THE PROJECT
A new and novel Portable Computed Topography (PCT) system will be developed to perform total structural integrity inspection of present and next generation composite Wind Turbine Blades (WTB) without taking them out of service. The Computerised Open Environment Portable Topography (COncEPT) system will provide the only means of detecting several significant defects, including disbonds on the nano-scale, in the thickest sections of 100m length blades intended in the future.
As a diagnostic tool to assure the safe operation of present and future wind farms it will provide a key technology to support the growth of wind power intended under global economic, environmental and societal policy initiatives.
Technical Objectives
- To develop an ultra-high energy nanofocus X-ray tube
- To develop a robust, high-resolution, digital detector capable of detecting high-energy X-rays
- To develop a stable, portable power source capable of powering the X-ray tube
- To develop a stable and flexible scanner / manipulator which will house the above components. The above components will be incorporated to produce a PCT system for in-service inspection of WTB
- To increase the accuracy of current inspections by eliminating dangerous working conditions, and operator fatigue and subjectivity
- Overall, to significantly develop and improve nanofocus NDT technology, CT, and sensor systems in a step change from their current capability in order that WTB defects resulting from in-service degradation and loading or damage are detected and monitored with accuracy.
Focal-spot size is a key factor in determining the resolution and quality of an X-ray image. As the focal spot decreases, the resolution and ability to detect detail are improved enabling geometric or projection magnification without peripheral shadowing. In practice, depending on tube design, a focal spot can be as small as 1?m in diameter. The aim of a nanofocal tube is to achieve a spatial resolution of less than 1?m, with a geometrical magnification of as much as several thousand times. Coupled with a high-energy (750kV) generator, the resultant X-ray tube will be a major step-change in the radiographic NDT industry, both as part of the COncEPT system and as a stand-alone component, in terms of portability, focal size and high power.
Imaging Detector
Noise is a random variation of signal that can obscure useful information in a diagnostic image. Inherent in any digital imaging chain, noise has long been recognised as a parameter that can have a dramatic impact on image quality, which degrades very quickly as noise increases. Low noise is therefore a prerequisite to good image quality at reasonable doses, particularly when viewing small, low-contrast objects. Dose Quantum Efficiency (DQE), expressed as a function of object detail or spatial frequency, combines noise and contrast performance into a single parameter that is widely accepted as the measure most representative of digital image quality and object detectability. Hence, maximising DQE is an important design aspect of digitally based imaging systems. Developing the digital detector to the specified requirements will be of major benefit to several industry sectors, especially with the rise in use of new digital radiographic technologies. This detector will place the SMEs partners in a very strong pre-competitive position within the market place
Power Source
Crucial to the quality of X-ray generation is the power supply. The goal is to provide a suitable stable power output to drive the high-power X-ray tube. Currently, for a typical 450kV fixed CT system, X-ray generators weigh in excess of 400kg. Clearly, for a portable system, weight is a determining factor in a practical application. The overall power system will provide a power output of over 2kW, with minimum weight attachments to the working manipulator. Advances will be made in current technology in terms of weight minimisation of the HT cable from the power source to COncEPT system, and low power AC conversion to stable high power DC. The system will also be capable of IP67 rating for environmental conditions and will provide a major step-change in X-ray power generation for portable deployment.
Automated Scanner
Hardware integration will be provided by a highly accurate, portable scanner for use on WTBs. This will be achieved through the development of an entirely new and novel manipulator designed to accept the hardware necessary for portable CT scanning. The overall philosophy is to achieve a high degree of accuracy commensurate with fixed CT scanning, combining maximum repeatability and positional accuracy in both absolute and relative terms. The manipulator will also be uniquely adapted to operate in remote locations. Whilst a desirable of the prototype design will be to make as much of the manipulator as generic as possible, it is understood that some modifications will be required to optimise the equipment for specific circumstances.
Final prototype
The development of the COncEPT system will be a major step-change in current advanced automated NDT methodology, enabling many in-service components to be inspected to a high degree of accuracy and repeatability, thus establishing accurate trend monitoring and increasing PoD and confidence levels in composite wind turbines.
The COncEPT Project is a collaboration between the following organisations; TWI Ltd, X-Tek Systems Ltd, Photonic Systems Ltd, General High Voltage Industries Ltd, Isotest Engineering srl, Innospexion ApS, Eon Plc, RWE nPower Plc,
Kaunas Technical University, London South Bank University and Germanischer Lloyd Wind Energy GmbH.
This project is managed and co-ordinated by TWI Ltd, and is partly funded by the European Commission under the Horizontal Research Activities Involving SMEs: Cooperative Research Programme reference COOP-CT-2006-032949.