Operated by Électricité de France (EDF), Brittany’s La Rance Power Plant is one of the world’s largest tidal power stations, with 24 turbines whose peak output is 240 megawatts (MW), and averaging 57MW. Its annual power output is about 500 GWh.
The plant’s original shaft seals—made of an ultra-high molecular weight polyethylene (UHMWPE) and carbon graphite material—required replacement due to their poor longevity and performance, explained Axel Swanson, Thordon Bearings’ Business Development Manager – Hydro, Pump & Industrial.
“We knew from experience that SXL seals not only perform substantially better than UHMWPE and carbon seals, but they significantly reduce leakage rates and extend the wear life far beyond the original installations. Thordon SXL shaft seals have a typical wear life of more than 15 years.
“For the EDF plant we came up with an improved radial seal design that would fit into the existing housing. Thanks to our industry-leading expertise in hydro turbine seals and bearings, EDF was convinced the new SXL segmented seal was the right solution for this application. Initial trials were a huge success,” said Swanson.
During the retrofit project, the existing shaft seals were replaced with the SXL segmented shaft seals, supplied through the Thordon authorized distributor for France, Wenex Equipements SA. The SXL seal is unlike traditional shaft seals in that the elastomeric polymer material used is specifically designed to optimize performance and reduce operational costs.
“The SXL segmented shaft seal has several unique features that make it a perfect match for EDF’s needs,” said Laurent Le Trouher, Wenex Equipements’ Area Sales Manager.
“Installation and replacement of all seal components can be carried out without removing the shaft. The main advantages of an SXL shaft seal over the carbon type, are reduced leakage, extended wear life, design flexibility, and a very robust material. Carbon-based seals can be brittle and break easily during installation. The SXL seal, however, lends itself to installation and operational simplicity. It is also easily maintained.”
Operating parameters for Thordon SXL segmented shaft seals are generally similar to those for carbon graphite or phenolic seals in terms of maximum interface pressure and almost always reduces leakage. Thordon segmented seals have in the past been designed for shafts up to 3.9m (12.7ft) diameter and can be designed for use in either radial or axial sealing systems.
Le Trouher welcomed EDF’s decision to invest further in Thordon’s products. “After being in service for one year, the utility has expressed its satisfaction with the performance of the new Thordon SXL seals and ordered a second set.”
When the La Rance facility, located on the estuary of the Rance River, in Brittany, France, opened in November 1966, it made headlines as the world’s first-ever tidal power station. It remained the world’s largest until 2011, when South Korea’s Sihwa Lake Tidal Power Station started operations.
