We discuss above the effect of the clearance of the conductors above ground on the electric field. The higher the clearance, the lower the field. Because the electric field exposure limit for the general public in populated areas in the UK is 9 kV/m, we list here the clearances required for the field to be below 9 kV/m. If the clearance is greater than the stated value, the electric field will be below 9 kV/m.
The field depends on several factors as shown in the table: the tower design, the conductor bundle, and the phasing (transposed, T, or untransposed, U - other phasings lie between these values).
Clearance to achieve 9Kv/m
| |||||
Line Voltage | Tower | Conductor System | Horizontal Bundle Spacing | T | U |
275/400kV | L2 | 2 x 400 ACSR | 400mm
| 7.3m | 8.5m |
L2/1 | 2 x 500 ACAR | 7.4m | 8.6m | ||
L2/2 | 2 x 500 AAAC | 7.4m | 8.6m | ||
L2/3 | 2 x 425 AAAC | 7.4m | 8.5m | ||
L2/4 | 2 x 570 AAAC | 7.4m | 8.6m | ||
L2/6 | 2 x 620 GTZACSR | 7.4m | 8.6m | ||
L2/7 | 2 x 591 ACC | 7.4m | 8.6m | ||
L2/8 | 2 x 780 ACC | 7.4m | 8.6m | ||
275kV | L3 | 2 x 175 ACSR |
| * | * |
L3/1 | 1 x 700 AAAC |
| * | * | |
L3/2 | 2 x 300 AAAC | 300mm
| * | * | |
275kV | L34 | 2 x 175 ACSR |
| * | * |
132kV | L4(M) | 1 x 175 ACSR |
| * | * |
275/400kV | L6 | 4 x 400 ACSR | 500mm | 8.9m | 9.9m |
L6/1 | 2 x 400 ACSR | 400mm
| 7.8m | 8.3m | |
L6/2 | 2 x 700 AAAC | 500mm | 8.0m | 8.6m | |
L6/3 | 2 x 500 AAAC | 400mm | 7.8m | 8.3m | |
L6/4 | 2 x 850 AAAC | 550mm | 8.1m | 8.8m | |
L6/5 | 3 x 700 AAAC | 500mm | 8.5m | 9.3m | |
L6/6 | 2 x 570 AAAC | 400mm
| 7.8m | 8.4m | |
275kV | L66 | 2 x 175 ACSR | 300mm
| * | * |
L66/1 | 1 x 700 AAAC | * | * | ||
L66/2 | 2 x 300 AAAC | * | * | ||
132kV | L7(C)/1 | 1 x 400 ACSR | 300mm | * | * |
L7(C)/2 | 2 x 400 ACSR | * | * | ||
275/400kV | L8 | 2 x 400 ACSR | 400mm | 7.5m | 8.4m |
L8/1 | 2 x 500 ACAR | 7.5m | 8.5m | ||
L8/2 | 2 x 500 AAAC | 7.5m | 8.5m | ||
L8/3 | 2 x 425 AAAC | 7.5m | 8.4m | ||
L8/4 | 2 x 570 AAAC | 7.6m | 8.5m | ||
L8/6 | 2 x 620 GTZACSR | 7.5m | 8.5m | ||
L8/7 | 2 x 591 ACC | 7.5m | 8.6m | ||
L8/8 | 2 x 780 ACC | 7.6m | 8.5m | ||
L9 | 4 x 400 ACSR | 500mm | 8.0m | 8.9m | |
L12 | 2 x 700 AAAC | 7.8m | 8.8m | ||
L12/1 | 2 x 850 AAAC | 550mm | 8.0m | 8.9m | |
L13 | 3 x 700 AAAC | 500mm | 8.4m | 9.3m |
* Minimum clearance to ground will apply