Thesis (PhD)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Square Kilometre Array (SKA) and its demonstrator MeerKAT are being designed to operate over
a wide frequency range and are expected to achieve greater sensitivity and resolution than existing
telescopes. The radio astronomy community is well aware of the negative impact that radio frequency
interference (RFI) has on observations in the proposed frequency band. This is because weak radio
signals such as those from pulsars and distant galaxies are difficult to detect on their own. The presence
of RFI sources in the telescope’s operating area can severely corrupt observation data, leading to
inaccurate or misleading results.
Power-line interference and radiation from electric fences are examples of RFI sources. Mitigation
techniques for these interference sources in the SKA system’s electromagnetic environment are
essential to ensure the success of this project. These techniques can be achieved with appropriate
understanding of the characteristics of the noise sources. Overhead power-line interference is known to
be caused mainly by corona and gap-type (commonly known as sparking noise) discharges. Sparking
noise is the dominant interference for the SKA. It is mainly encountered on wooden pole lines, which
are usually distribution lines operated at up to 66 kV AC in the South African network. At this voltage
level, the voltage gradients on the lines are insufficient to generate conductor corona. The power
requirements for SKA precursors will be below this voltage level.
The aim of the research in this dissertation is to evaluate the power line sparking characteristics
through measurements and simulation of line radiation and propagation characteristics. An artificially
made sparking noise generator, which is mounted on a power line, is used as noise source and the
radiation characteristics are measured. Measurements were carried out in different environments,
which included a high-voltage laboratory (HV-Lab), a 40m test-line, and another 22-kV test line of
approximately 1.5 km. The key sparking noise parameters of interest were the temporal and spectral
characteristics. The time domain features considered were the pulse shape and the repetition rate. The
lateral, longitudinal and height attenuation profiles were also quantified. Since sparking noise current pulses are injected or induced onto power line conductors, the line will
act as an unintentional antenna. The far-field radiation characteristics of the line were evaluated
through measurements on physical scale-model structures and simulations. 1/120th and 1/200th scaled
lines, using an absorbing material and metallic ground planes, respectively, were simulated in FEKO.
The measurements of the constructed scale models were taken in the anechoic chamber. Both
measurements and simulations showed that the line exhibits an end-fire antenna pattern mode. Line
length, pulse injection point and line configuration were some of the parameters found to affect the
radiation patterns.
The findings from this study are used to determine techniques to identify the sparking noise, and locate
and correct the sources when they occur on the line hardware. Appropriate equipment is recommended
to be used for the location and correction of sparking noise. / AFRIKAANSE OPSOMMING: Die Vierkante Kilometer Reeks (SKA) en sy demonstrasie projek, die Karoo Reeks Teleskoop (KAT),
word ontwerp om oor 'n wye frekwensie-bereik te funksioneer. Beide sal na verwagting beter
sensitiwiteit en resolusie as bestaande radioteleskope he. Die radio-astronomie-gemeenskap is deeglik
bewus van die negatiewe impak wat radio-frekwensie steurnisse (RFS) op waarnemings in die
voorgestelde frekwensieband het. Die rede hiervoor is dat swak radio-seine soos die van pulsars en
verafgelee sterrestelsels inherent moeilik is om te bepaal. Die teenwoordigheid van RFS bronne in die
teleskoop se onmiddellike operasionele gebied kan waarnemings nadelig beinvloed. Dit lei uiteindelik
tot onakkurate of misleidende resultate.
Kraglyne en uitstralings van elektriese heinings is voorbeelde van RFS bronne. Metodes om die
oorsake van die steurnisse van die SKA se elektromagnetiese omgewing te verminder is noodsaaklik
om die sukses van hierdie projekt te verseker. Dit vereis egter deeglike begrip van die eienskappe van
hierdie bronne. Steurnisse as gevolg van oorhoofse kraglyne word hoofsaaklik veroorsaak deur
korona en gapingtipe ontladings (algemeen bekend as vonkontladings). Vonkontladings word hier
beskou as die belangrikste oorsaak van steurnisse vir die SKA. Dit word in die Suid-Afrikaanse
netwerk hoofsaaklik aangetref op houtpaal-installasies, wat gewoonlik bestaan uit distribusie lyne
wat tot en met 66 kV wisselstroom (WS) bedryf word. By hierdie operasionele spanning is die
spanningsgradient op die lyn onvoldoende om korona op te wek. Die kragvereistes vir die SKA se
voorafgaande projekte sal sodanig wees dat hierdie spanningsvlak nie oorskry sal word nie.
Die doel van die navorsing omskryf in hierdie proefskrif is om die eienskappe van vonkontladings
rondom kraglyne te evalueer. Dit word gedoen met behulp van metings en simulasies van
uitstralings- en voortplantingspatrone wat met 'n spesifieke lyn geassosieer kan word. 'n Kunsmatige
vonkontladingsopwekker word op 'n kraglyn geplaas en dien as bron om die uitstralingspatrone te
meet. Metings is uitgevoer in verskillende omgewings, insluitende 'n hoogspanningslaboratorium
(HV-Lab), 'n 40 m toetslyn en 'n 22 kV WS toetslyn van ongeveer 1.5 km lank. Die hoof
vonkontladings eienskappe van belang is die temporale en spektrale eienskappe. Die tydgebiedeienskappe
wat ondersoek is, is die pulsvorm asook die pulsherhalingskoers. Die laterale,
longitudinale en hoogte-attenuasie profiele word ook gekwantifiseer. Aangesien stroompulse deur vonkontladings op die kraglyn geplaas of geinduseer word, sal die lyn as
'n ongewenste antenna optree. Die ver-veld uitstralingskenmerke van die lyn is ook geëvalueer deur
gebruik te maak van fisiese skaalmodelstrukture en -simulasies. 1/120ste en 1/200ste geskaleerde
lynmodelle, wat onderskeidelik 'n absorberende- en metaalgrondvlak bevat, was gebruik om 'n 3
spanlengte kraglyn te simuleer met behulp van FEKO. Metings van die fisiese skaalmodel strukture is
in 'n anegoise kamer geneem. Beide die metings en die simulasies toon dat die lyn 'n endpunt
uitstralingspatroon het. Lynlengte, die opwekkingsposisie van die stroompuls en die lynkonfigurasie
is 'n paar van die parameters wat die uitstralingpatroon beïnvloed, soos in die navorsing aangedui.
Die bevindinge van hierdie studie word gebruik om steurnisse as gevolg van vonkontladings op die
kraglyn te identifiseer, op te spoor en uiteindelik reg te stel. Toepaslike toerusting word voorgestel
wat gebruik kan word vir die identifisering en opsporing van vonkontladings.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17970 |
| Date | 12 1900 |
| Creators | Langat, Philip Kibet |
| Contributors | Reader, H. C., University of Stellenbosch. Faculty of Engineering. Dept of Electrical & Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 157 p. : ill. |
| Rights | Stellenbosch University |
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