System connection of very large variable speed drives for compressor purposes

For environmental as well as for economic reasons, large compressors with a power rating of 10 MW and more are increasingly fed by electric variable speed drives. The connection of such drives to the public medium or high voltage grid requires a thorough consideration of the entire system mainly in respect to voltage stability and harmonics to avoid any disturbances of adjacent loads. The paper summarizes the basic operational behaviour of such compressor drives with special consideration of system perturbations. Using examples from recently commissioned plants, possible mitigation measures as well as general experiences are presented. To ensure that everytime certain limits for system disturbances will be met, filters have to be coordinated with actual and future system conditions taking into account possible outage as well as loading conditions of the feeding grid. The consideration of transient disturbances such as starting or stopping the drive are important especially for the design of the auxiliaries. Examples from simulations show typical problems which have to be taken into account.