New requirements for system protection caused by distributed generation

The requirements for the protection of distribution networks are considerably changing due to the increased share of distributed generation (DG). Protection schemes and practices designed for unidirectional power flow may become ineffective. The purpose of this paper is to present results of simulation analyses of the impacts of DG. The emphasis lies on three problems: • Impact of DG on the fuse based protection of low voltage networks • Impact of DG on automatic reclosing • Loss-of-mains requirements and methods Additionally, the impact of small low voltage connected units on the protection of medium voltage feeders as well as aspects of the aggregate impact of several small DG units have been discussed. In this study the commercial transient simulation tool PSCAD™ has been applied. For this environment an extensive collection of simulation models has been developed. This collection includes models of MV and LV networks, different types of DG units, protection relays and fuses. Performance of system protection including interconnection protection has been analysed with various combinations of network parameters, relay settings, loads and faults.