High-Resistance Grounding and Selective Ground Fault Protection for a Major Industrial Facility

The high-resistance grounded system offers the distinct advantage of service continuity under single ground fault conditions which is critical to many industries such as petroleum, chemical, mining, textile, cement, pulp and paper, food, glass, utility, etc. A new major phosphate mine, with a total of 120 MVA electrical demand capacity, utilizes the high-resistance grounding method for the 480-V and 4160-V distribution systems. A complete ground fault protection scheme that includes both first fault alarm and second fault selective tripping protection was developed for the proper protection of the system. The design of this ground fault protection system has many unique features due to the complexity of the project. Design considerations including the system leakage current, the limitation of transient overvoltage, the grounding methods, the fault detection and annunciation, and selective isolation of faults based on circuit priorities, are analyzed.