even at that level and there was a blackout at Los Puertos de Altagracia since 11 pm yesterday March 14th. Today I got there to try to get my ID renewal …left around 10:30 am and still no sign of getting any power back…. will try Saime again tomorrow, if theres power of course!

  7. Rodrigo, when you say “Water available is proportional to the square of elevation” you mean total water volume ? Due to the Martini glass profile, as you lower the water volume each day the level will decrease faster and faster, from 10 – 12 cm per day it will increase to 14 – 16 cms. and so on …

    Another reason for the cavitation is that as the head /height of water) decreases you need more water flow through the turbines to generate the same amount of electricity,

    Another trick used by Corpoelec was to generate at 58 or 59 HZ instead of 60 HZ. You could see the effect in the microwave clocks losing severalminute sper day… But I have seen theclocks behave the last week so it seems tat they are generating closer to 60 HZ ?

  8. I worked at Guri and Macagua I few many years ago. Back then cavitation was already an issue due to the design of the original francis turbines and some (back then) perceived inefficiencies in the minimum operating head of the turbines (215m). Interesting enough, the upgraded turbines now require a higher head.

    In either case, there was plenty of papers indicated negative capacity may be reached as early a 2010 (like it happened), unfortunately those papers are not available anymore but you may be able to dig it out looking for something it was used to be called “EDELCA Reporte Anual”.

    Now, not everything is lost. I found the 2008 SEN (Servicio de Energia Nacional) report linked below and If you fine comb it, you will find that (1) demand has been growing since 2008 at a pace of 4.6% while installed capacity has grown about 2.3%. Power availability and unplanned disconnects continued to grow from 2004 to 2008. That report is 8 years vintage and was issued before the drought of 2010. Catch my drift?.

    Any way you cut it, it is a horrid situation, and not for the drought or el niño, but the shear size of stupidity and bagabunderia that some of my colleagues are authors, co-authors and ultimately accountable parties. Happily to know that in any other part of the world they would be prosecuted but not in Venezuela.

    Ali Primera song: “muchacho pasame los fosforos que esa madera va arder”

    http://www.soberania.org/Archivos/Informe_2008_SEN.pdf

    • …but the shear size of stupidity and bagabunderia that some of my colleagues are authors, co-authors and ultimately accountable parties. Happily to know that in any other part of the world they would be prosecuted but not in Venezuela.

      The issue of not increasing capacity to fill increased demand was discussed in 2010 on the 3 main English language blogs on Venezuela. There WERE plans to increase capacity when Chavez took power, but Chavez for the most part turned them down. The blame lies not with the electricity professionals you knew or didn’t know , but with Chavez. The professional proposes, but Chavez disposes.

    • Because hydropower in Venezuela was one of the big achievements of the so called “4th Republic”, and Chavez had to say that everything the 4th Republic ever did was bad.

      You see, the guy was a moron.

    • Chavez had an encyclopedic ignorance when it came to anything technical. He thought that we were at the mercy of the weather and that’s why we had shortages. He thought that fuel was more predictable. Just very backwards way of thinking.

  9. Andritz Hydro was one of the companies awarded with a contract to refurbish several of the Francis turbines in 2010, a Google search will give more info.

  10. Excellent article, very well explained. Just one question out of curiosity, how do you know the current water levels of the dam? Is that public information or has somebody recently gone to investigate?

  11. Guri levels are available at some independent websites like:

    http://www.lossinluzenlaprensa.com/?page_id=8205

    Rght now dropping at 16 – 18 cm per day…

    17 de marzo de 2016: 246,53 m.s.n.m.

    16 de marzo de 2016: 246,71 m.s.n.m.

    15 de marzo de 2016: 246,87 m.s.n.m.

    14 de marzo de 2016: 247,03 m.s.n.m.

    10 de marzo de 2016: 247,56 m.s.n.m.

    09 de marzo de 2016: 247,70 m.s.n.m.

    08 de marzo de 2016: 247,85 m.s.n.m.

    07 de marzo de 2016: 248,02 m.s.n.m.

    04 de marzo de 2016: 248, 44 m.s.n.m.

    03 de marzo de 2016: 248,58 m.s.n.m.

  12. Now that it appears that casa de máquinas 1 is gone and with it 2000 MW what can we expect?

    Why despite the rationing this hasn’t caused a more deep crisis?

    I’m not asking this as chisme, i’m starting to be genuinely scare.

    • The same than everything the cubans were supposed to fix, nothing, as we venezuelans say, “que sabe burro de chicle si lo que come es paja”. What tech background can possibly have the Cubans about a thermoelectric plant as planta centro.

      Only Chávez believed Castro’s and cuban’s bs.

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