Chapter 6
Case Studies Related to Overhead Transmission-Line System Disturbances
Case Studies 6.1 and 6.2 illustrate how the sequence of events can be derived from analysis using one DFR record or oscillogram record from only one end of the line, provided that the line voltages are monitored. Case Study 6.3 deals with the analysis of a three-phase fault caused by lightning, and the use of DFR technology that permits expansion of the recorded traces in the directions of both the time and magnitude axes, to determine that the fault began as a phase-to-phase-to-ground fault that evolved sequentially rather than occurring simultaneously as a three-phase-to-ground fault. Case Study 6.4 deals with analysis of an EHV horizontal line configuration double-phase-to-ground fault caused by lightning and the utilization of DFR technology, which permits expansion of the recorded traces in the direction of both the time and magnitude axes, to confirm the sequential nature of the fault as a direct hit on one phase followed by a voltage buildup to ground, causing involvement of the second phase. Case Study 6.5 deals with the analysis of a three-phase fault caused by lightning. The DFR software package is used to determine the nature of the occurrence of the fault. The analysis confirmed the sequential nature of the fault and flagged a problem with the transmission tower footing resistance.
Case Study 6.6 documents the occurrence of a ground fault caused by vandals shooting at insulators on a 115-kV ...