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.
This paper presents a new method for locating faults in multi-terminal direct current (MTDC) networks incorporating hybrid transmission media (HTMs), including segments of underground cables (UGCs) and overhead lines (OHLs). The proposed travelling wave (TW) type method uses continuous wavelet transform (CWT) applied to a series of line current measurements obtained from a network of distributed optical sensors. The technical feasibility of optically-based DC current measurement is evaluated through laboratory experiments using Fiber-Bragg Grating (FBG) sensors and other commercially available equipment. Simulation-based analysis has been used to assess the proposed technique under a variety of fault types and locations within an MTDC network. The proposed fault location scheme has been found to successfully identify the faulted segment of the transmission media as well as accurately estimating the fault position within the faulted segment. Systematic evaluation of the method is presented considering a wide range of fault resistances, mother wavelets, scaling factors and noisy inputs. Additionally, the principle of the proposed fault location scheme has been practically validated by applying a series of laboratory test sets.
This paper presents a method for accurate fault localisation of DC-side faults in Voltage Source Converter (VSC) based Multi-Terminal Direct Current (MTDC) networks utilising optically-multiplexed DC current measurements sampled at 5 kHz, off-line continuous wavelet transform and machine learning approach. The technical feasibility of optically-based DC current measurements is evaluated through laboratory experiments using commercially available equipment. Simulation-based analysis through Matlab/Simulink® has been adopted to test the proposed fault location algorithm under different fault types and locations along a DC grid. Results revealed that the proposed fault location scheme can accurately calculate the location of a fault and successfully identify its type. The scheme has been also found to be effective for highly resistive fault with resistances of up to 500 Ω. Further sensitivity analysis revealed that the proposed scheme is relatively robust to additive noise and synchronisation errors
In this work, we demonstrate hybrid optical-fibre/geopolymer sensors for monitoring temperature, uniaxial strain and biaxial strain in concrete structures. The hybrid sensors detect these measurands via changes in geopolymer electrical impedance, and via optical wavelength measurements of embedded fibre Bragg gratings. Electrical and optical measurements were both facilitated by metalcoated optical fibres, which provided the hybrid sensors with a single, shared physical path for both voltage and wavelength signals. The embedded fibre sensors revealed that geopolymer specimens undergo 2.7 mε of shrinkage after one week of curing at 42 • C. After curing, an axial 2 mε compression of the uniaxial hybrid sensor led to impedance and wavelength shifts of 7×10 −2 and -2×10 −4 respectively. The typical strain resolution in the uniaxial sensor was 100 µε. The biaxial sensor was applied to the side of a concrete cylinder, which was then placed under 0.6 mε of axial, compressive strain. Fractional shifts in impedance and wavelength, used to monitor axial and circumferential strain, were 3×10 −2 and 4×10 −5 respectively. The biaxial sensor's strain resolution was approximately 10 µε in both directions. Due to several design flaws, the uniaxial hybrid sensor was unable to accurately measure ambient temperature changes. The biaxial sensor, however, successfully monitored local temperature changes with 0.5 • C resolution.
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