33 kV overhead lines: electric fields

33 kV lines are either carried on small lattice steel pylons or on wood poles.  There are many different variants of lines design but they all produce roughly similar fields.

The maximum field shown here is produced by a lattice pylon design when the ground clearance is the minimum allowed – 5.5 m.  The field also depends on the phasing. 33 kV lines usually have Untransposed (U) phasing.

graph showing maximum field

Typical fields are lower than the maximum field because the clearance is usually higher.  The two curves shown here are for normal U phasing and two different line designs: a lattice steel pylon (the higher field), and a wood-pole design (the lower field).

graph showing typical field

33 kV double-circuit line: 33 single-circuit wood pole:
photo of 33 kV wood pole line photo of 33 kV wood pole line

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

         

electric field in V m-1 at distance from centreline

maximum under line

10 m

25 m

50 m

100 m

33 kV

larger lines on steel pylons

D
single conductors
r=9.8 mm

maximum

clearance 5.5 m
phasing U

897

46

30

10

3

typical

clearance 8 m
phasing U

543

81

21

9

3

smaller lines on wood poles

wood pole
horizontal array
+-2 m

maximum

clearance 5.5 m
single circuit

505

165

16

2

0

typical

clearance 8 m
single circuit

241

147

21

3

0

Note:

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

2.        All electric fields are calculated for the nominal voltage.  In practice, voltages (and hence fields) may rise by a few percent.

3.        All electric fields calculated here are unperturbed values.

4.        All fields are given to the same resolution for simplicity of presentation (1 V/m) but are not accurate to better than a few percent.

5.        Calculations ignore zero-sequence voltages.  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.

6.        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.

7.        Sometimes, a 33 kV circuit could be carried on a line designed for a higher voltage.  Then the electric fields could be larger than shown here.

For comparison of fields from different voltage lines click here:

link to page of comparisons

For more fields at this voltage and fields at other specific voltages see this index:

link to page of specific power lines