Subsea Pipeline Heating Cable Fault Detection via Negative Sequence Current
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Solution Overview
Problem
Existing fault detection systems for subsea pipeline direct electrical heating cables are inadequate as they fail to detect faults near the remote end due to minimal changes in conductor current, leading to undetected corrosion and potential pipeline meltdown, and are not suitable for existing installations.
Innovation Solution
A fault detection system utilizing ammeters to measure phase currents, calculating negative and positive sequence currents, and relative negative sequence currents to detect faults, along with a power supply that includes symmetrizing and balancing units to reduce errors and facilitate fault localization, all operable above the surface to avoid subsea operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current measurement methods are used at the in-feed end, then the system structure remains simple, but fault detection precision deteriorates due to minute current changes being undetectable
Solution Approach 1:
The patent transforms the detection approach from measuring current magnitude (one dimension) to analyzing current phase angles and sequence components (another dimension). By calculating negative sequence current and comparing phase angles between in-feed and distant ends, the system detects faults that cause minimal current magnitude changes, thereby improving measurement precision without requiring excessive measurement power.
Solution Approach 2:
The patent introduces intermediate calculation steps (sequence component decomposition, phase angle extraction, difference calculation) as mediators between the raw current measurements and fault detection. These intermediate parameters amplify the detectability of fault conditions while maintaining system structure simplicity.
2Reliability
If fiber optic elements are included in the heating cable as proposed in prior art, then fault detection capability improves, but the cable manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts the fault detection function from the heating cable structure itself and relocates it to the power supply system at the in-feed end. By using existing electrical measurement capabilities to detect faults through electrical parameter analysis rather than embedding physical sensors in the cable, the system achieves reliable fault detection while maintaining cable manufacturing simplicity.
Solution Approach 2:
The patent creates an electrical model/copy of the cable's electrical characteristics by measuring and comparing sequence components and phase angles at different locations. This electrical copying approach enables remote fault detection without physically modifying the cable structure, preserving ease of manufacture.
3Productivity
If the heating cable is placed close to the thermally insulated pipeline, then heating efficiency improves, but the risk of thermal damage from faults increases
Solution Approach 1:
The patent implements preliminary fault detection and alert mechanisms that enable early intervention before faults can cause thermal damage. By detecting faults through negative sequence current analysis and phase angle comparisons, the system can trigger alarms or shutdown procedures before the fault progresses to a point where thermal insulation melting occurs, thus protecting the pipeline while maintaining close cable-pipeline placement for heating efficiency.
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
Enables reliable detection of faults at the distant end of subsea pipeline direct electrical heating cables, reducing false alarms and allowing for timely repair, while being adaptable to existing installations and varying operating conditions.
Implementation Method 1
A first ammeter measures a first phase current, a second ammeter measures a second phase current, and a third ammeter measures a third phase current
Implementation Method 2
A first calculation unit calculates a negative sequence current from the first phase current, the second phase current, and the third phase current
Implementation Method 3
A first detection unit detects a change in the negative sequence current
Implementation Method 4
a power supply that includes symmetrizing and balancing units to reduce errors and facilitate fault localization
Data Source
AI summary
A fault detection system for subsea pipeline direct electrical heating cables is provided. The fault detection system includes a first ammeter for measuring a first phase current, a second ammeter for measuring a second phase current, and a third ammeter for measuring a third phase current. The fault detection system also includes a first calculation unit for calculating a negative sequence current from the first phase current, the second phase current, and the third phase current, and a first detection unit for detecting a change in the negative sequence current.