Application experience with 69 kV steel utility poles

Abstract

In 1997, a 69 kV single pole power line was designed and built by Dawson Public Power District in Central Nebraska using steel poles instead of wood. The power line is 9 miles in length and connects rural distribution substations. The construction also allowed for a voltage upgrade from 34.5 kV to 69 kV. The steel alternative to wood was initially considered as a means of extending the life of conventional southern yellow pine (SYP) poles. A closer examination of the physical characteristics revealed advantages in overall strength, buckling, and bending. The steel poles consisted of galvanized tubular steel, classes 1, 2 and 3, and lengths from 55 ft to 70 ft. The 2 piece tapered poles are slip fit (overlap approx. 24-in) together above ground line. The 12.5 kV underbuild utilizes fiberglass cross arms and standoffs. Conventional pole bands were replaced with guying tees, thimble eyes and eye bolts for both overhead and down guys respectively. The steel pole eliminated the need for the normal TM-9X shield wire ground and reduced framing labor and material cost. The overall result was a stronger and lower initial cost power line. The minimal inconvenience of setting a 2-piece pole was more than offset by the labor saved in transporting and framing. During 1998 grounding tests were conducted on steel poles with and without ground rods. These tests revealed that the steel poles were effectively grounded whether with or without a parallel ground rod. Rock fill around the poles in place of soil did not greatly reduce the grounding resistance to earth.