A 230-Kv Spar-Arm H-Frame Transmission-Line Design and Tests

1. The decision to use all spar-member construction for a 230-kv wood-pole H-frame line was based on 16 years of satisfactory service from 115-and 138-kv lines with spar arms. 2. The use of 12 insulators for suspension strings results in a co-ordinated design with liberal margin for switching surges and a low lightning outage probability. 3. All spar-member construction permits application of hardware which facilitates structure assembly with a minimum of field drilling. 4. Tests on full-size structures show they have a safety factor of more than 4½ times maximum design transverse loading. 5. Tests confirm earlier findings of others that crushed-rock backfill for poles holes is an effective way to increase resistance to uplift on poles. 6. Highly mechanized line-construction operations result in time and cost savings.