This technical specification provides principles and technical requirements for distributed energy resources (DERs) connected to the distribution network. It applies to the planning, design, operation and connection of DERs to distribution networks. It includes general requirements, connection scheme, choice of switchgear, normal operating range, immunity to disturbances，active power response to frequency deviation，reactive power response to voltage variations and voltage changes, EMC and power quality, interface protection, connection and start to generate electrical power, active power management, monitoring, control and communication, and conformance tests. This document specifies interface requirements for connection of generating plants with the distribution network operating at nominal frequency of 50 Hz or 60 Hz. DERs include distributed generation and permanently connected electrical energy storage in the form of synchronous generators, asynchronous generators, converters, etc., connected to the medium voltage (MV) or low voltage (LV) distribution network. NOTE: Mobile electrical energy storage devices (e.g. electrical vehicles) are under consideration for future editions. The requirements of this document can be superseded by laws and regulations where 147 applicable.