Distributed Discharge Detection Based on Improved COTDR Method With Dual Frequency Pulses

DAS signature of reservoir pressure changes caused by a CO2 injection: Experience from the CO2CRC Otway Project

Fiber optic distributed acoustic sensing (DAS) is a potential method to achieve partial discharge (PD) detection and fast localization in gas insulated metal enclosed transmission lines (GIL). In order to detect and locate the weak partial discharge signals in the GIL as early as possible, this paper proposes an integrated distributed fiber optic sensor installation method for the GIL, as well as a distributed partial discharge acoustic detection and localization system. Based on the fully insulating nature of the optical fiber, the optical fiber is installed inside the GIL to improve the sensitivity to partial discharge acoustic signals, and the length of the sensor unit is increased by repeated winding to further improve the detection performance of the acoustic signals. A true-to-life GIL partial discharge test platform was built to investigate the multi-point distributed sensing performance of the proposed coherent optical time domain reflectometer system for metal tip discharge. The test results show that the sensing distance of the sensing system can reach 120m, which can achieve the multipoint detection and localization of the partial discharge acoustic signal of 29.7pC. The proposed sensing method and system provide a new solution for GIL weak partial discharge optical fiber distributed acoustic signal detection.

We constructed an on-line partial discharge (PD) monitoring system (PDOM) with a CT sensor, an analogue-digital converter, and a tablet PC. A sampling frequency for data acquisition is 100 MHz, and we exchange on-site PD data through a cloud system. We successfully measured PDs in the early stage of insulation deterioration of a cross-linked polyethylene (XLPE) cable in a field site. Additionally, following PD detection by using a PDOM, we can locate a PD position by using a PD locator (PDL) system. By locating a PD, we can estimate the actual PD magnitude considering attenuation factor of a high frequency pulse. We show how the PDL system works on a XLPE cable network with time synchronization between two positions by using an injection current pulse. The locating accuracy of the PDL system is evaluated.

Partial discharge (PD) based condition monitoring has been widely applied to power cables. However, difficulties in interpretation of measurement results (location and criticality) remain to be tackled. This paper aims to develop further knowledge in PD signal propagation in power cables and attenuation by the PD monitoring system devices to address the localization and criticality issues. As on-line or in-service PD monitoring sensors commonly comprise of a high frequency current transformer (HFCT) and a high-pass filter, the characteristics of detected PD pulses depend on the attenuation of the cable, the HFCT used and the filter applied. Simulation of pulse propagation in a cable and PD monitoring system are performed, based on analyses in the frequency domain using the concept of transfer functions. Results have been verified by laboratory experiments and using on-site PD measurements. The knowledge gained from the research on the change in pulse characteristics propagating in a cable and through a PD detection system can be very useful to PD denoising and for development of a PD localization technique.

SUMMARY A 2-D orthogonal distributed acoustic sensing (DAS) array designed for seismic experiments was buried horizontally beneath the Kafadar Commons Geophysical Laboratory on the Colorado School of Mines campus at Golden, Colorado. The DAS system using straight fibre-optic cables is a cost-efficient technology that enables dense seismic array deployment for long-term seismic monitoring, favouring both earthquake-based and ambient-noise-based surface wave analysis for subsurface characterization. In our study, the horizontally orthogonal DAS array records ambient noise data for a period of about two months from November 2018 to January 2019. During this time, the array also detected seismic signals from an ML3.6 earthquake at Glenwood Springs, Colorado, which exhibit opposite signal polarities in the orthogonal DAS section recordings. We derive the transformation matrix for DAS strain measurements in horizontally orthogonal cables to retrieve both Rayleigh and Love wave dispersion information from the single-component DAS signals using the 2-D multichannel analysis of surface waves method. In addition, ambient noise interferometry is applied to long-term DAS noise recordings. Our theoretical derivation demonstrates that Rayleigh and Love wave Green's functions are coupled in the noise cross-correlation functions (NCFs) of DAS receiver pairs. Stacking NCFs over the horizontally orthogonal DAS array can constructively recover the radial Rayleigh wave component but destructively suppress the Love wave component. The multimodal Monte Carlo inversion of the earthquake-based Rayleigh wave and Love wave dispersion measurements and the noise-based Rayleigh wave measurement reveals a 1-D layered structure that agrees qualitatively with geological surveys of the site. Our study demonstrates that although straight fibre-optic cables lack broadside sensitivity, using appropriate DAS array configuration and seismic array methods can extend the seismic acquisition ability of DAS and enable its application to a broad range of scenarios.

Distributed acoustic sensing (DAS) strain rate and particle velocity can be compared through approximate scaling with medium velocity. We instead performed a direct comparison between array derived dynamic strain (ADDS) rate and DAS strain rate for six frequency bands. The PoroTomo project at Brady's Hot Springs, Nevada, deployed a 240‐geophone 3C array co‐located with fiber‐optic DAS system and 8.7 km of buried cable. We selected subsets of the geophone array to create four smaller arrays and computed ADDS. The horizontal components of the ADDS were rotated into the direction of the fiber‐optic cable and then compared with the observed DAS strain rates. From three example regional earthquakes of local magnitudes 2.9, 4.1, and 4.3, the ADDS are found to be coherent with DAS for frequencies ≤1 Hz. For frequencies >1‐Hz, this correlation decays quickly. Small differences between linear and areal dynamic strains at 1‐Hz suggest poor signal‐to‐noise or localized strain that is perturbed by shallow heterogeneities compare to the average strain propagating across the geophone array. The implication is that around 1‐Hz, straight fiber DAS is measuring axial strain along the fiber and can provide good approximations to translational particle motions. However, above 1‐Hz, DAS becomes more sensitive to shallow velocity gradients that can be beneficial for geophysical imaging yet becomes a limitation for traditional seismic analysis methods depending on absolute amplitude and phase from translational particle motions.

Signal fading severely affects the performance of optical fiber distributed acoustic sensing (DAS) systems based on coherent optical time domain reflectometry (COTDR), especially in terms of differentiated responses between channels. To eliminate fading, a polarization diversity COTDR system is established, which generates two pulse feedbacks with different fading components for P and S polarization. The rayleigh backscattered (RBS) signals from the two separate probing pulses exhibit different fading positions under the influence of external interference but have the same phase change rate. Through an improved rotational vector summation (IRVS) algorithm, the complex RBS signals of the two polarization states are effectively synthesized, simultaneously suppressing fading phenomena caused by orthogonal polarization. Experimental results demonstrate that the demodulated signal-to-noise ratio (SNR) can reach 65 dB@200 Hz. Moreover, by using 20% of the mean amplitude as a threshold, the probability of fade events decreases from 4.9% to 0.12%. The proposed fade mitigation distributed sensing system exhibits excellent performance and plays a crucial role in practical DAS systems.

Distributed acoustic sensing (DAS) is an emerging technology increasingly employed to monitor changes of formation properties, production noise and micro-seismic activity, and as an array of sensors in active seismic surveys. The data recorded with the DAS systems are very rich; some features observed in DAS records are often not well understood, and thus are underutilised. A systematic analysis of the data recorded passively with a DAS system in a 900-m deep well over a period of 12 weeks in the Perth metropolitan area, Western Australia, reveals the presence of several types of ambient energy in the subsurface, such as earthquakes, ocean swell and urban noise. In particular, over 85 days of the experiment, the analysis detected sixteen earthquakes, with epicentres ranging from 126 km to 900 km (for the local events) and from 2300 km to 6400 km (for the remote events). Signals with frequencies below 0.9 Hz are dominated by the oceanic swell. The recorded urban noise includes mine blasting, machinery and traffic. The experiment shows the ability of DAS to detect these events and as such is potentially useful for subsurface characterisation and monitoring.

Distributed acoustic sensing (DAS) is a rapidly evolving fiber-optic sensing technology that converts any standard fiber-optic cable into a distributed sensor capable of measuring acoustic events every meter over large (100 km+) distances. We describe a conveyance-agnostic DAS system for vertical seismic profiling (VSP) that has the capability to sense either single- or multi-mode sensing fibers, and encode all auxiliary seismic source signals directly onto the optical data stream using a series of piezo-electric fiber stretchers in-line with the sensing fiber. The DAS system can operate with latency-free synchronization via wireless telemetry between the seismic source controller and the DAS unit in either master or slave modes. Similar to geophone-based VSP data acquisition systems, the time-break signal is used to trigger data acquisition to ensure precise time synchronization at sub-millisecond accuracy between the DAS system and the seismic source. The system enables effective data management and the real-time generation of 1 millisecond sampled seismic and navigation data that conforms to the industry-standard seismic data formats, thus eliminating any latency between acquisition and field data deliverables.

The assessment of the insulation condition of high-voltage power transmission networks using a non-invasive method of online partial discharge (PD) monitoring is currently a common practice in maintenance programs for elements of the distribution and transmission networks. The joint-stock company „Elektromreža Srbije“ Belgrade (EMS AD) manages a large number of power equipment (EES), on which various partial discharge monitoring strategies can be applied to control the insulation condition. One of the goals of EMS AD is to implement a real-time monitoring system aimed at optimizing the maintenance process and conducting diagnostics for the early detection of insulation defects and predicting failures in cable lines. The paper describes the activities related to the implementation of an online monitoring system for partial discharge detection, which involves the installation of permanent high-frequency sensors at strategic locations to diagnose the insulation condition of cable lines. Additionally, different levels of diagnostics are presented through the use of a software tool for automatically eliminating partial discharges that do not originate from insulation defects, as well as a tool for localizing partial discharges along the length of the cable line.

Distributed acoustic sensors (DAS) based in coherent optical time-domain reflectometry (C-OTDR) provide a cost-effective solution for intrusion monitoring of large civil infrastructures like pipelines, railways or motorways. Although detection of events is well demonstrated, an estimation of the amplitude of these events is difficult to achieve. We propose a new method to recover the amplitude of the vibration from the conventional C-OTDR backscattered power traces. It is based on the FFT analysis of the DAS signals. Using a discrete accelerometer as a reference, we have calibrated the response of an optical fiber DAS using known stimuli. A correlation between the amplitude of the vibration and the ratios of the amplitudes of harmonics to the fundamental of the DAS signals is demonstrated. This analysis overcomes the main issues of the amplitude measurement, related to the interaction between the stimulus and the interference pattern.

This paper introduces a computerized online PD (Partial Discharge) monitoring and diagnostic system for power transformers, which has been installed in a 500 kV substation in China. It consists of wide-band active transducers and DAU (Data Acquisition Unit) with modularized and exchangeable components. This system has been developed to monitor multiple parameters of multiple power transformers, which is based on COM (Component Object Model). In addition, the system can also be used to monitor other power equipment. Some results of on-line monitoring are discussed.

Pushing distributed acoustic sensing (DAS) methods from typical seismic frequency ranges into higher frequencies (500 Hz to 1 kHz) will greatly advance the tools available for broad spatial scales of marine mammal monitoring. Recordings from an Orcasound hydrophone stationed near a pre-existing fiber optic cable in Puget Sound were analyzed throughout the fall of 2024 for Southern Resident Killer Whale (SRKW) calls. Simultaneously, the cable was illuminated and interrogated to gather DAS data. The acoustic calls were corroborated with citizen science data of visual sightings to filter the calls spatially relevant to the DAS system. The hydrophone data was processed in a method designed to mimic the DAS system specifications. Determining the exact power spectra of each call for specific frequencies (0–1 kHz) provides a much stronger framework for identifying killer whale calls on pre-existing cables with unknown armoring or positioning. This study allows for exploration and expansion of DAS into higher frequencies to monitor SRKW and other marine mammals with limited fieldwork required compared to studies that may require laying a specialized cable. Ultimately, using hydrophone data will accelerate the movement of DAS into the marine mammal observation realm for species with higher-frequency vocalizations. [Work supported by Orcasound.]

Seismic surveying has continuously evolved, transitioning from early mechanical seismoscopes to digital, multi-channel geophone arrays that defined the industry standard since 1970s. digital seismic reflection. Today, the field is undergoing a similar shift, with conventional inertial-based systems being challenged or complemented by Distributed Acoustic Sensing (DAS) systems. This paper examines the two primary seismic systems, such as geophones/accelerometers and DAS systems by focusing on their core principle and transduction systems. Methodologically, we employ a comparative performance framework based on key metrics including sensitivity, calibration, data volume, and spatiotemporal. Furthermore, a systematic review of experimental field trials from 2010 to 2025 is conducted across eight major seismic applications to ascertain practical differences. Results reveal that while traditional sensors excel in low-frequency sensitivity and discrete three-component recording, DAS offers superior spatiotemporal resolution and broadband frequency capabilities. Recent advancements in enhanced backscattering fibers (20 m gauge length) have demonstrated the potential to lower the noise floor of DAS systems to approximately 0.15 $$p\varepsilon /\surd Hz$$, significantly improving sensitivity to high-fidelity microseismic events. Field trial analysis shows heavy concentration of hybrid applications in borehole imaging, with emerging but limited use in environmental sensing, mineral exploration, and pipeline security. We also explore the potential of integrated sensing and quantum networks (ISAQN) to mitigate current signal-to-noise limitations. The study concludes that future of seismic acquisition depends on the continuous integration of these technologies via hybrid systems, leveraging the robust compartments of traditional sensors along the extensive coverage of DAS to overcome their respective uniaxial, low-frequency, and spatiotemporal limitations.

Summary This work presents a high-resolution seismic imaging study of a target sulphide mineralization located in the Kylylahti polymetallic mine, Eastern Finland. For this purpose, in-mine VSP measurements were carried out, using two different technologies: a conventional three-component VSP and a fibre-optic Distributed Acoustic Sensing (DAS) system. The two acquisition systems were placed in existing exploration boreholes adjacent to the deposit and successfully recorded reflections from the target and its host rocks. Subsequent application of a target-specific VSP processing and imaging workflow to the conventional and DAS data provided high-resolution reflectivity images from both systems. To support geological interpretation, a 3D seismic forward modelling study was conducted using a geological model created from exploration drilling data and laboratory petrophysical measurements. Cross-validation of the acquired VSP data with the synthetic seismograms and extensive logging data enabled identification of the target reflection as well as interpretation of several new geological contrasts. Between the two VSP methods, the conventional system exhibits slightly superior signal-to-noise ratio and bandwidth. However, the DAS system also provides images of satisfactory quality at much less acquisition time and logistical effort. Thus, DAS offers a powerful and particularly cost-effective exploration technology suitable for detailed delineation of mineral resources.