Abstract
Six typical on-line cable monitoring methods were outlined first. In the field, it has become a problem that in some cases measured insulation resistance values contain much error than expected, especially when the outer sheath resistance is lower. This was recognized as a phenomenon due to intrusion of unpredictable and unstable noise voltage “en” to the measuring system.
The Author presented his extensive investigation results relating to the origins of en, their various aspects, invasion route to the measuring circuit and degrees of influence on the measured resistance values, with the aid of many illustrations and the newly derived numerical formulas which serve as the indexes to tell practicability of each method. Also suggested that all the methods shall be categorized into 3 groups, (A) to (C), according to their extent of measuring error.
Finally, the Author presented and recommended the use of new techniques to reduce en effects, with the adoption of (B) group methods because of their good practicability.
