Potential of interference to global-navigation systems from power-line discharges. : A study based on laboratory measurements and plasma simulation.

Sammanfattning

Repeated reports of power lines or power-line equipment interfering with GPS and telecommunications devices require the phenomenon to be investigated further. In this thesis, interferences from a spark are investigated through charge and plasma simulations carried out in COMSOL and with laboratory measurements of electric field levels and signal-to-noise measurements. The charge simulations started with a capacitive model. Then charges were introduced and allowed to accelerate between the two plates. A Fourier spectrum of the radiated electric field from the charges was solved. This was performed to see the effects different geometries will have on an interference source. For the second simulation part of the project, the capacitive and a model of an insulator bell were simulated. The two models were surrounded by a medium meant to represent nitrogen gas, which was allowed to ionize. From these models, a frequency spectrum was calculated. For the final part of the thesis, two lab tests were performed: an SNR measurement of GNSS signals and spectral analysis of the radiation from a spark in the 800 MHz to 6GHz region. The goal of the SNR test was to record the SNR of different GPS signals with and without an interfering spark and compare the difference between the two to see if the spark interfered significantly with the signals. The goal of the spectral analysis measurement was to determine if the spark radiates interferences in the frequency ranges that GPS utilizes. From the charge simulations, the local peak electric field levels during the DC simulation were higher than the AC counterpart. The bandwidth of the local peaks of DC was smaller than its respective AC simulations. The local peaks were shifted upwards or downwards in the frequency spectra when the number of charges increased or decreased respectively. The last phenomenon observed was that the peaks were higher when the gap was shortened than if the gap was wider with increased voltage to achieve the same electric field levels. During the plasma simulations, a small peak in the electric field levels was observed in the ranges of 40-80 MHz, with decaying levels above and below these frequency thresholds. This peak was present in both models simulated but had a higher magnitude in the insulator bell model compared to the capacitor model. During the lab SNR measurements, a small decrease was observed in SNR between the background levels and the levels with the interfering spark present. During the spectral analysis measurements, the highest difference at the frequencies GPS operates at was 15-25 dB between background levels when a spark was present between two insulator bells.