Design and performance evaluation for a protection system utilising IEC 61850-9-2 process bus

The use of process-bus technology, designed in accordance with the IEC 61850 standard, introduces new opportunities for protection and control. However, before the technology can be deployed, adequate tests are required to prove use of the process bus does not have a detrimental impact on the operating performance of future protection, as expressed in terms of dependability, security and operating speed. The paper will describe an overview of the concepts and benefits of the process bus, and how it affects the design of prototype protection scheme suitable for the mesh-corner of a transmission substation. The operating characteristics of conventional hardwired relays and IEC 61850-9-2LE relays applied within a feeder protection scheme, were compared and assessed against conventional type-test results. The scheme includes Ethernet Switches from different manufacturers, configured to allow the assessment of different process-bus architectures. The effect of interchangeability and time offsets were investigated both experimentally and using the OPNET simulator. The scheme includes Merging Units (MU), tested to assess the magnitude of their time offset and how they drift with time and temperature. Causes of incorrect operation were recognized and recommendations presented to avoid the degradation of system performance. Given an appropriate configuration, the performance of a process bus based protection scheme is comparable to a conventional hardwired scheme. The presented results provides a fundamental reference for all the participating parties to create a roadmap for the efficient application and deployment of protection and control systems based on IEC 61850 process bus and digital Ethernet communications.