Protection, measurement and control IEDs in a substation compute if switches they control may be operated safely, according to interlocking rules or physical principles as well as the dynamic topology of the substation. The IEDs have access to the substation electrical topology, to real-time information generated by other IEDs, and to the rules for interlocking. A standardized Substation Configuration Description (SCD) of the substation for which a Substation Automation system is intended, and a standardized description of the implemented device functions or capabilities of an individual IED are utilized. The substation topology is available from SCD file, real time information about the position of switches and line voltage/current can be obtained via an appropriate protocol, and the interlocking rules are available in script form. These features apply both to simulated and real devices, and increase system testing possibilities by supporting an efficient configuration of a simulation.