Our technology in controlling power line substation is heading more and more towards a substantial automation. The remote terminal unit ( RTU) is the core element of this evolution: it has interfaces towards protection and control equipment, as well as metering devices and other automation products. Local/remote monitoring and control can be achieved easily via the integrated Human Machine Interface of the RTU. The IEC 61850 client and server functionality of the RTU opens up an additional application area. It allows the combination of traditional protocols, parallel wiring and the IEC 61850 station bus. The hybrid solution provides the possibility to upgrade the station gradually to an IEC 61850 architecture.