Study of Insulation Monitoring Device for DC System Based on Four-Switch Combination

The design principle of a new insulation monitoring device on DC system based on AT89LV52 has proposed in this paper. The method of measuring insulation resistance between ground and DC power supply using switch-controlled is introduced, by which the state of combination switch can be changed though programming, a variety of effective circuit structure can be produced, linear equations of voltage sampling on different circuit structure can be established, so resistance to ground of positive and negative electrode of dc bus and the value of bus voltage can be got. This paper gives designs of hardware circuit and software flow and analysis on testing results. The results of preproduction in Shandong Huineng Electric Co., Ltd. show that the design technique of this new type device has characteristics of flexible method of finding grounding branches, accurate measurement and low cost. Therefore, it is especially suitable for DC system insulation on-line monitoring of power plant and substation.