How to use distributed fiber optic temperature measurement for pipeline cables

Principle of Distributed Fiber Optic Temperature Measurement for Pipeline and Cable

The basic principle of distributed fiber optic temperature measurement system (DTS) is based on the optical time domain reflectometry (OTDR) principle of fiber optic and the Raman scattering effect of fiber optic. When laser pulses propagate in optical fibers, they interact with fiber molecules to generate various scattering phenomena, such as Rayleigh scattering, Brillouin scattering, and Raman scattering. The mechanism of fiber temperature measurement is based on the backward Raman scattering effect. By analyzing Raman scattering light, the temperature distribution along the fiber optic cable can be accurately measured because Raman scattering light contains temperature related information, and the fiber optic cable serves as both a sensing medium and a transmission medium in the entire system, guiding light. Therefore, measurement information and spatial distribution status along the fiber optic cable can be obtained at any time.

Distributed Fiber Optic Temperature Measurement Method for Pipeline and Cable

The distributed fiber optic temperature measurement system integrates the principle of backward Raman scattering and optical time domain reflection technology, realizing multiple functions such as optical signal generation, spectral analysis, photoelectric conversion, signal amplification and processing.

Firstly, a specially designed temperature sensing optical cable is used as the temperature sensor and laid along the pipeline cable. There are various ways to lay optical cables according to actual needs. For example, for pipelines, a winding installation method can be used, which utilizes the flexibility of the optical fiber itself to directly fix it in a spiral shape close to the outer wall of the pipeline, achieving 360 ° leakage monitoring of the pipeline; It is also possible to use a double-layer arrangement of optical fibers inside and outside, commonly found in insulation layers. An equal amount of independent optical fibers are evenly arranged inside and outside the insulation layer. By comparing the real-time temperature difference inside and outside the insulation layer with the initial temperature difference, the insulation failure can be determined; Temperature sensing optical fibers can also be directly implanted into cables to detect the temperature distribution of conductors and insulation layers.

Application Case of Distributed Fiber Optic Temperature Measurement for Pipeline and Cable

1、 The distributed fiber optic temperature measurement system is applied to the temperature monitoring of power cables in a power company in Anhui province. By laying temperature measuring optical cables on the surface or inside the cable, the system can monitor the temperature changes of the cable in real time and accurately. This helps to timely detect potential overheating hazards during cable operation, which is of great significance for ensuring the safe and stable operation of the power system. Because during the operation of cables, overloading, local short circuits, or poor heat dissipation can cause temperature rise. Distributed fiber optic temperature measurement systems can accurately measure the temperature at various points. When the temperature approaches or exceeds the set safety threshold, timely warnings can be issued to take corresponding measures, such as adjusting the load, repairing the circuit, etc.

2、 Application in pipeline leak detection

Application of leak detection in tap water pipelines in the field of water purification technology. Researchers placed photosensitive fiber cloth on the surface of the test pipeline 5mm away from the leakage point, and used a distributed fiber optic temperature measurement system to detect pipeline leaks. Because when a pipeline leaks, the temperature of the surrounding environment will change. Through the temperature sensing function of optical fibers, this temperature change can be sensed to determine whether there is a leak point and the approximate location of the leak.

For monitoring the infiltration of external water into the sewage pipeline network, the installation method of directly arranging the entire optical fiber inside the sewage pipeline is adopted. Due to the possible temperature difference between the incoming water and the sewage in the sewage network, the distributed fiber optic temperature measurement system can determine whether there is incoming water infiltration by monitoring temperature changes, thereby ensuring the normal operation of the sewage network.

In terms of energy transportation pipelines, such as oil and natural gas pipelines. By properly laying optical fibers, such as wrapping them around the outer wall of a pipeline, when a leak occurs in the pipeline, the temperature changes around the leak point will be sensed by the optical fibers. This is because leaked substances (such as natural gas leaks, which absorb surrounding heat and cause a decrease in temperature, and oil leaks, which may cause temperature changes due to heat exchange with the surrounding environment) can cause changes in the temperature of the surrounding environment. After fiber optic detection of temperature changes, the system can promptly report and locate the leak point, avoiding safety risks and economic losses caused by energy leaks.

3、 In terms of improving the reliability of equipment operation, Jiazhao distributed fiber optic temperature measurement system can provide real-time monitoring of pipelines, cable lines, heating furnaces, etc. For pipelines and cable lines, real-time temperature monitoring can detect potential fault risks in advance, such as local overheating caused by cable aging, temperature anomalies caused by pipeline corrosion or blockage, etc. For heating furnaces, monitoring their temperature distribution helps optimize the heating process, improve energy efficiency, and prevent equipment damage or safety accidents caused by local overheating, effectively avoiding accidents and improving production efficiency.

Precautions for Distributed Fiber Optic Temperature Measurement of Pipeline Cables

1、 DL/T1573-2016 is a technical specification for distributed fiber optic temperature measurement systems for power cables issued by the China Electric Power Industry Standardization Technical Committee. In the distributed fiber optic temperature measurement of pipeline cables, relevant technical specifications should be followed. For example, in terms of functional requirements, the system should be able to accurately measure temperature and issue timely alarms; In terms of performance indicators, there should be clear requirements for measurement accuracy, resolution, etc; For testing methods, it specifies how to conduct tests on accuracy, stability, and other aspects. Following these specifications helps ensure the reliability and accuracy of the temperature measurement system.

2、 Precautions for fiber optic cable laying

Selection of laying method

If choosing the winding installation method, it is necessary to ensure that the optical fiber is tightly attached to the outer wall of the pipeline, without any looseness or excessive gap, otherwise it may affect temperature conduction and lead to inaccurate measurement. At the same time, attention should be paid to avoiding excessive bending or twisting of the optical fiber during the winding process, so as not to cause damage to the optical fiber and affect the transmission of optical signals and temperature measurement.

For the double-layer arrangement of optical fibers inside and outside, when arranging optical fibers inside and outside the insulation layer, it is necessary to ensure uniform distribution of optical fibers and take protective measures to prevent the optical fibers from being cut by insulation materials or squeezed by other objects during installation.

When directly implanting temperature sensing optical fibers into cables, attention should be paid to the depth and position of implantation, which should not affect the normal performance of the cable, and ensure that the optical fibers can fully contact the conductors or insulation layers inside the cable for accurate temperature measurement.

Fiber optic cable protection

When laying optical cables, it is necessary to avoid mechanical damage to the cables, such as being cut by sharp objects or crushed by heavy objects. Cable protection can be achieved through methods such as conduit protection and installation of cable trays.

Attention should also be paid to the moisture and water resistance of optical cables, as moisture may affect the optical performance of optical fibers, leading to weakened or distorted scattered light signals. Measures such as sealed joints and waterproof tape can be used to ensure the sealing of the optical cable.

3、 Environmental factors impact and response

electromagnetic interference 

Although optical fibers themselves have the characteristic of resisting electromagnetic interference, they may still be subject to a certain degree of electromagnetic interference in some complex electromagnetic environments, such as near power cables or places with large electrical equipment. To reduce this interference, optical cables with good shielding performance can be used, and the laying path of the optical cable can be reasonably planned to be as far away from strong electromagnetic sources as possible.

Temperature adaptability

Consider the temperature range of the environment where the pipeline cable is located and choose a suitable temperature measurement system and optical cable. If the ambient temperature is too low or too high, it may affect the performance of the optical fiber and the accuracy of the temperature measurement system. For example, in high-temperature environments, it is necessary to ensure that the components of the system can work properly and will not be damaged or experience performance drift due to high temperatures; In low-temperature environments, it is necessary to prevent situations such as fiber brittleness and breakage from occurring.

How to operate pipeline cable distributed fiber optic temperature measurement correctly

1、 System installation and debugging phase

equipment installation 

Host installation: The distributed fiber optic temperature monitoring host should be installed in a dry, well ventilated, and easy to operate and maintain location. Ensure that the host is securely installed to avoid equipment damage caused by vibration or other reasons. At the same time, it is necessary to correctly connect power lines, communication lines, and other circuits according to the electrical connection requirements of the equipment, in order to prevent equipment failure caused by incorrect wiring.

Fiber optic cable laying: According to the precautions for fiber optic cable laying mentioned earlier, choose the appropriate laying method based on the different cable conditions of the pipeline. During the laying process, be careful to avoid damaging the optical cable. For example, before laying, it is necessary to conduct a visual inspection of the optical cable to ensure that it is not damaged or has any obvious defects. If it is a long-distance optical cable laying, attention should be paid to the tension control of the optical cable to avoid excessive tension and breaking the optical cable.

System debugging

Optical path debugging: After completing the optical cable laying, the first step is to conduct optical path debugging. Check if the transmission of optical signals is normal, and determine if the optical path is unobstructed by monitoring parameters such as optical power on the host. If the optical power is too low, it may be due to poor fiber connection or fiber loss. It is necessary to check whether the fiber connector is tightly inserted and whether the fiber has a bending radius that is too small.

Temperature calibration: Use a standard temperature source to calibrate the temperature measurement system. According to the system requirements, set different temperature points and check whether the error between the temperature values measured by the system and the standard temperature values is within the allowable range. If the error is too large, it is necessary to adjust the parameters of the system, such as adjusting the coefficients in the demodulation algorithm, to improve the measurement accuracy.

2、 Daily operation

Startup and shutdown operations

When starting up, turn on the power according to the operation manual of the host, wait for the system self-test to complete, and check whether the various parameters of the system are normal, such as fiber connection status, current temperature measurement range, etc. When shutting down, it is necessary to first stop data collection and other operations, and then turn off the host power to avoid sudden power outages causing damage to the system.

Data monitoring and recording

Regularly check the temperature data monitored by the system, which can be viewed through the built-in display screen of the host or the connected PC software. Record temperature data and establish a temperature data archive for analyzing temperature trends. If abnormal fluctuations or exceeding the set threshold are found in temperature data, timely analysis and processing should be carried out.

System maintenance and inspection

Regularly maintain the system, including cleaning the host equipment and checking for loose fiber optic connectors. At the same time, it is necessary to check whether the performance of the system has decreased, such as whether the measurement accuracy has decreased. The performance of the system can be ensured through regular temperature calibration and other operations. If a system malfunction is found, it should be repaired in a timely manner. Based on the fault prompt information or symptoms, the cause of the malfunction should be investigated, such as whether it is hardware damage, software failure, or fiber optic cable failure, and corresponding repair measures should be taken.

• Prev：How to use fluorescent fiber optic temperature measurement for switchgear
• Next：What is a fibre optic temperature sensor?