13
Transmission Line
Parameters
Manuel Reta-Herna ́ndez
Universidad Auto ́noma de Zacatecas
13.1 Equivalent Circuit ........................................................... 13 -1
13.2 Resistance ......................................................................... 13 -2
Frequency Effect.Temperature Effect.Spiraling and
Bundle Conductor Effect
13.3 Current-Carrying Capacity (Ampacity)........................ 13 -5
13.4 Inductance and Inductive Reactance............................. 13 -6
Inductance of a Solid, Round, Infinitely Long Conductor.
Internal Inductance Due to Internal Magnetic Flux.External
Inductance.Inductance of a Two-Wire Single-Phase Line.
Inductance of a Three-Phase Line.Inductance of Transposed
Three-Phase Transmission Lines
13.5 Capacitance and Capacitive Reactance........................ 13 -14
Capacitance of a Single-Solid Conductor.Capacitance
of a Single-Phase Line with Two Wires.Capacitance of a
Three-Phase Line.Capacitance of Stranded Bundle
Conductors.Capacitance Due to Earth’s Surface
13.6 Characteristics of Overhead Conductors .................... 13 -28The power transmission line is one of the major components of an electric power system. Its major
function is to transport electric energy, with minimal losses, from the power sources to the load
centers, usually separated by long distances. The design of a transmission line depends on four electrical
parameters:
- Series resistance
- Series inductance
- Shunt capacitance
- Shunt conductance
The series resistance relies basically on the physical composition of the conductor at a given temperature.
The series inductance and shunt capacitance are produced by the presence of magnetic and electric fields
around the conductors, and depend on their geometrical arrangement. The shunt conductance is due to
leakage currents flowing across insulators and air. As leakage current is considerably small compared to
nominal current, it is usually neglected, and therefore, shunt conductance is normally not considered for
the transmission line modeling.
13.1 Equivalent Circuit
Once evaluated, the line parameters are used to model the transmission line and to perform design
calculations. The arrangement of the parameters (equivalent circuit model) representing the line
depends upon the length of the line.