High-resistance grounding of low-voltage systems: a standard for the petroleum and chemical industry

Abstract

A debate has existed in the petroleum and chemical industry for years concerning low-voltage (480-600 V) power systems grounding. Since reliability and continuity of service are very important, some engineers in the past preferred using an ungrounded system. The practicality of such ungrounded system becomes questionable as the extent of coverage increases. Few ungrounded low-voltage systems are presently being designed due to the possible destructive nature of transient overvoltages resulting from an arcing ground fault. Most systems now utilize either a solidly grounded or high-resistance grounded source. This paper begins with a brief discussion on ungrounded, solidly grounded, and high-resistance grounded systems. Benefits and limitations of each system are also discussed. It is shown that the use of high-resistance grounded low-voltage systems makes good sense in the petrochemical industry. Design, construction, operation, and maintenance factors for such systems are discussed and analyzed together with systems when three-phase four-wire loads are present. Finally, operational problems and some appropriate solutions are discussed where significant variable-speed drive loads are utilized. It is suggested that this should become a standard of the industry and the solidly grounded system should be used only in applications where the high-resistance grounded system becomes impractical.

High-resistance grounding fault detection and location in DC railway system

“…(3) The rail and cable resistance is 0.0003 /m, the inductance is 1.78mH/km [8,9,10] . As for a 1500m length line, the whole resistance will be R all =0.45 .…”

“…Also, when the current dispersing in the ground, the potential gradient on the ground may exceed the upper limit of human endurance, touch voltage or step voltage endanger the safety of the public [10,11,12].…”

Ground fault location self-diagnosis in high resistance grounding drive systems

“…This is due to: (1) Continuity of service; (2) Minimized productivity impact with the scheduled system downtime; and (3) Improved safety concerns: elimination of arc flash hazards with phase to ground faults, suppression of transient line to ground over-voltages, and equipment damage reduction at the point of ground fault [1][2][3][4].…”

“…However, most of HRG GFI methods and papers focus on system level detection, such as generators, substations, power distribution panels, and so on [1][2][3][4][6][7][8]. Different methods must be combined in order to find the location of the fault.…”

“…As a result, National Electric Code (NEC) mandates the use of ground fault indicators when a ground fault occurs. References [1][2][3][4][6][7][8] discuss various Ground Fault Identification (GFI) methods in HRG systems.…”