The deployment of IEC 61850 process bus in substations calls for an impact evaluation of possible process bus architecture scenarios on the performance of numerical protection systems. Six alternative system architectures are proposed based on a component redundancy perspective. The functionality of each system is assessed using reliability block diagrams based on a success-oriented network. System reliability is calculated using the minimal tie sets method determined by the connection matrix. Sensitivity analysis is then carried out on the results using two approaches. One highlights those components with the greatest impact on system reliability and the other the importance of the task performed by each component in terms of how it affects the functionality of the system. Index Terms--IEC 61850, Process bus architecture, reliability block diagram, reliability, protection system, relaying.

The design of a new microprocessor based multifunctional relay for use on interconnected 33 kV circuits is described. The relay uses sequence component principles and rented low grade VF communication. It was needed urgently because rented metallic communication circuits, which are in widespread use, are being withdrawn in the UK. The relay development is unusual because of its measurement methods and because it can derive polarising voltage from existing 1 1 kV VTs. The time scales required were such that development, field trials and installation phases overlapped. The field experience is described.

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This paper investigates a number of design, operation and lifetime management experiences of feeder unit protection systems installed on National Grid Electricity Transmission (NGET) UK networks. The paper will consider the policy, application design and operational experiences under the following categories in particular since the move to numeric protection:Policy and application design SDH communication networks Operational experience to date Maintenance and post commissioning support Application of future current differential protection Future IEC61850 application GPS synchronised feeder current differential protection has been installed on NGET UK networks since early 2000. This paper highlights a number of problems and solutions of this type of protection, particularly NGET's experiences in the performance of GPS receivers. Finally NGET's application policy for future installation of feeder unit protection is also discussed.One relay mal-operated during a re-boot. Normally following a re-boot, the relay would have to wait for a valid GPS signal, and once the relays at both ends have been synchronised, the differential function "switches-in" at both ends. For this maloperation, it appeared that during the re-booting, the relay treated this as a short interruption of communication and released the differential element before the GPS signal was restored and the relays were synchronised. Category 5 -Drifting of synchronising clock of SDH communication networkAll NGET's feeder current differential protections operate with a SDH communication channel as presented above. Under normal conditions the timing signal of the communication channel at both ends of a circuit is synchronised, however under faulty condition or the communication channel is across a boundary of two communication services providers, the timing signal of the communication channel at one end of the circuit could slowly drift relatively to the timing signal at the other end.

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