Strikes causing concern

Damage to wind turbines by lightning is not uncommon and occurs despite measures taken by manufacturers to mitigate its effects. Britain's first wind farm suffered a strike shortly after commissioning and, more recently, a wind turbine in north west England was struck and a blade damaged. In Germany, 4% of all wind turbine outages in 1995 were caused by lightning, with the electronic control system especially vulnerable to damage -- as revealed in the data base of WindStats Newsletter, Windpower Monthly's sister publication. In America, with wind farm activity moving away from California, there is increasing concern that a better understanding is needed of lightning and wind turbines. The US National Lightning Safety Institute calculates that 1% of the cost of a turbine goes to lightning protection measures. Often, quite erroneously, lightning strikes on turbines are regarded as the cause of power faiures when, in practice, it is the grid which has also been struck. Now a research project, supported by the European Commission, is underway to examine the whole gamut of lightning problems.

The EC project aims to develop a general method of protection from lightning strikes. The size and hub height of turbines is increasing, making them potentially more vulnerable, and there are fears that the cost of lightning damage will rise unless something is done. Frequent lightning strikes could also threaten public confidence in wind energy.

The project will examine the effects of lightning on blades, both wood composite and glass-reinforced plastic, as well as on bearings. The effectiveness of various protection measures will be assessed. Computer analysis will be used to investigate the voltages induced by lightning in the control circuits and other systems. The application to wind turbines of the techniques used to protect aircraft and sensitive terrestrial installations from the effects of lightning will also be investigated.

The project is led by the University of Manchester Institute for Science and Technology (UMIST) and the team consists of UK blade manufacturers Taywood Aerolaminates of Southampton, German wind turbine manufacturer Tacke WindTechnik GmbH, the UK's AEA Lightning Test & Technology, and the University of Athens in Greece. The facilities of the project partners include a high current lightning test facility capable of developing 200 kA and a high voltage laboratory able to test up to 2 MV. The results of the research will be documented in the form of a designer's guide which will be made available to European Industry.