Maintaining a reliable network condition in transmission and distribution networks efficiently requires the optimal planning and operational use of ancillary services. In addition, the EU's Clean Energy Package results in fundamental regulatory adjustments for the planning and operation of ancillary services. To this end, the IAEW has developed various proven models, in particular for congestion management, electricity balancing and voltage control. For instance, optimization algorithms are available for the planning and operation of reactive power compensators. The demand of ancillary services in transmission and distribution networks can be determined in any level of detail by coupling scenario development with steady-state network analyses and time domain simulations. Last but not least, the network models for transmission and distribution networks available at the institute also allow the analysis of interactions between transmission and distribution networks. The IAEW also has expertise in the determination of network sections in existing distribution networks that are capable of being used in islanded mode. With the help of models for power and stability analyses, an optimal selection of islanded network sections during an interruption of supply of the overlaying network can be made.