High-Resistance Grounded Power System

To minimize ground fault during a line-to-ground fault condition, it has been a common practice to use high-resistance grounded (HRG) power systems, both at low voltage and at medium voltage (MV). The criteria for designing HRG systems are very well known to the industry; however, the opinion of industry experts has been divided on limiting the use of HRG systems for MV systems to voltages of less than 4.16 kV and phase-ground fault currents of less than 10 A without clarifying that it applies to systems that require continuous operation upon first detecting line-to-ground fault, as it is now in the Recommended Practice for Grounding of Industrial and Commercial Power Systems. This paper will review the background history of HRG power systems and their application to MV systems for specific industries and will make the case that voltages need not be limited to less than 4.16 kV and the phase-ground fault current to less than 10 A, so long as the faulted power system is isolated within ten cycles and that there are no directly connected motors. This paper will discuss the potential damage and protection requirements of HRG systems for MV applications to ensure that a line-to-ground fault is cleared before it involves other phases to make a multiphase arcing ground fault.