Increasing renewable energy penetration is leading to bottlenecks in distribution and transmission grids. However, with the right weather and an innovative sensor network with self-sufficient (autarkic) power supply, operators can tap reserve capacity by harnessing power line cooling. The technology will be on display from May 14th-16th at Sensor+Test 2013 in Nuremberg (Hall 12, Booth 537).

Storms in the north and east of Germany regularly lead to bottlenecks in local high and extra-high voltage power grids. Although the power grids were designed to prioritize power from renewable energy sources, time and again wind turbines have to be temporarily decommissioned because the energy supplied outstrips grid capacity. “The level of renewable energy fed into our high-voltage grid is currently very high and we’re expecting further dramatic increases. The problem is that the grids were not designed for such volumes,” reports Hanjo During of Halle’s MITNETZ STROM mbH, which operates approximately 6000 km high-voltage power lines in East Germany. Although additional power lines are planned, applications to obtaining the required approval can take years or are defeated by resistance from local communities.

For this reason, grid operators have already begun using a number of different power line monitoring systems to increase grid capacity in the short-term: They harness reserves yielded by the difference between standardized estimates of line operation under adverse weather conditions and the actual line condition. The approach has increased transmission capacity by 20 percent and more under favorable weather conditions. The distribution grid operator MITNETZ STROM is currently testing an innovative sensor network with self-sufficient power supply to monitor 110 kV lines. The new technology is being developed as part of the project ASTROSE^®, a collaboration between the Fraunhofer Institute for Reliability and Microintegration IZM in Berlin, the Fraunhofer Institute for Electronic Nano Systems ENAS in Chemnitz, and other research and industry partners. “Our sensor network with autarkic power supply is easy to retrofit and requires no additional infrastructure,” explains Fraunhofer IZM’s Dr.-Ing. Volker Großer. In contrast to conventional monitoring systems, it transmits measurement data from the highly synchronized sensor network directly along the power lines.

How much power an overhead line can transmit is largely dependent on the temperature. For example, if the power current or the sun heat up the overhead transmission lines, they extend and sag.

The effect is potentially life-threatening if the sag is so great that the line nears the ground, vehicles or people.  Consequently, operators are legally obliged to maintain defined safety clearances. At the same time, an overhead power line’s permissible current rating is calculated based on a surrounding temperature of 35 °C and maximum wind speed of 0.6 m/s. However, midsummer is often windless and most wind turbines only power up at a wind speed of 3 m/s or more. Conversely, they generate exceptionally large volumes of power in autumn and winter, when the overhead power lines are well-cooled.

To better harness these reserves in the power grid without compromising safety, the ASTROSE^® project participants are fitting the 110 kV overhead power lines with eGrains. Spaced approximately 500 meters apart, the cylindrical sensor nodes encircle the power line. “The ASTROSE^® eGrains comprise two half-shells that are plugged together and then clamped. They monitor a range of data, including the power line’s degree of sag, the power current and temperature. The data are relayed from eGrain to eGrain, until they reach the nearest substation, where they are fed into the grid operator’s remote monitoring systems,” explains Großer. The operating power required by the ASTROSE^® eGrains is pulled from the electrical field surrounding the power line. However, the ASTROSE^® sensor network not only helps operators use power line capacity more efficiently. It also guards against the dangerous sag caused by ice on the power lines during winter. This, along with all other features, has already been verified after a six-month evaluation. The sensor network will be on display from May 14^th-16^th at Sensor+Test 2013 in Nuremberg (Hall 12, Booth 537).