Transmission Line Magnetic Field Calculator

This calculation tool is intended to assist with the derivation of magnetic fields associated with overhead and underground transmission lines. The tool provides the user with the magnetic field resulting from balanced three-phase circuits, where the phase conductors are defined by their average coordinates.

Input Parameters

The calculation methodology assumes there is no zero sequence current flowing in the line, the phase currents are balanced and there are no harmonic currents. Some conservative assessments may rely on the minimum mid span clearances for overhead lines as the mid span magnetic field is a function of the conductor clearances along the line. Single core underground cables should be modelled by entering the coordinates for the centre of the cables. The backfill is assumed to have a magnetic permeability of unity, which may be slightly affected by large quantities of steel reinforcing. In all cases, the coordinates should refer to the centre of the conductor or conductor bundle.

Variations in phase current direction or vector group can be adjusted by specifying the vector adjustment for the second circuit. Circulating currents in the earthing systems are often ignored in magnetic field calculations. However, these may be included for overhead lines by selecting an earth wire and entering the equivalent current phasors derived from an EMTP-style analysis. The current phasors in underground cable screens should be added to the phase angle current phasor. The resulting imbalanced phasors can be modelled by superimposing the two earth wire phasors on one (or two) of the cable cores.

Line 1:

Units to be used in this calulation		microTeslamilliGauss
Line 1 phase current (Amperes)
Height above ground (m)		Offset from Centreline (m)
Phase A		Phase A
Phase B		Phase B
Phase C		Phase C

Line 2:

Line 2 phase current (Amperes)
Phasors relative to Line 1 (deg)		0 (in phase)30 Degrees60 Degrees90 Degrees120 Degrees150 Degrees180 (opposing)210 Degrees240 Degrees270 Degrees300 Degrees330 Degrees
Height above ground (m)		Offset from Centreline (m)
Phase A		Phase A
Phase B		Phase B
Phase C		Phase C

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Number of overhead earthwires: None One Two

Earth Wire 1:

Circulating Current (Amperes)
Angle to phase A of Line 1(deg)
Height (m)		Offset (m)

Earth Wire 2:

Circulating Current (Amperes)
Angle to phase A of Line 1(deg)
Height (m)		Offset (m)

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Your User Name

Terms of Use

This package is intended to provide assistance with common transmission line calculations. Before using this tool, you must understand that we are not providing advice and the results should be used for indicative purposes only. In performing this calculation you are agreeing not to hold WeatheRate (or any of its associates) responsible for any liability, loss or harm associated with the use of this site's contents.

Calculation Results

References