Effect of Cable Geometry on Induced Zero Sequence Ground Currents with High Power Converters

This paper investigates a field site phenomenon in which a large zero sequence current was found to circulate in the plant ground grid, even though the main supply transformer was ungrounded. The magnetically induced ground current is explained and seen to be influenced by cable geometry and operating characteristics of non-linear power converters. Finite element analysis (FEA) models of various cable geometry´s are generated with their respective impedance coupling matrix models that are further embedded into a circuit simulator program to determine induced ground current magnitude. Simulation results are shown to relate with field ground current measurements. Induced ground current is also analyzed as a function of line current magnitude, linear/non-linear load operation, and phasing arrangement of parallel cables. The paper concludes using analysis results to formulate application guidelines to minimize the effects of induced ground current phenomenon prior to equipment installation