Principle of Cambodian Underground Temperature Measurement Optical Cable

Underground temperature measurement with optical cables relies on distributed temperature sensing (DTS), where optical fibers act as continuous linear sensors detecting temperature changes via light scattering effects.

Working Principle

Distributed Temperature Sensing (DTS) systems use optical fibers as sensors to measure temperature along the entire length of the cable, rather than at discrete points. A laser pulse is sent through the fiber, and as it propagates, a small portion of light is scattered due to interactions with the fiber material. This scattering occurs in three main forms: Rayleigh scattering: Light scattered at the same wavelength as the incident light, used for locating events along the fiber.

Raman scattering: Light scattered at different wavelengths, sensitive to temperature changes. The ratio of Stokes and anti-Stokes components varies with temperature, allowing precise measurement. Brillouin scattering: Low-frequency scattering influenced by both temperature and strain, useful for combined thermal and mechanical monitoring.

Measurement Techniques

There are several methods to interpret the scattered light: Optical Time-Domain Reflectometry (OTDR): Measures the time it takes for backscattered light to return, similar to radar, to locate temperature events along the fiber.

Optical Frequency-

Domain Reflectometry (OFDR): Uses frequency-modulated light and Fourier transformation to obtain high-resolution local temperature profiles.

Code Correlation DT

S: Sends coded light sequences into the fiber, spreading optical energy over a sequence to improve signal-to-noise ratio and allow long-distance measurements with high accuracy.

Advantages for Underground Cables

Using optical fibers for underground temperature monitoring offers several benefits: Continuous temperature profile: Unlike point sensors, DTS provides a full thermal map along the cable length. Long-distance monitoring: Systems can measure over tens of kilometers, suitable for extensive underground networks. Electromagnetic immunity: Optical fibers are not affected by electromagnetic interference, making them ideal for power cable environments.

High spatial and temperature resolution: Typical systems achieve 1 m spatial resolution and ±1°C accuracy, with some systems capable of 0. 01°C resolution.

Practical Considerations

For underground power cables, the DTS system helps in: Monitoring cable ampacity: Ensuring the cable operates within safe thermal limits. Detecting hotspots: Identifying potential failures at joints or insulation defects. Optimizing maintenance: Providing real-time data to plan preventive actions and extend cable lifespan.

In Cambodia, such systems can be applied to medium- and high-voltage underground networks, improving safety, reliability, and operational efficiency while reducing the risk of overheating and cable damage.