Efficient and sustainable digitalisation of smart secondary substations with current and voltage sensors integrated in cable connection bushings

Digital secondary substations (DSS) are becoming a key element for distribution system operators (DSO) in terms of automation, monitoring and efficient operation of their grids. They provide more transparency of the distribution grid by measuring energy flows and can ensure that loads are minimized, the most efficient and stable operation is guaranteed and also monitor whether the technical limits of the components have been reached or even been exceeded. IEC-compliant low power instrument transformers (LPITs) for current and voltage measuring, integrated into cable connection bushings of F-gas-free gas-insulated ring-main units, are essential components in this regard to provide operational values from the grid. Standardized output signals ensure that a large number of short-circuit and earth fault indicators, as well as measuring and protection devices are compatible with such LPITs. Beside to the measurement of current and voltage on the medium voltage side in the secondary transformer substation, a measurement of the outgoing currents from the low-voltage distribution with intelligent LV HRC fuse links provides a more precise grid monitoring. All measured operational data are transmitted to a gateway which collects all data of a secondary substation and transfer them to the control centre or/and to the cloud.