Three-Phase PI Section Line

The Three-Phase PI Section Line unit represents a balanced three-phase transmission line using a U-shaped substitution diagram.

In contrast to a linear distributed parameter model in which resistance, inductance and capacitance are uniformly distributed along the line, the Three-Phase PI Section Line block combines the line parameters into a single U-shaped section as shown in the figure below.

The line parameters , and are set as forward and zero sequence parameters that take into account the inductive and capacitive coupling between the three-phase conductors, as well as grounding parameters. This method of setting line parameters assumes that the three phases are balanced.

The intrinsic and mutual resistances ( , ), intrinsic and mutual inductances ( , ) of the three connected inductance coils, as well as the phase capacitances and ground capacitances are derived from the forward and zero sequence RLC parameters as follows.

Let us take the following line parameters as an example:

First, the general parameters of the direct and zero sequences, including hyperbolic corrections, are estimated:

where

, , , , , are hyperbolic correction factors of direct and zero sequence.

For a short line section (approximately < 50 km) these correction factors are negligible (close to unity). However, for long lines, these hyperbolic corrections must be taken into account to obtain an accurate model of the line at the specified frequency.

The RLC parameters of the line section are then calculated as follows: