132 kV overhead lines: magnetic fields

132 kV overhead lines are usually carried on lattice steel pylons, but smaller than used for 275 kV and 400 kV lines.  Sometimes they are carried on wood poles.

The maximum field is produced by the largest design of line – the L7 – when the ground clearance is the minimum allowed – 7.0 m – and the loads are the highest allowed – 1.4 kA in each circuit.  The field also depends on the phasing. 132 kV lines usually have Untransposed (U) phasing.

Typical fields are lower than the maximum field because the clearance is usually higher and the loads are usually lower.  The three curves shown here are for typical loads, the normal U phasing, and three different line designs: L7 (the highest), a smaller pylon design, the L132, and a wood-pole design (the lowest field).

132 kV pylon:	132 kV wood pole:

This table gives some actual field values for the same conditions.

Note:

1. All fields calculated at 1 m above ground level.

2. All fields are given to the same resolution for simplicity of presentation (1 nT = 0.001 µT) but are not accurate to better than a few percent.

3. Calculations ignore zero-sequence current.  This means values at larger distances are probably underestimates, but this is unlikely to amount to more than a few percent and less closer to the line.

4. The “maximum field under the line” is the largest field, which is not necessarily on the route centreline; it is often under one of the conductor bundles.

5. Sometimes, a 132 kV circuit could be carried on a line designed for 275 kV or 400 kV.  Then the magnetic fields could be larger than shown here.