Electrical problems at a substation at Rotterdam The Hague Airport have led to communication breakdowns between the tower and pilots. The cause was tracked down using an acoustic imager.
Communication between ground staff and pilots was interrupted for ten to twenty seconds at a time. The problems occurred on all approaches from the UK in early January, according to a statement from manufacturer Fluke, whose acoustic imager (model ii910) was used by TenneT to solve the problem. TenneT is the grid operator responsible for the substation from which the faults originated.
Even though the faults are electrical, they were found via an acoustic diagnosis. The cause turned out to be corona discharges - electrical discharges that occur in the shape of a ring (corona = ring) on high-voltage lines and can cause EMC problems. Among other things, they depend on the cable structure, air humidity and deposits on the cable. The discharge occurs in a shock-like manner and can also be perceived acoustically. Planners of high-voltage overhead lines therefore treat them as noise immissions and are encouraged to pay attention to the boundary field strength in the cable during design.
The acoustic imager used was developed to detect partial discharges and gas leaks. To do this, an acoustic map (sound map) is superimposed on a video image, showing frequencies between 2 kHz and 100 kHz, the source of which can be up to 120 m away.
Important for the interference suppression at the airport was the camera's field of view of 63 °. »Thanks to the large field of view, we can quickly scan an entire substation with the Fluke ii910 and find out where partial discharges are present,« Roel Van Hees summarizes. The maintenance engineer at TenneT was involved in the fault clearance process and was probably able to make use of functions in the acoustic imager that he himself suggested as a product tester. Van Hees was part of the working group that tested the Fluke ii910 during development and »gave us valuable feedback,« as Fluke's product manager Tako Feron explains. Van Hees also knows the alternative to the acoustic imager: »In the past, we would have had to simply listen or use a UV camera,« which would have taken much longer, according to the maintenance engineer.
Once the problem was identified, the areas affected by corona discharges were repaired and air traffic control communications were de-jammed.