Protecting the world’s largest hydro facilities

Our products are used to monitor and protect the largest machines and operations on the planet. That’s not hyperbole – that’s fact. In this series of articles, we have examined the world’s largest gas and steam turbines and our role in protecting them. We now conclude this 3-part series with a look at our historic role in bringing the world’s largest hydropower facility online and how we today monitor many of the world’s largest hydro units elsewhere.


The truth is that large machines aren’t necessarily monitored differently or with different equipment. They may have more measurement points. They may have more complex voting logic. And they may qualify for the most extensive complement of protection and condition monitoring measurements because so much is on the line in terms of lost production when they fail. But it’s basically a matter of more – not different. The consequences of a missed alarm or false alarm is what sets these machines apart. Big means expensive and highly consequential. In this 3-part series we have focused on big machines and big plants. And not just big – the world’s biggest in terms of power output.

We conclude the series now with a look at massive hydro units and our expertise in monitoring such machines. In keeping with the theme of this series, we start by examining our historic role bringing the first 8 units online several decades ago at the world’s largest hydro plant: China’s Three Gorges Dam. Not only is it the largest hydro plant in the world, it’s the largest power plant of any kind – whether gas, steam, or hydro – tipping the scales at an astounding 22.5 GW. Table 1 summarizes the scope and scale of this amazing civil engineering feat.

Table 1 - Three Gorges Dam Key Details

Number of Turbine-Generators34 (32 @ 700MW + 2 @ 50MW)
Dam Length2.335 km
Dam Height175 m
Reservoir Length660 km
Reservoir Capacity39.3 cubic km
Volume of Concrete Used16 million cubic meters
Generation Capacity22.5 GW
Capacity Factor45%
Years under Construction1994-2015 (includes locks and lift)
Peak # of Construction Workers26,000

What makes them spin?

The waterwheel was first described in an ancient Chinese text around 200 BC. This makes the hydro turbine by far the earliest prime mover we have discussed in this article series, predating Hero’s steam turbine by several centuries and Barber’s gas turbine by 20 centuries. The modern hydro turbine uses three basic impeller (runner) types: the Pelton, the Francis, and the Kaplan – all named after their respective inventors and all appearing on the scene within a 65-year period from 1848 (Francis) to 1913 (Kaplan).

Each runner type has its “sweet spot” where it delivers the best efficiency in converting the energy entrained in the flow and pressure (i.e., head) conditions of the water to mechanical power to drive a generator. Pelton machines are generally best for high head conditions. In contrast, Kaplan machines are at the other end of the continuum and are best for low head conditions. Francis machines fill the middle and function best in between these two extremes; i.e., under moderate head conditions.

The Three Gorges Dam has an enormous reservoir as per Table 1 and the level of head varies throughout the year as the reservoir depth fluctuates1 with the seasons. Regardless, the flow and head conditions are such that Francis-type runners (Figure 1) are used in all 32 turbines2, each designed for average head conditions of 80 meters and flow that can vary from 600-950 m3/s. To put this volume of flow into perspective, it is the equivalent of draining 23 Olympic-sized swimming pools every minute.

Figure 1. One of the massive 700 MW Francis turbine runners installed at Three Gorges.

Bringing the units online

The idea for a dam along the Three Gorges area of China’s Yangtze River dates back more than 100 years to 19193 when Sun Yat-sen predicted that 22GW of power could be extracted from such a dam – amazingly close to the 22.5GW that Three Gorges actually produces today. However, it would take another 75 years before construction would actually commence on such a mammoth project. As the largest concrete gravity dam in the world, it is more than 2.3 km long and a $64M concrete plant4 had to be constructed nearby to supply the 16 million cubic meters required3.

Figure 2. Three Gorges is the largest concrete gravity dam in the world, the largest hydropower plant in the world, and the largest power plant in the world at 22.5 GW. By comparison, the largest thermal power plant in the world is only about one-third this size – an 8.6 GW combined cycle facility in the United Arab Emirates. The flood discharge section with its 23 spillway outlets can be seen in the center of the dam. The left bank houses 14 turbine-generators while the right bank houses 12. Another 6 turbine-generators are housed in an underground powerhouse. Each turbine-generators is rated at 700 MW. A 5-step ship lock (not shown) is on the right bank and takes 3-4 hours to traverse. For those ships that cannot spare this transit time, a gigantic 3000 ton lift is also available that cuts the time to a mere 30 minutes.

The project was built by a consortium of companies as the philosophy was such that no single aspect of the project would be awarded to a single supplier. Instead, things were split among multiple engineering companies and machinery / product suppliers and technology transfers from consortium partners to Chinese companies occurred as a condition of numerous contract awards.

Table 2 - Summary of Three Gorges Turbine-Generator Units5

Unit #Powerhouse / PhaseTurbine / Generator
1-6Left Bank IConsortium710
7-10Left Bank IIConsortium700
11-14Left Bank IIIConsortium700
15Right Bank IConsortium700
16Right Bank IChinese700
17-22Right Bank IIChinese700
23-25Right Bank IIConsortium710
26Right Bank IIIChinese710
33-342Right Bank IIIChinese50
27-28Underground IConsortium700
29-30Underground IIChinese700
31-32Underground IIIChinese700

Table 2 summarizes the construction phases with respect to the three powerhouses and the number of machines.  Notice that although the initial machines came from consortium partners, the mix then started to shift as a greater percentage of the project began to come from China itself.  

Construction of the dam started in 1993. The first turbine went into service in 2003 and the last in 2012. Construction on other parts of the facility continued until 2015 when the ship lift was the last aspect of the massive project to be completed, reflecting a total construction time of more than 20 years.

The Trophy Case

Three Gorges is the “biggest” in numerous facets. It’s not only the largest hydro plant in the world, but the largest power plant of any kind at 22.5GW. It’s the longest concrete6 gravity dam in the world. It also used the most concrete. As large as the reservoir may seem at 660 km, however, it is well down the list of the world’s largest reservoirs at a mere #27. The units themselves are 700MW, and though unquestionably big, are actually 30% smaller than the most powerful hydro turbines in the world that can now exceed 1GW in size.

What We Monitor

Meggitt’s vibro-meter products were selected for 14 of the units at Three Gorges. Indeed, not just any 14 units, but the very first 14 units to be installed and thus at the cutting edge of the project. This decision reflected a very high level of trust by the consortium partners in our products along with a proven track record of reliably monitoring such assets. As with all machines of this size, a full complement of radial vibration and axial position (thrust bearing) measurements were provided. As is also the case on generator rotors of this power rating and the corresponding diameters involved, air gap measurements were supplied. You can read more about air gap in our companion article detailing this important measurement.

Beyond China

The platform we supplied for those first units to come online in the mid-2000s was our VM600. It has been an extremely successful and dependable system for us with nearly a quarter million channels installed globally. In 2022, we completely refreshed the platform with the release of the VM600Mk2. You can learn more about its history, its benefits, its backward compatibility, and its numerous customer-focused enhancements in this comprehensive 24-page whitepaper.

Figure 3. Our VM600 platform (right) was selected for the first 14 units of the Three Gorges project. The popularity and dependability of this platform resulted in a complete refresh in 2022, resulting in the all-new VM600Mk2 (left).

As proud as we are to have been selected for those first 14 units at Three Gorges, we are prouder still of our very large global footprint in the hydropower space today.

Table 3 - Selected Global End Users

End-User CountryCapacity under vibro-meter monitoring% of end user’s business
Canada18.5 GW98%
Norway7.9 GW50%
Mexico6.7 GW25%
Portugal3.4 GW56%
Switzerland1.7 GW75%

Table 3 summarizes our work with five very large and influential end-users. Combined, across these end users and many more, we monitor thousands of hydro units worldwide – some as large as the 700MW units at Three Gorges. We also monitor not just the turbines, but additional assets such as spillway gates for proper operation and penstocks for damaging pulsations. You can learn more about our offerings for the hydro industry by accessing our informative application page, reading our Tech Bytes publication, and by contacting your nearest vibro-meter sales professional.


1Maximum depth sustained in overfilled conditions is about 165m (the top of the dam is 175m). 

2There are actually 34 hydro turbine-generators at Three Gorges.  32 machines are rated at 700 MW. Two much smaller machines are rated at 50 MW and supply power to the hydroelectric station itself to ensure its stability.

3Handwerk, B. “China’s Three Gorges Dam by the Numbers” National Geographic, June 9, 2006. Accessed 15 Feb 2023.

4“Three Gorges Dam Hydropower Station”, NS Energy, Accessed 15 Feb 2023.

5These are not unit ID numbers and are used for summary purposes only; the actual unit designators used in the plant may differ from those shown here.

6Earthen gravity dams also exist and can be larger.  The largest gravity dam in the world at present is for an artificial lake to hold mine tailings at Syncrude in Alberta, Canada.  It is more than 18km in length. 

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