132 kV

thumbnail photo of 132 kV pylon     thumbnail photo of 132 kV wood pole

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.

Magnetic field

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.

graph of maximum field 132 kV

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).

 graph of typical fields 132 kV

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

 

magnetic field in µT at distance from centreline

maximum under line10 m25 m50 m100 m
132 kVlargest lines

L7

twin bundles

0.305 m

lynx

maximumclearance 7 m
phasing U
load 1.4/1.4 kA
30.44520.5325.5531.5280.392
typicalclearance 10 m
phasing U
load 0.13/0.13
1.8481.3590.4680.1380.036
smaller lines

L132

single conductors

0.4 sq in

maximumclearance 7 m
phasing U
load 1.2/1.2 kA
24.58517.2174.5871.2470.318
typicalclearance 10 m
phasing U
load 0.13/0.13 kA
1.7311.3170.4510.1320.034
smallest wood-pole design

trident

150 m span

single conductors

lynx

maximumclearance 7 m
single circuit
load 0.7 kA
12.3473.6330.7380.1920.048
typicalclearance 10 m
single circuit
load 0.1 kA
1.7640.3850.0990.0270.007

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.

Electric field

The maximum field is produced by the largest design of line – the L7 – when the ground clearance is the minimum allowed – 7.0 m.  The field also depends on the phasing. 132 kV lines usually have Untransposed (U) phasing.

graph of maximum field 132 kV 

Typical fields are lower than the maximum field because the clearance is usually higher.  The three curves shown here are for 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).

graph of typical field 132 kV 

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

132 kV

largest lines

L7

twin bundles

0.305 m

lynx

maximum

clearance 7 m
phasing U

3615

913

182

81

23

typical

clearance 10 m
phasing U

2372

890

103

72

23

smaller lines

L132

single conductors

0.4 sq in

maximum

clearance 7 m
phasing U

2628

697

154

66

19

typical

clearance 10 m
phasing U

1780

689

86

59

18

smallest wood-pole design

trident

150 m span

single conductors

lynx

maximum

clearance 7 m
single circuit

1174

588

73

11

2

typical

clearance 10 m
single circuit

583

458

89

15

3

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

Underground cables

Two main types of 132 kV underground cable are used.

  • separate cores: the three conductors for the three phases are laid separately but close together in the ground, typically 1 m deep
  • single cable: the three cores are twisted round each other in a single outer sheath. 

With a single cable, because the cores are so close together and twisted, the fields they produce directly are very small.  Instead, the field comes from any net current in the sheath.  This cannot be predicted accurately.

The following graph shows typical fields for these two types of cable (separate cores produce higher fields close to the cable but lower fields away from it).

graph of typical field 132 kV underground 

Underground cables do not produce any external electric fields.

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

    

magnetic field in µT at distance from centreline

0 m

5 m

10 m

20 m

132 kV

separate cores (flat formation)

0.3 m spacing

1 m depth

typical

9.62

1.31

0.36

0.09

single cable

1 m depth

typical

5.01

1.78

0.94

0.47

Notes

1. All fields calculated at 1 m above ground level

2. All fields are given to the same resolution for simplicity of presentation (0.01 µT = 10 nT) but are not accurate to better than a few percent.

3. Calculations for separate cores 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.

4. Cable designs are not standardised to the same extent as overhead lines and the examples given here are representative.

5. In practice, there are often several cables nearby, and the fields interact with each other.