How to use distributed fiber optic temperature measurement for cable conduits

Sensor de temperatura de fibra óptica, Sistema de monitoreo inteligente, Fabricante de fibra óptica distribuida en China

1、 Application of Distributed Fiber Optic Temperature Measurement in Cables

Distributed fiber optic temperature measurement systems have many important applications in cable temperature measurement.

（1） In terms of principle, Sistemas distribuidos de medición de temperatura por fibra óptica are usually based on the principle of backward Raman scattering and optical time domain reflectometry (OTDR) Tecnología. The principle of Raman scattering enables optical fibers to sense temperature changes, and the intensity of Raman scattering light varies at different temperatures. Optical time domain reflection technology is used for positioning, which can determine the location of temperature change points at different positions along the optical fiber. Por ejemplo, when the temperature of a certain part of the cable rises, the Raman scattering light in the optical fiber at that part will change accordingly. By detecting and analyzing this change, the temperature change can be known, and at the same time, OTDR technology can be used to determine the specific location of this temperature anomaly point in the cable.

（2） Regarding the monitoring of cable operation status

Real time monitoring of temperature distribution
Capable of real-time, online, and continuous monitoring of temperature at various points along the cable route. This is crucial for cables because during operation, heat is generated due to the current passing through the cable. If the heat dissipation is not timely, the local temperature will be too high, which will affect the insulation performance of the cable and even cause faults. Through a sistema de medición de temperatura de fibra óptica distribuida, the temperature distribution of the entire cable line, including cable core temperature, can be accurately grasped. Por ejemplo, in some large substations or long-distance transmission cable lines, it can promptly detect areas with abnormally high temperatures, providing guarantees for the safe operation of cables.
Fault Warning and Prevention
Temperature warning threshold can be set. Once the temperature at a point along the cable approaches or exceeds this threshold, the system can issue an alarm in a timely manner. Por ejemplo, in cable trenches, if the temperature of the cables rises due to overload or local short circuits, the distributed fiber optic temperature measurement system can quickly detect this temperature change and provide early warning before serious cable failures occur, preventing accidents and improving the safety of power cable operation.
Determine the current carrying capacity of the cable
Accurate temperature monitoring data helps determine the current carrying capacity of cables. By monitoring and analyzing the temperature changes of cables under different loads for a long time, the maximum current that the cables can withstand can be accurately evaluated, so as to plan the power transmission capacity reasonably, avoid cable damage due to overload operation, and extend the service life of the cables.
（3） Application in different types of cables

Ordinary power cable
It is widely used in ordinary underground power cables and overhead power cables. For underground power cables, due to their relatively poor heat dissipation conditions, distributed fiber optic temperature measurement systems can more accurately monitor their temperature changes, preventing problems such as cable aging and short circuits caused by high temperatures. In overhead power cables, it can cope with the impact of environmental temperature changes, sunlight and other factors on cable temperature, and detect abnormal situations in a timely manner.
High temperature superconducting cable
It also plays an important role in the engineering application of long-distance high-temperature superconducting cables. Por ejemplo, in the engineering application research of 100 meter distributed optical fibers in the liquid nitrogen temperature range, a distributed optical fiber temperature measurement system was built to conduct temperature measurement tests on a 30m three-phase coaxial high-temperature superconducting cable under various working conditions. The temperature of the superconducting cable during operation can be monitored in real time, ensuring that the cable operates within the appropriate temperature range and guaranteeing its superconducting performance and safety.

2、 Application of Distributed Fiber Optic Temperature Measurement in Pipelines

Distributed fiber optic temperature measurement technology has a wide and important application value in pipeline monitoring.

（1） The relationship between principles and pipeline monitoring

Based on the principles of light scattering and optical time domain reflection for localization
The distributed fiber optic temperature measurement system is also based on the principles of light scattering (such as Raman scattering) and optical time-domain reflection positioning in pipeline applications. In the pipeline environment, temperature changes along the fiber optic cable can cause changes in Raman scattering light. By detecting these changes and combining them with optical time domain reflection technology, it is possible to accurately measure the temperature at different positions along the pipeline and locate temperature anomalies accurately. Por ejemplo, in heating pipelines, when there is a leak or abnormal temperature rise or fall in the pipeline, the optical signal in the fiber optic cable will change, and the system will judge the operating status of the pipeline based on these signal changes.
Adapt to the characteristics of pipeline environment
The environment in which pipelines are located is complex and diverse, and may be high-temperature and high-pressure environments underground, underwater, or above ground. The distributed fiber optic temperature measurement system can adapt to these environments. Due to the corrosion resistance and electromagnetic interference resistance of the fiber optic itself, it can work stably in various pipeline environments. Por ejemplo, in submarine pipelines, optical fibers can monitor pipeline temperature stably for a long time without being affected by seawater corrosion and electromagnetic interference.

（2） Applications in different types of pipelines

Power pipeline
In terms of power pipelines, it is mainly used for fire monitoring. The power pipelines in cities are usually the carriers of cables, and once a fire occurs, the consequences can be serious. Distributed fiber optic temperature measurement technology can utilize power optical cables in the same channel for distributed temperature monitoring, and detect fire hazards in a timely manner by monitoring changes in pipeline temperature. When the temperature inside the power pipeline rises abnormally, it may be a prelude to heating or fire caused by cable faults. The distributed fiber optic temperature measurement system can quickly detect this temperature change and issue an alarm, thereby reducing the investment cost in sensor deployment and improving the operational reliability of urban power grid cables.
Thermal pipeline
For high-temperature steam pipelines and other thermal pipelines in thermal power plants, due to their long transportation distance and difficulty in finding leakage points, distributed fiber optic temperature measurement systems can monitor the temperature field of steam pipelines. By using Raman scattering principle to demodulate the temperature information contained in the reflected light signal of the optical cable laid along the pipeline, when there is a leak in the pipeline, the temperature near the leak point will change, and the system can determine the leak location based on the temperature change. And in the heating pipeline network, this system can be used as a mature fiber optic distributed temperature measurement method, with advantages such as long measurement distance, high measurement accuracy, Velocidad de respuesta rápida, Interferencias antielectromagnéticas, and portability. It can be widely applied to leak monitoring in the heating pipeline network.
Transportation pipelines (such as oil and gas pipelines, etc.)
In the field of transportation pipelines, it is mainly used for leak detection. Fiber optic cables can be laid along pipelines, whether by winding, double-layer arrangement, internal or external methods. When a pipeline leaks, the temperature at the leak location will change due to the leakage of substances (such as oil and natural gas leaks that carry away heat or generate frictional heat). Distributed fiber optic temperature measurement systems can detect this temperature change and locate the leak point, thereby ensuring the safe operation of the pipeline. Al mismo tiempo, the system can also monitor the temperature distribution of the pipeline during normal operation, ensuring that the pipeline operates within the appropriate temperature range, preventing damage to the pipeline due to high or low temperature, and extending the service life of the pipeline.

3、 Operation method of distributed fiber optic temperature measurement for cables and pipelines

（1） Operation method for distributed fiber optic temperature measurement of cables

System setup and installation
Fiber optic laying:
For cable temperature measurement, the first step is to choose a suitable temperature sensing optical cable. Fiber optic cables should be selected based on factors such as cable type and operating environment. In terms of laying method, if it is an underground cable, the temperature sensing optical cable can be laid parallel to the cable in the cable trench, or the optical fiber can be directly embedded inside the cable during the cable manufacturing process to achieve direct monitoring of the cable core temperature. Por ejemplo, in some high-voltage power cables, optical fibers can be integrated as part of the cable during the production process. For overhead cables, optical fibers can be wound and laid along the direction of the cable.
Device connection:
Connect the various equipment components of the distributed fiber optic temperature measurement system. Including light sources, light detectors, signal processing units, etc. The light emitted by the light source is transmitted through optical fibers, where Raman scattering occurs. The photodetector collects the scattered light signal and then transmits it to the signal processing unit. The signal processing unit needs to set parameters according to the system requirements, such as sampling interval, Resolución espacial, etc. Por ejemplo, in the temperature measurement test of long-distance high-temperature superconducting cables, when the operating configuration parameters are spatial resolution of 2m, sampling interval of 1m, and sampling period of 60s, fiber optic temperature measurement can meet the requirements of superconducting cable monitoring and protection as well as temperature measurement accuracy.
Data Collection and Analysis
Data collection:
After starting the distributed fiber optic temperature measurement system, the system will collect temperature data along the cable according to the set parameters. The collected data includes temperature values at different locations and corresponding location information. These data are updated in real-time and can reflect the temperature status of the cable at different times.
Data analysis:
Use the accompanying software to analyze the collected data. The analysis content includes the trend of temperature changes, whether there are abnormal temperature points, etc. It is possible to determine whether the cable is in normal operation by setting a temperature threshold. Por ejemplo, if the temperature at a certain point of the cable exceeds the normal operating temperature range (which can be determined based on the rated parameters and historical operating data of the cable), the system will issue an alarm. Al mismo tiempo, comparative analysis can be conducted on the temperature of different parts of the cable to evaluate the overall heat dissipation and operating status of the cable.
Calibration and maintenance
Calibration:
Regularly calibrate the distributed fiber optic temperature measurement system to ensure measurement accuracy. Calibration can use a standard temperature source to calibrate the temperature of the optical fiber and check whether the measured value is consistent with the actual temperature value. If there is a deviation, it is necessary to adjust the parameters of the system, such as the sensitivity of the photodetector.
maintain:
The maintenance work includes checking whether the optical fiber is damaged, whether the connection is loose, etc. In the cable operating environment, optical fibers may be affected by mechanical stress, Corrosión química, and other factors. Por ejemplo, in underground cable trenches, optical fibers may be corroded by humid environments, and it is necessary to regularly inspect the appearance of the optical fibers for signs of damage or corrosion. Al mismo tiempo, regular inspections and maintenance should be carried out on the hardware devices of the system, such as light sources and signal processing units, to ensure their normal operation.

（2） Operation method for distributed fiber optic temperature measurement in pipelines

Fiber optic installation process
Select different fiber optic installation processes based on the function and characteristics of the pipeline.
Winding method:
For some above ground pipelines, such as thermal pipelines, optical fibers can be wrapped around the outer surface of the pipeline. During the winding process, attention should be paid to the tight fit between the optical fiber and the surface of the pipeline to ensure accurate sensing of temperature changes in the pipeline. The spacing of winding should be determined based on factors such as the diameter of the pipeline and measurement accuracy requirements. Por ejemplo, for pipes with smaller diameters, the winding spacing can be appropriately reduced to improve measurement accuracy.
Double layered arrangement:
In some special pipelines, such as subsea pipelines or pipelines with high insulation requirements, a double-layer layout can be used. Arranging optical fibers between the inner and outer layers of the pipeline can not only monitor the temperature of the medium inside the pipeline, but also monitor the impact of the external environment on the pipeline, such as the influence of seawater temperature on submarine pipelines or the influence of external temperature on insulated pipelines.
Internal and External:
In transportation pipelines such as oil and gas pipelines, optical fibers can be embedded inside the pipeline wall or externally placed outside the pipeline wall. The built-in optical fiber can more directly monitor the temperature changes of the medium inside the pipeline, while the external optical fiber can monitor the temperature of the surrounding environment and the temperature of the pipeline wall. The combination of the two can provide a more comprehensive understanding of the operating status of the pipeline.
data acquisition and processing
Data collection:
The pipeline distributed fiber optic temperature measurement system also collects data according to the set parameters. The collected data includes temperature information at different locations along the pipeline. The focus of collection may vary for different types of pipelines. Por ejemplo, in a thermal pipeline, it is important to collect the temperature distribution of the pipeline to determine if there is any heat leakage; Pay close attention to whether there are temperature anomalies in the transportation pipeline to detect any leaks.
Data processing:
Process the collected data to remove interference factors such as noise. Due to the complex operating environment of pipelines, the collected data may be subject to external interference, such as electromagnetic interference. By using data processing methods such as filtering, the accuracy of data can be improved. Then analyze the temperature change pattern in the data to determine whether the pipeline is in normal operation. Por ejemplo, in a heating pipeline network, if the temperature of a certain section of the pipeline suddenly drops, it may indicate a leakage situation, and the system can judge and issue an alarm based on this temperature change characteristic.
System maintenance and updates
maintain:
Check the installation of optical fibers on the pipeline to ensure that they are not damaged or displaced. During pipeline operation, optical fibers may be affected due to factors such as pipeline vibration and medium flow. Por ejemplo, in oil pipelines, the impact of oil flow may cause external optical fibers to loosen or shift, requiring regular inspection and re fixation. Al mismo tiempo, maintain the hardware equipment of the system, such as checking the operating status of devices such as optical time domain reflectometry, to ensure their normal operation.
to update:
Update the distributed fiber optic temperature measurement system according to the operational requirements and technological development of pipelines. Por ejemplo, as the running time of the pipeline increases, it may be necessary to improve measurement accuracy or add monitoring functions. En este caso, the software of the system can be upgraded or some hardware devices can be replaced, such as higher sensitivity photodetectors.

4、 Precautions for Distributed Fiber Optic Temperature Measurement of Cables and Pipelines

（1） Precautions for Distributed Fiber Optic Temperature Measurement of Cables

Fiber optic laying and protection
Laying requirements:
When laying optical fibers in cables, relevant standards and specifications should be followed. Por ejemplo, according to DL/T1573-2016 “Technical Specification for Distributed Optical Fiber Temperature Measurement System of Power Cables”, there are clear regulations on the laying method of optical fibers and the spacing between them and cables. If fiber optic cables are embedded inside, it is necessary to ensure that the embedding process of the fiber optic cables does not affect the insulation and mechanical properties of the cables. For optical fibers laid parallel to cables in cable trenches, it is necessary to avoid them being squeezed by cables or scratched by other objects.
Protective measures:
Take appropriate protective measures for optical fibers. In underground cable trenches, it is necessary to prevent optical fibers from being affected by moisture, Corrosión química, and other factors. Sealed and corrosion-resistant fiber optic protective sleeves can be used. In overhead cables, it is necessary to prevent the optical fibers from being damaged by natural factors such as wind, sun, and rain. Por ejemplo, protective tubes can be used to wrap the optical fibers.
Precisión de la medición de la temperatura
Calibration frequency:
Regularly calibrate the distributed fiber optic temperature measurement system to ensure the accuracy of temperature measurement. The frequency of calibration should be determined based on factors such as the operating environment and importance of the cable. Por ejemplo, important transmission cables operating in harsh environments may require quarterly calibration; For cables operating in general environments, calibration can be performed every six months.
Environmental factors impact:
Consider the impact of environmental factors on temperature measurement. The environmental temperature, humidity, and other factors around the cable may affect the fiber optic sensing of temperature. Por ejemplo, in high temperature and humid environments, the optical properties of optical fibers may change, thereby affecting the accuracy of temperature measurement. Por lo tanto, in the process of data processing, it is necessary to compensate for environmental factors or use appropriate fiber optic materials to reduce the impact of environmental factors.
System reliability and compatibility
Equipment reliability:
Choose reliable distributed fiber optic temperature measurement system equipment. The reliability of the equipment is directly related to the effectiveness of cable temperature monitoring. Consider the stability and anti-interference ability of the equipment. Por ejemplo, selecting light sources and detectors with high stability to ensure that the system can operate stably for a long time without frequent malfunctions.
compatibility:
Ensure compatibility between the system and the power system where the cables are located. Por ejemplo, the communication protocol of the distributed fiber optic temperature measurement system needs to be compatible with the monitoring system of the power system, so as to accurately transmit temperature monitoring data to the monitoring center of the power system. Al mismo tiempo, the electrical performance of the system should also be matched with the power system to avoid interference with the power system.

（2） Precautions for Distributed Fiber Optic Temperature Measurement in Pipelines

Fiber optic installation safety and stability
Installation safety:
When installing optical fibers on pipelines, attention should be paid to safety issues during the installation process. If installing optical fibers on running pipelines, such as heating pipelines or oil and gas pipelines, necessary safety measures should be taken to prevent accidents such as leaks and explosions. Installation personnel must undergo professional training and strictly follow the operating procedures for installation.
Stable installation:
Ensure the stability of fiber optic installation. Whether using winding, double-layer arrangement, internal or external methods, optical fibers must be firmly fixed on the pipeline. During the operation of the pipeline, due to factors such as vibration, thermal expansion and contraction, the optical fiber cannot loosen or shift. Por ejemplo, on high-temperature steam pipelines, the thermal expansion and contraction amplitude of the pipeline is relatively large, and the fixation of optical fibers should be able to adapt to this change, otherwise it will affect the accuracy of temperature measurement.
Temperature monitoring range and accuracy
Monitoring scope:
Select a suitable distributed fiber optic temperature measurement system based on the operating temperature range of the pipeline. The operating temperature range of different types of pipelines varies greatly. Por ejemplo, the temperature of a thermal pipeline may reach several hundred degrees, while the temperature of an oil pipeline is relatively low. To ensure that the system can accurately measure the temperature changes of the pipeline throughout the entire operating temperature range.
Accuracy requirements:
Consider the accuracy requirements for temperature measurement. For some pipelines that are highly sensitive to temperature changes, such as chemical pipelines, high measurement accuracy is required. When choosing a distributed fiber optic temperature measurement system, one should refer to the accuracy indicators of the system, such as temperature resolution. Al mismo tiempo, it should be noted that various factors in the actual operating environment may affect the measurement accuracy, such as fiber aging, surface roughness of pipelines, etc. Corresponding measures should be taken to improve the measurement accuracy.
Long term operation and maintenance
Maintenance plan:
Develop a long-term operation and maintenance plan for the pipeline distributed fiber optic temperature measurement system. The maintenance plan should include regular checks on the installation of optical fibers and the operational status of system hardware equipment. Por ejemplo, check the fiber optic cable for damage once a month and conduct a comprehensive inspection of the system hardware equipment once a quarter.
Fault response:
Establish a fault response mechanism. When the system malfunctions, it should be able to quickly locate the cause of the fault and carry out repairs. Por ejemplo, if a fiber optic cable breaks, it is necessary to be able to promptly determine the location of the break and carry out repairs. Al mismo tiempo, it is necessary to consider how to ensure the safe operation of pipelines during faults, such as using backup monitoring systems or strengthening manual inspections.

5、 Case analysis of cable distributed fiber optic temperature measurement

A 4km long cable requires temperature monitoring. Due to the long length of the cable, traditional temperature monitoring methods are difficult to achieve accurate and real-time monitoring of the entire cable line. Además, during the operation of the cable, the temperature may rise due to factors such as overload and environmental temperature changes, which may affect the safe operation of the cable.
Application of distributed fiber optic temperature measurement system:
In this project, a distributed fiber optic temperature measurement system was adopted. Firstly, suitable optical cables were selected and laid out in a reasonable manner. The system operates based on the fundamental principles of Raman scattering temperature measurement and optical time domain reflectometry (OTDR) positioning. Through real-time monitoring of the system, temperature information at different locations along the cable can be obtained. In practical operation, the system can promptly detect temperature anomalies in cables. Por ejemplo, when a section of the cable experiences an increase in temperature due to overload, the system quickly issues an alarm, allowing the power supply company to take timely measures such as adjusting the load, ensuring the safe operation of the cable and providing reference data for determining the cable’s current carrying capacity.