Analysis of neutral-to-earth voltage characteristics along rural electric power distribution systems through computer simulation and field testing.

摘要

The multi-grounded rural electric power distribution systems in the U.S. can produce neutral-to-earth voltage (NEV) on a dairy farm which may affect milk production of a dairy cow. In this study, computer simulation models were developed and farm field tests were conducted to facilitate the investigation and analysis of this NEV phenomenon.;The computer models of nearly 4.3 kilometers long, 4.8 kV rural power distribution systems simulated the NEV changes arising from high resistance segments in the neutral of the primary line, primary heavy loading demand, substation and other ground resistance changes, different levels of the neutral line grounding, primary operating voltage change, secondary ground faults and primary phase-to-earth faults. Based upon the analysis of the simulation results, guidelines were established for power suppliers to identify the sources of NEV originating from the parameter changes of the power distribution system. It is expected that the overall NEV is substantially lower along the electric power distribution system of a balanced three-phase four-wire ;The farm field tests revealed the NEV gradient distribution near the ground electrode systems on the primary and secondary sides of the neutral isolated distribution transformer. The NEV gradient which the isolated secondary ground electrode coupled from the primary side ground system was determined and analyzed. The equivalent circuit of the isolated secondary ground system was developed to study the parameters that influence the neutral separation. Low farm grounding system resistance to earth is important for effective neutral separation. Increased separation distance between the primary and secondary ground rods is a factor for separation effectiveness increasing. Resistivity of the soil is also an important parameter. The low resistance of the isolated farm ground will result in low NEV on farm.