Implementation of the IEC61850 9-2 Process Bus used for Protection Systems in the Digital Substation

The IEC61850 standard, "Communication Networks and Systems in Substation", provides the basis for the communication system of the digital sub-station. The Ethernet based communication network for data transfer between process level switchyard equipment and bay level IEDs, the process bus is defined in Section 9-2. This process bus facilitates the communication of two types of real-time, peer-to-peer communication messages. Generic object-oriented substation event messages, the GOOSE messages and the data sample values, SVs which include the measured currents and voltages. Although this standard describes the message structures and the timing requirements, it does not describe the process bus topology. This paper describes different LAN topologies that can be used in the design of the process bus for protection systems. It considers the implications of the different structures on the operation of the protection scheme and how these relate to the operational strategy of different operators. It provides an assessment of the data handling capabilities of the system and how the demands of the protection system can be met. Several potential problem areas are identified and analysed. It also provides an insight into the implementation of the alternative topologies and their performance when applied to a transmission line feeder protection.