DC Diagnostic Tool

Insulation resistance testing is used to quantitatively evaluate the overall health condition of the insulation medium in electrical equipment, and is a core method for preventive maintenance and fault diagnosis. By applying DC high voltage and measuring leakage current, the insulation resistance value is calculated (R = V / I). Its main purposes include:

① Detecting common insulation defects such as moisture ingress, aging, carbonization paths, and surface contamination;

② Establishing baseline data and tracking trends to determine whether insulation performance is degrading over time;

③ Performing Polarization Index (PI) and Dielectric Absorption Ratio (DAR) diagnostics to distinguish between uniform moisture and localized aging;

④ Verifying maintenance quality to ensure that equipment meets safety thresholds before being put into operation.

At the initial stage of applying DC voltage, the total current flowing through the insulation medium consists of three components: capacitive charging current (rapid decay), absorption current (slow decay), and leakage current (constant). As the charging current and absorption current gradually decrease to zero, the total current continuously decreases, so the calculated insulation resistance value increases monotonically over time and eventually stabilizes (determined by the leakage current).

This characteristic is not an insulation fault, but a normal physical phenomenon of dielectric polarization. By utilizing this feature and comparing resistance values at different time points (such as 15s/30s, 60s, 10min), DAR and PI can be calculated, thereby evaluating the dryness and cleanliness of insulation independently of geometric size. If the resistance fails to stabilize for a long time or the DAR/PI values are low, it usually indicates moisture ingress or thermal aging.

By applying a stable DC voltage and measuring leakage current, insulation resistance is calculated. The smaller the leakage current, the better the insulation condition. Combined with PI, DAR and other ratio tests, it can distinguish between different defects such as moisture, aging, or surface contamination.

D1103 corresponds to the basic model, which is lighter and more economical, meeting routine diagnostic testing needs. D1110 corresponds to the advanced model. The D1110 has more comprehensive functions and performance, with stronger anti-interference capability, and is suitable for high-interference environments (such as substations).