Overhead transmission line and underground cable segments (or right-of-ways) are represented in two parts: The definition of the transmission segment itself, which can include the admittance/impedance data or the conductor and insulation properties, ground impedance data, and geometric position of all towers and conductors; and the interface to the rest of the electrical system, through electrical interface components (one at each end). If the transmission line is configured in Direct Connection mode, the interface components are not required.
Transmission segments considered to be electrically short in length (i.e. less than 15 km for a 50 ms time step), may also be represented using an equivalent p-section representation. This is accomplished by either: Using the p-section component in the master library, where only the admittance and impedance data of the line segment is required, or by using the p-section equivalent component creator feature in the Line Constants Program (LCP). P-sections are essentially a network of passive elements, and hence do not represent propagation delay.
NOTE: A 15 km line length to a 50 ms time step is derived assuming that waves propagate through the line at the speed of light. In general however, wave propagation speed is less than the speed of light.
Using the data provided by the cross-sectional definition of the segment, the transmission lines and cables are modeled using one of two distributed (travelling wave) models:
Bergeron (Single Frequency)
Frequency Dependent (Phase) (Multiple Frequencies)
The most accurate of these is the Frequency Dependent (Phase) model, which represents all frequency-dependent effects of a transmission line. When using the Bergeron model, impedance/admittance data can also be entered directly to define the transmission segment.
For the frequency-dependent model, detailed conductor information (i.e. segment geometry, conductor radius) must be given. For more details on the differences between models available in PSCAD, see Transmission Lines and Cables in the EMTDC section.