Protective Earth Circuit Compensation for Marine Stray Currents
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Solution Overview
Problem
Stray currents in marine electrical supply systems cause electrolytic corrosion and galvanic corrosion, leading to damage and potential flooding of vessels due to improper wiring, leakage, and unbalanced current delivery when connected to shore power, especially when multiple vessels share the same facility.
Innovation Solution
A method involving a protective earth circuit with current sensors and controllable induction coils to monitor and counteract stray currents, reducing them to near zero, thereby preventing corrosion and electrical damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective earth circuit is connected to shore power safety ground, then electrical protection is provided, but stray currents cause electrolytic corrosion and depletion of sacrificial elements
Solution Approach 1:
The patent introduces an intermediary device between the protective earth circuit and the shore power safety ground. This intermediary monitors stray currents and actively compensates for them, preventing the harmful electrolytic corrosion while maintaining the electrical protection function. The intermediary acts as a buffer that isolates the vessel's protective earth system from the contaminated shore ground.
Solution Approach 2:
The system implements feedback by continuously monitoring stray currents in the protective earth circuit and automatically adjusting compensation measures. Current sensors detect the magnitude and direction of stray currents, and this information feeds back to control systems that activate counter-measures such as adjustable resistors or isolation mechanisms, dynamically preventing corrosion while maintaining safety.
2Adaptability or versatility
If multiple vessels are connected to the same shore facility, then power sharing is enabled, but galvanic corrosion is accelerated due to combined effects
Solution Approach 1:
The patent segments the protective earth circuits of multiple vessels by introducing individual isolation or compensation devices for each vessel. This segmentation prevents the galvanic corrosion effects from one vessel from affecting others connected to the same shore facility, while still allowing all vessels to share power from the common shore power source.
3Reliability
If AC leakage to vessel ground occurs, then electrical connection is established, but serious harm and failure occur to underwater parts
Solution Approach 1:
An intermediary monitoring and compensation device is introduced between the vessel ground and the shore power system. This intermediary detects AC leakage currents and either blocks them or compensates for their corrosive effects, maintaining the necessary electrical connection for safety while preventing corrosion damage to underwater parts.
4Power
If shore AC power is connected into DC ground systems, then power delivery is achieved, but through-hull fittings are corroded and destroyed
Solution Approach 1:
The patent extracts or separates the harmful AC power delivery path from the DC ground system. By providing dedicated AC power pathways and isolating the DC ground system from AC connections, the system achieves power delivery functionality while preventing the electrolytic corrosion that would otherwise attack through-hull fittings.
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
Effectively mitigates electrolytic and galvanic corrosion, preventing damage to underwater components and ensuring the integrity of marine vessels by maintaining balanced current flow and reducing corrosion risks.
Implementation Method 1
a controllable induction coil (415) arranged to output a counter-current to the protective earth line in response to the control signal
Implementation Method 2
a current sensor (311) arranged to detect a stray-current in the protective earth circuit
Data Source
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AI summary
The invention relates to a method and a system for cancelling stray currents in a marine electrical supply system, which system comprises a protective earth circuit (101; 201) connecting a vessel (100; 200) to ground when a source of power (102; 202) is connected to the vessel. The method involves the steps of monitoring the current in the protective earth circuit using a current sensor (311; 411; 511); determining if a stray current is detected by the current sensor, and, if a stray current is detected, counteracting the stray-current in the protective earth circuit to reduce the stray current to a value at or near zero current. The invention further relates to the system applied to a marine vessel.