The influence of voltage sags on the stability of 10 kV distribution networks with large-scale dispersed co-generation and wind generators

In large areas of the county of North-Holland a significant amount of combined heat and power (CHP) is applied in agriculture to meet the demand of heat and electric power in glass houses. The CHP units are equipped with synchronous generators that vary from 400 kVA up to 2000 kVA and they are connected to the 10 kV cable grids. Besides the glass houses and the CHP units North-Holland is characterized by a high penetration of wind energy conversion systems (WECS) with asynchronous generators in the range of 750 to 1500 kVA. The wind generators are also connected to the 10 kV grid being part of the grid which also energizes parts of villages and towns with households and small industries. The 10 kV distribution networks are connected to the 50 kV-meshed grid through 50/10 kV substations. The 10 kV networks are radial under normal operation conditions. In this paper the stability of a distribution network during voltage sags, which could be initiated by disturbances in the 50 kV or 10 kV grids, is investigated. The study and simulations show the voltages and currents in the 10 kV network, the dynamic behavior of the generators and the impact of protection devices in the 50/10 kV substation and the 10 kV network and the influence of series coils to reduce the short-circuit power