The TeKaF project (German acronym for temperature dependent capacity utilization for overhead-lines) aims to increase reliability, safety, and capacity of the Swiss electric transmission grid. As the electrical power transfer is increasing, a dynamic evaluation of the maximum transmission capacity of the existing overhead-lines is desired. The maximum current and thus the resulting conductor temperature is influenced by local weather conditions.

The minimum ground clearance of the stranded overhead-line conductor has to be ensured at all times to guarantee a safe and reliable grid. Resistive heating due to electrical current causes thermal elongation and increased conductor sag. Elevated conductor temperatures also reduce lifetime because of material deterioration and creep.

The influence of the local weather must be taken into account to determine the conductor temperature accurately. This enables a dynamic rating of the maximum current of specific overhead-lines, which is incorporated into several optimal power flow approaches leading to an optimized extended-energy management system that includes day-ahead market, balancing market and real-time operation.

Evaluating temperature scenarios of overhead-lines is part of the lifetime prediction. In addition, the temperature and time dependent material properties are first investigated on the basis of single wires and then in full conductor experiments and simulations, where influences of the manufacturing process are taken into account. In contrary to the free-span, where mechanical stresses and strains are regularly distributed, the situation near the clamps is more complex. Therefore, thermal-electrical-mechanical coupling effects are investigated near the tension clamps, where temperatures are lower but mechanical stresses and strains can be higher than in the free-span. The conditions at suspension clamps are studied due to the increased risk of fretting fatigue, which is caused by wind-induced vibrations.

 

Tension clamp assembly with stranded conductor

 

The TeKaF project is conducted by three different research groups: The High Voltage Laboratory of ETH Zurich under supervisions of Prof. Christian Franck; the High Temperature Integrity Group, which is part of the Laboratory for Mechanical Integrity of Energy Systems at Empa supervised by Prof. Edoardo Mazza and Dr. Stuart Holdsworth; and the Distributed Electrical Systems Laboratory supervised by Prof. Mario Paolone and Dr. Rachid CherkaouiThe project website is to be found here.