Effect of Electromagnetic Fields from Power Lines on Metallic Objects and Human Bodies

This paper investigates the interference between electromagnetic field produced by high voltage power lines and liv ing organisms and metallic objects underneath the transmission lines such as ships, at rivers crossing, and vessels passing under or near to power lines. Metallic pipelines buried in the same corridor are affected with many factors, namely : the power line configuration, separation distance between transmission line and pipeline, separation distance between conductors, the transmission line tower height, existence of the earth wire, the sequence of the power supply, the length of corridor and the fault conditions. The equations of magnetic fields of the transmission lines and the density of currents induced in the human bodies and metallic ships surface were introduced. The induced voltage on the neighbouring pipelines was calculated. A computer program was developed to model and simulate the magnetic fields produced by power lines. The program calculates the current density induced in objects underneath or in the neighbourhood of the transmission line. The results obtained using the developed program illustrated to be consistent with previous literature results. The obtained results showed to be satisfactory and consistent with the experimental ones.


Introduction
It is co mmon that elect ro magnet ic fields produced by transmission lines causes dangerous effects on both living organisms and any metallic objects. If the hu man bodies are projected to high levels of magnetic fields the ma in effect of interferences is the production of electric currents within the body. Electric and magnetic fields differ, in their effects, when they pass across the body of living organis ms at low frequencies. An elect ric field d irected on an unsh ielded p erson d isch arges to g rou nd wh ile the magnet ic field permeates the body inducing a magnetic flu x that generates secondary electric fields inside the body and then induce currents dens ity that causes a change in p rotein , DNA syntheses, enzyme activ ity, heart dysfunction and possible n erv o us effects . W h ile metallic s t ru ct u res near to transmission lines are subjected to interference arising from in du ct ive, cap acit ive and res ist ive cou p ling as in [1]. Inductive coupling arises when the structure is placed in a time v ary ing magnet ic field . Cap acit ive coup ling on ly affects structure located above ground since these have a capacitance to both the transmission line and to the earth as in [2,3]. Resistive coupling between a transmission line and metallic p ipeline is only relevant during ground fault when significant levels of currents flow into the ground.
This interference with metallic objects causes corrosion of the object material or risks for people entering in contact with this objects. In case of cathodic protection of metallic objects magnetic interference may produce mal-operation. This paper studies the inductive interference to the human bodies and metallic objects and the factors affecting the interference. It simulates the process using the developed computer program.

Theoretical
Where R is the distance from any point of interest and the centre point of power line o, φ r is the angle between the vector R and the horizontal central line as shown in figure.1.a. The magnetic field density B in Tesla can be found as in (2)

The Induce d Electric Fiel d and Current Density
For any structure may be considered as a homogeneous cylinder, the magnetic field will induce an electric field E in the structure, according to Faradays law, is given as in (3), [5,6].
Where r: radial d istance from the centre of the cylinder to the point where E is evaluated. E: vector lines in a plane perpendicular to B and is oriented tangentially to circles of radius r.

Induced Voltage on Pi peline
The mutual impedance with earth return in Ω/ m between pipeline and phase conductors of transmission line, which carry an ac current of frequency 50 Hz, can be found using Carson's formu la as in (7). where δ in meter is the depth of the earth return path with soil resistivity ρ in Ω .m, space permeab ility μ o , angular frequency ω and distance between pipeline and phase conductors D ph-p can be found as in (8), [7]. 1.85 Two conditions can be considered: 1. Without overhead earth wire -At normal conditions: The induced voltage V p on pipeline due to fu ll load currents I A ,I B ,I C with mutual impedances between phases A,B and C and pipeline Z AP ,Z BP ,Z CP is given as in (9), [8].
At fault conditions: The induced voltage V p on pipeline due to fault current I fault for a single line to ground fault is given as in (10), [9].
2. With overhead earth wire -At normal conditions: The impedance of earth wire with earth return Z E for the earth wire resistance R E and geometric mean radius of R GM is given as in (11), [7].
The mutual impedance between the phase conductor, earth wire and the pipeline is given as in (12), [9].
Then the induced voltage V p on the pipeline is given as in (13), [9].
At fault conditions: Considering earth wire at fault conditions there are a shielding factor K that can be found as in (14), [9].
The induced voltage V p on the pipeline at fau lt condition is given as in (15)

A 500 kV Horizontal Configuration
According to The separation distance between conductors of s=11m, the height of tower is h=37.5m and the conductor current of I=650A.then by using equation (1)

A 220kV Double Circuit Power Line Configuration
According to The distances between conductors s=6m, height of tower h=41m and the conductors current I=1000A. Then by using equation (2) the magnetic field density can be seen in figure.5.

Figure 5.
Magnet ic Field Density From 220kV Double Circuit Configuration Figures. 4,5. show that the magnetic flu x density produced fro m 220kV double circu it line configuration is less than that fro m 500kV horizontal configuration single circu it. Th is is due to the fact that the magnetic field produced fro m each conductor of the double circu it will be balanced by other ones. This will reduce the net magnetic field seen by any object.

Current Density Induced in Human Body
The current density in A/m2 induced due to electric field which is produced fro m the magnetic field can be determined using equation (6). For a person having a head of radius=0.1m and body of radius=0.3m and body conductivity σ= 0.2 S/ m, the current density for different distances from the 500kV horizontal single circu it transmission line can be seen in figure. 6.
The results of current density for different distances fro m 220kV double circu it transmission line can be seen in figure.8. Figures. 6,8 show that the induced current density on human body in case of single circuit is greater than that of a 220kV double circu it. Th is is due to the magnitude of magnetic field density.

Induced Current on Metallic Shi ps and Vessels Underneath Power Line
By applying the same method on ships and vessels such as missile boats of radius=9m, destroyer of radius=29.5m, cargo of radius=23.5m, frigate of radius=11.5m and Aircraft carrier ships of radius=47.5m wh ich are subjected to electro magnetic fields fro m 500kV horizontal single circu it power lines crossing over rivers or canals with s=11m, h=140m, I=650A and the conductivity of metallic material σ=0.3* 10 6 S/ m the results of current density can be seen in figure.9.

Interference wi th Pi pelines and the Factors
Affecting It

Power Line Configuration
The induced voltages on pipelines are significantly dependent on the configuration of the power line. The electro magnetic fields produced by the overhead line phases, generally balance each other and significantly reduce the net field seen by the pipeline and then affect the magnitude of the induced voltage on pipeline [10]. Figures. 2, 3 show different configurations of 220 kV, transmission line with a phase current I=1000A at normal conditions, distance between conductors d=6m, length of parallelism of pipeline L=10km and soil resistivity of 100 Ω.m. Figure. 12 shows that the vertical configuration caused the height magnitude of induced voltage for the first 40m separation distance between the centre of power line and the pipeline than any other configuration [11]. This is due to the high density of the resultant electromagnetic field EMF produced from the vertical power line than the others and still has the higher magnitude than the delta configuration until reaches 80m. Then as we move laterally away fro m the centre, the vertical configuration gives the lower magnitude of induced voltage than the other configurations; the delta configuration causes a mediu m value of induced voltage between vertical and horizontal configurations. It can be seen that the horizontal configuration caused a smaller amount of induced voltage, fro m 0m to 25m separation distance. From 40m although its value decays with increasing distance but it is higher than all other configurations. Figure. 12 illustrated that, for all configurations, as the separation horizontal d istance from power line increases the magnitude of the induced voltage on pipelines decrease. Different separation distance between conductors for horizontal configurations 1-Fo r a 220 kV horizontal configuration -The induced voltages on pipelines, for different separation distance between conductors as d = 4m, 6m and 8m, is ind icated in figure.13.

Distance between Conductors
2-For a 220 kV vert ical configuration -The induced voltage on pipeline was calculated for different separation distances between conductors d = 4m, 6m and 8m is shown in figure.14.

Figure 14. Different separation dist ance between conductors for vertical configurations
It can be concluded that as the separation distance between lines increase the induced voltage increases for any configurations. This is due to the fact that the outer phase gets nearer to the pipeline which enhances this phenomenon. Also, it may be due to the fact that the mutual effect of the two neighbour conductors is reduced as they get separated fro m each other.
3-For a 220 kV delta configuration -For the 3-phase 220 kV delta configuration there are two configurations triangle equilateral and triangle which has different spacing as shown in figure. 3.a,b.  The triangle which has different spacing shows the height of the hump of the curve at the left hand side is higher than that at right hand side. This is because when the pipeline was p laced at left side of power line it is more affected by phases A and B which C is much more far out of it, wh ich has a separation distance of 6m. When it is placed at right hand side of the power line it is more subjected to phases C and B, with separation distance of 4.3m.

Height of Towers
For the studies 220 kV horizontal system with d=6m and the height of tower is h=41m, 38m and 35m. Figure. 16 shows that as the height of the tower increases the net electro magnetic field EMF seen by the pipeline decreases, then the induced voltage on pipeline decreases. This is the general trend for all power line configurations. The OHEW will break the magnetic field balance of the system and leads to higher induced voltage on the pipeline at normal condition [9].
• Triton 37/3.75 AAC which has R GM of 0.00982m and resistance of 0.0869 Ω /km can be using as OHEW.
As the resistance of earth wire increases the mutual impedance increases according to equation (12). And then the total induced voltage increases according to equation (13) this is consistent with figure. 17.  For the sa me 220 kV horizontal configuration the separation between pipeline and power line is 50m and the length of system parallelism are L=5km, L=10km, L=20km and L=30km.
The ma ximu m induced voltage occurs at the two ends of the pipeline because of the strong discontinuity of the EMF at these two points and the minimu m induced voltage occurs at the midpoint of pipeline because the induced EMF in the pipeline on both sides of this point has the same magnitude and of opposite direction resulting in a min imu m induced voltage on this point. Figure. (19) shows the induced voltage along the pipeline for different length of parallel section. As the parallel section increases, the induced voltage on pipeline increases too [12,13]. For any configurat ion the fault condition causes higher induced voltage on pipeline according to the magnitude of the I fault = 5000A as in [14].
Under the fault condition the existence of the OHEW will reduce the impact on the induced voltage on the pipeline due to the resistance of the OHEW affects direct ly the value of the induced voltage as in [15]. This is attributed to the size of the conductor. The OHEW with large size induces the smallest voltage. This can be verified using the different types of OHEW as in [

Conclusions
This paper has explained and analysed the interference between high voltage transmission lines and human bodies, metallic ships and pipelines which have different factors that affect the interference.
Modelling and simulat ion of induced current density on human bodies, metallic ships surface and the induced voltages on pipelines for various configurations of power lines is investigated.
The magnetic field of over head transmission line with different configurations was determined using Ampere law.
A computer program was developed to calcu late the values of the induced current density and induced voltages. This developed program showed to be very effective and with least running time. This method was compared with the results obtained using EMTP and showed to be more accurate and having a smalle r running time.
The electromagnetic field interference is significantly dependent on the power line configurat ions, separation distance between transmission line and objects underneath, separation distance between conductors of transmission line, the transmission line tower height, existence of the earth wire, the sequence of the power supply, the length of system parallelism and fault conditions.