When the temperatures become icy in the winter, we protect ourselves and dress warmly. A jumper, jacket, boots and gloves are essential. If we spend a long time outside without gloves, we certainly all know the feeling that our skin is about to burst from the cold. This can really happen to our lines: ice can cause them to crack. So it’s not just people who can freeze, our lines can too.
When the temperature drops to freezing point and the humidity is high enough, a layer of ice forms around the conductors. The ice can build up and make the layer thicker and thicker. Due to the ice load, the conductors sag and, if they become too heavy, they can even crack. Electricity pylons can also collapse under the ice load. In order to recognise this at an early stage and take action, tension measuring boxes were previously installed on selected lines. They work with the weight of ropes and are connected via cables. As these installations need to be replaced due to their age, a project team set out to find a replacement. In collaboration with the Berlin-based Fraunhofer Institute for Reliability and Microintegration IZM, since last winter Swissgrid has been testing a new technology called ASTROSE® developed by Fraunhofer IZM. ASTROSE is a radio sensor network for monitoring high and extra-high-voltage power lines. The radio sensor network is based on the delocalised provision of measured values and enables adjustments to be made regarding operational management.
Swissgrid is the first transmission system operator to use the ASTROSE radio sensor network to measure ice loads. This system is currently implemented on the Chringe Pass on the Innertkirchen – Bickigen line, where the pilot project is being carried out in partnership with Fraunhofer IZM. 22 sensors were mounted on the conductor leading from the Chringe Pass towards Innertkirchen. The first results are positive.
The radio sensors measure the rope inclination in each span and establish data communication with the grid control room. They also measure the temperature and rotation of the rope and the amount of current flowing through it. The system is self-sufficient in terms of energy and does not use public transmission technologies, which makes it more secure against attacks from outside. The sensors communicate with each other via radio. The first radio sensor sends its data set to the second sensor, which adds its data and sends it to the third, and so on until the data reaches the radio base installed on the Chringe Pass. There, the data is stored, analysed and fed into the grid control room.
With the old system, the individual tension measuring boxes did not communicate with each other. With ASTROSE, the complete infrastructure is only required at the radio base, as the sensors are able to pass on their data.
If the ice load becomes too high and the conductors sag as a result, the SGC operators normally receive a message. As the project is still in the pilot phase, the notifications are currently sent to the project team, including Fraunhofer IZM. The operators can view the measurement data – listed in tables and visualised as graphics – and intervene via a secure web interface. After that, however, the procedure remains the same: lines threatened by heavy ice loads are heated by means of a short-term, much higher electricity flow to such an extent that the ice melts and falls off the line.
Looking to the future: proactively addressing risks
At the moment, the new data is still being evaluated and compared with the old data. Some fine tuning will be needed, for example so that the system triggers the alarms at the correct values. Once the pilot phase is over, and provided that the results remain positive, the project team can well imagine applying this system at other locations. Besides improving ice load measurement, ASTROSE could lead to further optimisations in the future. A merger with Dynamic Line Rating is possible thanks to the existing infrastructure. As the sensors also measure the conductor temperature, voltage and intensity of current, the ASTROSE system can be used to increase transportability, as well as for early event and hazard detection. This will enable Swissgrid to proactively address risks.