TenneT is a leading European electricity transmission system operator with its main activities in the Netherlands and Germany. With over 23,900 kilometres of high-voltage connections, TenneT ensures the secure supply of electricity to 42 million end-users.
TenneT’s core tasks following its appointment as grid operator under the Dutch 'Elektriciteitswet' (E-wet) and the German 'Energiewirtschaftsgesetz' (EnWG), are:
- To ensure a secure and continuous supply of electricity
- To provide transmission services by transporting electricity along the high-voltage grid from where it is produced to where it is consumed.
- To provide system services to guarantee the flow of electricity in the Netherlands and large parts of Germany.
- To support the large-scale transition to renewables.
Interference at Rotterdam The Hague Airport
Rotterdam The Hague Airport is a minor international airport serving Rotterdam, the Netherlands' second largest city and The Hague. It is located 3 NM north northwest of Rotterdam in South Holland and is the third busiest airport in the Netherlands. The airport handled more than two million passengers in 2019 and features scheduled flights to European destinations, including London.
In the latter part of 2020, the Dutch Radiocommunication Agency was contacted by Rotterdam The Hague Airport air traffic control. The airport reported strong radio interference between the pilots and air traffic control on all incoming flights from the UK – one of the airport’s busiest routes.
The interference meant that for a period of 10-20 seconds, no communication was possible between the pilot and air traffic control. And while this issue was not causing flights to be diverted or significant delays, the airport was keen to identify and fix the problem so trouble-free communication could resume.
Track and trace
In January 2021, the Dutch Radiocommunication Agency started a field investigation to identify the cause of the interference. This included direction finding vehicles ‘mapping’ the area to locate the interference location. The Dutch Radiocommunications Agency identified that the interference was coming from the substation, ‘De Lier 150’, one of the many substations in the country managed and maintained by TenneT.
TenneT immediately responded to the news by dispatching Roel Van Hees, an Operational Maintenance Engineer at TenneT. At the substation,Roel Van Hees undertook further investigations to identify the potential root-causes of the interference. Initial audible and visual inspections showed no abnormal findings.
Roel Van Hees then conducted a partial discharge inspection, using the Fluke™ ii910 Precision Acoustic Imager. The cause of the interference was instant.
Introducing the ii910
The Fluke™ ii910 Precision Acoustic Imager was developed to help engineers detect electrical discharge quickly and easily. The durable, handheld casing of the Fluke ii910 has a seven-inch LCD touchscreen which overlays a SoundMap™ on a visual image for rapid identification of discharge or leaks between frequencies of 2-100 kHZ. The array of integral microphones converts ultrasound signals into clear visual images on the backlit touchscreen. Captured data can be transferred via an integral USB-C socket directly to a PC. From here, the data can be uploaded to the Machine Learning PDQ Mode™ Reporting Platform. This will provide the most important partial discharge insights, including partial discharge type identification. The ii910 provides video recording of up to 5 minutes and has a battery life of at least 6 hours.
“The Fluke ii910 Precision Acoustic Imager proved invaluable in helping to quickly and easily identify the partial discharge issue,” says Roel Van Hees. “In the past, we would have had to listen and/or use an ultraviolet (UV) camera, which are slow and inefficient methods compared to the Fluke ii910. With its wide view, the Fluke ii910 enabled us to quickly scan the substation and identify the partial discharge places of concern.”
“The Fluke ii910 Precision Acoustic Imager was developed with the end-user in mind,” comments Tako Feron, Product Manager Acoustic Imaging at Fluke Corporation. “Roel Van Hees was part of a working group that helped to test and feedback on the product during its development. Their feedback was invaluable in helping us to address some of the pain points they face on a daily basis, and we continue to work with the group to add new features to the software.”
Corona discharge
The ii910 was able to identify partial discharges in a high frequency range. Further investigation by the operational maintenance engineer quickly identified that rail clamps were suffering from corona discharge. Corona discharge, one of the most common forms of partial discharge, is caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage.
After removing the upper part of the clamp, excessive corrosion was found. The end of the spring strip (to contact the rail tube) showed traces corresponding to damage from corona discharges. The degree and composition of the corrosion under the left spring strip suggested that the fastening material had decayed.
Over time, an accumulation of salt and dirt deposits had settled between the spring strip and rail tube. As no more voltage equalization could take place, a potential could arise between the spring strip and rail tube. The built-up potential was therefore equalized by means of partial discharges.
The discharges had increased in intensity over time and damaged the spring strip and rail tube, with the presence of several degraded rail terminals having a cumulative effect. This made it possible to build up an interference signal with sufficient energy and high frequency to disrupt radio communication of air traffic hundreds of meters away.
Fixing the problem
To fix the problem the upper clamping parts were sanded down, rotated 180 degrees, and reassembled. Following this, communication between the airport control tower and pilots is now back to normal.
However, it is plausible that partial discharges will occur again in the future. In the past, power grid operators were not overly concerned with corona discharge as it has a negligible impact on the grid network. Public complaints due to noise pollution was the main reason this issue had been previously addressed. Though, given the communications issue at Rotterdam The Hague Airport, the engineering team at TenneT is currently investigating a proactive maintenance plan to help mitigate the impact of future corona discharge throughout its network.
Concludes Roel Van Hees: “TenneT has been using Fluke instruments for a number of years and they play a key role in our day-to-day mission to provide a safe, secure and continuous supply of electricity to our end-users. The team believes in the quality associated with the Fluke brand, and at a personal level, I also use Fluke products at home.”
