Power-line sparking noise characterisation in the SKA environment

[摘要] ENGLISH ABSTRACT: The Square Kilometre Array (SKA) and its demonstrator MeerKAT are being designed to operate overa wide frequency range and are expected to achieve greater sensitivity and resolution than existingtelescopes. The radio astronomy community is well aware of the negative impact that radio frequencyinterference (RFI) has on observations in the proposed frequency band. This is because weak radiosignals such as those from pulsars and distant galaxies are difficult to detect on their own. The presenceof RFI sources in the telescope's operating area can severely corrupt observation data, leading toinaccurate or misleading results.Power-line interference and radiation from electric fences are examples of RFI sources. Mitigationtechniques for these interference sources in the SKA system's electromagnetic environment areessential to ensure the success of this project. These techniques can be achieved with appropriateunderstanding of the characteristics of the noise sources. Overhead power-line interference is known tobe caused mainly by corona and gap-type (commonly known as sparking noise) discharges. Sparkingnoise is the dominant interference for the SKA. It is mainly encountered on wooden pole lines, whichare usually distribution lines operated at up to 66 kV AC in the South African network. At this voltagelevel, the voltage gradients on the lines are insufficient to generate conductor corona. The powerrequirements for SKA precursors will be below this voltage level.The aim of the research in this dissertation is to evaluate the power line sparking characteristicsthrough measurements and simulation of line radiation and propagation characteristics. An artificiallymade sparking noise generator, which is mounted on a power line, is used as noise source and theradiation 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 ofapproximately 1.5 km. The key sparking noise parameters of interest were the temporal and spectralcharacteristics. The time domain features considered were the pulse shape and the repetition rate. Thelateral, longitudinal and height attenuation profiles were also quantified.Since sparking noise current pulses are injected or induced onto power line conductors, the line willact as an unintentional antenna. The far-field radiation characteristics of the line were evaluatedthrough measurements on physical scale-model structures and simulations. 1/120th and 1/200th scaledlines, 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. Bothmeasurements and simulations showed that the line exhibits an end-fire antenna pattern mode. Linelength, pulse injection point and line configuration were some of the parameters found to affect theradiation patterns.The findings from this study are used to determine techniques to identify the sparking noise, and locateand correct the sources when they occur on the line hardware. Appropriate equipment is recommendedto be used for the location and correction of sparking noise.

[发布机构] Stellenbosch University