Chapter 7
Case Studies Related to Cable Transmission Feeder System Disturbances
Analysis of cable disturbance case studies provides a description of the power system affected and its associated protection systems, sequence of events, analysis of the failure, power system phenomena, corrective actions, and lessons learned. The cases can be summarized as follows.
Case Study 7.1 describes the design of the relay system protection zones and demonstrates how optimum design of relay protection zones can lead to a quick identification of the faulted cable section to provide information for quick service restoration. Case Study 7.2 provides an analysis of an undesired trip of an underground cable feeder during the soaking process of a generator step- up (GSU) transformer, which was due to a design error that resulted in reverse polarity connections at one end for the numerical current differential relaying systems. Case Study 7.3 describes the failure of a high-pressure fluid-filled cable connecting the high side of a GSU transformer and the substation, and how the use of relay targets coupled with a complete knowledge of the protection zones can lead to correct analysis and determination of the faulted area. The correct determination is achieved despite the mechanical failure of the cable pot head porcelain, which can give a false indication to the faulted area. Case Study 7.4 documents a 345-kV high-pressure fluid-filled cable trip by the operation of the relay systems, and how the ...