Locating faults in boundary wires for autonomous lawn mowers : An investigative study on methods used to locate faults in underground, low-voltage cables with focus on implementing Time Domain Reflectometer (TDR)

Abstract: Purpose:The purpose of this thesis was to identify a useful solution to find the location of a broken boundary wire. By useful we mean that the solution should be inexpensive, user friendly and accurate. However, this thesis will only investigate the accuracy of the method where the hypothesis is that an investigated method is applicable for all underground wires. Method:This study conducted a literature research in order to investigate what methods that are used in other industries to locate faults in underground, low-voltage electrical wires. After the research, the most commonly used fault locating methods were described and the one that seemed most useful was chosen as a possible solution.For the solution to be useful the accuracy was investigated. The method used to conduct an experiment and gather data to validate the solution was Design Science Research. Result:Three methods were investigated as possible solutions:Time Domain Reflectometry (TDR), Frequency Domain Reflectometry (FDR) and Murray bridge where experiments were conducted using TDR.TDR proved to be unapplicable in locating faults in boundary wires, although it was confirmed to be a valid solution to locate faults in coaxial cables with <1% error margin.What makes TDR and other reflectometry methods unsuitable methods within the autonomous lawn mower industry is the lack of characteristic impedance in the used boundary wires. The hypothesis that an investigated method is applicable for all underground wires is thereby refuted. Limitations:Experiments were conducted in laboratory environment with a signal generator and an oscilloscope. One experiment was conducted on a boundary wire in the ground which provided no reflected signal.