Abstract
A earth monitoring system which consists of a zero-phase-sequence current transformer (ZCT), current
relay (OCG) and three condensers was constructed in order to detect the accident point for the lower ground
fault resistance on the electrical machinery, apparatus and lines. It was installed on a a.c. 100V feeder panel in
the research and training vessel Umitaka maru, while measurement was carried out to evaluate the performance
of the device. As a result, the following issues were clarified. 100mA in the ground fault current was measured
by this device, and then the alam of a 'lower ground fault resistance' was confimed on the data-logger when
the ground fault resistance was Iowered to 0.6kΩ. In this case, the decrease of 20 mA in the ground fault current
was confirmed when the condenser was not comected to the feeder. However, the detection of the lower ground
fault resistance while not comected to the condenser was still possible.
