Re: earth impedance
Karl, as I don't have more information than I can put in a single message, I think my answer can stay within this thread.
Yes, that's very high although it's the average at street level. It's lower in the houses. All distribution in Stockholm is underground with the cables run under the pavements.
The report (Swedish only) can be found at
http://www.elforsk.se/publish/show_report.phtml?id=311
The abstract in my translation. My comments in []brackets.
"The magnetic field from [electric] cable networks i Stockholm has been measured one meter above ground along 104 km of pavement. The instrument used has range and accuracy as follows:
Range: 0.05 microTesla - 100 microTesla
Frequency: 30 Hz - 2 kHz (-3 dB)
Accuracy: ?10 % of presented value ? 0.05 microTesla
For the central parts of the city the average is 0.39 microTesla and 66% of the readings are above 0.2 microTesla. The magnetic field is lower in the suburban areas, with an average of 0.19 microTesla and 33,2% of the readings above 0,2 microTesla. In the majority of the streets in the central parts of the city, magnetic fields between 1.0 and 2.5 microTesla have been recorded. In some extreme cases 6-7 microTesla have been recorded.
The strenght of the the magnetic field increases and decreases constantly in jumps, usually in the magnitude of ?0,30 microTesla to ?0,60 microTesla. The duration of each jump varies randomly between two seconds and 20 seconds.
The strength of the magnetic field is not necessarily load dependent but also connected to the degree of superimposition of single phase loads. [I don't quite follow that in part Swedish]
The observations indicate that the magnetic field can attributed to net currents and that the fields therefore decrease inversly proportional to the distance to the cable."
{Edited to correct mistranslation in last phrase concerning the net currents. Mea culpa.}
[ December 07, 2003, 01:10 PM: Message edited by: c-h ]
Karl, as I don't have more information than I can put in a single message, I think my answer can stay within this thread.
Yes, that's very high although it's the average at street level. It's lower in the houses. All distribution in Stockholm is underground with the cables run under the pavements.
The report (Swedish only) can be found at
http://www.elforsk.se/publish/show_report.phtml?id=311
The abstract in my translation. My comments in []brackets.
"The magnetic field from [electric] cable networks i Stockholm has been measured one meter above ground along 104 km of pavement. The instrument used has range and accuracy as follows:
Range: 0.05 microTesla - 100 microTesla
Frequency: 30 Hz - 2 kHz (-3 dB)
Accuracy: ?10 % of presented value ? 0.05 microTesla
For the central parts of the city the average is 0.39 microTesla and 66% of the readings are above 0.2 microTesla. The magnetic field is lower in the suburban areas, with an average of 0.19 microTesla and 33,2% of the readings above 0,2 microTesla. In the majority of the streets in the central parts of the city, magnetic fields between 1.0 and 2.5 microTesla have been recorded. In some extreme cases 6-7 microTesla have been recorded.
The strenght of the the magnetic field increases and decreases constantly in jumps, usually in the magnitude of ?0,30 microTesla to ?0,60 microTesla. The duration of each jump varies randomly between two seconds and 20 seconds.
The strength of the magnetic field is not necessarily load dependent but also connected to the degree of superimposition of single phase loads. [I don't quite follow that in part Swedish]
The observations indicate that the magnetic field can attributed to net currents and that the fields therefore decrease inversly proportional to the distance to the cable."
{Edited to correct mistranslation in last phrase concerning the net currents. Mea culpa.}
[ December 07, 2003, 01:10 PM: Message edited by: c-h ]
