Under the watchful eye of experts from TenneT and research agency KEMA, the new Wintrack high-voltage pylon with reduced magnetic field intensity has been subjected to a massive surge current of 50 kA for 0.5 seconds, with current strength peaking at 125 kA. The innovative pylon design passed the short-circuit test with flying colors.
The short-circuit test of the Wintrack pylon was performed as part of a series consisting of four tests in total. The new high-voltage pylon is designed to meet the changing requirements imposed by society on high-voltage connections. The new pylon is characterized by its slender appearance, but particularly by the fact that it generates a far lower magnetic field than existing lattice pylons. This allows for more opportunities to construct buildings in the direct vicinity of the high-voltage line.
With the current type of 380-kV pylon and line, construction restrictions would apply to a strip of land of approximately 300 ms around the high-voltage line, according to the guideline issued by the Dutch Ministry of Housing, Spatial Planning and the Environment. If the Wintrack concept would be used, however, this strip (also referred to as the ‘magnetic field zone’) would be reduced to less than 100 m in width. The reduced intensity of the magnetic field is due to the fact that the two 380-kV circuits have been placed as close together as possible in two separate pylons. A shorter distance between the two circuits allows for a smaller magnetic field zone.
The plan is for the Wintrack pylon to be used in the new high-voltage connections currently being constructed in the Randstad region of the Netherlands. This new connection between Wateringen and Bleiswijk is scheduled for completion in mid-2011. A European call for tenders was recently issued for the construction and installation of the Wintrack pylons.
Although short-circuits in high-voltage lines are extremely rare, the line is subject to extremely high current intensities when one does occur. The conductors and jumpers come under enormous strain because the mechanical forces increase quadratically with the strength of the electrical current. In order to find out whether the new pylon could withstand these forces, TenneT decided to put it to the test at KEMA’s short-circuit laboratory in Arnhem. The short-circuit test was conducted in several phases, with the pylon subjected to ever higher current intensities for longer periods of time until a current intensity of 50 kA was reached for 0.5 seconds with a peak at 125 kA. Despite the short duration, the impact of the actual short circuit is enormous: an extremely loud bang is produced and the conductors lash violently in every direction. The event was recorded in detail by a high-speed camera. The resulting information has been stored in the database and will be interpreted by the experts.
The short-circuit test was the second in a series of four. The first was a mechanical test of the suspension of the conductor bundles from the insulators in the so-called ‘braced-V’ configuration. On the day following the short-circuit test, a successful type-test of the new bundle spacers was conducted. In the event of a short-circuit, these spacers are subject to very high pinch stress. The previous type-test of these spacers was conducted as far back as twelve years ago. A voltage test will follow in the spring of 2009. This test will measure noise nuisance due to the ‘corona effect’, among other things.