As part of the modernization of its 1,551.2 MW Eng. Souza Dias (Jupia) plant, Companhia Energetica de Sao Paulo is installing self-lubricating bearing materials in all 14 units. This conversion will save the utility money and improve performance of the units.
By Rui Riyo Ueda, Adelino Sussumo Serizawa, Alex Ricardo Ferrer de Andrade, Giulliano Batelochi Gallo and Paulo Pereira
Rui Riyo Ueda is coordinator of Companhia Energetica de Sao Paulo's mechanical engineering maintenance division. Adelino Sussumo Serizawa is supervisor of mechanical maintenance at the Jupia plant. Alex Ricardo Ferrer de Andrade is division manager of electromechanical maintenance engineering and Giulliano Batelochi Gallo is a maintenance and mechanical engineer with CESP. Paulo Pereira is hydro application manager for Federal Mogul Deva GmbH, which supplied the bearings installed at Jupia.
A modernization program performed by Companhia Energetica de Sao Paulo (CESP) at its 1,551.2 MW Eng. Souza Dias (Jupia) plant includes installing self-lubricating bearings on the upper guide vanes and Kaplan runner hubs. The bearings chosen contain bronze and graphite and offer higher load capacity, more efficient lubrication compared with the oil-lubricated bronze bearings, practically no wear of sliding components, increase in bearing component lifetime of at least 50%, and elimination of the use of oil.
To date, seven of the 14 units have been converted, and their performance is meeting expectations, with units running as long as 10 years without maintenance needed on the bearings. For the runner hubs, it cost about $12,000 per self-lubricated bearing inserted. Each runner hub has 10 bearings.
CESP's maintenance program
CESP owns six hydro plants with total capacity of 7,455.3 MW. They are 3,444 MW Ihla Solteira, 807.5 MW Tres Irmaos, 1,551.2 MW Jupia, 1,540 MW Porto Primavera, 85 MW Paraibuna and 27.6 MW Jaguari.
CESP uses a General Periodic Preventive Maintenance (MPPG) program to define the frequency of maintenance work performed at these projects. This program is part of CESP's policy to increase the availability and operational reliability of its units. This is a large maintenance job in turbines with complex characteristics that involve complete disassembly of the machine, maintenance, improvements and repair of components, and reassembly.
Parameters considered when evaluating each piece of equipment are: results of tests, examinations and inspections; operating system and number of operations; environmental conditions; year of manufacture and available time for operation. The MPPG program also takes into account the specific characteristics of each plant and its units, equipment status (especially operational conditions), and the results of previous inspections and predictive tests. Thus, each generating unit is treated as an individual production unit.
The largest preventive maintenance job is scheduled between 160,000 and 240,000 hours of operation or based on conditions assessed through monitoring of unit behavior, when the unit is completely dismantled. This maintenance, performed on at least one unit per year at Jupia, involves investing in special materials and techniques that enable CESP to eliminate equipment weak points and overcome faults, defects and operational restrictions.
Maintenance at Jupia
The Jupia plant, on the Parana River, began operating in 1969. It contains 14 vertical Kaplan turbine-generating units and two 4.75 MW turbine-generator groups for auxiliary service. Each turbine has five blades. For the main units, five were manufactured by Riva, seven by Asgen and two by Escher Wyss. The 8.4 meter-diameter units have a rated speed of 78.3 rpm. Their maximum efficiency point is at a head of 22.10 meters, with water flow of 515 m3/sec.
MPPG performed on the Jupia units consists of repair of worn turbine parts; generator maintenance; improvements to the shaft seal, distributor mechanism and runner hub; and modernization of mechanical equipment. To execute this maintenance, it is necessary to completely disassemble the unit and have some parts sent to a factory for machining and implementation of improvements, such as installation of self-lubricating bearings.
Eliminating water infiltration through the guide vane bearings
The lifetime of a guide vane bearing depends, among other factors, on operating without contaminants. The original bearings for Jupia were bronze lubricated with grease, and a seal was installed only on the upper bearing. Thus, the intermediate and lower bearings were exposed to water. Besides contaminating the grease with solid materials (sand), the presence of water can cause corrosion on the guide vane trunnion, affecting bearing performance and lifetime.
CESP decided to install self-lubricating materials in the Jupia turbines. These materials consisted of a foil of polytetrafluoroethylene (PTFE or Teflon). The first step was to install rubber seals in the intermediate bearing to prevent water from entering the bearing system.
Use of a technically more appropriate seal had to wait until the introduction of self-lubricating bearings made of sintered bronze and graphite, to replace the PTFE foils. The technology chosen was deva.bm bearings from Federal Mogul Deva GmbH of Germany. This self-lubricating material has a high load capacity, which allows it to work with a smaller sliding surface. In other words, the height of the working surface of the bearings is reduced, allowing space to adapt the new seal without affecting bearing function.
|Plant personnel install the self-lubricating bearings in the runner hub outer bearing of one of the units at Jupia.|
The seal improvement consisted of applying a seal with a "U" profile because of its easy adaptation and installation in the bearing assembly and its proven performance in similar applications. The seal material specified was nitrile rubber with a hardness of 85 Shore-A.
The complete service performed on the guide vanes consists of the following:
— For the trunnion, inspection and dimensional check of the bearing journals; pre-weld machining of a 5 mm radius on each journal; fill with welding material using stainless steel AISI 410; grinding to achieve the final dimensions according to the design tolerance and roughness; machining of a chanfer to facilitate installation of the bearing with the assembled seal; adjustment and finishing of the transition radius; and inspection. The maximum tolerance of concentricity between the trunnion journals is 0.05 mm.
— For the lower bearings, machining the bronze bearings for installation of the self-lubricating bearings, eliminating greasing tubes and closing the holes, and machining the inner bearing diameter of to be the container for the self-lubricating bearing. Tolerances must comply with the specifications of the manufacturer.
— For the intermediate and upper bearings, the same steps as for the lower bearings, with the addition of adaptation of the seal and development of a device to facilitate its assembly or modification.
|The 1,551.2 MW Jupia powerhouse in Brazil is being retrofit with self-lubricating bearings on all four turbine-generating units and related components.|
Adapting self-lubricating material in the runner hub guide bearings and shoes
Because of concerns regarding the high cost of maintenance and the lifetime of the turbine components (such as the servomotor and distributor mechanism), CESP implemented an adaptation of PTFE during the 1990s. This decision had positive technical and economic effects, especially in the application as a sealing ring of the distributor servomotor.
Based on previous success, CESP decided to use the deva.bm material in the turbine runner hub assembly.
For bearings and shoes, this self-lubricating material consists of a bimetal structure — a stainless steel support and a bronze sliding layer with small particles of graphite solid lubricant homogenously distributed. The self-lubricating segments of the shoes and the flanges of the bronze bearings are fixed with countersunk screws.
Self-lubricating materials were installed in many components of the turbine runner hub:
— Bottom inner and upper outer bearings of guide shaft: Machining bronze bearings and installing self-lubricating bearings; machining the existing bronze bearing inner diameter for installation of the self-lubricating bearings; and adaptation of the seal.
— Servomotor cover and cylinder bearing: Machining bronze bearings and installing self-lubricating bearings; performing a dimensional check; and machining the bronze bearing inner diameter radius for installation of the self-lubricating bearing.
— Servomotor guide shoes: Machining the runner hub servomotor guide shoes and installing them.
— Lifting eyebolt bearings: Grinding the side faces of the five eyebolts, where the inner and outer rods work; inspection and dimensional check of the side faces for parallelism, flatness and eccentricity; grinding the side faces to restore surface and design tolerance; machining bronze bearings of the eyebolts and installing self-lubricating bearings; and machining the inner diameter for adaptation and self-lubricating bushing assembly.
— Linkage bearings: Machining the bronze bearings and installing self-lubricating bearings and machining the bronze bearing inner diameter for installation of the self-lubricating bearing.
— Runner hub blades: Grinding runner hub blade trunnions; dimensional check of blade trunnion journals; analysis and definition of the values of the diameters of the final grinding, based on the smallest pair of values found; grinding the diameters in accordance with design tolerances; dimensional control and check of parallelism of the related trunnions; rehabilitation of the sealing mating surface on the blade trunnions; pre-machining of work parts; and flange and seal mating surface pre-machining of work parts, filling in with welding material of martensitic stainless steel AISI 410.
— Runner hub outer bearing: Grinding the bronze bearing; machining the bronze bearing inner diameter for installation of the self-lubricating bearing; machining of the flange outer surface for installation of the self-lubricating segments; and installation of five sets of runner hub blade radial and axial outer self-lubricating bearings.
— Runner hub inner bearing: Machining the bronze bearing inner diameter for installation of the self-lubricating bearing and installation of five sets of runner hub blade radial inner self-lubricating bearings.
|The roller bearings in the distributor mechanism of the units at Jupia are being replaced with self-lubricating bearing materials.|
Adapting self-lubricating material in the distributor mechanism
The load and frequency control system of a hydraulic turbine is equipped with an electronic control system where the system frequency can be monitored (from 59.98 to 60.02). The generating unit tries to keep the unit within this range by adjusting the electrical, electronic and hydraulic mechanical controls continuously.
Thus, the turbine is actuated through the hydraulic circuit by a linear movement of the hydraulic cylinder rod, which transmits the movement to the regulating ring. As the regulating ring is connected to the guide vanes by the linkages, it actuates all the guide vanes in a synchronized manner and allows passage of water through the turbine. Depending on the degree of guide vane opening, more or less water will flow through the turbine, therefore controlling the speed in the turbine as a response to the load frequency in the related generating unit.
In the original turbine design, the regulating ring assembly had an axial thrust bronze block fixed to its bottom surface, which slid in a channel full of oil. CESP decided to eliminate the oil through the use of self-lubricating materials, and the PTFE foils solution was adopted.
Self-lubricating materials were installed in the bearings of the connection of regulating ring to linkages, bearings of the connection of linkages to guide vane levers, bearings of the regulating ring pulleys, servomotor rod bearings, and sliding segments of the regulating ring.
To adapt self-lubricating materials in the distributor mechanism, the following services were performed:
— Distributor mechanism bronze bearings were machined in the inner diameter to be transformed into containers for the self-lubricating bearings;
— Shaft journals were refurbished to work without grease. Some received a layer of martensitic stainless steel weld and others had a stainless steel sleeve installed;
— Six sliding supports for the regulating ring and six self-lubricating axial segments were manufactured;
— Bearings connecting the regulating ring and linkages were machined, self-lubricating bearings were installed, lubrication tubes were eliminated, and existing lubrication holes were closed;
— New pins in AISI 410 martensitic stainless steel were manufactured for all linkages and regulating ring connection;
— Self-lubricating bearings (48) were installed;
— Twelve existing bronze bearing of the regulating ring pulleys were machined, carbon steel bearings were installed, the bearings were machined, and self-lubricating material axial segments were installed;
— Inner diameter of the bronze bearing was machined to install the self-lubricating bearings and axial segments;
— Eight bearings were installed for rollers with diameter of 80 mm;
— Eight bearings were installed for rollers with diameter 100 mm;
— Eight self-lubricating segments were installed for rollers with diameter of 82 mm;
— Four pieces were installed with diameter of 110 mm.
With seven Kaplan turbines modernized to date at Jupia, the results achieved are in accordance with expectations and CESP policy to increase the availability and operational reliablity of its units.
The solution adopted — to implement the use of deva.bm self-lubricating material replacing grease lubricated bearings and PTFE foil — has provided better safety for energy production in a sustainable manner following company concerns with the social and environmental aspects of its business.
The main advantages of deva.bm material when compared to PTFE foil are its higher load capacity, as PTFE foils can be deformed when submitted to high loads, and its longer lifetime.
Although none of the seven refurbished turbines have yet been disassembled for inspection, their performance is meeting expectations and CESP has not noticed any evidence of premature wear, such as oil leakage and increase of clearances in bearing assemblies of the Kaplan runner hub and in the guide vanes of the distributor mechanism.