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We report on recent developments in hybrid optical protection schemes that make use of passive fibre Bragg grating (FBG) based transducers for the distributed measurement of voltage and current. In addition to the details of the hybrid optical sensor technology, and its full integration with a commercial busbar protection relay, we report on the first-time laboratory demonstration of a centralized three-ended unit protection scheme featuring hybrid optical sensors, capable of passive and wide-area coverage. Furthermore, we discuss the impact of this technology on present and future protection applications that may be improved or enabled by the proposed scheme. Index Terms-power system protection, optical fiber sensors, distributed protection, smart grids I. INTRODUCTION ONVENTIONAL unit type protection schemes rely on the communication of measured currents and/or voltages between relays at different locations. In most cases this continuous communication of sampled values, phasors, or Boolean flags is transmitted digitally using optical fiber or other media [1]. In this configuration, the protection relays are always situated close to the measurement points, and additional relays are required for non-local measurements. Differential schemes based on this historical approach are therefore limited in flexibility and extensibility by the communication bandwidth, the requirement for local power at each measurement point, and the size, weight and insulation requirements of conventional instrument transformers. The latency of the communications link and the requirement to encode and decode the communicated data can also result in the communications system making a significant contribution to the operating time of the protection system. Optical sensing is an established technology that provides solutions to a number of measurement problems posed by adverse environmental conditions, such as those commonly encountered in the oil and gas sector, nuclear industry and electrical power generation and distribution [2-4]. In many Manuscript received 20 th October, 2012. This work was supported in part by the Engineering and Physical Sciences Research Council and in part by Toshiba Corporation.

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In this paper we describe recent developments in flexible protection schemes that make use of passive fibre Bragg grating (FBG) based transducers for the distributed measurement of voltage and current. The technology underpinning the passive optical approach is described in detail, and both the present development and the future potential of the approach are discussed. In co-operation with Toshiba, the integration of the technique with an existing busbar protection relay is demonstrated, illustrating the flexibility offered by protection schemes that are based on the use of small, passive, multiplexable, dielectric transducers

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