This paper presents a method for rapid detection of faults on VSC multi-terminal HVDC transmission networks using multi-point optical current sensing. The proposed method uses differential protection as a guiding principle, and is implemented using current measurements obtained from optical current sensors distributed along the transmission line. Performance is assessed through detailed transient simulation using Matlab/Simulink R models, integrating inductive DC-line terminations, detailed DC circuit breaker models and a network of fiber-optic current sensors. Moreover, the feasibility and required performance of optical-based measurements is validated through laboratory testing. Simulation results demonstrate that the proposed protection algorithm can effectively, and within very short period of time, discriminate between faults on the protected line (internal faults), and those occurring on adjacent lines or busbars (external faults). Hardware tests prove that the scheme can be achieved with the existing, available sensing technology.

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.

We report on the design and prototyping of a robust high-speed interferometric multiplexer and interrogator for fibre Bragg grating sensors. The scheme is based on the combination of active WDM channel switching and passive, instantaneous interferometry, allowing the resolution of virgin interferometric interrogators to be retained at MHz multiplexing rates. In this article the system design and operation are described, and a prototype scheme is characterised for three sensors and a multiplexing rate of 4 kHz, demonstrating a noise floor of 10 nε/√Hz and no cross-sensitivity. It is proposed that the system will be applicable to demanding monitoring applications requiring high speed and high resolution measurements across the sensor array.

In this paper we demonstrate a novel, all-optical differential current protection scheme. By monitoring the optical power reflected from two matched hybrid fiber Bragg grating current sensors and using a simple optoelectronic threshold detector, an immediate response to an increase in differential current is achieved. A preliminary laboratory embodiment is constructed in order to characterize the performance of the scheme. The proposed technique does not require a complex sensor interrogation scheme, usually characterized by a limited sampling frequency, and thus will be capable of facilitating inexpensive and fast-acting differential protection over long distances

This paper reports on the design, construction and initial testing of a fiber-optic voltage sensor for applications in the field of wide area monitoring, protection and control of high voltage power networks. The 132-kV sensor prototype, combining a capacitive voltage divider (CVD) and an optical low voltage transducer (LVT), was evaluated through laboratory testing and its performance was assessed based on the accuracy requirements specified by the IEC standards for low-power passive voltage transformers. The preliminary results show that the device has the potential to comply with the requirements of the 0,2 class for metering devices, and the 3P and 0,5P classes for protective and multipurpose devices, respectively, as specified by IEC 61869-11. As the device is based on a fiber Bragg grating written in a standard, low-loss, single-mode telecommunication fiber, it has the potential to be deployed as part of a distributed network of sensors along the power network over a wide geographical area, enabling novel power system protection and control strategies.