The liberalization of the German gas market poses novel and difficult planning problems to transmission network operators. They are obliged by the Gas Grid Access Ordinance to offer as much freely allocable capacity as possible. Freely allocable capacities enable gas shippers (usually gas traders or bulk consumers) to feed in or withdraw gas at their entries and exits without having to care where the gas is withdrawn or fed in, respectively. This flexibility shall contribute to increasing competition and establishing an efficient gas market.

When offering transmission capacities, the transmission system operator has to ensure free allocability, which means that all gas flow situations that may result from exercising these capacities can be realized by the gas transmission network. This requirement can hardly be verified with existing simulation-based planning methods. The goal of this research cooperation is therefore to develop and implement optimization-based methods for checking realizability of gas flow situations. Moreover, we are also working on methods that provide cost-effective network expansion measures to increase freely allocable capacities.

At the heart of our methods is a mixed-integer nonconvex model describing the technical realizability of a gas flow situation. The pressure loss in a pipe is approximated by a quadratic equation, whereas the operation range of a compressor is modelled by a suitable polytope. The possible operation modes of compressor stations are described by binary variables. We developed a custom-tailored algorithm exploiting special properties of this model which can determine suitable controls for each gas flow situation or decide that no such controls exist.