Lightning Interferometry, attachment, and wind energy

Lightning is the largest operating-environment cause of catastrophic blade

failure, and the number of strikes grows supra-linearly with wind turbine height and

rotor diameter. Despite relatively extensive studies of lightning strikes to tall

towers and aircraft, lightning "attachment" is not well understood. Most lightning

strikes begin with a streamer-leader system descending from a thundercloud.

Electric-field-driven streamers feed into higher-current leaders

and heat air to the point of thermal ionization. Prior to a strike, the high E from an

approaching leader causes structures to emit upward streamers (and radio

pulses). When upward streamers intercept the downward leader, a return stroke

occurs. Engineering models of this dynamic process are limited, and for wind-

turbines include wholly inadequate electrostatic field models to evaluate lightning

protection systems. In lightning rod studies, it was learned that a very sharp

point protects itself by creating a cloud of space charge which suppresses

upward streamer emissions. A moving wind turbine blade can outrun the space

charge (corona discharge) that it produces, making it even more vulnerable to lightning than

an equally tall stationary structure.

The suite of lightning research instrumentation has recently been enhanced by the three-dimensional

lightning interferometer. A lightning interferometer is effectively a small

radio telescope optimized to locate up to a million sources per second. Astronomers

measure right ascension and declination and have to infer range. A 3D-lightning

interferometer gets range intrinsically and can thus produce a full X, Y, Z

moving image of lightning flashes with resolution as high as five meters. We hope to

apply a 3D interferometer combined with high-speed video and current measurements

to gain insight into the process of lightning attachment to wind turbines and

further enable this crucial energy source while illuminating a basic question

of lightning science.

We acknowledge Prof. Ashok Ghosh and Sidharth Arunkumar for work on the attachment

problem in the prototype NM Tech spark lab. We thank Paul Clem of Sandia National Labs for helping

obtain funding for the spark lab.