From Handbook of Electric Power Calculations, Third Edition


Consider a transmission line consisting of two straight, round conductors (radius a meters), uniformly spaced D meters apart, where (Fig. 9.1). Calculate the inductance of the line.

Figure 9.1: A two-wire transmission line.

Calculation Procedure

1. Consider Flux Linkages

It is realistic to assume uniform and equal but opposite current density in each conductor. The oppositely directed currents, there- fore, produce a net total flux linkage of zero because the net current in any cross section of both conductors is zero. This is true for any multiconductor system whose cross-sectional currents add to zero (for example, in a balanced three-phase system).

2. Calculate Inductance of One Conductor

Use ?=( i/2 ?)[1/4+ln( D/ a)] Wb turns/m. Because L= ?/ i, L=(2 10 7) [1/4+ln( D/ a)] H/m. Inductance L may be expressed in more compact form by L=(2 10 7) ln( D/ r ?), where r'= a exp( 1/4) is the geometric mean radius, GMR. The value of r ? is 0.788 a.

3. Calculate Total Inductance, L T

L T =2 L=(4 10 7) ln( D/ r ?) H/m. In more conventional units, L T=1.482 log( D/ r ?) mH/mi.

Products & Services
RF Inductors
RF inductors are special inductors designed to be used in radio frequency (RF) and microwave applications.
Electrical Inductance Sensors
Electrical inductance sensors measure the inductance of an electrical component or system.
LCR Meters
LCR meters and impedance meters measures inductance (L), capacitance (C), and resistance or impedance (R).
Inductors, Coils, and Chokes
Inductors coils and chokes are passive components that are designed to resist changes in current and store energy in the form of a magnetic field. 
Inductance Standards and Decades
Inductance standards and decades provide highly accurate and digitally variable standard values of inductance for calibration, comparison and testing.

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