Optical Fiber Current Distribution Measurement in Power Cables
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Solution Overview
Problem
Current methods for detecting and localizing damage in high-voltage and medium-voltage power transmission cables, particularly those causing current losses due to water intrusion or mechanical damage, are inadequate as they fail to accurately identify and pinpoint faults in the cable structure.
Innovation Solution
The method employs polarisation-sensitive optical reflectometry using a single-mode optical fibre wound around the metallic layer of the cable to measure longitudinal variations in the magnetic field induced by circulating current, allowing for the detection and localization of cable faults by analyzing the rotation angle of the polarisation state along the cable length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current measurement methods are used in high-voltage cables, then the measurement can be performed with simple equipment, but the measurement precision is insufficient to detect low-level current losses
Solution Approach 1:
The patent replaces conventional electrical current measurement methods with optical measurement technology. An optical fiber sensor is wound around the cable's metallic layer to detect the magnetic field generated by circulating current through the Faraday effect. This substitution of electrical measurement with optical measurement enables high-precision detection of current losses while maintaining system compatibility with high-voltage environments.
Solution Approach 2:
The patent introduces an optical fiber sensor as an intermediary element that indirectly measures current by detecting the magnetic field rather than measuring current directly. The optical fiber acts as a mediator between the magnetic field generated by current flow and the measurement system, enabling precise detection of current distribution and losses without electrical contact with the high-voltage cable.
2Measurement precision
If electrical sensors are used to detect water intrusion in cable screens, then water damage can be detected, but the method cannot accurately localize the damage position along the cable
Solution Approach 1:
The patent divides the cable into discrete measurement segments along its length by using the optical fiber sensor to measure magnetic field at multiple positions. The cable is effectively segmented into measurement zones, allowing identification of specific locations where current losses occur. This segmentation enables precise localization of damage positions by comparing current distribution across different segments of the cable.
Solution Approach 2:
The patent transitions from point-based electrical sensing to distributed optical sensing along the cable length. By winding the optical fiber around the cable and measuring magnetic field at multiple longitudinal positions, the system adds the spatial dimension to damage detection, enabling accurate localization of faults along the cable rather than merely detecting their presence.
3Reliability
If DC voltage is applied between water sensor and cable screen to detect water intrusion, then water damage can be identified, but the method generates additional energy consumption and potential safety risks
Solution Approach 1:
The patent replaces electrical voltage application methods with optical field-based detection. Instead of applying DC voltage between sensors and cable screens, the system uses an optical fiber sensor to detect the magnetic field generated by current flow. This substitution eliminates the need for additional voltage application, reducing energy consumption and safety risks while maintaining reliable detection capability.
Solution Approach 2:
The patent utilizes the existing current flow in the cable to generate the magnetic field that is measured by the optical sensor. The cable's own operating current serves the dual purpose of power transmission and providing the magnetic field signal for detection. This self-service approach eliminates the need for external DC voltage application, reducing energy consumption and simplifying the detection system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively detects and localizes current losses in power transmission cables, even at low loss levels, enabling timely repair and minimizing downtime by providing precise identification of fault positions within the cable.
Implementation Method 1
Measurement of the intensity of an electric current by using an optical fibre wound around a current path as a sensor is generally known (see for example U.S. Pat. No. 5,365,175). Optical fibre sensors use the Faraday effect, whereby the magnetic field generated by the electric current induces a rotation of the plane of polarisation, called Faraday rotation, of the light travelling through the fibre.
Data Source
AI summary
A method for detecting an electrical current longitudinal variation in a power transmission system including a power cable. Electric losses and their location along the cable length can be detected. Current variation in a grounded metallic layer of a power cable is measured from Faraday rotation of polarised light travelling in a single-mode optical fiber wound in a radially external position with respect to the grounded metallic layer. Measurements of the Faraday rotation are carried out by means of polarization-sensitive optical time domain reflectometry (POTDR) or by polarization-sensitive optical frequency domain reflectometry (POFDR) while a direct current is injected in the metallic layer.