Substation primary plant and instrument transformers generally remain in service for many years and are only renewed when physically or mechanically life-expired. However, substation protection and control systems, also known as secondary systems, are changed more frequently, especially electronic or computer based systems. One way to overcome the lifecycle-coordination problem is to develop a new architecture for substation secondary systems by deploying new technology such as standard interface modules, the bay process bus and IEC 61850 communication protocol. IEC 61850-9-2 'process bus' has proposed an Ethernet based communication network to replace traditional hardwiring and cabling, for communication of analogue and binary signals with Ethernet messages. The application of processbus in substations is able to reduce the life-time cost of the secondary systems and improve flexibility and functionality. Sufficient confidence must be demonstrated in the application of this new technology. This thesis describes the design and performance evaluation of a prototype protection scheme suitable for application on a corner of a mesh transmission substation of the type used in the UK on the transmission network.

As the use of renewable energy and the implementation of smart grids becomemore prevalent in Europe, there will be a need to ensure that the quality ofpower supply is not compromised during the integration of distributedgeneration to the main grid. Europe's electricity networks should be flexible,accessible, reliable and economic. In the UK, National Grid has standardisedits substation protection and control equipment commissioning andreplacement policies, yet issues affecting system long life availability remain,one reason being long outage periods during substation secondary equipmentinstallation, commissioning and maintenance. The present use of directhardwired point to point connections between the primary power system plantequipment and substation secondary system protection and control devicesdoes not allow for easy upgrading or replacement of these substationsecondary devices without an outage of the primary plant or substation. Outage and the consequent availability problems associated with secondaryequipment can be addressed by the open utility communication architecturestandard IEC 61850. A well-designed simple, highly reliable, secure, flexibleand long-life communication IEC 61850-based architecture can help mitigatethe impact of using protection and control IEDs (Intelligent Electronic Devices).Faulty IEDs can be replaced with little or no interruption to the overall operationof the substation. Interoperability is a key feature of the adoption of IEC 61850in substations. IEC 61850-compliant protection and control devices cancommunicate with one another, even if they made from different manufacturers. This thesis has proposed a simple, long life IEC 61850 based communicationarchitecture which is expected to be flexible and robust enough to cope withboth growth and outages. Reliability analyses have been carried out on varioushypothetical applications of the proposed process bus architecture to NationalGrid substation bays. A detailed description of how to determine the optimalprocess bus architecture using the life cycle cost evaluation technique has beenprovided. The design and implementation of a test bed used for evaluating theperformance characteristics of merging units has been presented. The resultsof the tests have been fed back to National Grid and the manufacturers, whomay then use the data to assist with the drafting of a Merging Unit Test BedSpecification, and also to help the manufacturers to make refinements to themerging units in order to make interoperability more readily achievable.