Since it is impossible for the IP dummy leakage to be higher than the total leakage, the absolute accuracy of the IP dummy leakage was called into question. A 500-MW supercritical Westinghouse BB44 turbine with a distorted and damaged IP dummy ring seal.

This best practice has been used since the 1990s to finally reduce impulse turbine thrust pad temperatures to acceptable levels without the use of “band aid” modifications (questionable fixes that may not last). Some designers also use a balance piston on impulse turbines that have a high thrust.

Fortunately, the broken portion of the seal could be extracted from the inner shell, minimizing the duration of the outage. A review of the turbine cross section and of detailed IP dummy drawings revealed that the holes were supposed to be there. Answer:  A reaction turbine utilizes a jet of steam that flows from a nozzle on the rotor. if(MSFPhover) { MSFPnav10n=MSFPpreload("../Formulas/_derived/formulas.htm_cmp_strtedge110_vbtn.gif"); MSFPnav10h=MSFPpreload("../Formulas/_derived/formulas.htm_cmp_strtedge110_vbtn_a.gif"); } The HP dummy seals were also in poor condition, with numerous teeth broken off by axial movement. For the same load on the turbine, if wheel chamber pressure increases it indicates turbine fouling.

SCG engineers then decided to conduct the manufacturer’s bell seal leakage performance test. Go to the source. The initial steam pressure and temperature are not up to design conditions. 5. ), 4.

In this extreme case, a bad bell seal was determined to be the cause of excessive leakage that raised the unit’s heat rate.
6. The total IP efficiency, measured from the hot reheat to the LP crossover pipe, includes the effects of leakage through the IP and LP dummies, the bell seals, the HP exhaust piston rings, the hot reheat inlet piston rings, the governor valve stems, and the seal at the end of the governor shaft. Narrowing them reduced HP to IP leakage rates. Other sources of internal leakage. A reaction turbine is constructed of rows of fixed blades and rows of moving blades. //-->. Answer:  Reaction turbines have axial thrust because pressure on the entering side is greater than pressure on the leaving side of each stage. The test also revealed that total HP to IP leakage had increased from 6% of hot reheat flow to 13.5%. That’s because the former units require balancing the thrust loading of the reaction blading. Fail the seal (open clearance significantly), and thrust bearing failure can result. Among the sources of nondesign leakage are: For the BB44 design, two values of apparent IP efficiency should be measured. Analysis of that data indicated that closing the No. 10. Changing the usually distorted IP dummy ring on BB44s to an improved design offered by the manufacturer. Stuffing box using woven or soft packing rings that are compressed with a gland to prevent leakage along the shaft. It is between fisrt stage( Impilse stage ) nozzle and balance piston. Knowing the actual direction of the thrust can be very useful during troubleshooting exercises in determining the root cause of thrust position changes. The bell seals were in good condition. if(MSFPhover) { MSFPnav15n=MSFPpreload("../_derived/vendors.htm_cmp_strtedge110_vbtn.gif"); MSFPnav15h=MSFPpreload("../_derived/vendors.htm_cmp_strtedge110_vbtn_a.gif"); } Figure 6 highlights these sources for 75-MW Allis-Chalmers units, of which SCG has three. IP1 efficiency values account for the effect of leakage of HP exhaust steam leakage to the IP1 inlet through the IP dummy seals. The result is a small increase in velocity over that of the moving blades. However, a pre-outage test had not been conducted. Replacing any HP-IP-LP dummy and reheat diaphragm packing seals with excessive clearance or broken teeth. The seal clearances of the IP dummy and the horizontal joint of the IP dummy ring, and the fit of the IP dummy ring into the outer cylinder had always been found acceptable. The LP dummy seals also were worn, and two leaking bell seals were found as well. Not a subscriber or a registered user yet? To avoid higher than expected thrust pad temperatures in impulse turbines, consider undercutting the turbine shaft to act as a balance drum, and reduce the load on the thrust bearing during the project pre-bid phase (before vendor final priced proposals are submitted). The results of testing using these wells still indicated some stratification of IP exhaust temperature. Use predictive techniques to guide your mercury compliance strategy, Application determines DG system configuration, Detecting and solving lube oil varnish problems, PSNH’s Northern Wood Power Project repowers coal-fired plant with new fluidized-bed combustor, Performance Improvements in Fossil Fuel Power Plants with Multivariable Model - Predictive Controls and Artificial Intelligence, Advantages of Ultrasonic Flow Meters in Combined Cycle Power Plants, How Protecting SAIFI Metrics & Customers Improved So Much More. Courtesy: Southern Company Generation, 3. google_ad_height = 90; 7 and 8 valves, which feed a common nozzle block, produced the biggest change in temperature. ((navigator.appName == "Microsoft Internet Explorer") && (parseInt(navigator.appVersion) >= 4 )));