The ground plane represents the earth ground return path for your transmission line or cable system. The ground plane may be approximated with a constant resistivity (default setting), or the user may choose to represent the ground with a frequency-dependent conductivity using Portela's method.
In addition to allowing the adjustment of ground resistivity and permeability, this component also gives the user control over how the complex ground impedance integral (i.e. Carson's Integral) is numerically approximated. Two options are given as described below:
Analytical Approximation: The Transmission Line and Cable Constants program solves the ground impedance integral by analytical approximation. For overhead transmission lines, this is the Deri-Semlyen approximation of Carson's Integral method as described in PSCAD general reference [20]. For underground cable systems, this can either be set as the Saad approximation (EMTDC Chapter 8 reference [29]) or the Wedepohl approximation method of Pollaczek's Integral. For aerial cable systems, the mutual quantities between underground and overhead can either be set as the Ametani or LUCCA approximation (Mutual Impedance with Earth Return).
Numerical Integration: The Transmission Line and Cable Constants program solves the ground impedance integral (either Carson or Pollaczek) through direct numerical integration. Although very accurate, this solution method may add a huge amount of time, as compared with the equivalent Analytical Approximation. This becomes very apparent when solving lines with more than three conductors.
NOTE: It is recommended that Analytical Approximation be selected for most practical situations, due to the huge time savings. The approximation methods are normally accurate to within 5% of the exact solution, however if the user is in doubt, simply run the simulation with each method and compare results.
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Constructing Transmission Line Systems Constructing Underground Cable Systems |