Tower Top Geometry and Mid Span Clearances

For a line the dimensions of the tower top are determined by phase-to-earth and phase-to-phase clearances. The position of conductors and earth wire at tower and the sag at mid span change with climatic conditions. Practices of several countries are compared. The study results in the proposal to consider "still air" and "high wind" cases to withstand respectively overvoltages and power frequency voltages.