Subsea Pipeline DEH Cable Fault Detection Using Fiber Optic Sensors
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Solution Overview
Problem
Conventional fault detection systems for subsea pipeline direct electrical heating (DEH) cables face challenges in accurately detecting faults at the remote end due to the grounded connection, which causes minimal changes in conductor current, making it difficult to detect mechanical damages like cuts in the cable insulation, especially when the fault is far from the in-feed end.
Innovation Solution
A fault detection system utilizing a fiber optic current sensor (FOCS) that measures electric current using a single-ended optical fiber around the conductor, leveraging the magneto-optic effect to accurately detect changes in current at the remote end, combined with a signal processing device to compare signals and raise warnings for potential faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current measurement methods are used at the in-feed end, then the system can monitor overall current, but it cannot accurately detect small fault currents at the remote end due to phase shifting and minimal current changes
Solution Approach 1:
The patent transitions from electrical current measurement to optical measurement by placing a fiber optic sensor in the magnetic field of the conductor. This dimensional change from electrical to optical domain allows detection of current changes at the remote end without being affected by electrical phase shifting or signal attenuation issues.
Solution Approach 2:
The patent replaces conventional electrical current sensing with optical sensing using a fiber optic sensor. The sensor detects the magnetic field generated by current flow through optical means rather than electrical contact, eliminating the problems of phase shifting and small signal detection at the remote end.
2Reliability
If the piggyback cable is placed close to the thermally insulated pipeline, then DEH system efficiency is optimized, but fault detection at the remote end becomes more difficult due to the grounded connection
Solution Approach 1:
The patent introduces a fiber optic sensor as an intermediary element that indirectly measures current by detecting the magnetic field rather than making direct electrical contact. This intermediary approach allows fault detection at the remote end without being affected by the grounded connection or the cable's proximity to the pipeline.
3Reliability
If a fault occurs in the remote region of the cable, then the fault current shunts to ground, but the change in conductor current at the in-feed end becomes minute and extremely difficult to detect
Solution Approach 1:
The patent places the fiber optic sensor at the remote end of the cable before a fault occurs, so that when a fault happens, the sensor has already been positioned to detect the magnetic field changes. This preliminary positioning allows immediate detection of fault currents without relying on distant measurements at the in-feed end.
Solution Approach 2:
The patent replaces electrical current measurement with optical magnetic field detection. The fiber optic sensor measures the magnetic field generated by fault current through optical means, providing accurate detection even when the fault current is small and shunting to ground at the remote end.
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
The system provides increased speed and accuracy in fault detection with improved reliability, enabling timely identification of faults at the far end of the DEH cable, even when the fault current is small compared to the overall conductor current.
Implementation Method 1
A fault detection system utilizing a fiber optic current sensor (FOCS) that measures electric current using a single-ended optical fiber around the conductor, leveraging the magneto-optic effect to accurately detect changes in current at the remote end
Data Source
Figure 1
Figure 2~3
AI summary
The present invention relates to a fault detection system (10) for a direct electrical heating (DEH) cable (1) for a subsea pipeline (2). The system comprises a first conductor (3) having a first end (3a) and a second end (3b) and a second conductor (6) having a first end (6a) and a second end (6b). Said first ends (3a, 6a) are both connected to a power supply system (5) provided at a first position (X1); where the second end (3b) of the first conductor (3) is connected to the pipeline (2) and where the second end (6b) of the second conductor (6) is connected to the DEH cable (1) at a second position (X2) proximal to said first position (X1). The DEH cable (1) is electrically connected to the pipeline (2) at a third position (X3) distal to the first position (X1). A first current sensing device (11) is configured to provide a signal S1 representative of the current into or out from the power supply system (5), while a second current sensing device (12) is configured to provide a signal S2 representative of the current in the DEH cable (1) at the third position (X3). A signal processing device (15) is configured to compare the signal S2 representing the current in the DEH cable (1) at the third position (X3) with the signal S1 representing the current into or out from the power supply system (5).