West Burton Power Plant, UK owned by EDF energy has 4 steam turbo-generator (TG) units for power generation. These units were installed and commissioned between 1967 and 1969 and have since operated smoothly without any major problems up to 2007. In 1995 and 1996, two TG sets, namely units 2 and 3, were retrofitted with the new design LP rotors and in 2005, retrofitting of HP rotor for all four TG units was commenced. The retrofitting was done without changing the foundation, but only with the aim to enhance the power output by 20MW (10 MW through LP retrofit and 10MW through HP retrofit). Cracking of the last stage blades of LP1 and LP2 turbine, steam-end blades has been observed in TG units 2 and 3 only. Hence the in-situ vibration measurements have been carried out on TG unit 3 and compared with healthy TG unit 1 to understand the dynamics of both units. This paper presents observations made on the dynamics of TG units 1 and 3, and results from the root cause analysis which may possibly lead to the solution to the blade failure problem in TG units 2 and 3.

Cracking of the last stage blades of the low pressure (LP) turbines has been observed after 2007 in the 2 steam turbo-generator (TG) units out of the 4 units at the West Burton Power Plant UK. These 2 units were retrofitted with the new design LP rotor including blades in 1995 and 1997. Recent vibration measurements during machine transient and steady state operations confirms that the TG sets are running close to the machine critical speed and the blades are expected to have high vibration. Now the Unit 3 is fitted with the blade tip timing (BTT) system to monitor the LP1 last stage blades. Hence the present effort to compare the vibration of the blades by the BTT system with the bearing vibration to establish the correlation such that the status of the blade vibration can be accessed even without BTT measurement and the correlation may be used for other units with similar dynamics. The paper presents the comparison of the in-situ vibration measurement on bearings during machine run-up with online BTT data, observations, and possible correlation.

There have been a number of significant power outages caused by unexpected levels of flowinduced vibration of valves in partially-open operating conditions and as such the understanding of this phenomena is critically important. On-site testing is normally expensive and inherently difficult given typical flow rates but while computational fluid dynamics (CFD) offers a feasible alternative, it demands careful use and analysis to capture the highly coupled physical phenomena present. This paper reports on the fluid flow around a spindle in a highpressure valve and related flow by means of 2D unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and the k-ω-SST turbulence model. Following a mesh sensitivity study, the measured force frequencies and shockwave patterns predicted around the valve head indicate a high level of agreement with experimental reference data. The unsteady flow is then assessed at various stages of valve-opening; conditions which are increasingly common in the context of power throttling to balance supply from more variable renewable energy sources. Although, the averaged force on the valve head reduces linearly with the lift of stem, the fluctuating component of the force rises by almost 50% when the valve opening changes from 25% to 50%. This quantity, significant in the identification of violent high-frequency vibration, is then observed to reduce steadily upon further opening. Spectral analysis and flow field data provide the basis for further insight with respect to the formation and evolution of a series of shock-wave/boundary-layer interactions along the valve head.

Purpose Generating electricity from wind turbines is currently a viable option to meet the electric power requirements in many countries. The structure of offshore wind turbines is constantly subjected to external dynamic loads due to wind, waves and rotor loads due to the rotation of blades. The frequency content of these dynamic loads is in the range of natural frequencies of the wind turbine. Therefore, determining the in situ dynamic characteristics of a wind turbine is very beneficial, as it can lead to further improvements in its design, performance and safety. Methods In this paper, the dynamics of the structure of an offshore wind turbine is investigated numerically and experimentally. The finite element (FE) model of structural components is developed based on design specifications. The model takes the effect of rotor-nacelle assembly into account by considering its mass and moment of inertias relative to the top centre of the tower. In situ modal tests using impulse excitations were carried out on the actual wind turbine when the rotor blades were not rotating to identify the modal parameters. Results This paper presents predicted natural frequencies from the FE model based on design conditions and those identified from the modal and ambient excitation tests. Conclusion It was observed that the first two bending modes are close to the natural frequencies identified experimentally by the in situ modal tests. It was also observed that the in situ modal tests were not able to excite other higher natural frequencies of the structure.

No abstract