Full resolution (JPEG) - On this page / på denna sida - 1958, H. 7 - The Quarter-Wave Dipole, by Bengt Josephson - The Military Electronics Laboratory of Sweden, by T Gussing - Reduced Insulation Level for the New Swedish 380 kV Stations and Lines, by S G
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Fig. IS. Measured impedances of a cylindrical unipole with
the height ’i50 mm and the diameter .3.5 mm.
■– 2 times the impedance when base driven.
.....impedance when driven at mid height.
In figure 18 the solid curve is two times the
measured impedance of a base driven unipole of height
450 mm and diameter 3.5 mm. The dashed curve
shows the measured impedance of the same unipole
driven at mid height. Although end effects may cause
noticeable error, the agreement with formula (29)
is quite good within a considerable frequency range
at the low-frequency side.
It is clear that even in the case where the unipole
is not driven exactly at the mid point this method of
impedance calculation may be applied using the
above mentioned formula of Zuhrt for the
calculation of Zoc in equation (27).
Acknowledgement
The work described has been carried out at the
Research Institute of National Defence, Stockholm.
The permission to publish the paper is greatly
appreciated.
References
1. IIallkn E: Admittance Diagrams for Antennas and the Relation
betiueen Antenna Theories. Technical Report No 46, Cruft
Laboratory, Harvard University.
2. Brown G tl, Woodward O M: Experimentally Determined
Impedance Characteristics of Cylindrical Antennas. PIRE, April 1915.
3. Williams II P: Antenna Theory and Design, Vol II.
4. Hallhn’ E: Traveling Waves and Unsymmetrically fed Antennas.
Technical Report No 49, Cruft Laboratory, Harvard University.
5. Zuhrt II: Elektromagnetische Strahlungsfelder. Springer-Verlag
1953.
The Military Electronics Laboratory of Sweden
The Military Electronics Laboratory (Försvarets
Teletekniska Laboratorium, FTL) is organized as a subdivision of
The Research Institute of National Defence (Försvarets
Forskningsanstalt, FOA) with the purpose to serve as
a centre for type testing and standardization of electronic
components and materials, used by the Swedish Defence
Forces. The planning of the Laboratory’s work is directed
by a commission with delegates from the Air Force, the
Army and the Navy.
The well-known, evergrowing complexity of military
electronic equipment, and the simultaneous demand for
higher reliability, means that the performance of
components and materials under severe environmental and
electrical conditions must be studied in detail and for
prolonged periods of time. Such studies are one of the main
objects of the work at FTL.
To furnish manufacturers, etc. of electronic equipment
with information of current interest concerning
components, FTL acts as a "clearing cèntre". This is
accomplished by collecting test reports, etc. from testing
laboratories throughout the country and — after some editorial
work —■ by distributing this information to the
manufacturers, etc. concerned. It is hoped that this information
will save time and money by avoiding unnecessary testing
and result in more reliable electronic equipments by
selecting tested and approved components.
Finally, FTL works out specifications and test procedures
for electronic components and materials. There is a close
cooperation within the standardization sphere between FTL
and the Swedish Electrotechnical Commission (SEK) and
thus also with the IEC, and the recommendations by the
1EG are followed wherever possible. Swedish Military
Standards are, eventually, published by the Military
Standardization Commission (FSD). T Gassing
Reduced Insulation Level for the New Swedish
»80 kV Stations and Lines
It has become possible to reduce the insulation level
since the shortcircuit power in the network has increased,
non-restriking circuit breakers are available and the
properties of the lightning arresters have been improved.
The first power lines were equipped with 20 insulator
units with 170 mm spacing in standard strings. Later the
number of units was reduced to 19. Lines with lengths
of less than 550 km shall from now be equipped with 17
insulators with 170 mm spacing or the nearest of another
type. The maximum operating voltage is assumed to be
420 kV. According to SEN 2107 this new standard
corresponds to a one-minute withstand voltage in rain of 640
kV RMS and a surge withstand voltage in rain of 1 275 kV,
which during dry conditions corresponds to about 1 425
kV.
The maximum voltage rise of operating frequency at the
open line terminal has for a line length of 530 km been
calculated to 560 kV RMS, therefore non-restriking circuit
breakers must be employed for the lines.
The lightning fault frequency will increase with about
25 °/o to 0.18 faults per 100 km and year. As compared
with the most recently constructed 380 kV lines a saving
of £ 100 per km is effected.
An insulation level of 1 775 was chosen for the first
380 kV stations. Even at an early stage it was found that
the insulation level could be reduced to 1 500 for
transformers and switchgear. For apparatus at the line
terminals, the level of 1 775 was retained. More recently the
level of 1 675 has begun to be adopted. In all these cases
dry and wet surge tests were required.
From now transformers and cables are constructed in
accordance with insulation class 1 425 and only dry surge
tests are to be made. The transformer lead-in ducts and
cable bushings as well as the switchgear are designed for
insulation class 1 550. The one-minute withstand voltage
is 630 kV RMS and 680 kV RMS respectively (G Jancke,
Swedish State Power Roard. SV 906, 1958). S G
1 102 ELTEKN I K 1958
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