How HV t ransmission lines af fects humans, plants and animals? Elect ric and Magnet icf ields?

http://electrical-engineering-portal.com/how-hv- transmission- lines-affects-humans-plants January 22, 2013

How HV transmission lines affects humans and plants?

IntroductionBy increasing population of the world, towns are expanding, many buildings constructnear high voltage overhead power transmission lines. The increase of power demand hasincreased the need f or transmitting huge amount of power over long distances. Largetransmission lines conf igurations with high voltage and current levels generate largevalues of electric and magnetic f ields stresses which af f ect the human being and thenearby objects located at ground surf aces.

This needs to be investigating the ef f ects of electromagnetic f ields near thetransmission lines on human health.

The electricity system produces extremely low f requency electromagnetic f ield whichcomes under Non ionizing radiations which can cause health ef f ects. Apart f rom humanef f ect, the electrostatic coupling & electromagnetic interf erence of high voltagetransmission lines have impact on plants and telecommunication equipments mainlyoperating in f requency range below UHF.

Is power line EMF safe?

This is the controversy Discussion directly eludes on Government Regulation policy andPower Company. There are lots of supporting documents and research paper in f avorand crit icize this arguments.

What are the electric and magnetic fields?Electric and magnetic f ields, of ten referred to as electromagnetic f ields or EMF,occur naturally and as a result of the Power generation, Power Transmission, Powerdistribution and use of electric power..

EMF is f ields of f orce and is created by electric voltage and current. They occuraround electrical devices or whenever power lines are energized..

Electric fields are due to voltage so they are present in electrical appliances andcords whenever the electric cord to an appliance is plugged into an outlet (even ifthe appliance is turned of f )..

Electric f ields (E) exist whenever a (+) or (-) electrical charge is present. They exertf orces on other charges within the f ield. Any electrical wire that is charged willproduce an electric f ield (i.e. Electric f ield produces charging of bodies, dischargecurrents, biological ef f ects and sparks). This f ield exists even when there is nocurrent f lowing. The higher the voltage, the stronger is electric f ield at any givendistance f rom the wire..

The strength of the electric f ield is typically measured in volts per meter (V/m) or inkilovolts per meter (kV/m). Electric f ields are weakened by objects like trees,buildings, and vehicles. Burying power lines can eliminate human exposure to electricf ields f rom this source..

Magnetic fields result f rom the motion of the electric charge or current, such aswhen there is current f lowing through a power line or when an appliance is plugged inand turned on. Appliances which are plugged in but not turned on do not producemagnetic f ields..

Magnetic f ield lines run in circles around the conductor (i.e. produces magneticinduction on objects and induced currents inside human and animal (or any otherconducting) bodies causing possible health ef f ects and a multitude of interf erenceproblems). The higher the current, the greater the strength of the magnetic f ield..

Magnetic f ields are typically measured in tesla (T) or more commonly, in gauss (G)and milli gauss (mG). One tesla equals 10,000 gauss and one gauss equals 1,000

milli gauss..

The strength of an EMF decreases signif icantly with increasing distance f rom thesource..

The Strength of an electric f ield is proportional to the voltage of the source. Thus,the electric f ields beneath high voltage transmission lines f ar exceed those belowthe lower voltage distribution lines. The magnetic f ield strength, by contrast, isproportional to the current in the lines, so that a low voltage distribution line with ahigh current load may produce a magnetic f ield that is as high as those produced bysome high voltage transmission lines..

In f act, electric distribution systems account f or a f ar higher proportion of thepopulation’s exposure to magnetic f ields than the larger and more visible highvoltage transmission lines..

Electrical field: the part of the EMF that can easily be shielded..

Magnetic field: part of the EMF that can penetrate stone, steel and human f lesh. Inf act, when it comes to magnetic f ields, human f lesh and bone has the samepenetrability as air!.

Both fields are invisible and perfectly silent: People who live in an area withelectric power, some level of artif icial EMF is surrounding them..

The magnetic f ield strength produced f rom a transmission line is proportional to:load current, phase to phase spacing, and the inverse square of the distance f romthe line..

Many previous works studied the ef f ect of dif f erent parameters on the producedmagnetic f ield such as: the distance f rom the line, the conductor height, lineshielding and transmission line conf iguration and compaction.

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Electric and Magnetic Field (EMF) EffectsExtremely high voltages in EHV lines cause electrostatic ef f ects, where as short circuitcurrents & line loading currents are responsible f or electromagnetic ef f ects.

The ef f ect of these electrostatic f ields is seen prominent with living things like humans,plants, animals along with vehicles, f ences & buried pipes under & close to these lines.

Power f requency elect ric f ields

1) EMF effects on human beingsThe human body is a composed of some biological materials like blood, bone, brain,lungs, muscle, skin etc. The permeability of human body is equals to permeability of airbut within a human body has dif f erent electromagnetic values at a certain f requency f ordif f erent material.

The human body contains f ree electric charges (largely in ion-rich f luids such as bloodand lymph) that move in response to f orces exerted by charges on and currents f lowingin nearby power lines. The processes that produce these body currents are calledelectric and magnetic induction.

In electric induction, charges on a power line attract or repel f ree charges within thebody. Since body f luids are good conductors of electricity, charges in the body move toits surf ace under the inf luence of this electric f orce. For example, a positively chargedoverhead transmission line induces negative charges to f low to the surf aces on the upperpart of the body. Since the charge on power lines alternates f rom positive to negativemany times each second, the charges induced on the body surf ace alternate also.Negative charges induced on the upper part of the body one instant f low into the lowerpart of the body the next instant.

Thus, power-frequency electric fields induce currents in the body (Eddy Current) aswell as charges on its surface.

The currents induced in the body by magneticf ields are greatest near the periphery of thebody and smallest at the center of the body.

It is believed that, the magnetic f ield mightinduce a voltage in the tissue of human bodywhich causes a current to f low through it due toits conductivity of around them.

The magnetic f ield has inf luence on tissues inthe human body. These inf luences may bebenef icial or harmful depending upon itsnature.

The magnitude of surf ace charge and internalbody currents that are induced by any givensource of power-f requency f ields depends onmany f actors. These include the magnitude of the charges and currents in the source, thedistance of the body f rom the source, the presence of other objects that might shield orconcentrate the f ield, and body posture, shape, and orientation. For this reason thesurface charges and currents which a given field induces are very different fordifferent Human and animals.

When a person who is isolated f rom ground by some insulating material comes in closeproximity to an overhead transmission line, an electrostatic f ield is set in the body ofhuman being, having a resistance of about 2000 ohms.

When the same person touches a grounded object, it will discharge through his bodycausing a large amount of discharge current to f low through the body. Discharge currentsf rom 50-60 Hz electromagnetic f ields are weaker than natural currents in the body, suchas those f rom the electrical activity of the brain and heart.

For human beings the limit f or undisturbed f ield is 15 kV/m, R.M.S., to experience possibleshock. When designing a transmission lines this limit is not crossed, in addition to thisproper care has been taken in order to keep minimum clearance between transmissionlines.According to research and publications put out by the World Health Organization(WHO),EMF such as those f rom power lines, can also cause:

Short term Health Problem

1. Headaches

2. Fatigue

3. Anxiety

4. Insomnia

5. Prickling and/or burning skin

6. Rashes

7. Muscle pain

Long term Health Problem

Following serious health Problems may be arise due to EMF ef f ects on human Body.

(1) Risk of damaging DNA.

Our body acts like an energy wave broadcaster and receiver, incorporating andresponding to EMFs. In f act, scientif ic research has demonstrated that every cell in yourbody may have its own EMF, helping to regulate important f unctions and keep youhealthy.

Strong, artif icial EMFs like those f rom power lines can scramble and interf ere with yourbody’s natural EMF, harming everything f rom your sleep cycles and stress levels to yourimmune response and DNA!

(2) Risk of Cancer

Af ter hundreds of international studies, the evidence linking EMFs to cancers and otherhealth problems is loud and clear. High Voltage power lines are the most obvious anddangerous culprits, but the same EMFs exist in gradually decreasing levels all along thegrid, f rom substations to transformers to homes.

(3) Risk of Leukemia

Researchers f ound that children living within 650 f eet of power lines had a 70% greaterrisk f or leukemia than children living 2,000 f eet away or more.(As per British MedicalJournal, June, 2005).

(4) Risk of Neuro degenerative disease

“Several studies have identif ied occupational exposure to extremely low-f requencyelectromagnetic f ields (EMF) as a potential risk f actor f or neuro degenerativedisease.”(As per Epidemiology, 2003 Jul; 14(4):413-9).

(5) Risk of Miscarriage

There is “strong prospective evidence that prenatal maximum magnetic f ield exposureabove a certain level (possibly around 16 mG) may be associated with miscarriage risk.”(As per Epidemiology, 2002 Jan; 13(1):9-20)

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2) EMF Effects on AnimalsMany researchers are studying the ef f ect of Electrostatic f ield on animals. In order to doso they keeps the cages of animals under high Electrostatic f ield of about 30 kV/m.

The results of these Experiments are shocking as animals (are kept below highElectrostatic f ield their body acquires a charge & when they try to drink water, a sparkusually jumps f rom their nose to the grounded Pipe) like hens are unable to pick up grainbecause of chattering of their beaks which also af f ects their growth.

3) EMF Effects on Plant LifeMost of the areas in agricultural and f orest lands where high power transmission linespass. The voltage level of high power transmission Lines are 400KV, 230KV, 110KV, 66KVetc. The electromagnetic f ield f rom high power transmission lines af f ects the growth ofplants.

Gradually increases or decreases and reaches to maximum current or minimum currentand thereaf ter it starts to f all down to lowest current or raises to maximum current or aconstant current. Again the current, it evinces with litt le f luctuations till the next day

morning.

Current in Power transmission lines varies according to Load (it depending upon theamount of electricity consumed by the consumers). Hence the ef f ect of EMF (due tocurrent f lowing in the power lines) upon the growth of plants under the high powertransmission lines remains unaltered throughout the year.

From various practically study it was f ound that the response of the crop to EMF f rom110 KV and 230 KV Power lines showed variations among themselves. Based on theresults the growth characteristics like shoot length, root length, leaf area, leaf f reshweight, specif ic leaf weight, shoot/root ratio, total biomass content and total watercontent of the f our crop plants were reduced signif icantly over the control plants.

Similar trend were observed in the biochemical characteristics like chlorophyll. Reducedgrowth and physiological parameter was primarily due to the ef f ect of reduced celldivision and cell enlargement. Further the growth was stunted which may be due to pooraction of hormones responsible f or cell division and cell enlargement.

The bio-chemical changes produced in this plant due to EMF stress quite obvious and itaf f ects the production leading to economic loss. It is concluded that the reduced growthparameter shown in the crop plants would indicates that the EMF has exerted a stress onthat plants and this EMF stress was quite obvious and it af f ects the production leading toeconomic loss. So f urther research activit ies are needed to safe guard plants f rom EMFstress.

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4) EMF Effects on Vehicles parked near LineWhen a vehicle is parked under high voltage transmission line an electrostatic f ield isdeveloped in it. When a person who is grounded touches it a discharge current f lowsthrough the human being. In order to avoid this parking lots are located below thetransmission lines the recommended clearance is 17 m for 345 kV and 20 m for 400 kVlines.

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5) EMF Effects on Pipe Line/Fence/CablesA fence, irrigation pipe, pipeline, electrical distribution line f orms a conducting loops whenit is grounded at both ends. The earth f orms the other portion of the loop. The magneticf ield f rom a transmission line can induce a current to f low in such a loop if it is orientedparallel to the line.

If only one end of the f ence is grounded, then an induced voltage appears across theopen end of the loop. The possibility f or a shock exists if a person closes the loop at theopen end by contacting both the ground and the conductor.

For f ences, buried cables, and pipe lines proper care has been taken to prevent themf rom charging due to Electrostatic f ield. When using pipelines which are more than 3 km inlength & 15 cm in Diameter they must be buried at least 30 laterally f rom the line center.

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6) EMF Effects Maintenance WorkerFor providing continuous and uninterrupted supply of electric power to consumersmaintenance operations of power lines are of ten perf ormed with systems energized orlive.

This is live line maintenance or hot line maintenance. The electric f ields and magneticf ields associated with these power lines may af f ect the health of live line workers. Itselectric f ield and current densities af f ect the health of humans and cause severaldiseases by af f ecting majority parts of the human body. These electric f ield and currentdensities af f ects humans of all stages and causes short term diseases in them andsometimes death also.

Contradiction of EMF Effect on Human HealthThere are two reasons why electromagnetic f ields associated with power systems couldpose no threat to human health.

First, The EMF f rom power lines and appliances are of extremely low f requency and lowenergy. They are non-ionizing and are markedly dif f erent in f requency f rom ionizingradiation such as X-rays and gamma rays. As a comparison, transmission lines have a lowf requency of 60Hz while television transmitters have higher f requencies in the 55 to 890MHZ range. Microwaves have even higher f requencies, 1,000 MHZ and above. Ionizingradiation, such as X-rays and gamma rays, has f requencies above 1015 Hz. The energyf rom higher-f requency f ields is absorbed more readily by biological material. Microwavescan be absorbed by water in body tissues and cause heating which can be harmful,depending upon the degree of heating that occurs. X-rays have so much energy that theycan ionize (f orm charged particles) and break up molecules of genetic material (DNA)and no genetic material, leading to cell death or mutation. In contrast, extremely lowf requency EMF does not have enough energy to heat body tissues or cause ionization.

Second, all cells in the body maintain large natural electric f ields across their outermembranes. These naturally occurring f ields are at least 100 times more intense thanthose that can be induced by exposure to common power-f requency f ields. However,despite the low energy of power-f requency f ields and the very small perturbations thatthey make to the natural f ields within the body.

When an external agent such as an ELF f ields lightly perturbs a process in the cell, otherprocesses may compensate f or it so that there is no overall disturbance to the organism.Some perturbations may be within the ranges of disturbances that a system can

experience and still f unction properly.

During Research on health ef f ects of electric and magnetic f ields, it has come forwardthat electric f ield intensity exposure of about 1-10 mv/m in tissue interact with cells butnot proved to be harmful. But strong f ields cause harmful ef f ects when their magnitudeexceeds stimulation thresholds f or neural tissues (central nervous system and brain),muscle and heart.

Surface Current Density(mA/m2)

Health Effect

Absence of any established ef f ects

1 to 10 Minor biological ef f ects

10 to 100 Well established ef f ects(a) Visual ef f ect.(b) Possiblenervous system ef f ect

100 to 1000 Changes in central nervous System

> 1000 Ventricular Fibrillation (Heart Condition 0. Health hazards

In India it is stipulated that electric f ield intensity should not exceed 4.16 kV/m andmagnetic f ield intensity should not exceed 100μT in public areas.

Even when ef f ect is demonstrated consistently on the cellular level in laboratoryexperiments, it is hard to predict whether and how they will af f ect the whole organism.Processes at the individual cell level are integrated through complex mechanisms in theanimal.

Mitigation of EMF Effect of Transmission Line

1) Line shielding

There are two basic 60-Hz magnetic f ield mitigation (reduction) methods: passive andactive.

Passive magnetic f ield mitigation includes rigid magnetic shielding with f erromagnetic andhighly conductive materials, and the use of passive shield wires installed neartransmission lines that generate opposing cancellation f ields f rom electromagneticinduction.

Active magnetic f ield mitigation uses electronic f eedback to sense a varying 60-Hzmagnetic f ield, then generates a proportionally opposing (nulling) cancellation f ield withina def ined area (room or building) surrounded by cancellation coils. Ideally, when the two

opposing 180-degree out- of -phase magnetic f ields of equal magnitude intersect, theresultant magnetic f ield is completely cancelled (nullif ied).

This technology has been successfully applied in both residential and commercialenvironments to mitigate magnetic f ields f rom overhead transmission and distributionlines, and underground residential distribution (URD) lines.

2) Line Configuration and Compaction

Line compaction means that, bringing the conductors close together keeping the minimum(safe) phase-to-phase spacing constant. Keeping all the parameters the same and theonly variable is the phase-to- phase spacing. The magnetic f ield is proportional to thedimensions of the phase-to-phase spacing.

Other studies showed that, increasing the distance between phases by increasing theheight of the central phase conductor above the level of the other phase conductorsleads to the reduction of the peak value of the magnetic f ield.

Reducing the phase-to-phase distance, leads to the decrease of the magnetic f ield. Thisreduction between phases is limited by the electrical insulation level between phases.

(A) For single circuit lines, compaction causes a great reduction to the maximummagnetic f ield values. This reduction of magnetic f ield allows f or lower conductor heightsabove the ground. This leads to transmit the same power on shorter towers. This gives agreat reduction of the tower cost.

(B) For double circuit lines, some studies showed that, the use of optimum phasearrangement causes a drastic reduction to the maximum magnetic f ield values f or bothconventional and compact lines i.e. with vertical conductor

3) Grounding

Induced currents are always present in electric f ields under transmission lines and will bepresent. However, there must be a policy to ground metal objects, such as f ences, thatare located on the right-of -way. The grounding eliminates these objects as sources ofinduced current and voltage shocks.

Multiple grounding points are used to provide redundant paths f or induced current f lowand mitigate nuisance shocks.

4) Providing Right of Way(R.O.W)

Overhead transmission systems required strips of land to be designed as right-of -ways(R.O.W.). These strips of land are usually evaluated to decrease the ef f ects of theenergized line including magnetic and electric f ield ef f ects.

5) Maintaining Proper Clearance

Unlike f ences or buildings, mobile objects such as vehicles and f arm machinery cannot begrounded permanently. Limiting the possibility of induced currents f rom such objects topersons is accomplished by maintaining proper clearances f or above-ground conductorstend to limit f ield strengths to levels that do not represent a hazard or nuisance.

Limiting access area by increasing conductor clearances in areas where large vehiclescould be present.

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Conclusion:Based on the review and analysis and other research projects it is of the opinion thatthere is no conclusive and convincing evidence that exposure to extremely low f requencyEMF emanated f rom nearby high voltage Transmission lines is causally associated withan increased incidence of cancer or other detrimental health ef f ects in humans. Even if itis assumed that there is an increased risk of cancer as implied in some epidemiologicalstudies, the empirical relative risk appears to be f airly small in magnitude and theobserved association appears to be tenuous.

Although the possibility is still remain about the verse ef f ect on health by EMF.

Ref erences:

SSGBCOE&T, Electronics and Communication Engineering-Girish Kulkarni1,Dr.W.Z.Gandhare

Pharmacology, School of Medicine, Chung-Ang University, Seoul, Korea-Sung-HyukYim, Ji-Hoon Jeong.

Electrical Engineering Department, Shoubra, Benha University, Cairo, Egypt- NagatMohamed Kamel Abdel-Gawad.

Madurai Kamaraj University-S. Somasekaran.

Electrical Engineering Department at King Fahd University of Petroleum & Minerals-J. M. Bakhashwain, M. H. Shwehdi, U. M. Johar and A. A. AL-Naim.

Dept. of Electrical Engineering. College of Engineering – University of Tikrit-Iraq-Ghanim Thiab Hasan, Kamil Jadu Ali, Mahmood Ali Ahmed.

Originally published at Electrical Notes & Articles