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A Novel Approach for Ground Fault Detection

Ratan Das Steven A. Kunsman
ABB Inc.
7036 Snowdrift Road
Allentown, PA, 18106, USA
E-mail: [email protected]
Introduction However, a small percentage of the ground faults
Electric power systems have grown rapidly over the have very large impedance, often comparable to load
past fifty years. This has resulted in a large increase of impedance, and consequently has very little fault com-
the number of lines in operation and their total length. ponent of current. Although, these high impedance
These lines experience faults which are caused by faults do not create imminent danger to power sys-
storms, lightning, snow, freezing rain, insulation break- tem equipment, but they are a considerable threat to
down and, short circuits caused by birds and other ex- humans and properties. The IEEE Power System Relay
ternal objects. In most cases, electrical faults manifest Committee working group on High Impedance Fault
in mechanical damage which must be repaired before Detection Technology [1] defines High Impedance
returning the line to service. Faults are those that ‘do not produce enough fault
A vast majority of these faults are ground faults. Con- current to be detectable by conventional overcurrent
ventional protection system based on overcurrent, relays or fuses’.
impedance or other principles is suitable for detecting High impedance faults result when an energized pri-
relatively low impedance faults which has relatively mary conductor comes in contact with a quasi-insulat-
large fault current. These conventional methods are ing object, such as a tree, a structure or equipment, a
used with success for a long time to detect such low pole crossarm, or falls to the ground. Typically, a high
impedance faults and take necessary action to isolate impedance fault exhibits arcing and flashing at the
the faulted section of the system. point of contact.

Industry Journal 3