Impact of characteristics of block-transformers on inrush currents and voltage distortions at the connection point of wind parks

In the procedure of connecting large wind parks (WP) to the external power grid, TSO´s or DSO´s request is that WPs in operation do not excessively affect the power quality in the connection point. In the process of determining WP operating procedures it is necessary to include switching operations in the WP main feeder. The transformers connected near the wind generator units are then energized and a transformer inrush current appears, followed usually by voltage distortions. Those currents may cause nuisance tripping of protection devices and power quality problems in the WP connection point. For illustration, the connection to a real power grid of a large WP with twelve generators and block transformers is simulated. Considered network short circuit power is comparable to typical parameters of the transmission or distribution medium-voltage networks. Simulated inrush currents depend on the characteristics of connected devices in the network. Results of our study can be useful for correct protection relay device setting and determining optimal WP exploitation procedures.