Methods to Determine Overhead Ground Wire Sizes in Distribution Systems

Abstract

This paper presents an approach to analyze the overhead ground wire (OHGW) sizes in distribution system focus on the i2t of line to ground fault current. For line to ground fault, the fault current and duration time when fault take place as well as the relay operating time have been concerned. The Line Type 1, OHGW not connected to the neutral of substation power transformer, give the short circuit current magnitude which is less than the current from Line Type 2, OHGW connected to the neutral of substaion power transformer. So the Line Type 1 gives the smaller OHGW sizes than Line Type 2. To find the suitable OHGW sizes, the fault current magnitude, the duration time when fault take place and the relay operating time have to be considered. For the short circuit current is not greater than 3 kA, the 25 mm2 can be used. For the short circuit current is not greater than 7 kA, the 35 mm2 should be used for distance of 500 m from the substation, 25 mm2 for line beyond that location should be used. For the short circuit current is not greater than 12 kA, the 50 mm2 should be used for 500 m from substation, 35 mm2 should be used between 500 m-3 km and 25 mm2 for line beyond that location should be used.