Limitations of the ruling span method for overhead line conductors at highoperating temperatures

This report summarises the work by the Task Force to review the accuracy of the ruling span method for conductors operated at high temperatures. The b asics of the ruling span approximation method have been examined. The tradi tional ruling span approach can be used with little or no error for a typic al overhead line crossing a rolling terrain to predict sags in suspension s pans for conductor operating temperatures in the range of 50 degrees C to 7 0 degrees C. Sensitivity studies were performed using conductors "Lapwing" and "Tern" in order to quantify such ruling span assumptions as the effect of the longitudinal swing of suspension and line post insulators on conduct or sags at high temperatures, and the effect of the suspension insulator st ring length on the equalization of conductor tensions in adjacent spans. Si gnificant errors in estimating the sag at conductor temperature above 100 d egrees C may occur if the tension differences are not taken into considerat ion in line sections consisting of a series of spans of non-equal lengths. It was confirmed that the ruling span method is the most practical way to s tring conductors in multi-span line sections.