How do you model the transposition of overhead lines?

Power Equipment Models

The impedances of each phase of an overhead line differs from each other due different relative geometries of each ohase of the line. In order to mitigate / reduce unbalances in the system, overhead lines are usually transposed.

There are different options in PowerFactory to model the transposition of overhead lines. The following options are shown in the attached example:

Ideal Transposition:

  • Overhead lines can be transposed by internal routines that adjust the impedance and admittance matrix of the multiphase system (off-diagonal elements are recalculated)
  • PowerFactory provides different routines for the ideal transposition of the overhead line. They are described in the Technical Reference

Explicit / Detailed Transposition:

  • Detailed modelling of the transposition based on the actual design of the overhead line. Each line section is modeled explicitly
  • Single circuit overhead lines:
    • Transposition is based on single phase switches that connected different phases at the point of transposition (A-B,B-C,C-A)
    • A multiple of three transposition line sections is required in order to get a correct phase rotation throughout the system
  • Multi-circuit overhead lines:
    • Transposition is based on single phase switches:
      • See above
    • Transposition is based on internal routines:
      • The phasing is defined directly in the ElmTow for each parallel system

The attached projects provides example both for ideal/detailed transposition of overhead lines. The transposition scheme is documented in the attached pdf document.