Fault Detection for Aircraft Power Systems using the Impedance at Third Harmonic Frequency

A novel fault identification and location scheme designed for small distribution systems as found on aircraft is presented. Under normal operating conditions, the aircraft power supply contains only a low level of triplen harmonics, resulting from slight mismatches in the distribution of single phase nonlinear loads across the three phases. When cable faults occur, the change of conduction modes of components such as rectifiers will result in the increase in the level of triplen harmonics. The resistance of the short-circuit contact and the fault location will greatly effect the distribution of harmonics over three phases within the system, especially for triplen harmonics. This presents an opportunity to identify the fault location as a function of the estimated impedance at triplen harmonic frequencies. In this work, a line-line impedance is defined to estimate fault location. Simulation studies show that the impedance can be used to help locate short circuit cabling faults.