In the world of wind turbines, blade size and shape are key factors. The longer its blades, the more energy a turbine can capture from the wind — and the greater its electricity-generating capacity; and in addition to size, the efficiency of a wind turbine blade is determined by the precision of its airfoil profile.

Given the difficulty of measuring the world’s largest blades, which are 80m-long and are used on the V164-8.0MW turbines made by MHI Vestas Offshore Wind, high-precision measuring technology is an essential part of producing the 80m-long blades — almost the length a football field. MHI Vestas Offshore Wind is a joint venture between Vestas Wind Systems A/S and Mitsubishi Heavy Industries (MHI). The company designs, manufactures, installs and services wind turbines for the offshore wind industry, and it aims to drive down the cost of energy from offshore wind parks by reducing manufacturing costs and increasing production efficiency.

MHI Vestas’s V164-8.0 MW prototype turbine broke the record for power production by a wind turbine in a 24hr period from 6 to 7 October 2014, by producing 192,000kWhr during steady wind conditions — enough to meet the energy needs of about 13,500 households. MHI Vestas Offshore Wind’s CEO, Jens Tommerup, said: “This record further underlines both the quality of the technology and the skills of the team involved, which has been working hard to ensure that the turbine is performing according to our testing schedule.”

DONG Energy recently ordered 32 of the V164-8.0MW turbines, which will be installed on the 258MW Burbo Bank Extension project, located in Liverpool Bay. The turbines will produce enough energy to meet the requirements
of some 180,000 homes.

Production upgrade

Encouraged by the efficiency of this wind turbine, MHI Vestas Offshore Wind has invested in upgrading the production capabilities of its Vestas Blades Technology Centre on the Isle of Wight. Designed to develop large blades for the latest wind turbines, the site has two ‘halls’, each 170m long x 50m wide — one for testing and verification, the other for blade production.

Vestas metrology engineer John Hodgkins says: “The blades for the V164-8.0 MW prototype were designed, manufactured and tested at our Isle of Wight facility. Given the sheer size and demanding dimensional tolerances of the blades we now produce, one of the most important capabilities we have developed is our precision measuring expertise.

“The precise dimensions and profile of blades are critical to their operating characteristics; these dimensions are also important to ensure the correct depth of composite material to optimise blade strength without adding unnecessary weight that could have a detrimental effect on performance. In addition, the need for precision increases in proportion to the size of a blade. For instance, a small error at the hub end of a large blade can result in a huge inaccuracy at its tip.

“Traditionally, we used manual measuring systems, such as wooden templates and hard gauging. While these methods provided the required accuracy for smaller blades, we needed a more-precise, repeatable means of gathering traceable data on larger blades.”

Laser tracking

While attending a major UK exhibition, Mr Hodgkins saw a demonstration of a Faro Laser Tracker ION (www.faro.com). “This instrument was more straightforward to use — and faster — than the other systems that we looked at. It also provided the high-accuracy results that we needed, and it presented its findings in an easy-to-follow graphic format. Further in-house demonstrations on typical blade applications confirmed our opinions, and we were happy to place an order. As the use of our Laser Tracker ION had delivered many advantages in terms of accuracy and speed as our volume of work grew, when Faro later launched its Laser Tracker Vantage, we bought two of them. In addition
to performing precise measuring routines on completed blades, one of our most critical measurement functions is to make very accurate measurements when setting up the moulds we use to give each blade its required precise
profile.

“Our implementation of Faro Laser Tracker technology represented a step-change in our measuring technology. Indeed, the use of Faro products has allowed us to develop highly efficient metrology methods. Because of the expertise developed by the Isle of White metrology department, our duties now involve travelling throughout the world to other Vestas facilities, to accurately set up blade production moulds.

“We either hire a Faro laser tracker from a local supplier on arrival or bring one of our own Faro units, such is their compact size and low weight.”