Iranian Journal of Environmental Health, Science and Engineering Iranian Association of Environmental Health (IAEH) ISSN: 1735-1979 Vol. 7, Num. 2, 2010, pp. 181-188

Iran Journal of EnvironHealth Sci Eng, Vol. 7, No. 2, July-December, 2010, pp. 181-188

Article

Electromagnetic fields near transmission lines - problems and solutions

*H. Ahmadi, S. Mohseni, A. A. Shayegani Akmal

School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran

Correspondence Address: * School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran, h.ahmadi@ut.ac.ir

Date of Submission: 12-Jun-2009
Date of Decision: 16-Feb-2010
Date of Acceptance: 25-Feb-2010

Code Number: se10021

Abstract

Nowadays, people are highly concerned about the effects of high voltage transmission lines on their health. Probable risk for leukemia, breast cancer, neuropsychological disorders and reproductive outcomes has been reported due to this exposure. In this study, several measurements around different areas such as overhead transmission lines, GIS compartments and some appliances have been conducted and compared with the standard tolerances. The emphasis of this research is on high voltage substations and publics. Field magnitudes above 10kV/m have been measured under wires. Results show that there is no serious concern for the people living near the transmission lines but for the individuals who are beneath those lines for long. Recent achievements about electric fields' effect on human health are reviewed in the present paper. In a case study, three types of 230kV structures are analyzed and the best phase arrangement for reducing the electric and magnetic fields is determined (the circular arrangement). It is concluded that the most effective solution is for the governments to use the best phase arrangement and replace outdoor substations with GIS to reduce the radiations and for the people to be near the high voltage overhead lines as rarely as possible.

Keywords: Transmission lines, Electromagnetic fields, Public health

Introduction

Humans are continuously exposed to electromagnetic fields (EMF) emitted from such sources as electric transmission lines (TL), telecommunication and radio-television antennas. Thus, EMFs of various frequencies are ubiquitous in our environment. The extensive network of high voltage (HV) transmission limits (TLs), electric engines in cars, trains and trams, welding devices, and the electrical appliances are the primary sources of extremely low frequency (ELF) EMFs. All countries set their own national standards for exposure to EMFs. However, the majority of these national standards draw on the guidelines set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The effects of chronic exposure to environmental EMF have been the subject of intensive researches (Djanab, 1960) leading to no definitive answers. Possible risks for childhood and adult leukemia have been acknowledged (Portier and Wolfe, 1998), (Wartenberg, 1998), (Yang et al., 2008), but many other health outcomes are reported, among them are breast cancer (Stevens, 1993; Brainard et al., 1999), neuropsychological disorders (Sobel et al., 1996; Verkasalo et al., 1997; Liu et al., 2008), decrease in blood sugar (Abbasi and Nakhjavani, 2002), and reproductive outcomes (Hatch, 1992; Roychoudhury et al., 2009).

An underlying mechanism that could explain all of these potential effects is alteration of melatonin secretion as a result of EMF exposure (Reiter, 1993). Melatonin secretion is important in the regulation of circadian rhythms and sleep (Brzezinski, 1997), but could also be involved in the aging process (Poeggeler et al., 1993), carcinogenesis (Blask, 1997; Fedrowitz and Loscher, 2008), , and reproduction (Reiter, 1998).

In crowded regions, as a result of city′s expansion during the past years, TLs which were far from houses are now nearby buildings. Though previous investigations had shown no serious effects on human health from the EMFs due to TLs (California Health Department, 2001), but recent studies have taken the opposite side (Sher, 1997; Huss et al., 2009). Workplaces have also been studied for finding possible risks (Akbar Khanzadeh, 1982; Zahiroddin et al., 2006; Garcia et al., 2008). Besides TLs, there are a lot of appliances that produce EMFs such as electric blankets, copy machines, monitors and televisions which need to be studied.

As a gap in pertinent literature, especially in Iran, this research was conducted to analyze the real situation and make clear the vague probability of danger. Reminding the responsible institutions for applicable solutions is another goal of the authors, because, informing the people about the health risks and giving them scientific advice are mandatory.

Materials and Methods

Current study was conducted by measuring EMFs at different areas in Tehran. These measurements are meaningful when compared with the standard limits. [Table - 1] is a summary of the exposure guidelines for three frequency levels: ELF, mobile phone base stations and microwave ovens. These guidelines have been last updated in April 1998 by ICNIRP. Each measurement was done in increasing distance from instrument or overhead line (for TLs, every 10m away from the line and for devices like copy machines every 1m) and the measured data were recorded.

The employed device for EMF measurement was "Extech 480826 Triple Axis EMF Tester." By the aid of this device, frequencies ranged from 30Hz to 300Hz were measurable in RMS value.

Three substations in Tehran were selected including Kan, Azadegan and Ghourkhaneh, each one with a distinct feature. Kan has an income 400kV line, Azadegan is in neighborhood of inhabited houses and Ghourkhaneh is a GIS. A public park was also suspicious of being a hazardous place, as shown in [Figure - 1].

The outgoing 230kV line from Azadegan to Firouzbahram, a 63kV feeder inside Azadegan SS and the incoming 400kV line from Vardavard to Kan were the outdoor test places.

The mentioned problem only affects the people who are continuously exposed to emitted radiations such as workers in HV substations (SS), copy machines′ operators and people who are under TLs for a long time.

Different arrangements of phase conductors were analyzed to find the best solution for field reduction. A powerful program for reaching this purpose was employed known as COMSOL, MULTIPHYSICS MODELING AND SIMULATION, copyright 2008. It is a finite element analyzer and a solver software package for various physics and engineering applications, especially coupled phenomena.

Results are reported in two categories. The simulated fields are alternative and thus the simulation is time dependent. Therefore, first group includes figures which are only for specific time. In the second group, each plot pertains to 1/20 of a period. Hence, the maximum and minimum values are apparent which are more important than other values. It should be considered that in the second type, the simulation was done at a height of 2m above the ground.

Results

Measurements of electric and magnetic fields

TLs are ubiquitous even in publics, as shown in [Figure - 1].The measurements were done in most probable areas of high intensity fields. Wires′ weight brings them closer to the ground in the middle point of the span. The downward displacement for a 230kV line with a span of 300m is about 11-11.5m (the wire′s sag). [Table - 2],[Table - 3],[Table - 4] show the results of measurements near some TLs and inside SSs.

These outcomes show that in about 40m far from the TLs, the field intensity is lower than the standard thresholds. But for palaces that are beneath the lines, especially the public areas such as parks in which people spend much time, there is a possible danger.

Information about the current and voltage of TLs was collected for the time of measurement which is reported in the table captions. There was no big difference in current magnitude during the working hours in SSs and the voltage was constant.

Besides TLs, other appliances produce relatively high intensity EMFs about which people are probably not aware. [Table - 5] exhibits the measurement results for common devices. As it is obvious, these results indicate that these instruments produce high levels of electric and magnetic fields which are actually lower than the standard thresholds.

[Table - 6] and [Table - 7] indicate the measurement results for two places inside Ghourkhaneh GIS. More data had been collected, but there was no weighty difference between them. It′s apparent that GISs are significantly safer than the outdoor ones with respect to electric field intensity. Cables have a conductive shield under their insulator and so the electric field cannot reach outside the cable.

In outdoor SSs, wires were near the ground and the intensity of the electric field was too high that in the whole area, it was more than 10kV/m.

Simulation results of various configurations for 230kV TLs

There are several types of towers for TLs with different designs. Spans between the towers are different depending on the geographical properties of area. Wires′ sag in a 300m span may exceed 11m.We set up the worst case in current study - under maximum sag of the wires. Characteristics of four usual arrangements for 230kV conductors are shown in [Figure - 2]. Simulation results, using COMSOL, for ENT intensity are shown in [Figure - 3],[Figure - 4],[Figure - 5]. Electric potential of ground was assumed to be zero.

In this simulation, the wires in X-Y plane were considered because of the symmetrical situation that exist toward the Z-axis; this is a time wires was not remarkable because of the ELF of the current. Thus, only the effect of electric potential was considered.

Discussion

Previous studies have shown controversial outcomes about adverse impacts of continuous exposure to ELF-EMFs, especially for workers in HV SSs (Yousefi Rizi, 1997).

Results reported by Yousefi Rizi follows the results of this research. According to the standard limits, intensity of electric field in SSs is in danger zone. Moreover, staying a long time beneath the HV TLs, as the reported data has confirmed, is also a risky region which was not exactly addressed in earlier researches. Children play in such places and other people may sit for hours on the benches provided there. Considering these as environmental health risks, people should be informed about potential hazards.

High voltage power lines produce clouds of electrically charged ions as a consequence of corona discharge. It is suggested that they may increase the deposition of airborne pollutants on the skin and on airways inside the body, possibly adversely affecting health. However, it seems unlikely that corona ions will have more than a small effect, if any, on long-term health risks, even in the individuals who are most exposed (Allen et al., 1996).

ELF-EMFs induce currents in the human body. But various biochemical reactions within the body itself generate currents as well. The cells or tissues will not be able to detect any induced currents below this background level. Therefore, at low frequencies, exposure guidelines ensure that the level of currents induced by EMFs is below that of natural body currents.

The conclusion that ELF magnetic fields are possibly carcinogenic is still valid. This was concluded based on studies indicating that children exposed to relatively strong magnetic fields from power lines were more likely to develop leukemia (Draper et al., 2005). In European countries, the proportion of children exposed to such levels is less than 1% (Annual Report of WHO, 2007). Whether recommended exposure limits ought to be changed is a risk management decision.

Nevertheless, the lack of identified plausible mechanisms does not rule out the possibility of health effects existing even at very low field levels providing the basic scientific principles are adhered to.

Of the numerous suggested mechanisms proposed for the direct interaction of fields with the human body, three stands out as potentially operating at lower field levels than the others: induced electric fields in neural networks, radical pairs, and magnetite.

Electric fields induced in tissue by exposure to ELF-EMFs will directly stimulate myelinated nerve fibers in a biophysically plausible manner when the internal electric field strength exceeds a few volts per meter. Much weaker fields can affect synaptic transmission in neural networks as opposed to single cells. Such signal processing by nervous systems is commonly used by multi-cellular organisms to discriminate weak environmental signals. A lower bound of lmV/m on neural network discrimination was suggested, but based on current evidence threshold values around 10-100mV/m seem more likely.

The radical pair mechanism is an accepted way in which magnetic fields can affect specific types of chemical reactions, generally increasing reactive free radical concentration in low fields and decreasing them in high fields. These increases have been seen at less than 1mT.

Magnetite crystals, small ferromagnetic crystals of various forms of iron oxide, are found in animal and human tissues. Calculations based on extreme assumptions suggest a lower bound for the effects on magnetite crystals of ELF fields of 5μT.

Other direct biophysical interactions of fields,such as the breaking of chemical bonds, forces on charged particles and the various narrow band width "resonance" mechanisms, are not considered to provide plausible explanations for the interactions at field levels encountered in public and occupational environments.

With regard to indirect effects, the surface electric charge induced by exposure to ELF electric fields can be perceived and it can result in painful micro shocks when touching a conductive object. This produces small electric fields, possibly above background noise levels, in bone marrow. However, whether these present a risk to health is unknown.

ELF-EMFs can affect the nervous systems of people exposed to them, resulting in adverse health consequences such as nerve stimulation, at very high exposure levels (Huss et al., 2009). Exposure at lower levels induces changes in the excitability of nervous tissue in the central nervous system which may affect memory, cognition and other brain functions. These acute effects on the nervous system form the basis of international guidelines. However, they are unlikely to occur at the low exposure levels in the general environment and most working environments (Clements-Croome, 2004).

Influences of EMFs on the human health were studied and deduced that there is no concern for the inhabitants living outside the Right of Way (ROW) of TLs. The warning is for individuals who are under the HV lines for long times like workers in HV SSs (Zahiroddin et al., 2006): there may be harmful effects for them.

Alignment of the wires affects the resulted electric field of TL. To decrease the field intensity, many designs have been proposed (Stewart and Oppel, 1996). One method is to compact the former towers which also has been discussed in other literatures (Amman et al., 1998; Tsanakas et al., 2000). Conductor bundling will mitigate the electric field by 25% to 30%. Placing the wires close to each other will decrease the electric field, but the safety of system would decline. The second method is to change the conductors′ arrangement (Tsanakas et al., 1997; Feng et al., 2008). As suggested by Tsanakas, changing symmetrical arrangement into mirrored one lowers the EMFs. Anyhow, the mentioned circular design in this paper will be more effective in this aspect, although it is more expensive. The third method is to plant trees along TLs in order to reduce the electric field and subsequently the ROW for TLs (Ismail and Al-Kandari, 2003). Besides the indicated impact, there is no doubt about the other favorable environmental effects of cultivating trees. These methods are helpful, but considering the conditions and available instruments, the configuration which is showed in right side of [Figure - 2], may be the optimum choice. However, the reduction in magnetic field intensity according to the circular arrangement is remarkable.

Acknowledgements

The authors wish to acknowledge the support of High Voltage Laboratory of University of Tehran, especially Prof. Hossein Hohseni, the manager.^[34]

References

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