Detection and location of single cable fault by impedance spectroscopy

Abstract

Time-Domain Reflectometry (TDR) and Frequency-Domain Reflectometry (FDR) are typical methods for cable fault location. Because the TDR method has the worse signal-to-noise ratio (SNR), it is difficult to detect soft cable faults (frays, chafes, and joints) which cause tiny impedance changes in the cable and small reflected signals. The FDR method has better SNR than the TDR method because of using a power signal as incident signals and signal processing for cable fault location. However it is difficult to identify the type of cable fault. A new method using impedance spectroscopy (IS) for cable fault location is described in this paper. With the new method not only cable fault can be located, but also the type of cable fault can be identified. The periods of cable's impedance can locate hard (open and short circuits) and soft wire faults (frays, chafes and joints). The angle of the cable's impedance in low frequency domain can identify the types of the faults. A signal processing algorithm is developed to accurately locate the cable fault and provide enhanced resolution and range. The details and test results with IS system on realistic twisted pair lines are described. Only one single fault is detected in this work.