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Aerospace technology has provided an improvement to one of the most underrated elements of generator performance - the hydrogen seal.
The influence of the hydrogen seal on the generator and its performance has been underestimated in the past, given he fact that seal-related problems contribute to a significant number of all generator issues.
Conventional hydrogen seal systems are often the source of three main generator concerns: Seal rub damage, oil ingrvess into the generator and low levels of hydrogen purity. Seal rubs are caused by the loss or variation of seal oil pressure, shaft vibration or temperature differentials (cold oil). When a rub occurs, the gap between the shall and the seal is increased due to material being removed. The larger gap requires more seal oil to be pumped to the hydrogen side to maintain seal pressure. The resultant increase in seal oil flow sometimes overpowers the labyrinth seals and causes oil to ingress into the generator sump, as well as going to the defoaming tank. Reduced purity is caused by excessive levels of oil, which brings impurities, including water, into contact with the hydrogen gas.
A new hydrogen seal system addresses these issues using proven aerospace technology. Siemens has collaborated with a leading aerospace seal vendor (Stein Seal Company) to develop an advanced oil-seal assembly for hydrogen-cooled generators and turbo-machinery based on state-of-the-art segmented carbon seal technology. The system is already in use on a half dozen U.S. generating units.
This new seal system, marketed as Performance Plus, is designed to virtually eliminate the risk of future seal rub damage. It significantly reduces oil ingress into the generator and maintains a high level of hydrogen purity, thereby increasing generator efficiency. The system also makes it possible to increase generator hydrogen operating pressures.
SEAL ASSEMBLY DISCRIPTSON
The seal itself is provided pre-assembled in a stainless steel cartridge, which allows retrofit into existing gland seal brackets on in-service units. The seal cartridge features a horizontally split housing with two segmented carbon seal rings (Figure 1). High-pressure oil enters the seal-housing...