A novel pulse echo correlation tester for transmission line fault location and identification using pseudorandom binary sequences

摘要

A novel pulse echo test methodology, using a pseudorandom binary sequence (PRBS) stimulus, is presented as a competitive alternative to Time Domain Reflectometry (TDR) for transmission line fault tracing and identification. The essential attribute of this scheme is the fault response cross correlation (CCR) with the PRBS test input which results in a unique identification signature for fault distance estimation from the point of test sequence injection. This fault location strategy can used in a number of key industrial applications embracing printed circuit boards, overhead transmission links and underground cables in inaccessible locations which rely on a pathway for power dispatch or telecommunications. As an improved fault tracing technique PRBS injection can performed over several cycles online at low amplitude to reject normal signal traffic and extraneous noise pickup for the purpose of multiple fault pickup, resolution and identification. In this paper a high frequency (HF) co-axial transmission line model is presented, with PRBS injection under known load terminations, to simulate fault conditions encountered in practice for proof of concept. CCR response simulation, for typical fault scenarios, demonstrate the effectiveness of the PRBS test strategy in fault type identification and location. Essential experimental test results are presented for co-axial cable fault finding, under laboratory controlled conditions, which substantiates the accuracy of PRBS-CCR troubleshooting technique of fault identification and location using a range of resistive fault terminations. Fault finding accuracy is further enhanced through theoretical calculation using known co-axial cable parameters, fault resistance terminations and link distances in transmission line experimental testing. The anticipated effect of exponential decay of fault echo CCR response peak with link distance, due to the presence of a small but finite attenuation coefficient at HF, is also presented. Deri--ved 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 validate the PRBS test method.