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.
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).
This table gives some actual field values for the same conditions.
magnetic field in microtesla 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 load 1.4/1.4 kA | 30.445 | 20.532 | 5.553 | 1.528 | 0.392 |
| typical | clearance 10 m phasing U load 0.13/0.13 | 1.848 | 1.359 | 0.468 | 0.138 | 0.036 | |||
| smaller lines | L132 single conductors 0.4 sq in | maximum | clearance 7 m phasing U load 1.2/1.2 kA | 24.585 | 17.217 | 4.587 | 1.247 | 0.318 | |
| typical | clearance 10 m phasing U load 0.13/0.13 kA | 1.731 | 1.317 | 0.451 | 0.132 | 0.034 | |||
| smallest wood-pole design | trident 150 m span single conductors lynx | maximum | clearance 7 m single circuit load 0.7 kA | 12.347 | 3.633 | 0.738 | 0.192 | 0.048 | |
| typical | clearance 10 m single circuit load 0.1 kA | 1.764 | 0.385 | 0.099 | 0.027 | 0.007 | |||
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.
Magnetic fields - different types of line
132 kV lines come in various designs. We compare here the typical magnetic field from three different designs:
A double circuit lattice design - one circuit each side of the body
A single circuit lattice design - one circuit split either side of the body
A "trident" wood pole design - a single circuit
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.
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).
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 | 3615 | 913 | 182 | 81 | 23 |
typical | clearance 10 m | 2372 | 890 | 103 | 72 | 23 | |||
smaller lines | L132 single conductors 0.4 sq in | maximum | clearance 7 m | 2628 | 697 | 154 | 66 | 19 | |
typical | clearance 10 m | 1780 | 689 | 86 | 59 | 18 | |||
smallest wood-pole design | trident 150 m span single conductors lynx | maximum | clearance 7 m | 1174 | 588 | 73 | 11 | 2 | |
typical | clearance 10 m | 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).
Underground cables do not produce any external electric fields.
This table gives some actual field values for the same conditions.
magnetic field in microtesla 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.