Non Conventional Current Sensors
National Grid Electricity System Operator
National Grid TO Innovation Team
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Innovation Funding Incentive
Gas Distribution Networks
Public perception towards Overhead Lines (OHL) and limitations on rights-of -ways in populated
areas could potentially lead to an increase in construction of Cable only and
Cable & OHL hybrid circuits in future. This situation presents a unique challenge
for cable protection systems especially on the Hybrid one as protection systems
must differentiate between cable and OHL faults to ensure the greater reliability
of the power system.
Current practice in National Grid is to implement two main unit protection
schemes sourced from two different suppliers by using conventional Current Transformers (CT) for
275kV and 400kV cable systems. However, CT installation and maintenance on
cable circuit is immensely cumbersome due to bulk structure of CTs and space
constraints associated with cable tunnels and trenches.
Moreover, CTs on cable circuits are subject to a high magnitude of
charging/discharging current during switching on and off, a condition which could
lead to potential CT core saturation and mal-operation of the protection relays.
For green field application these constraints may be addressed by an
appropriate design solution; however on refurbished circuits especially where
part of the OHL circuit is undergrounded by using cables, it becomes challenging
to achieve the prescribed selectivity and security with conventional CT based
This R&D project aims:
This will help to formulate a technical and operational knowledge base for Non
Conventional Instrument Transformer (NCIT) protection systems which could
lead to evaluation of future technical and procurement strategy to deploy as
replacement and/or new Cable system protection.