Analysis of overvoltage in nonhomogeneous distribution cable grids

Overvoltage in 6 (10) kV cable lines is one of the factors that have the strongest impact on the grid reliability.The paper discusses the resultsof testing the lengthwise distribution of overvoltage values in a typical section of a 10 kV distribution cable grid as induced by a single phase-to-ground fault; it also presents a method for minimizing such overvoltage. Tests were run by simulation in ATPDraw. The cable-grid ATP model was based on elements with distributed reactive and active parameters. Cable-line overvoltage was found to change significantly depending on the configuration and design choices of cable types and cross-section values. Dead-end feeders had maximum overvoltage at the very end, where the research team observed both monotonic increase in overvoltage towards the end, and local maxima. In case where the line was not a dead end, maximum overvoltage was observed towards, but not at the end. Maximum overvoltage in a grid was found to correlate with the cable cross-sections. The practical output of this research is guidelines on how to optimize the design for further cable grid development by minimizing the factor of projected overvoltage. The paper proposes visualizing the results as diagrams showing changes in maximum overvoltage along cable lines. Plotting such diagrams when designing, operating, or upgrading a grid will help pre-identify the most vulnerable points of cable lines where overvoltage could cause insulation failure. The paper shows that the best grid design and the worst grid design may differ by > 12 % in peak overvoltage.