Abstract: Aiming at the requirements of portable DC insulation detection devices，a dynamic difference

algorithm based on single-arm was proposed，and a portable DC insulation detection and verification integrated

machine was designed based on this algorithm. The principle of the single-arm insulation monitoring system to reduce the risk of malfunction of the relay protection device was analyzed in detail，and the zero drift change of DC leakage current sensor was demonstrated. The dynamic difference algorithm that can overcome the zero drift of DC leakage current sensor was deduced. The experimental result of the DC insulation detection and verification integrated machine shows that the algorithm has high calculation accuracy，the zero drift effect of DC leakage current sensor can be solved effectively，and the safety of DC power system can be ensured.

      Key words: portable DC insulation detection；dynamic difference algorithm；single-arm；unbalanced bridge；

one point ground fault