Performance assessment of an IEC 61850-9-2 based protection scheme for the mesh corner of a 400kV transmission substation

The primary plant and instrument transformers used in transmission substations generally remain in-service for many decades, typically 40 - 70 years, and are renewed only when physically or mechanically life-expired. However, the secondary systems, which include protection and control, are changed significantly more frequently. The current replacement rate for protection and control on the UK transmission network is about 5% per annum, i.e. it take approximately 20 years to complete the replacement cycle. However, the asset life of numerical protection and control is often considered to be 15 years, although 10 years may be more realistic due to declining technical knowledge and support, product obsolescence and difficulties in obtaining spares. One way to overcome the problem is to develop a new architecture for substation secondary systems by deploying technologies such as standard interface modules, the bay process bus and the IEC 61850 communication protocol. IEC 61850-9-2 Process Bus proposes a local communication network that replaces traditional hard-wiring with serial communication of analogue and binary signals using Ethernet messages. A Process Bus solution reduces the lifetime cost of the system, improves flexibility and functionality and allows substation secondary equipment retrofitting to proceed without the long circuit outages normally required. Once the new technology is installed, secondary equipment renewals, particularly those occurring mid-life in the primary plant lifecycle, can be undertaken in a safer, quicker and easier way with reduced or no outages of primary systems. This enables vendor interoperability and provides easier modification and extension of the secondary schemes; particularly those related to reconfiguration and feature enhancement by software means, rather than the hardwiring changes required in the past. As a precursor to the widespread deployment of IEC 61850 technology within the UK utility AS3 (Architecture of Substation Secondary System) project, it must be ensured that the reliability and performance of IEC 61850 based protection and control schemes meets or exceeds that of its hardwired SICAP (Substation Information, Control and Protection) predecessors. The aims of the AS3 Architectures are to allow the replacement of faulty Intelligent Electronic Device (IED) without outages; enable the refurbishment of bay level secondary systems with minimal disruption to the primary system; simplify the isolation procedures between the primary and secondary systems; and reduce the risk of mal-operation. This paper presents the research outcomes of two industry-university projects (Working Stream 1 & 2) aligned to the AS3 project-WS 1: Evaluation of the IEC 61850 Process Bus Architecture and Reliability. This was designed to study the AS3 generic architecture, the process bus reliability and the optimal architecture when considering the life cycle costs and the design of a testing system; WS 2: Protection Performance Study for Secondary Systems with IEC 61850 Process Bus Architecture. The objective was to design and evaluate the performance of a prototype protection scheme, implemented using the Process Bus architecture and applicable to the corner of a mesh transmission substation. The scheme was evaluated in a laboratory, using a series of test scenarios designed to verify the operating performance, and the results are reported in this paper.