TEST & MEASUREMENT FEATURE
all of the tests. It was, in fact, the only instrument to do so – the non-Megger instruments in the trial performed no better than the DET4. As further validation of the results produced by the DET2/2, these were compared with the historical earth
The DET2/2 can even measure earth resistance in wind farm installations while the turbines are in service
resistance measurements made when the wind farm site was initially surveyed. Excellent agreement was found in every case, confirming that the DET2/2 can be relied upon for measuring earth resistance in wind farm installations, even while the turbines are in service. There is, however, one caveat. For this
initial trial, SSE and Megger elected to carry out measurements on the earth systems associated with turbines around the edge of the site, largely because of the difficulty in achieving sufficient spacing for the test electrodes at the centre of the site, where the turbines are closer together. Work is ongoing to address this limitation. In the meantime, both SSE and Megger
consider the results produced to date to be of great value and significance, not least because it is unlikely that the centre of a wind farm site would be
affected by conditions so localised that they would materially change its earth resistance without this change being reflected, to some extent at least, by a change in the earth resistance of the peripheral areas of the site. The joint trials carried out by Megger and SSE have shown that earth resistance measurement on an in-service wind farm is every bit as challenging as had been expected. Nevertheless, with commercial equipment that is readily available right now, it is possible to obtain accurate, reliable results, making routine periodic testing a realistic and financially viable option. Such testing has a major role to play in helping operators keep their wind farms safe, and to minimise risk to the public, even under fault conditions.
Megger
megger.com
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