Development and Verification of 3000 Rpm 48 Inch Integral Shroud Blade for Steam Turbine

Abstract

The 3 000 rpm 48 inch blade for steam turbine was developed as one of the new standard series of LP end blades. The new LP end blades are characterized by the ISB (Integral Shroud Blade) structure. In the ISB structure, blades are continuously coupled by blade untwist due to centrifugal force when the blades rotate at high speed. Therefore, the number of the resonant vibration modes can be reduced by virtue of the vibration characteristics of the circumferentially continuous blades, and the resonant stress can be decreased due to the additional friction damping generated at shrouds and stubs. In order to develop the 3 000 rpm 48 inch blade, the latest analysis methods to predict the vibration characteristics of the ISB structure were applied, after confirming their validity to the blade design. Moreover, the verification tests such as rotational vibration tests and model turbine tests were carried out in the shop to confirm the reliability of the developed blade. As the final verification test, the field test of the actual steam turbine was carried out in the site during the trial operation, and the vibration stress of the 3 000 rpm 48 inch blade was measured by use of telemetry system. In the field test, the vibratory stress of the blade was measured under various operating conditions for more than one month. This paper first presents the up-to-date design technology applied to the design of the 3 000 rpm 48 inch blade. In the second place, the results of the various verification tests carried out in the shop are presented as well as their procedure. Lastly, the results of the final verification tests of 3 000 rpm 48 inch blade carried out in the site are presented.

Progress of Technology on Mechanical Design of Steam Turbine Blade in Japan

“…Figure 10 shows the example of the wiring used in the recent field test of the last blade of the steam turbine. It is reported that no damage of the strain gage and the wiring was observed after the field test of around one month, and the valuable verification data was obtained (78) .…”

“…Fig. 10 Blade with Strain Gauge (After Field Test) (78) Journal of System Design and Fig. 11 Campbell diagram of blade measured by non-contact measurement method (82)…”

Study on the Damping Mechanism of the Shrouded Blade considering Contact Features

“…In order to make the rotating blade more reliable, the method of adding shrouds to the blade is often used to solve the problem in engineering. e shroud can increase the rigidity and the natural frequency of the blade, and when the blade is vibrating, the working surface of the shroud can rub against each other to absorb vibration energy [1]. e process of contact vibration with shrouded blades is very complex and usually includes separation-contact-stick-slip states, with typical nonlinear characteristics.…”

Analysis of Fretting Fatigue Strength of Integral Shroud Blade for Steam Turbine

“…In order to develop the new LP end blades with high reliability, analysis methods for the vibration characteristics of the ISB structure were developed and their validity was confirmed before applying them to the blade design (2) (3) . Moreover, the final reliability of the developed blades has been confirmed by verification tests such as rotational vibration tests and actual loading tests, and these test results have been accumulated into the database (4) . The accuracy of the predicted frequency and the vibratory stress has been improved, using the database of the test results.…”