While inspecting electrical substations, specifically wind turbines and solar farms, Paul Twite with Delano Municipal Utilities, sees it all. He was able to find partial discharge at a customer’s site in South Dakota with an ii910 Precision Acoustic Imager. The partial discharge was slowly damaging the equipment over time. By using the ii910 he was able to fix the root cause of the problem and eliminate the damaging PD.
Inspecting a wind farm with the ii910 acoustic imaging camera
While inspecting a wind farm, Twite came across some audible chattering and buzzing from a vacuum circuit breaker. He pulled out his thermal camera and an ii910. The thermal camera did not detect any heat or abnormal conditions coming from the bushings.
The thermal camera was not able to capture the same issue as the acoustic imaging camera. 
Paul Twite’s ii910 scan catching the partial discharge.However, the ii910 measured about 14 dB near the vacuum bushings showing audible energy. Even in the significant wind conditions Twite was facing, “Relative wind was 10-12 MPH with gusts of 15 MPH. This makes for a noisy background from an ultrasonic inspection point of view,” the ii910 caught the problem.
Finding the root cause of nuisance tripping
These issues were noted to the customer, but about a week later Twite was back on the wind farm because of some nuisance tripping on the SF6 vacuum breakers. Again, Twite pulled out the ii910 and discovered corona tracking or partial discharge. And with a closer look he was able to determine that the noise was coming from the interior of the ceramic bushings. It was pretty evident there was an issue since the white porcelain was covered in a dark dust from the arching discharge.
Dust covering the porcelain of the vacuum breakers due to arching discharge.The cause of the partial discharge issues
The most likely culprit for this kind of issue is a lack of regular maintenance. While the wind farm was relatively new, less than four years old at this point, weather and temperature variations likely sped up the problem. The bolted connections were loose, probably from a couple years of freezing and thawing, as the weather tends to do in South Dakota.
Temperature variations, like freezing and thawing repeatedly, cause dissimilar metals to expand or contract at different rates from one another. This can easily cause bolts to loosen over time.
Partial discharge testing leads to cost savings
Issues like this can lead to tens of thousands of lost revenue per day depending on the market conditions and about of energy generated by the wind farm. The revenue lost just to the nuisance tripping exceeded $24,000. Even though the solution was a simple one, replace the bushings and institute a regular maintenance program to check on the connections, the savings generated quickly adds up.