Method for measuring grounding insulation resistance of electric power DC system

A method for measuring insulation resistance against ground of a power DC system is characterized in that the measurement method comprises the following steps of: (A) determining a positive bus-bar as +KM and a negative bus-bar as -KM; (B) selecting a computer for control and selecting a precise Hall sensor as the current and voltage measurement instrument; (C) changing the position of a current sensor A to connect the current sensor A with the positive bus-bar +KM to obtain a circuit and to connect the current sensor A with the negative bus-bar -KM to obtain another circuit; adding a known precise measurement resistor r in the current sensor current; and measuring R1 and R2 by the first and the second circuits according to the formulas R1=[U-(I1+I2)r]/I1 and R2=[U-(I1+I2)r]/I2. Accordingly, the insulation resistance against ground of the power DC system can be measured. The method has the advantages of accurate measurement of resistances against ground of the positive and the negative bus-bars, which solves the difficulty in measurement due to insulation declination of the both ends. The measurement result is independent of distributed capacitor between the DC system and the group, and the measurement process is not influenced by the external environment and does not influence the DC system.