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At the heart of Itaipu: turbine shaft inspection
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Visitors going on the special tour are awed by the constant spinning of turbine shafts. However, at machine 07, its shaft is still and firmly locked.   


Around it, the technical team is hard at work to service the speed regulating system, as part of the inspection the generator unit undergoes every four years. 


The crew took apart two servomotors and removed the 24 intermediate bearings one by one. The latter are parts that go between the blades and the operating rim to prevent water from the scroll case from going up to the turbine cover. Easy, now, there are too many technical terms and not enough explanations. Like the good folks in Maintenance, let's break it down bit by bit.


The system keeps the turbine rotation speed constant, ensuring the quality of Itaipu's power. In other words, always at a 50 or 60Hz frequency, depending on the generator unit. But how does that happen? The answer is provided by expert technician Gilvan de Souza, from SMMU.DT, in charge of the mechanic maintenance of the speed regulating system.


According to Gilvan, the synchronic action of several parts is what keeps the speed constant. There are two powerful hydraulic arms – the servomotors – weighing 10 tons each, and they turn an 80 ton operating rim. This rim is connected to 24 blades (seven tons each, don't lose count) located between the turbine wheel and the scroll case. As these blades open and close they take a higher or lower amount of water from the scroll case to the turbine wheel. Whew! Have you managed to keep up with the technical explanation so far? Well, there's more.


Bear hug


To turn the rim, much like a DJ does with vinyl records, the servomotor hydraulic arms exercise a pressure of 700 tons. Imposing numbers and pinpoint precision. This movement requires a great amount of oil: 15,000 liters stored in three tanks and other pipes throughout the system. The oil has gone through a filtering process and the tanks have been inspected.


To prevent this ocean of oil from leaking out, the servomotor seal is also changed. “The original seal system is from the '80s”, said Gilvan as he held a rubber ring in his hand. The ring, also technically known as a gasket, is now made of polyurethane, much more resilient and efficient. There are two per servomotor.


On their part, the intermediate bearings play a similar role: preventing water from going up the blades to the turbine shaft distribution cover. “The blades are moving parts. That is why they need to be sealed so the water won't go up”, explained Cláudio Urbano de Mattos, from SMMU.DT, in charge of the turbine. He closes with yet more numbers: the 24 parts, weighing two tons each, have been inspected. The one that presented a leak has had its seal replaced.