Factors Affecting Minimum Surface Leakage Distances in D-C Power Systems

A summary of the mniminium leakage distances for the several insulating materials investigated is presented in Table II. These data were obtained for direct current applications using the measuring techniques described in the appendix. The determination of safe minimum leakage distances for power installations is dependent upon the following considerations: 1. The minimum safe distance is dependent upon the leakage current across the surface of the insulation. The voltage associated with the minimum safe current, namely tracking voltage, serves as a criterion for establishing this minimum distance. Exceeding this criterion either by increased voltage or reduced distance will result in ultimate breakdown and complete destruction of the insulating properties of the insulation. 2. The establishment of minimum safe leakage distances requires an accurate knowledge of the environmental conditions where the insulation will be employed. The deposition of water and soluble conducting contaminants such as sodium chloride and sodium sulfate will affect the tracking voltage greatly. 3. The arc resisting qualities of an insulating material will, to a large extent, determine the safe minimum leakage distance. Further investigation should be made to determine the factors affecting leakage distances in alternating current systems and the relationship to direct current values. Surge voltages and the benefits derived from barriers should also be analyzed to add further knowledge to the limitations of insulation and insulated structures.