Full resolution (JPEG) - On this page / på denna sida - Field Measurements of Lightning Currents, by Nils Hyltén-Cavallius and Åke Strömberg
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
Field Measurements of Lightning Currents
Nils Hyltén-Cavallius and Ake Strömberg, ASEA, Ludvika
Under en följd au år har Asea i samarbete med
Ingeniörsvetenskapsakademiens åskkommitté nr 3
mätt blixtströmmar med en helautomatisk apparatur
som samtidigt ger blixtens strömstyrka, halvvärdetid
och fronttid. Mätningarna har omfattat 1 125
mätpunktsår. Avsikten med mätningarna var
huvudsakligen att skaffa information om blixtströmmarnas
fronttider, eftersom litteraturuppgifterna om denna
parameter går mycket isär. En information om
fronttiden enbart är emellertid av föga värde och därför
har även blixtens strömstyrku och halvvärdetid
uppmätts. Det mätta materialet är naturligtvis inte
alltför omfattande men har dock möjliggjort viss
statistisk bearbetning. Fronttidens logaritmiska
medelvärde har visat sig vara ca 2 us men fronttider inom
(jmrådet 0,3—12 fis har registrerats.
Vid bedömningen av resultatet från fältmätningar
av de snabba förlopp det här gäller, är det av vikt,
att noggrant känna mätegenskaperna hos den
mätutrustning som användes. I artikeln ges därför en
ganska fullständig redogörelse härför.
In this article is given a summary of measurements
of lightning strokes to tall structures, mainly
chimneys. The amplitude, steepness and time above half
value of the currents have been measured by an
automatic device. The measurements altogether have
involved 1 125 station years (measuring stations
multiplied by measuring seasons).
The main purpose of the investigation was to
record front times or current steepnesses. The
logarithmic average of recorded front time has been
about 2 us but front times within the range of U.3—
12 as have been measured.
Introduction
During the years 1950—1958 Asea has, in
collaboration with Lightning Committee No. 3 of IVA
(The Swedish Academy of Engineering Sciences),
undertaken measurements of amplitude, steepness
and duration of lightning currents. The main
interest of this investigation was not so much the current
amplitudes which nowadays are fairly well known,
but rather the current steepnesses. Correct
information about this factor is of great practical
importance when calculating the risk for back-flashovers
to power lines but unfortunately the literature gives
rather divergent opinions regarding the steepness
and its dispersion range. For practical conclusions,
the information about the current steepness for a
certain discharge must be considered in combina-
621.317.31 : 551.594.221
tion with the current amplitude and sometimes also
its duration. Therefore measuring devices have been
used which measured all these three factors
simultaneously.
During the first years about 90 and later about 175
measuring devices were set up on the ground side
of lightning rods of tall structures, mainly
chimneys. This means totally 1 125 measuring stations
multiplied by measuring seasons (in the following
called "station-years").
The devices which were fully automatic were
mainly mounted in the Southern third of Sweden which
can be assumed to have about 10 thunderstorm days
per year. They were generally set up in May and
taken down at the end of September. Thereby the
main part of the lightning season was covered but
of course some strokes may have struck the
measuring stations at times where no equipment was
mounted. As the statistical influence on the result
from this factor can be assumed to be small, no
correction is made for this.
The measuring equipments were generally
mounted and dismounted by the owners of the chimneys
where the measurements were made, or by some
power company in their vicinity. It is a pleasant
Fig. 1. A fully automatic measuring device for recording
of amplitude, duration and steepness of lightning
strokes.
ELTEKNIK 1959 1 109
<< prev. page << föreg. sida << >> nästa sida >> next page >>
