400 V and 230 V refer to the same lines - 400 V is the designation when it is three phase, 230 V when it is single phase (more on single phase and three phase). These voltages used to be 415 V and 240 V but were reduced to harmonise with Europe.
400 V lines are mostly carried on wood poles with four (or sometimes five) wires in a vertical array, but sometimes the conductors are twisted together in a single "aerial bundled conductor" (abc).
Magnetic field
At 400 V, the magnetic field depends as much on the net current as on the load current.
The maximum field shown here is produced when the ground clearance is the minimum allowed – 5.5 m. The maximum loads assumed are 200 A load current and 10 A net current but higher values might exceptionally be found.
Typical fields are lower than the maximum field because the clearance is usually higher and the loads are usually lower. This graph is for 8 m clearance, load current 50 A and net current 5 A.
Sometimes, the separate conductors are insulated and twisted together, called “aerial bundled conductors” (abc). Then the fields are even lower. The load currents make no contribution to the magnetic field, which now comes solely from the net current:
Please note the fields depend on the current that is assumed. That is, of course, true for all power lines, but is particularly important for 400 V lines, where the currents can vary greatly.
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 | |||||
| 400 V | wood pole | vertical array 50 mm2 | maximum | clearance 5.5 m single circuit load 0.2 kA net 0.01 kA@90° | 1.227 | 0.277 | 0.088 | 0.041 | 0.020 |
| typical | clearance 8 m single circuit load 0.05 kA net 0.005 kA@90° | 0.215 | 0.099 | 0.041 | 0.020 | 0.010 | |||
| abc | typical | clearance 8 m single circuit net 0.005 kA | 0.143 | 0.082 | 0.039 | 0.020 | 0.010 | ||
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. Supplies to single houses could be carried on different arrangements of conductors which could produce different fields.
Electric field
400 V lines are mostly carried on wood poles with four (or sometimes five) wires in a vertical array. The bottom wire is an earth wire which screens the fields produced by the wires above it, making electric fields from 400 V lines very low.
The maximum field shown here is produced when the ground clearance is the minimum allowed – 5.5 m.
Typical fields are lower than the maximum field because the clearance is usually higher. This graph is for 8 m clearance.
Sometimes, the separate conductors are insulated and twisted together, called “aerial bundled conductors” (abc). Then the fields are even lower.
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 | |||||
400 V | wood pole | vertical array 50 mm2 | maximum | clearance 5.5 m | 1 | 1 | 0 | 0 | 0 |
typical | clearance 8 m | 0 | 0 | 0 | 0 | 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. Supplies to single houses could be carried on different arrangements of conductors which could produce different fields.
Underground cables
400 V underground cables are usually a single cable: the three cores are twisted round each other in a single outer sheath. 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 is very variable and cannot be predicted accurately. The average is about 4 A. more on net currents.
The following graph shows typical fields from the net current in a 400 V cable.
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 | ||||
400 V | single cable | 0.5 m depth | typical | 0.50 | 0.14 | 0.07 | 0.04 |
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. These calculations are for a single, isolated cable. This is rare in practice. Other nearby cables would modify the field.