Delay modeling for virtualization-based Co-simulation of IEC 61850 substations

Increasing digitization in station automation enables new applications for intelligent functionalities in substations of electrical power systems. The use of IEC 61850 as a uniform communication standard is an important requirement in this context, but also changes the vulnerability to cyber-attacks. Real-time cyber-physical cosimulation platforms are necessary to investigate cyber security threats and countermeasures in digital substations. Essential to the real-time capability and validity of the co-simulation is the compliance with requirements of IEC 61850 - especially the arising transfer times between the substation components. We present here a queue-based delay model for the used Software-Defined-Network architecture to derive a maximum permissible size of the virtual network. This model can capture various influences during the information exchange between OpenFlow-based switches and a centrally hosted controller. The dependency of the transfer time on the number of switches, considered data rates and handover probabilities between controller and switch limits the network size of the virtualization. We present here the adaption of well-known queueing delay models to our IEC 61850 substation use case and their usage in presented co-simulation approach, by taking the network topology, estimated network traffic and simplifications for single-controller architecture with uniformed Open-Flow Switches into account. In this context, the presented architecture of the co-simulation has a structurally limited area of validity, which is introduced and described here analytically. The work also complements already existing delay models by an input prioritization of packet-in events. We can approximate a theoretical limit of 16 sampled values streams in the current setup of co-simulation in a simple and completely interconnected star topology, which will have to highest impact on the transfer time delay.