Implementation of centralised, numerical busbar protection using distributed photonic current sensors

Fast and robust busbar protection is critical to ensuring the reliability and safety of transmission substations and the connected power networks. For the most part, modern numerical busbar protection techniques remain based upon the interrogation of conventional current transformers (CTs) by copper secondary wiring feeding multiple IEDs ("peripheral units") which communicate measured currents to one or more central units using dedicated optical fibre digital communication links. Numerical busbar protection requires copper secondary wiring in the yard that presents safety and cost challenges, particularly during substation refits. With the transition to digital substations, it becomes possible to collect all the measurements in sample value format from different bays on a common network (the process bus) without having dedicated wiring for each measurement, however there is a limited number of sample value streams that busbar protection IEDs available today can handle. Combining multiple active units into a single system and substantially eliminating copper wiring would lead to reductions in civil work, materials, outage times, and therefore to both capital and operational expenditure. In this paper, we report on the design and testing of the first centralised busbar protection scheme that makes use of distributed photonic current sensors. By utilising distributed, passive sensors which are interrogated purely using standard optical fibre, the requirement for active units in the substation yard is completely eliminated. Additionally, the use of copper wiring from CTs to measurement units may be eliminated. The scheme, designed and built for Statnett by Synaptec, will be installed and trialled at Statnett's Furuset R&D substation near Oslo, Norway. A prototype centralised busbar protection algorithm, validated with the University of Strathclyde, will run on the central merger unit to prove the principle of centralised busbar protection using a single active IED. The goal of developing and deploying the presented system is to enhance both redundancy and failure detection probability of busbar protection, and to enable the safe, continued operation of the busbar protection scheme during refurbishment projects for control systems. With further development, or following integration of the instrumentation platform with a conventional protection IED, it is proposed that this technique could be deployed in a business as usual context.