Grid interaction of MV-connected CHP-plants during disturbances

Nowadays the amount of distributed generation (DG) units is increasing rapidly. Most dominant are combined heat and power (CHP) plants and wind turbines. At this moment, in most systems, there are no requirements defined for short-circuit behavior of such generators connected to the medium voltage grid. However in the future this situation will not be acceptable anymore, since with the present protection settings of DG a fault in the transmission grid may lead to disconnection of a large amount of DG over a large geographical area. This paper focuses on CHP-plants connected to the MV-grid. New settings for the under-voltage protection will be proposed. These settings will be based on voltage dip profiles and the fault ride through capability of the CHP-plants. With the aid of dynamic simulations it is shown that the new settings of the under-voltage protection can lead to a significant improvement of the availability performance without loosing the stability of the generators.