İletim hatlarının oluştuduğu elektrik ve magnetik alanların insan sağlığı üzerindeki etkileri
Effects of electric and magnetic fields produced by transmission lines on health
- Tez No: 46526
- Danışmanlar: PROF.DR. NESRİN TARKAN
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 59
Özet
ÖZET Elettik gücü iletimi ve kullanımı esnasında yayılan elektrik ve magnetik alanların biyolojik etkileri dünyada pekçok araştırmacı tararından incelenmekte ve yakın bir gelecekte uluslararası güvenlik standartlarına ulaşılması hedeflenmektedir. Elektromagnetik alanların olumsuz etkilerinin olabileceği bugün bütün dünyada tartışılırken, evlerde kullanılan elektrikli aletlerden ya da iletim hatlarından yayılan alanların düşük seviyede olması ve güç kullanımı arttıkça sağlık üzerindeki etkilerinin aynı oranda artmaması nedeniye herhangi bir risk oluşturmayacağım belirtenler de var. Ancak genel olarak yapılan çalışmalarda biyolojik sistemlerin güç frekansındaki elektrik ve magnetik alanlara karşı duyarlı olduğu sonucuna varılmıştır. Bu çalışmada ise öncelikle kısa bir şekilde güç iletimine değinilmiş, daha sonra iletim hatlarının iki önemli parametresi olan endüktans ve kapasite üzerinde durulmuş son olara da elektrik ve magnetik alanların insan sağlığı üzerindeki etkileri incelenmiştir. Ayrıca güvenlik açısından yerleşim bölgelerinin, okul veya parkların iletim hatlarından ne kadar uzakta bulunması gerektiğiyle ilgili bir bilgisayar çalışması yapılmıştır. ix
Özet (Çeviri)
SUMMARY EFFECTS OF ELECTRIC AND MAGNETIC FffiLDS PRODUCED BY TRASlVaSSION LINES ON HEALTH Public interest has recently focused on the biological effects of exposure to electric and magnetic fields associated with electric power transmission and utilization. in this study power transmission systems were considered and health effects of electric and magnetic fields were investigated. By transmission, is normally implied, the bulk transfer of power by high voltage links between main load centres. Distribution on the other hand is mainly concerned with the conveyance of this power to consumers by means of lower voltage networks. Transmission lines transmit electrical power from a sending-station (s) to a receiving-station (R) without supplying any consumers route: by contrast, a distribution line ör distribütör supplies consumers directly at short intervals along the üne. Thus a distribütör is subject to the legal requirement that power should be supplied at a voltage within T 6% of a declared voltage, whereas a transmission line is not subject to the restriction and its voltage can carry as much as 10 ör even 15 % due to variations in load. in practice the distinction betvveen transmission and distribution is not so clear-cut as several large consumers are now being supplied at 132 kV and above, and single-phase loads are being taken from two phases of a 132 kV line. The transmission system is referred to collectively as the grid, the 275 and 400 kV systems being referred to as the super-grid. Although the present 400-420 kV network of some 7000 km length is expected to meet the main transmission requirements untü about the end of the century, research continues at higher voltages. The two ends of a transmission line can terminale at generating-stations, grid- switching stations ör grid-supply points. The terminals of a modern generating station are now normally outdoor. Grid-switching stations have similar outdoor terminals but are not associated with a particular generating station. They comprise transformers for interconnecting the various voltage levels of the grid and circuit breakers for clearing faults and controlling the system. xThe primary parameters of a transmission line are its series and shunt resistance, its series inductance (şelf and mutual) and its shunt capacitance. Inductance is due to the magnetic fields set up by the line currents and is a series inductance carrying a line current. Capacitance, and its charging current due to the electric field set up by the system voltage and appear as a shunt circuit across the system voltage. The insulation of a line is seldom perfect and leakage currents flow över the surface of the insulators especially during foul weather. This leakage is simulated by a shunt resistance of high ohmic value across the system capacitance. Leakage causes a power loss which is a function of the system voltage. Corona causes a power loss from the system which, being dependent on the system voltage, is lumped together with the leakage effect. Normally leakage and corona effects are ignored since the effective shunt resistance is generally many times greater than the shunt capacitive reactance. in the next chapter, effects of electric and magnetic fields on health were examined. The action of human cells depends on the action of ions ör charged particles. Calcium ions have a powerful influence on how a cell's membrane works, and on muscle contraction, egg fertilisation and celi division. Magnetic fields can transfer energy to these ions, causing them to move faster. If a charged partide is exposed to a steady magnetic filed, such as the earth's, it beings to adopt a circular motion at right angles to the applied field. If an oscillating magnetic field is applied parallel to the steady field, it can, if it is at the right frequency, transfer energy to the partide. The frequencies of alternating fields that cause resonance with the earth's own steady magnetic field, lie between l and 100 Hz. f (Hzl/K*.' resonance ( 60 Hz. 0,2 G ) /U* 100Hz/ /oa / ^N° 50 Hz///'s'* O Hz|__^_> O 020.610B (Gauss) Fiğ. 1. Steady Magnetic Field. xiWhether these energised ions cause cancer has not been proved. Current opinion is that resonance does not initiate tumours, but may cause the conditions that promote them. Table 1. Magnetic flux densities from 400 kV power transmission line. LocationMagnetic flux density (/*T).Maximum at ground level ander 4QQ kV line40.25 m from centreline of line8.Maximum at ground level above 400 kV 200 underground cable.At head height above underground cable25.5 m lateral displacement from underground10 cable Most of the reported findings of associations between the occurance of a disease and electromagnetic fıelds are the results of epidemiologic studies and, therefore, depend on an understanding of the scientifîc principles involved. in brief, epidemiology is the study of how disease is distributed and how various factors determine this distribution. The ideal way to look at the risks and causes of human disease is to study human beings themselves. The issue disappeared from the news until 1979 when Nancy Wertheimer, an epidemiologist at the University of Colorado, examined the relationship between childhood cancers and the proximity of transmission lines. She found that fields of 300 nT from power lines produced an abnormal number of childhood cancers. But critics dismissed these results because statistical error could not be ruled out. Since that time, several other studies have explored associations between various measures of residential electric and magnetic fields exposures and cancer risk. A large number of studies have also examined cancer risk among adults with respect to occupational electromagnetic fields exposures. in the occupational studies, exposure has been assessed for the most part by the identification of persons who have worked in electrical occupations and industries. Among both children and adults, the focus has narrowed to brain cancer, leukaemia, and adult male breast cancer. in brief, investigators are in agreement that the ascertainment of true relevant exposure in electric and magnetic fields studies is subject to considerable misclassification that could generate systematic ünderestimation of the relative risk. xiiThus, it can be inferred that the relative risks linking electromagnetic fîelds to childhood cancers, if truly elevated, should in fact be much higher than the empirically derivated relative risks, unless they have been biased upward by other methodologic shortcomings such as control selection bias. Electricity consumption increased exponentially in this century. If a rapidly increasing wide spread exposure were indeed strongly associated with childhood cancers, and if no strong countervailing trends in other risk factors were occurring, we should be witnessing an observable epidemic of childhood cancers. However, there is little, if any, evidence of such an epidemic of childhood cancer. Öne of the most difficult and complicated areas of research is that of reproductive risks. Because ali reproductive problems have multiple and frequently interrelated causes and putative causes. Öne difficulty in predicting the effect that an environmental exposure, such as from electric and magnetic fields, may have on the developing embryo stems from the normally observed variation in the incidence of embryonic and fetal loss with the stage of gestation. Öne approach in evaluating environmental hazards is to determine vvhether there is any correlation between the incidence of the disease ör diseases in question and changes in exposure. Electric power generation and residential consumption of power during in this century have increased by nearly three orders of mağnitude. it is obvious that a large proportion, probably approaching 100%, of the population is exposed to electric and magnetic fîelds from electric povver transmission and consumption. However reliable data are not avaible for evaluating secular trends for ali of the reproductive effects. The three outcomes that would be appropriate for a trend analysis are birth defects, spontaneous abortions, and stillbirths. Of these, data dealing with the occurrence of birth defects are the most occurate and, as noted earlier regarding the lack of an association between childhood cancer and electric power transmission, do not show any increasing secular trend. There are some studies that report a mutagenic effect, but the predominance of the reports indicates that electric and magnetic fields are not mutagenic agents, as are some reproductive toxins. it has been suggested that many of the studies are negative because there is not only a threshold for some of these effects, but a ceiling as well. Thus, the concept has been introduced that electric and magnetic fields effects may have a narrow window of apportunity to produce biologic effects, but this aspect has not been adequately explored. The suggested reproductive risks of electric and magnetic fields are not supported by the totality of the basic science and human studies that pertain to xiiireproduction. However, the fact that a reproductive effect may not seem biologically plausible and that adequate documentation of an increased risk has not been demonstrated in human studies does not mean that these concerns should be summarily dismissed. Changes in behavior may be the initial signs of nervous. System problems, but performance, which is observable represents more than just the action of the nervous system. It is often not possible to find structural damage under conditions that produce profound behavioral changes. The scientific literature has been evaluated with regard to possible electromagnetic fields effects with measures of both behavioral interactions and central nervous system activities. Studies of electric and magnetic fields, and their possible effects on both behavior magnetic fields, and their possible effects on both behavior and the nervous system, have been conducted under a range of conditions, but the data on the relationship between measured effects in these two domains are extremely limited. Although the detectability of an electric or magnetic field by the subject is neither a necessary nor a sufficient condition for health effects, an analysis of such stimulus functions could help elicudate mechanisms of action. Most of the literature involving human subjects shows that electric fields can be detected, but the mechanism or mechanisms of detection remain to be established. The results of several animals studies addressing the issue of avoidance of electric field exposure appear to support the conclusion that such effects, to the extent that they have been demonstrated, are small and of minor importance. Over the past two decades, several investigators have addressed the problem of magnetic filed effects on general activity, with equivocal results. At the level of the laboratory primate and the human research subject, there is little or no indication that magnetic fields have any significant effect on general activity. The ability of electric and/or magnetic fields to influence the nocturnal production of melatonin has been examined. Each of these exposures, under certain circumstance, has been shown to change the nighttime production and secretion of melatonin in mammals, including humans. The magnitudes of the changes varied among the studies and have not been defined in reference to exposure parameters, nor have dose-response relationships been found. The behavior of human subjects, as indicated by mood, daily life activities, reaction time, memory, time content of melatonin in the pineal and also in the blood because the hormone is quickly released from the cells of the gland. This review indicates that there is no convincing evidence to support the contention that exposures to extremely low frequency electric and magnetic fields generated by sources such as household appliances and power transmission lines, but insufficiency of the data must not mean that the subject is completely negligible. xxvTable 2. Range of daily time- weighted average exposures of power industry workers to 60 Hz electric fields and magnetic flux densities. Finally, a computer program, calculating the required distance of public facilities such as houses, schools, parks from the transmission lines due to the security limits of 200 nT magnetic field and 10 kV/m electric field that are accepted as security limits in several countries, was established in the study. xv
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