Estimating and pinpointing partial discharge locations on shielded power cables: Parameter estimation and instrumentation

Date of Completion

January 1995


Engineering, Electronics and Electrical|Energy




Partial discharge is a well-recognized precursor of failure of extruded dielectric power cables. A field diagnostic instrument that is capable to locate and pinpoint PD sites on shielded power cables in situ is in demand, as competition in the utility industry requires that cables have lower operating cost and higher reliability. An instrument system developed by the Electrical Insulation Research Center (EIRC) at the University of Connecticut comprises three subsystems: a PD location estimator, a cable position locator, and a PD pointer. This thesis deals with the development of digital PD location estimation algorithms and of the pointer instrumentation.^ The performance of a PD location estimator which uses observations from time domain reflectometry (TDR) measurements via the classical Cramer-Rao lower bound analysis is theoretically analyzed for the first time. As a result of this analysis, a guide for the selection of system design parameters is provided. Two PD location estimation algorithms are developed using the crosscorrelation method and the Estimate-Maximize (EM) algorithm. Both algorithms are tested using computer generated and field recorded data. The performance comparison between these two algorithms is inconclusive. The EM algorithm requires less computation power than the crosscorrelation method.^ A novel PD pointer instrument is developed using PD sensors that measure external electromagnetic fields generated by the PD. The differential configuration of two PD sensors effectively reduces the environmental noise level and eliminates possible interference from the terminal reflections. Both laboratory and field test results are presented and discussed. The instrument pinpoints PD sites with high accuracy ($\pm$2 in. in laboratory tests) and is easy to operate. ^