Impact on Distribution System Protection with the Integration of EG on the Distribution Network

A significant increase in EG connections on the distribution network over the past decade in Ireland has presented challenges to the Distribution System Operator (DSO). The connection of EG can cause co-ordination of Distance protection to be altered and has resulted in variations in short circuit levels. Multidirectional power flow has been introduced into a Distribution system that was not designed for the direction change in current flow. The impact of connecting EG to a typical 38 kV Distribution Network was demonstrated as part of this study. Increasing fault levels and protection co-ordination selectivity problems were identified when the network was fed as a closed network. The increase in short circuit fault levels was evident when the fault contribution from the EG was considered. This increase in short circuit fault current could be a concern if EG is installed in an area where the maximum current rating of the switchgear could be exceeded. The co-ordination of Distance protection IEDs were also affected when EG was connected. Case studies on a typical Distribution Network were presented as part of this study. The impact that EG can have on the short circuit fault levels and the co-ordination of Distance protection when the network is feeding as a closed loop network was identified. When incorporating EG to a typical 38 kV Distribution Network, considerations must be made to ensure that the connection of the EG does not inhibit the performance of the overall protection system. A protection review of the network is required before any EG is connected. The issues identified the miscoordination of Distance protection IEDs. A revision of current IED settings in the vicinity of the installed EG and the addition of duplicate protection IEDs may be required.