A strategy for replacing electricity transmission protection and control systems to minimise the requirement for network outages

The primary plant and instrument transformers used in electricity transmission substations generally remain in-service for many decades, typically 40 - 60 years, and are renewed only when physically or mechanically life-expired, or technically not supported. However, the secondary systems, which include protection and control (P&C), have a much shorter asset life, and can require replacing more than twice during the life of the primary. Outages on the National Grid Electricity Transmission (NGET) networks to replace P&C equipment on a circuit using current methods takes typically 6 - 7 weeks. System access, or outages of equipment, is a constraint on successful delivery of the increasing volumes of work required on the electricity transmission systems. This paper presents National Grid´s strategy and high level design principles to allow for the implementation of IEC 61850 architecture and using a standard interface box (switching box) to minimise installation, commissioning and subsequent asset replacement outages for protection and control systems. The lifetime issues with respect to operation and maintenance of the protection and control systems are also discussed. This strategy will increase the number of protection changes that can be scheduled, and by shortening the outages required, will also increase the number of opportunities that can be taken to coordinate these with other site work taking place.