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HUMAN BODY MODELING IN THE VICINITY OF HIGH VOLTAGE TRANSMISSION LINES.

Byline: Alireza Fereidouni Behrooz Vahidi Farnaz Shishehgar Tahoura Hosseini Mehr and MahdiTahmasbi

ABSTRACT: Interactions of electric and magnetic fields at power line frequencies (50 and 60 Hz) in humans have been the subject of intensive scientific inquiry and considerable public concern during the last two decades. As a part of the scientific effort extensive evaluations of induced electric field and current density in the human body have been performed. Realistic heterogeneous high-resolution models of the body have been analyzed using various numerical methods. For this reason this paper investigates the induced currents in the human body organs (such as brain heart and kidney) and on the surface of it (skin) when exposed to a 200 kV transmission line (TL) 50 Hz. Hence firstly a numerical method has been employed to calculate the induced currents in the organs and on the surface of the body. Secondly A test object which can represent the human body in experiments near energized high-voltage (HV) conductors has been developed. All in all in this paper it is aimed to obtain the induced

current level changes of the human body due to its distances (0 5 10 15 and 20 meter) from the center of an energized high-voltage transmission line. The numerical results present a good agreement in compare with the experimental results.

Keywords: Human model electric field magnetic field transmission line and induced current.

1. INTRODUCTION

Electrical energy can be taken into account vital for all places of society industrial domestic and social in such a way that it is hard to assume a human activity that does not have some relationship with electricity. Electrical Energy is transferred from the power station to the substation through high-voltage (HV) transmission lines (TLs) and from there to the final users through distribution grids of medium and low voltage [1-2].

Public concerns about power-frequency fields first emerged in the late 1960s as power companies turned increasingly to HV transmission lines to handle large increases in electricity use. HV lines carry electric power with lower energy losses and with smaller land usage than multiple lower-voltage lines with the same power-delivery capacity. Public attention to HV transmission lines focused first on the aesthetic impact of their large towers on the aesthetic and ecological impacts of their rights-of-way and on various nuisance effect created by their strong electric fields. This nuisance effect include audible noise TV/radio interference and induced shocks that can occur when a person standing beneath an HV line touches a large ungrounded metal object such as a truck or farm vehicle.

By the early 1970s the American national standards institute (ANSI) had issued voluntary standards to address nuisance effect. The first evidence that power-frequency fields might have a direct effect on human health appeared in 1972 when Soviet investigators reported that workers in Soviet HV switchyards suffered from a number of non-specific ailments [3]. Although these reports were greeted with much skepticism by western scientists they served to stimulate public concern. By the mid-seventies health effect had become acentral issue in transmission line in several states. The issues have been investigating until now.

Overhead line workers (linesmen) become exposed to high electric and magnetic elds on a regular basis as a result of working close to HV transmission lines. These elds can cause induced currents and voltages. The electric elds induce currents on the body surface while the magnetic elds induce internal body currents [4]. The capacitance coupling the body to the HV lines combined with its capacitance to ground dictates the induced voltage levels. The work reported here considers the short-term impact on linesmen resulting from the electric elds. Routine checks and inspections of overhead transmission lines are performed by linesmen during non-outage conditions. A typical task which exposes them to electric elds is tower condition assessment where linesmen climb a 200-kV tower to its peak while maintaining the safety distances to the live conductors.

These conditions occasionally lead linesmen to experience unpleasant discharges that may reach levels that require them to put off their working activity.

For this reason this paper aims to calculate the induced currents in the organs of a human body such as brain heart kidney and also on the surface of it (skin) while he is working under a 200 kV TL 50 Hz. This goal has been reached by:

Analytically calculating the incident electromagnetic field surrounding a typical 200 kV transmission line Numerically calculating the induced currents in the human organs (brain heart kidney and skin) produced by the incident electromagnetic field and Experimentally obtaining the induced currents in the human organs (brain heart kidney and skin) produced by the incident electromagnetic field in the HV laboratory.

Numerical methods are often employed to determine the eld distributions within or around a human body from realistic electromagnetic sources. With detailed anatomical models [5] induced elds within a human body can be computed with greater resolution. In this paper a numerical technique based on the finite element method (FEM) [6] and electromagnetic quasi-static approximations is applied in the analysis of low frequency electromagnetic exposure to human body. For verifying the numerical results an experimental test has been carried out. A simplied 3-D test object has been designed to represent the human body in experiments that took place inside the HV laboratory. This experiment aims to examine how the induced current levels of a test object change according to its distance from an energized overhead line and a relatively large grounded object such as a 3 m tall tower placed inside the laboratory. This means that a human model which includes the human organs in it has been

developed and located under an energized conductor for measuring the induced currents. Note that because the human organs could not be prepared the organs of a sheep have been used. The numerical results show a good agreement with the experimental measurements.

2. The Electromagnetic Field of Transmission Lines

The HV transmission line system part of the power network includes the huge generating plants that gather power through hydroelectric processes like Niagara Falls through the burning of fossil fuels like oil and coal or through nuclear fission at nuclear-power plants [7]. The voltage form of these plants is shortly raised in step-up transformers and is moved along HV transmission lines strung on tall specially designed towers. When it arrives the community where it is needed the voltage is decreased in step-down transformers in power substations. The energy can then be used by final users (such as houses and industries) through the distribution grid.

There are various configurations of HV overhead power transmission lines. Typical three-phase three-wire (conductor) power lines can be arranged horizontally vertically or equilaterally (Figure 1) [7]. In this paper horizontal configuration will be considered. This type which is a 200 kV TL is depicted in Figure 2 (case study). The information of this TL is given in Table 1.

TABLE 1

ParametersL dIfa

200 kV TL###3###15###300###50###0.012

2.2. The Formulation

The sources of electrical and magnetic fields in the environment of TLs are the electrical currents and charges that exist in their conductors as well as those which are induced in the earth and/or in nearby objects. The starting points for the calculation of these variable fields with time are Maxwell's equations [2-3]. Generally electrical and magnetic fields are coupled and it is essential to solve Maxwell's equations to acquire them. Some authors [8-15] have suggested models that solve Maxwell's equations to obtain the value from the magnetic field generated by TLs. In practical terms these models are not the most suitable for the calculation of the magnetic field in the proximity of TLs due to their complex math. Thanks to this a simpler mathematical model but one that represents similar results to the real values will be more useful. Though the electromagnetic fields generated by TLs are coupled in many cases and under certain conditions

some approximations can be assumed and electromagnetic fields calculated in an independent way. This is often the case for fields created by TLs because of the fact that the field changes so slowly in time that Maxwell's equations are altered into the electro-static and magneto-static equations.

The three components of the electric field in the cylindrical coordinates###z of horizontal electric dipole with the electric moment I dx at a height d in air over a plane earth are given in [8]. The corresponding formulas in rectangular coordinates are readily derived.

3. INDUCED CURRENT IN THE HUMAN BODY

3.1. Numerical Method (Simulation Method)

Maxwell's equations can be represented in complex phasor The vector potential A is equivalent to the magneto-static vector potential A0 which is totally decoupled from the electric eld. If the permeability###is constant over the entire computation domain A0 can be calculated by the BiotSavart law [16]:

The electromagnetic elds can be calculated by solving Eq. (28) for the EQS case and solving Eq. (29) and (30) for the MQS case respectively. The partial differential equations can be solved efciently by Finite Element Method [16-17] and using 3D Cartesian grids. In this research as depicted in Figure 4 a human body model of a male from the Virtual Family" package is utilized.

The dielectric properties of biological tissues vary substantially dependent to frequency. In low frequency range biological tissues are chiefly diamagnetic (###0 ) and exhibit high relative permittivity and low conductivity. The tissue conductivity and permittivity values utilized in this paper are acquired from [17-19]. A list of tissue

TABLE 2.

###RELATIVE CONDUCTIVITY ( ) AND PERMITTIVITY ( r ) VALUES OF TISSUES [19]

###Tissue###Fat###Muscle###Bone###Heart###Kidney###Brain###Liver

###r###1.14 A- 10

###6###1.77 A- 10

###7###8867.###8.66 A- 10###6

###1.01A- 10###7

###5.29 A- 10###6

###1.83 A- 106

###8

###(S / m)###0.019###0.23###0.02###0.083###0.037###0.053###0.037

3.2. Experimental Test Setup

After explaining the numerical method it is time to perform experimental test and obtain the induced currents by these methods. When a linesmen is working under a TL (the position of the feet (0yz=0)) (Figure 5) based on [8] the most important electric field which effects its body is E1z (x=0yz=1) component. Therefore these electric fields are considered for the experimental tests. The experimental test have been conducted for measuring the induced currents in the human organs (such as brain heart kidney and skin) when it is exposed to the electric fields E1z (x=0y=0:20z=1)-Table 3) of a 200 kV TL at the various distances (0 5 10 15 and 20 m) from the center of the tower (Figure 5). For reaching to this goal initially it is needed to fabricate a human body model. Two notes should be taken into account in this stage. First the inside of the model should be empty for placing the human organs in it therefore this model must not be made by conductive material and second because the induced surface current is also measured therefore the surface of this model should be conductive. Hence based on the notes as seen in Figure 6 a wooden human body model (the first note) (a 3-D test object) which can be covered by layer of aluminum [1] (the second note) has been designed and fabricated. During measuring the induced currents of the human organs the aluminum cover is removed from the surface of this model (Figure 6(a)) on the contrary when the induced current of the surface is measured a layer of aluminum cover (0Figure 6(b is put on the model.

TABLE 3.

###inc###inc

###THE VALUES OF E1z AND B1z NEAR THE HORIZONTALLY ARRANGED 200 kV TL (MAXIMUM VALUES)

###Z=1 m

###V/m###T

###Y m###inc

###E1x###inc

###E1y###inc

###E1z###inc

###B1x###inc

###B1y###inc

###B1z

###0###1.46 A- 10-5###86###94###0.189###0.3###0.39

###5###6.04 A- 10-5###46###434###0.011###1.40###0.2

###10###5.69 A- 10-5###9###523###0.0015###1.72###0.05

###15###2.97 A- 10-5###22###416###0.0047###1.38###0.10

###20###1.1 A- 10-5###18###289###0.0044###0.96###0.08

###25###2.49 A- 10-5###12###195###0.0032###0.65###0.05

###30###9.29 A- 10-5###8###134###0.0021###0.44###0.034

organs are not easily accessible sheep organs (brain heart and kidney) have been provided (Figure 7). At the next step equipment for producing the electric field of the 200 kV transmission line and also measuring the induced current should be provided. For creating the electric field and measuring the induced current respectively a metal rod as seen in Figure 8 and a digital scope digital including a voltage source and a computer as seen in Figure 9 have been chosen. A 1.77 meter metal rod has been used for producing the electric field of the 200 kV transmission line (Table 2) in the laboratory. Therefore it is needed to obtain the true voltages which should be applied to the metal rod for producing the exact electric fields of a 200 kV TL in the experimental test. The formula has been acquired by the Finite Element Method (FEM) (0Fig. 10). After calculation the final equation is as (30).

After preparing the required equipment and calculating the values of the applied voltages it is the time to obtain the induced currents. For measuring and observing the induced currents in the organs they are placed in the human model in their real places and then the human model is located under the metal rod (Fig. 11 Fig. 13 Fig. 15 and Fig. 17) which has been energized by the power transformer at the calculated voltages (0Table 4). For observing the induced currents by the scope each organ is connected to the earth by a resistance and the across voltage of this resistance is measured which can be observed by the scope. Therefore the induced current is calculated by dividing the across voltage to the value of the resistance (10.31 M ).

TABLE 4.

###APPLIED VOLTAGES TO THE METAL ROD FOR PRODUCING THE ELECTRIC FIELD OF THE 200 kV TL IN THE LABORATORY

###Y=Distance from the center of the tower (m)###0###5###10###15###20

###Electric Field (V/m)###94###434###523###416###289

###Applied voltage (kV) RMS###1.861###8.592###10.354###8.236###5.722

4. RESULTS

In this section the induced currents from the numerical method and the experimental test are obtained and compared to each other. The results are as follows:

Brain experiment

When the rod metal is energized by the transformer for example at 1.86 kV (Table 4) it produces electric field around it; this electric field induces current in the brain that flows to the ground via the resistor (Fig. 11(b)). This current creates a voltage across the resistor as shown in Fig. 12(a). The induced current is obtained by dividing this voltage by the resistance value. The induced currents for 5 different applied voltages are obtained and compared by the simulation method in Table 5. These values should increase initially thanks to increasing the applied voltage and then decrease after 10 m because of decreasing the applied voltage which can be seen in Fig. 12 and Table 5. This method for measuring the induced currents is similar for the rest of the experiments (Heart kidney and feet).

Brain experiment

Heart experimentThe results obtaining from the scope are shown in Fig. 14. The results are compared in Table 6.

TABLE 5.

###THE INDUCED CURRENTS IN THE BRAIN PRACTICAL AND SIMULATION RESULTS.

###Y (m)###Applied Voltage (kV)###Induced Current###Induced Current

###(Practical-Test) (A)###(Simulation-Numerical) (A)

###0###1.861###10-8 A- 4.12###10-8 A- 4.40

###5###8.592###10-7 A- 1.76###10-7 A- 2.02

###10###10.354###10-7 A- 2.14###10-7 A- 2.44

###15###8.236###10-7 A- 1.70###10-7 A- 1.94

###20###5.722###10-7 A- 1.15###10-7 A- 1.35

TABLE 6.

###THE INDUCED CURRENTS IN THE HEART PRACTICAL AND SIMULATION RESULTS.

###Y (m)###Applied Voltage (kV)###Induced Current###Induced Current

###(Practical-Test) (A)###(Simulation-Numerical) (A)

###0###1.861###A-10-8 2.74###A-10-8 2.86

###-7

###5###8.592###A-10 1.10###A-10-7 1.31

###10###10.354###A-10-7 1.32###A-10-7 1.58

###-

###15###8.236###A-10 1.07

###7

###A-10-7 1.26

###20###5.722###A-10-8 7.68###A-10-8 7.95

TABLE 7.

###THE INDUCED CURRENTS IN THE KIDNEY PRACTICAL AND SIMULATION RESULTS.

###Y (m)###Applied Voltage (kV)###Induced Current###Induced Current

###(Practical-Test) (A)###(Simulation-Numerical) (A)

###0###1.861###A-10-8 1.76###A-10-8 1.95

###5###8.592###A-10-8 8.78###A-10-8 9.12

###10###10.354###A-10-7 1.10###A-10-7 1.36

###15###8.236###A-10-8 8.58###A-10-8 9.10

###20###5.722###A-10-8 6.31###A-10-8 6.69

From the paper it can be concluded that an EMF always exists when there is an electric current flowing in normal environment. A static EMF is naturally generated by earth and in case of direct current and a man-made alternative magnetic field is produced by alternating current sources. Numerous investigations with EMF reported the alterations in cell tissue and animal models. These reported changes have included alterations in endocrine and immune functions developmental effect and biochemical metabolism. However there has been a controversy on the biological effect of EMF because several studied has not been successfully replicated. Additionally there have been no consistent evidences in human studies and epidemiological investigations. Despite the controversial results in laboratory and human studies we are not able to ignore the ultimate biological effect of

EMF including its health risk and therapeutic value. In the near future a large number of laboratory studies and clinical application for therapeutic facilitators should be done to assess the real effect of EMF.

TABLE 8.

###THE INDUCED CURRENTS ON THE SURFACE PRACTICAL AND SIMULATION RESULTS.

###Y (m)###Applied Voltage###Induced Current###Induced Current

###(kV)###(Practical-Test) (A)###(Simulation-Numerical)

###(A)

###0###1.861###A-10-7 1.92###A-10-7 2.18

###5###8.592###A-10-6 1.06###A-10-6 1.28

###10###10.354###A-10-6 1.31###A-10-6 1.44

###15###8.236###A-10-6 1.00###A-10-6 1.12

###20###5.722###A-10-7 7.37###A-10-7 7.51

5. CONCLUSION

In this paper the impact of the electric field of the 200 kV transmission line in the organs (brain heart and kidney) of a linesman and on the surface of it in the different distances have been investigated experimentally and numerically.

An efficient numerical technique for solving the Maxwell's equations with quasi-static approximations has been applied for calculating the induced currents when the human body is exposed to the incident electric field of the under studied TL in simulation.

For comprehending that the results obtained from the numerical method are true and accurate an experimental test in the HV laboratory has been conducted. A human body model which its inside is empty for locating the organs in has been fabricated by wood because the body must not be conductive. But on the contrary when the induced current on the surface is measured a layer of aluminum is covered on it.

The compared results revealed a good agreement between the numerical results and the experimental results. Moreover the obtained results (the induced currents) are lower than the critical values due to standard which are perilous to people's health. REFERENCES

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