Recently, for the purpose of preventing the corrosion of a vessel, the electrical corrosion protection device that prevents the corrosions of the hull and the propeller is widely used. However, the electrical corrosion protection method artificially emits the current into the seawater around the hull using the power supply in order to make the hull and propeller be in the state of not being corrosion, so that electromagnetic field is generated outside the hull by the current emitted into the seawater. In this paper, the static and alternating constituents of the electromagnetic field generated in underwater outside the hull are analyzed and a countermeasure is investigated to reduce the strength of the electromagnetic field.
A current path is formed through the propeller, the shaft, and the hull by the emitted current into seawater by electrical corrosion protection device. When the electrical corrosion protection device of a vessel operates, the impedance on the current path is varied due to the rotation of the propeller. Therefore, alternating current component reflecting the impedance variation due to the propeller rotation is generated and alternating electromagnetic field is newly generated by this current, resulting in the increase of the electromagnetic field strength. So, the ships will be subjected to significant threat from mine detection system by larger electromagnetic field strength. In this paper, an active shaft grounding electrical corrosion protection system is studied which eliminates the alternating current component from the total current flowing through the current path and reduces the electromagnetic field strength generated in underwater outside the hull by detecting the current variation in real time and compensating it.
Until now, in domestic, there is no research on the design and development of the active shaft grounding system. Therefore, in this paper, firstly the electromagnetic field aspects generated in underwater by electrical corrosion protection device are analyzed and also any changes in the electromagnetic field aspects are analyzed which are occurring when electrical corrosion protection device and active shaft grounding system operate. Secondly, an active shaft grounding system configuration and a controller model for eliminating the alternating electromagnetic field are proposed and verified by simulation based on an equivalent model incorporating the control concept. Finally, a simulator is designed and manufactured, and a test system is built with it. By showing that the experimental results from the test system are the same as the simulation results, a base technology is presented for designing practical active shaft grounding system.