A lot of programs have been developed for the calculation of field distribution, though they use a separate software in viewing the calculated results. And most of the time, these programs provide information that is difficult for a non-technical person to understand. With this, we are developing a user-friendly, Graphics User Interface (GUI) software for the calculation of EMF distribution under the vertical-type transmission line[1]. This software seeks to provide research scientist a theoretical calculation of the magnetic field distribution as well as the common people.
2. Calculation Method
By Biot-Sabart's law, magnetic flux density B at point P produced by an infinite straight, a distance away from the line, is expressed by the equation :
In this research paper, the magnetic field is referred to as the magnetic flux density.
Since the power line consists of 6 line currents, summation of the magnetic field by each line currents must be calculated repeatedly at different points P.
The program is simulated by varying the arrangement of phase angle of the transmission lines. With this variation, the magnetic field distribution is then compared. Magnetic fields are also calculated and observed setting one side of the transmission line currents to a value lower than the other.
The total magnetic field is obtained from simulating the strength equation by increasing ( t 1 degree from 1 to 360 degrees. Since an ellipse is formed, the total magnetic flux density corresponds to the magnitude of the major semi-axis of the ellipse[2].
3. Transmission Line Model
The model used, shown in Fig. 1, is the vertical-type transmission line. There are six 60-Hz line currents arranged to form a hexagonal shape. Conditions below are adapted in the calculation.
1. The current direction is taken as going towards the user's direction illustrated in Fig. 1.
2. The tower center line is considered as the x-axis zero-point and the ground as the z-axis zero-point.
3. Drooping of the line currents are neglected.
Fig. 1. Transmission line configuration.
The magnetic field distribution obtained presented either a symmetrical curve with zero as the axis of symmetry or a non-symmetrical one with magnetic field peak value at either +3m or -3m mark. The non-symmetrical magnetic field distribution shows the lowest amount of all combinations. On the other hand, the line configuration with the 2nd and 5th line current being equal in phase angles has the lowest magnetic field distribution among the symmetrical curves.
Setting one circuit of the transmission line currents to a value lower than the other circuit, all the curves results in a non-symmetrical graph and their peak point is located at the side where the line currents are higher.
5. Conclusion
The developed MFTL software proved to be very useful in determining the magnetic flux distribution under the overhead 2-circuit vertical-type transmission line. The software is, therefore, recommended for revisions to include the calculations about the horizontal-type transmission line and the consideration of the electric fields in the calculations.
References
[1]R. Mansfield, "Visual Guide to Visual Basic 4.0 for Windows", Ventana Press Inc., 1995.
[2]T. Matsumoto, et al., "Relationship between Magnetic Field Profile and Magnetically Induced Current in Biological Model under Power Transmission Lines", Proceedings of the seminar on effects of EMF on biological systems, pp. 1-12, Bandung, 1997.
