Restrictions on transmission capacity are based on safety limits for how hot the wires may become. By constantly measuring the temperature of the wires, rather than relying on statistical estimates of how hot the wires are likely to become, means that transport capacity can be increased. On a pilot stretch of the E.ON network, the much used 110 kV transmission line between Flensburg and Niebüll in the windy northern part of Germany, the capacity increase at times was at times as much as 50%.
Shortly before E.ON launched its pilot project in September 2006, wind station owners had been preparing legal action against the company over lost income due to overly zealous "generation management" in the name of protecting the network and for failing to provide adequate transmission capacity for wind generation.
E.ON Netz says its temperature monitoring process is "unique worldwide." Temperature sensors along the wires deliver information on weather conditions. The transport capacity is calculated, rising as temperatures drop, and the data used for online control of network transmission capacity.
Applying the pilot
The company is now making preparations, including upgrading transformer stations, to operate temperature monitoring on further 110 kV cables in the Schleswig-Holstein region and is investigating its use on 380 kV cables too. The company notes, however, that "stability requirements of the European high voltage network restrict possible capacity increases of the 380 kV cables."
Despite the capacity improvements achieved through temperature monitoring, transmission network expansion to integrate and transport growing wind power output is still needed, the company stresses.