On-line insulation monitoring of heavy duty coal face electrical drives using zero sequence current harmonics

One of the major drawbacks of a restricted-neutral system of electrical power supply used in underground coal mines of many countries is the lack of on-line insulation monitoring facility and early warning capability during deterioration of system insulation level. The paper outlines a novel technique of noninvasive on-line insulation monitoring for a restricted neutral system of power supply using harmonics content of zero sequence current reflected in the secondary winding of a core balance transformer.