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Distributed Temperature Sensing: Review of Technology and Applications
A. Ukil, H. Braendle, P. Krippner
TL;DR
DTS provides continuous temperature profiles through optical fibers, but existing technologies and applications differ in sensing capability, range, and deployment maturity. The paper comparatively reviews scattering principles and applications, finding roles for DTS in cable ampacity and power-system monitoring while noting cost and online-monitoring boundaries.
Problem
DTS technologies and their standard, emerging, and power-system applications require comparative review across differing temperature and strain-sensing capabilities.
Method
The paper synthesizes DTS technologies, applications, manufacturers, and future trends, covering Rayleigh, Raman, and Brillouin principles.
Results
The review covers distributed temperature sensing for cable ampacity assessment and power-transformer hot-spot monitoring, alongside other power-system and industrial applications.
Takeaways & Limitations
DTS supplies continuous temperature profiles and can also measure distributed strain with Brillouin scattering, supporting monitoring of cables and other power-system devices.
Takeaways & Limitations
DTS deployment remains constrained by high and application-dependent system and installation costs, and some applications remain development tools rather than broad online monitors.
Abstract
from arXiv · showhide
Distributed temperature sensors (DTS) measure temperatures by means of optical fibers. Those optoelectronic devices provide a continuous profile of the temperature distribution along the cable. Initiated in the 1980s, DTS systems have undergone significant improvements in the technology and the application scenario over the last decades. The main measuring principles are based on detecting the back-scattering of light, e.g., detecting via Rayleigh, Raman, Brillouin principles. The application domains span from traditional applications in the distributed temperature or strain sensing in the cables, to the latest smart grid initiative in the power systems, etc. In this paper, we present comparative reviews of the different DTS technologies, different applications, standard and upcoming, different manufacturers.
I. INTRODUCTION
DTS uses optical fibers to provide continuous temperature profiles over long distances. This review compares scattering-based technologies and surveys their applications and development.
- DTS measures temperature through optical fibers and provides a continuous temperature profile along the fiber cable.
- Developed from concepts in the 1980s, DTS systems improved in accuracy and measurement distance over subsequent decades.
- DTS is insensitive to electromagnetic interference, supporting interest in electrical applications such as power systems and cables.
- The review comparatively examines DTS technologies, applications, and manufacturers, while excluding quasi-continuous arrays of fiber Bragg gratings.
- The principal sensing approaches detect optical back-scattering through Rayleigh, Raman, or Brillouin effects.
B. Brillouin Scattering
Brillouin scattering uses light–acoustic-wave interactions and supports distributed temperature or strain sensing. Its frequency-domain implementation can improve spatial resolution, but simultaneous temperature–strain measurement is not standard.
- Brillouin scattering arises from nonelastic interaction between a light wave and acoustic waves in the fiber.
- The Brillouin frequency shift varies linearly with fiber strain and temperature, enabling distributed sensing of either quantity.
- Brillouin systems can sense distributed temperature or strain, but not both simultaneously in standard operation.
- BOTDA measures Brillouin scattering in the time domain, whereas BOFDA measures it in the frequency domain and usually provides higher spatial resolution.
C. Other Fiber Optic Methods
Other fiber-optic methods extend distributed sensing through Rayleigh back-scattering, interferometers, rare-earth doping, and temperature-dependent amplifier gain. Reported systems target temperature or strain measurement with varied resolution, range, and speed.
- Rayleigh back-scattering measured distributed temperature with 0.6% full-scale accuracy, 1 cm spatial resolution, and reach up to 850 °C.
- A frequency-domain comb reduced BOTDA strain-measurement time for a 120 m fiber cable to 256 μs, or 3.9 kHz.
- A merged Sagnac–Michelson interferometer obtained perturbation distance by combining outputs proportional to phase change and phase change multiplied by distance.
- D. Use of Rare Earth Ions: Rare-earth-doped fibers provide wavelength-dependent thermal sensitivity, with holmium showing strongest sensitivity in the cryogenic range around 650 nm.
- A temperature-dependent erbium-doped amplifier gain enabled a potentially cheaper DTS configuration modeled on optical time-domain reflectometry.
E. Comparison
The review compares DTS technologies and illustrates their use in power cables and cable-temperature monitoring. Brillouin offers broad sensing capability, while continuous profiling identifies hot spots relevant to ampacity.
- Brillouin scattering offers the best fiber-length range, highest temperature sensitivity, relatively good measurement time, and distributed-strain sensing among the compared methods.
- Brillouin systems cannot typically measure distributed temperature and strain simultaneously, so applications usually target one quantity.
- B. Cable Temperature and Ampacity: Underground cable ampacity is limited by maximum allowable conductor and surface temperature, while heterogeneous soil conditions create thermal imbalance and hot spots.
- B. Cable Temperature and Ampacity: Raman DTS monitored 275 kV XLPE cable joints in real time with significant accuracy within a 1 min acquisition timeframe.
- B. Cable Temperature and Ampacity: Raman DTS profiling identified cable hot spots between 533 and 609 m, with 1 m resolution and measurement times of 5–10 s depending on distance.
C. Other Cable Related Applications
DTS applications extend beyond temperature monitoring to cable damage detection and thermal-parameter estimation. These uses support monitoring mechanical integrity and informing safe cable ampacity.
- DTS monitored cable temperature and mechanical damage using separate fibers placed in the cable core and outer bedding.The application targeted anchor damage and wire-armor defacement in a 6.6 kV XLPE submarine cable.
- DTS measurements of cable surface temperature were combined with finite-element and gradient-based optimization methods to estimate soil thermal diffusivity and conductivity.The estimates support prediction of maximum allowable ampacity for safer cable overloading specifications.
IV. POWER SYSTEMS APPLICATIONS
Power-system applications use DTS to characterize temperature distributions in transformers, switchgear, and other high-temperature equipment. The reviewed examples emphasize localized thermal conditions and operational monitoring.
- Long-range DTS was developed to monitor undersea cables, requiring spatial resolution around 10 m, and the section reviews further power-system applications.
- Transformer Monitoring: DTS provides real temperature distributions along transformer windings, but is currently used mainly to validate thermal models and support type tests rather than online monitoring.Localized temperature rises can rapidly degrade insulation, making winding temperature distribution relevant to transformer development.
- Transformer Monitoring: Raman-based DTS measured the temperature profile of a 22 MVA oil-cooled transformer winding over a fiber run of approximately 1000 m.The fiber was housed in a v-groove with paper isolation in the copper winding wire.
- Traction Transformer Monitoring: DTS monitored winding-temperature variations in a traction transformer while a 607 ton locomotive traveled a route with changing altitude and loading conditions.
- Switchgear Monitoring: Rayleigh-based DTS in a 2.4 kV switchgear cell identified the maximum temperature near the top of the bottom cluster.
D. Rotating Machine Monitoring
DTS is applied to monitor temperatures across power-plant equipment exposed to demanding thermal conditions. Examples include high-temperature pipelines, reformer vessels, boiler furnaces, and rotating machines.
- Rotating Machine Monitoring: DTS monitored rotor-winding temperature in a synchronous condenser, with distributed measurements agreeing with simulated data.
- Rotating Machine Monitoring: DTS successfully monitored motor-winding temperature under different loading conditions and measured stator and air-passage temperature rise above ambient as a function of motor current.
- PFBC Pipeline Monitoring: DTS monitored a roughly 4000 m fiber loop along steel surfaces in a PFBC plant to detect temperature problems in insulated high-pressure pipelines.The monitored equipment carried corrosive gases whose temperatures could exceed pipe operating limits.
- Surface Monitoring of Reformer Vessel: A DTS system successfully monitored reformer-vessel surface temperature over an approximately 1700 m fiber loop, identifying variations across the vessel.The system was intended to detect hot spots associated with internal burner failures and refractory-brick damage.
- Monitoring of Boiler Furnace: A DTS system was developed for real-time monitoring of high temperatures in boiler furnaces, including their spatial and temporal distributions.These distributions are relevant to assessing and controlling polluting sources such as NOx.
H. Monitoring of Overhead Transmission Lines
Overhead-line monitoring uses temperature profiles to assess ampacity and sag-related safety under environmental variation. DTS remains one option alongside lower-cost model-based and indirect measurement approaches.
- Monitoring of Overhead Transmission Lines: Overhead-line ampacity depends on current-versus-temperature characteristics, while temperature profiles vary with ambient temperature, wind speed, and snow conditions.Estimating these profiles is therefore important for transmission and distribution operation.
- Monitoring of Overhead Transmission Lines: STAMP provides conductor temperature, sag, and tension in real time from weather conditions and uses a single-mode DTS system as a benchmark.The software-based approach was aimed at providing a low-cost solution.
- Monitoring of Overhead Transmission Lines: Excessive conductor temperature can accelerate aging and elongate conductors beyond safe sag limits above ground.Sag monitoring can use surface temperature, conductor tension, image processing, GPS, or pole-angle measurements.
- Monitoring of Overhead Transmission Lines: A sag-based method indirectly estimates average conductor core temperature by measuring induced current on a grounded high-resistance wire between transmission-line towers.
- Monitoring of Overhead Transmission Lines: DTS competes with model-based solutions using few temperature points and sag measurements, and is currently used more during development than for cost-sensitive online monitoring.
V. OTHER APPLICATIONS
DTS applications extend beyond cable monitoring to structural health and leakage detection in civil infrastructure and pipelines. These applications use distributed temperature or strain profiles to identify conditions requiring attention, while leakage interpretation may require separating environmental effects.
- Structural health monitoring: Brillouin-scattering DTS measured strain and temperature in reinforced concrete beams, supporting continuous structural health monitoring.Both standard single-mode and polarization-maintaining fibers were embedded using the Brillouin time-domain method.
- Structural health monitoring: Continuous sensors along concrete structures could indicate incipient damage that human inspection may miss before catastrophic failure.
- Leakage detection: DTS was used to monitor leakage in dams and dikes, where conventional manual inspection is described as unreliable.
- Leakage detection: Leakage-driven water flow changes temperature relative to the ground, enabling DTS to provide a distributed temperature profile along a dam.
- Leakage detection: Seasonal variation and precipitation can also change temperature, so source-separation analysis is required for reliable thermometric leakage detection.
- Pipeline leakage detection: 1 °C accuracy over 55 km with measuring time under 10 min was reported for Brillouin-based leakage detection in a brine pipeline.
C. Application in Oil and Gas
Oil and gas applications use DTS to interpret temperature logs in wells and detect leakage or safety-relevant thermal conditions in industrial settings. The section also describes dynamic temperature monitoring in mine cables and simultaneous atmospheric-parameter monitoring.
- Oil and gas wells: DTS installations in oil and gas wells are categorized as retrievable, semipermanent, or permanent.
- Oil and gas wells: Well temperature logs can be associated with liquid flow, gas-entry cooling, water-injection cooling, and steam breakthrough.
- Fire detection: Raman-based linear optical fire detection tracked rapid temperature-profile changes and localized fires within buildings at 1 m resolution.
- Mine safety: Shuttle car trailing cables in mines should remain below the approximately 90 °C safety limit to reduce the risk of premature insulation failure.
- Mine safety: DTS embedded in metallic conductors measured mine-cable temperatures at 1 m intervals along the entire cable length.
- Mine safety: Fiber-optic monitoring was also used for methane and carbon monoxide alongside distributed temperature measurement.
VI. MANUFACTURERS
The review describes a growing DTS manufacturer landscape while emphasizing that costs vary substantially by application and that the list is not exhaustive. It frames distributed monitoring value through safety-critical assets and total cost of ownership.
- Manufacturer landscape: The manufacturer list is growing and is explicitly non-exhaustive; its ordering does not indicate relative performance or standing.
- Manufacturer landscape: Examples include Sensa, omnisens, es&s, and LIOS TECHNOLOGY, offering systems for temperature, strain, leakage detection, fire detection, and thermal rating.
- Related organizations: The Fiber Optic Association, Subsea Fiber Optic Monitoring Group, and IEEE Photonics Society are listed as related organizations.
- Costs and value: USD 100 000 is a typical cost range cited for some power-system and cable applications, while oil and gas applications typically cost USD 50 000–150 000.
- Costs and value: A future need identified in the review is cost-effective DTS in the range of USD 10 000–20 000 or less.
- Review scope: The conclusion surveys DTS technologies, applications, and manufacturers across cable, power-system, structural, leakage, fire, and mine-safety contexts.