05.01.2018 | Emergency for Axpo grid operations
The storm Burglind hurtled over Switzerland with peak wind speeds yesterday and caused a great deal of damage in some areas. In the Canton of Schwyz, where one of Axpo's 50-kilovolt line sections is located between Siebnen and Grynau, two masts were pulled down. What do our experts do in this kind of an emergency?
It was a turbulent start into the New Year for some Axpo employees. The force of the storm Burglind experienced in Baden on Wednesday left its mark over large areas of Switzerland. In Tuggen, at the upper end of Lake Zurich, the roof of an industrial building could not withstand the wind gusts and blew onto the 50-kilowatt overhead line. The damaged line dangled close to the ground of a football field and the main road, and also fell onto the intersection point of a 16-kilowatt line. As a result, numerous wooden poles and lines were pulled down. The damage to the 16-kilowatt line led to a power outage in the region.
Roland Ziegler, Head of Line Operations, and his team do not know the cause of a power outage immediately. "Over 50 per cent of all breakdowns are rectified when the line is reconnected," says Roland. Reconnection takes place automatically or manually from the Network Control Center in Baden. When failures occur, close cooperation between the Network Control Centre and Line Operations is a must. If a reconnection is unsuccessful, employees begin looking for the cause of the breakdown. Getting a picture of the situation on site is the first step. This includes estimating the damage and material needed for line repair. The damage report is forwarded directly to the Network Control Center and measures are defined. All the staff required is notified and, in this particular case, many had to return from their holidays.
Once the accident site has been inspected, the staff does everything possible to secure the area. Tasks include disabling reconnection and grounding the lines to prevent a reconnection of the line and ensure that it is inverted to ground potential so that no induced voltage is present. All this work is performed in close cooperation with the Network Control Center in Baden.
Induced voltage can charge metal parts, for example a door handle. If the object is touched the charge is transmitted to the person and an electric shock occurs. When touching a door handle this is unpleasant. Contact to a high-voltage line would have even more severe consequences.
After securing the accident area, it was high time for the team to repair the 16-kilovolt line. The priority here is to carry out the line switch-over so that power is restored to the affected regions as quickly as possible.
«The Swiss power grid is designed to make switch-overs possible at nearly all times, Switch-overs are carried out manually or automatically depending on the network level.»ensure Roland Ziegler.
The repair of the 50-kilovolt line presented an additional challenge because the conductor cable was under such extreme tension that it could not be cut. First the 50-kilowatt line had to be removed from the tin roof of the industrial building and the 16-kilowatt lines had to be released from the fallen masts. This greatly eased the tension on the masts that were still standing.
It will take about two months to completely repair the line section. At the moment, the repairmen are working on a temporary solution. A parallel line that is not in use will be connected.
The hanging conductor cable blocked the main street. The line was lifted to 8 metres by means of wooden structures to achieve a safe clearance height. The structures are made of concrete blocks and wooden poles. A crossbar is then fastened to the upper end of the wooden pole to hold the lines. Power supply via this line section will be redirected and remain interrupted until the repairs are completed.