Orkot® TXMM vs Greased Bronze Bearing: 300MW Pump Turbine

Electrical power is critical to maintaining today’s way of life around the globe. An essential element of the US electrical grid is hydroelectric power plants, with conventional generators supplying about 6.3% of the total operating electricity in the US for 2021. According to the US Energy Information Administration, hydroelectric facilities in the US have been in operation for 64 years on average.

At the time they were built, greased bronze bearings were the standard in hydropower plants. A lot can happen in 64 years, which begs the question: are greased bronze bearings still the best of the best? 

Advanced polymer Orkot® TXMM went head-to-head with greased bronze bearings at Dinorwig Power Station in Snowdonia National Park, Gwynedd, North Wales. The two-year test on a 300MW Pump Turbine compared the former “standard” greased bronze bearings to Orkot® TXMM to determine which was the top of the line today.

Dinorwig Pump Turbine Challenges

Like most hydropower stations, the Dinorwig hydropower station was designed and built in the late 1970s. Grease lubricated bronze, the standard for the industry at the time, was used in the turbine guide vane bearings. At Dinorwig, the operating conditions were especially challenging. For example, Dinorwig’s operating conditions included up to twenty spiral casing pressurizations and approximately thirty mode changes per day.

The severe wear that these conditions created made it necessary to replace the upper bearing of the guide vane every two years. When considering these problems, along with the increased operational and maintenance costs and the inherent difficulties associated with frequent pumping of grease, plus potential negative impacts on the environment, alternative designs that included self-lubricating bearings appeared to be the more viable solution.

Orkot® TXMM vs. Greased Bronze Bearings

To determine wear data on the upper guide vane bearing, Dinorwig proposed a real-time test. The Orkot® manufacturer agreed to participate and provided two samples of each product, at no charge, for the test. Crews would install the samples on Dinorwig’s Pump Turbine Unit 4 and monitor them for a two-year period. To ascertain any effect on position, they separated the pair of bearings.

Guide Vane Shaft Material Specifications

These are some of the specifics of the guide vane shaft materials:

• BS 1630 Grade B stainless steel
• Hardness: 200 HB
• Journal size: 207 mm
• Bearing: 207 mm ID, 235 mm OD
• Length: 100 mm
• Recommended greased bronze clearance: 0.05 to 0.14 mm
• Housing material: mild steel, 25 mm thick
• Service conditions: Load 20N/mm2 maximum
• Temperature: 10 to 15 0 C
• Shaft speed: 0.625 rpm
• Arc of rotation: 300
• Environment: dry, relatively clean, with an O ring provision to prevent debris contamination

This test was specifically designed with the operating conditions of Dinorwig in mind, namely dry running while making frequent stops and starts.

Comparison Test Results

All of the bearings were checked at the two-month mark, and all showed signs of accelerated bedding wear, as was expected. Following this check, the Orkot® bearings showed a slow, steady rate of wear which then stabilized. The Orkot® products demonstrated no further significant increase in wear over the next twelve months. 

It was only after seventeen months in service that the grease-lubricated bronze bearings reached the same level of stability.

Test Results: One Year

Set B of the bearings was removed for inspection after 6422 spiral casing pressurization and twelve months of continuous service. 

Orkot® TXMM

• Maximum wear in mm: 0.04 mm
• Maximum wear per 0.001 inches: 1.6

Greased Bronze

• Maximum wear in mm: 0.175 mm
• Maximum wear per 0.001 inches: 6.9

The Difference

Orkot® TXMM experienced a lower wear rate with a difference of 0.135 mm maximum wear and 5.3 maximum wear per 0.001 inches compared to greased bronze.

Test Results: Two Years

After two years in service, from May 1996 to April 1998, all the bearings were removed and thoroughly inspected.

Orkot® TXMM

• Maximum wear in mm: 0.0425
• Maximum wear in mm: 0.055

Greased Bronze

• Maximum wear in mm: 0.1925

The Difference

There was 0.15 mm and 0.1375 mm less wear on the Orkot® TXMM bearings versus the greased bronze bearings after two years of service.

Test Conclusions

The study results found that the life expectancy of the tested Orkot® products could be as much as five times longer than the greased bronze bearings in the upper bearing position. The overall working environment improves when grease isn’t used as a lubricant: the risk of lake water contamination from constant grease contact and the cost of grease and dispensing equipment are removed. Learn more about why hydropower plants should switch away from greased bronze bearings.

Orkot® Outperforms Greased Bronze Bearings

Orkot® TXMM’s composite polymer bearings proved superior to the previously standard greased bronze bearings. Hydropower is an integral component of the nation’s power delivery organizations. Failure or interruption in the flow of hydropower can significantly impact operations vital to business, security, and safety. The crucial function of hydropower plants makes it imperative that they get the absolute best in maintenance and products used for replacement parts and equipment upgrades.

Refurbishing hydroelectric power plants with Orkot® self-lubricating thermoset composite products in place of outdated greased bronze bearings is a cost-effective way to upgrade aging power plants. A hydropower plant refurbishment with Orkot® can include trunnion bearings, wear pads, thrust washers, and wicket gate bearings to name a few.

See what it would take to install Orkot® at your hydropower plant. Get a free quote from our team of Orkot® experts today!