A novel pseudonoise tester for transmission line fault location and identification using pseudorandom binary sequences

Abstract

A novel pulse echo test methodology, using PRBS excitation, is presented in this paper as an alternative to Time Domain Reflectometry (TDR) for transmission line fault location and identification. The essence of this scheme is the cross correlation (CCR) of the fault echo response with the input PRBS test perturbation which results in a unique signature for fault type identification, if any, or load termination present as well as its distance from the point of test stimulus injection. This fault location technique can used in a number of key industrial applications incorporating printed circuit boards, overhead transmission lines and underground cables in inaccessible locations which rely on a metallic conductor pathway for power transfer or signal propagation. As an improved method pseudonoise (PN) fault identification can be performed over several cycles at low amplitude levels online to reject normal signal traffic and extraneous noise pickup for the purpose of fault coverage location and identification. In this paper a high frequency co-axial transmission line model is presented for transmission line behavioural simulation with pseudorandom binary sequence (PRBS) stimulus injection under known load terminations to mimic fault conditions encountered in practice for proof of concept. Simulation results, for known resistive fault terminations, with measured CCR response demonstrate the effectiveness of the PRBS test method in fault type identification and location. Key experimental test results are also presented for a co-axial cable, under laboratory controlled conditions, which substantiates the accuracy of PRBS-CCR diagnostic method of fault recognition and location using a range of resistive fault terminations. Results demonstrating the effectiveness of multiple PN cycle correlation with inherent transmission link noise rejection, which accentuates the peak fault CCR-to-noise ratio, for improved echo response resolution along with a theoretical analysis for same are also presented. The accuracy of the method is further validated through theoretical calculations via known co-axial cable parameters, fault resistance terminations and link distances in transmission line experimental testing. Derived quantities from experimental testing such as estimated reflection coefficients, fault termination resistances and VSWR, which are in close agreement with theoretical considerations, demonstrate the accuracy of and further enhance confidence in the PN test method.