After its two 750 kW wind turbines were off-line for two months, the Nebraska Public Power District (NPPD) in Columbus has solved a mystery about why the presence of the turbines was creating noise on the phone lines of citizens. The Zond turbines are now up and running again. The district was initially stumped about the source of the noise because NPPD has no phone service out to the site, says Mike Hasencamp, manager of the Nebraska Distributed Wind Generation Project. But engineers discovered the phone lines were picking up noise from power lines near the site. The sounds came from electronic equipment on the wind turbines that switched power on and off at a frequency of 1000 hertz. The district added filters to the electric distribution lines and increased the frequency of the turbines' electronic equipment, which seems to have solved the problem, says Hasencamp. Mary McCann of Enron Corp, which provided the turbines, points out that the company has 145 turbines in the Midwest without any reports of noise on phone lines. She notes that Enron provided construction supervision, but did not hook the turbines up. Hasencamp says the project met all the standards that apply to electronic equipment and NPPD is still confused about how the noise affected phones. "Somehow it got onto the phone line from the power line, and we haven't figured out how," he comments. The district's customers, who are enthusiastic supporters of wind power, are happy the turbines are up and running again, says Hasencamp. "They were getting anxious and were worried that something was wrong with the turbines," he adds.