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TRANSCRIPT
Exposure of workers and the general public to electromagnetic fields
at power frequency
Scientific evidence – region dependent legislation –mitigation possibilities
K. Van Reusel
CONTENTS
Chapter 1 Scientific evidence
Chapter 2 Region dependent legislation
Chapter 3 Mitigation possibilities
CONTENTS
Chapter 1 Scientific evidence
Schematic representation of electromagnetic spectrum showing some typical sources
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The effects of EMF in different frequency ranges
5/54
(frequency intervals are not to scale)
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Applicable limits in Belgium(general public)
Limits [µT] Legislation RemarksFederal 100 European Council
1999/519/ECNo federal law
Flanders - chronic > 365 days 0.4 - acute 1-14 days 20
Belgian official journal07.09.2018
Averaging over time
Wallonia 100 Arrêté du 01/12/2005(≥1500 kVA)
Arrêté du 21/12/2006(100 <TF<1500 kVA)
Brussels 100 (permanent)1000 (short duration)
Arrêté du 09.09.1999 du Gouvernement de la Région de Bruxelles-
Capitale
250 kVA<TF<1000 kVA(1000 kVA: no treshold)
In practice*:-Target value 0.4 µT- Intervention: 10µT
(for children < 15y)
*average value over 24h
Imbroglio:Broad range in “limits”
0.4 µT (Flanders)------ 100 µT (Wallonia)
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- residential fields (>< occupational)
- childhood: < 15 years old (not for adults)
- leukemia (not brain tumours or other kinds of solid tumours)
- 0.4 µT: epidemiological cut off point between exposed group and control group
Scientific base: IARC epidemiology
Scientific base: ICNIRP dosimetry
“It is the view of ICNIRP that the currently existing scientific evidence that prolonged exposure to low frequency magnetic fields is causally related with an increased risk of childhood leukemia is too weak to form the basis for exposure guidelines.”
“In this guideline, the physical quantity used to specify the basic restrictions on exposure to EMF is the internal electric field strength Ei, as it is the electric field that affects nerve cells and other electrically sensitive cells.”
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Basisrestrictions in terms of internal electric field strength
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Reference levels for exposure to time varying magnetic fields
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Reference levels for general public exposure to time varyingelectric and magnetic fields
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(unperturbed rms values)
Reference levels for occupational exposure to time varyingelectric and magnetic fields
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(unperturbed rms values)
CONTENTS
Chapter 2 Region dependent legislation
Occupational exposure --- General public
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ICNIRP EU Federal Flanders Wallonia BrusselsOccupational
[µT] 1000 1000 1000 - - -
General public [µT] 200 100 - 0,4
20 100 0,410
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Applicable limits in Belgium
Limits [µT] Legislation RemarksFederal 100 European Council
1999/519/ECNo federal law
Flanders - chronic > 365 days 0.4 - acute 1-14 days 20
Belgian official journal07.09.2018
Averaging over time
Wallonia 100 Arrêté du 01/12/2005(≥1500 kVA)
Arrêté du 21/12/2006(100 <TF<1500 kVA)
Brussels 100 (permanent)1000 (short duration)
Arrêté du 09.09.1999 du Gouvernement de la Région de Bruxelles-
Capitale
250 kVA<TF<1000 kVA(1000 kVA: no treshold)
In practice*:-Target value 0.4 µT- Intervention: 10µT
(for children < 15y)
*average value over 24h
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Comparison with neighbouring countries
Limits Legislation Remarks
EU 100 µT COUNCIL RECOMMENDATION of 12 July 1999 on the limitation of exposure of the general public to electromagnetic
fields (1999/519/EC)
FRANCE 100 µT Agence Nationale des Fréquences
GERMANY 200 µT 26. BImSchVhttp://www.gesetze-im-internet.de/bundesrecht/bimschv_26/gesamt.pdf
LUXEMBOURG Safety distance100-220 kV: 30 m
65 kV: 20 m
Circulaire n° 1644 du 11 mars 1994
NETHERLANDS 0.4 µT - zone Rijksinstituut voor Volksgezondheid en Milieu
Sensitive dwellings(new houses, schools, crèches,…)
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0.4 µT (red) zone – 2 x 80m – and0.2 µT (yellow) zone around 150 kV overhead line
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Limits Legislation Remarks
UK 360 µT Public Health England (PHE)
SWITZERLAND 100 µT Ordonnance sur la protection contre le rayonnement non ionisant (ORNI)du 23 décembre 1999
ITALY 100 µT Loosely application + safety distances
Comparison with other countries
Fundamental problem for measuring low frequency – low magnitude magnetic field
Low frequency (50 Hz)
Low field magnitude
Low measurement signalin noisy electro smog environment
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Typical values for magnetic fields [µT] near substations
5.618.5
10.3At 3 m in the corridor of the neighbour
Cabine 30/R00261Avenue du pont de Luttre 35
Transformator : 400 kVA
Charge : 33.9 %.
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Typical values for magnetic fields [µT] near substations
3164
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Typical values for magnetic fields near substations
N° Position Height[cm]
B field[µT]
1 At 30 cm from fence transformer 150 312 At 30 cm from door fuses entry LV 150 643 In the corner behind door entry (side street) 100 5.64 At wall, in corridor of neighbour (3 m from door) 150 18.55 At 30 cm from wall, in corridor of neighbour (3 m from door) 150 10.3
Time-Variation of Magnetic Field in Substation
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o Measurement time-variation of magnetic field
o Measurement time-variation of unbalance
→ Link: unbalance ↔ magnetic field
Time-Variation of Magnetic Field in Substation
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o Unbalance: main source of magnetic field
o Magnetic field limits: average over time!
Brussels: 0,4 µT avg 24h
Wallonia: 100 µT avg 6 minutes
Flanders: 20 µT avg 2 weeks
0,4 µT avg 1 year
Time-Variation of Magnetic Field in Substation
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oMeasurement time-variation of current in neutral
oStrong link unbalance ↔ field
oAvg over one week: 16 µT
oMaximum: 35 µT
CONTENTS
Chapter 3 Mitigation possibilities
• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb28/54
Chapter 3: Mitigation possibilities
• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb29/54
Chapter 3: Mitigation possibilities
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I = 100 A
Distance r = 1 mB ?
B = μr . μ0 rIπ2
121001041 7
••= −
ππ
= 20 µT
Distance as the most important parameter
Distance as the most important parameter
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B = 0,25 . 100 . 0,05 1²
= 1,25 µT
𝑩𝑩(µ𝑻𝑻) ⋍𝟎𝟎,𝟐𝟐𝟐𝟐. 𝑰𝑰 𝑨𝑨 .𝑺𝑺(𝒎𝒎)
𝑿𝑿𝑿(𝒎𝒎)
Unbalanced B ~ 1/rBalanced B ~ 1/r²2 symmetrical, balanced busbars B ~ 1/r³
Distance as the most important parameter
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Reduction of φ to φ distance
— Compact busbars
— 3φ cables
— Isolated busbars (to reduce distance between φ’s)
Distance between transformer and low voltage panel as short as possible
Distance as the most important parameter
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• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb34/54
Chapter 3: Mitigation possibilities
B can not be annihilated
B can be cancelled by - B
Shielding – Fundamental Principle
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Active shielding
—External equipment supplies a suitable (M & φ) current
—greater reduction of B than passive shielding
—Detailed design is needed
—Rather for EMC shielding
Active shielding
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Passive shielding
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dEdtΦ
= −
• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb38/54
Chapter 3: Mitigation possibilities
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Passive shielding
Magnetic field without shielding Magnetic field with shielding
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Passive shielding
Substation of Beguines
• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb41/54
Chapter 3: Mitigation possibilities
Shielding - Materials
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μr ρ [10-8
Ωm]kg/m³ €/kg
steel 2000* 16* 7850 0.6*Cu 1 1.7 8940 5Al 1 2.7 2712 2
* order of magnitude
Shielding with µ-steel
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µ-steel
Lowering of the cable tray
ALU plating on the ceiling
Reduction of the M-field towards micro Tesla overkill
µ-steel is an ageing component
Conductivity is parameter among project variables (copper or aluminium are often a good trade-off between costs and performance)
Ferromagnetism (shielding efficiency ~ 1/r) or conductivity (shielding efficiency ~ r) or both
Best results with aluminium (+ ferromagnetic material: strong reduction at d < 1,5m)
Shielding material
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• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb45/54
Chapter 3: Mitigation possibilities
U (C) – shape or flat?
Flat plate (U-shape gives not so much additional reduction of shielding effect)
Shielding - Shape
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Minimum overlap, maximum bolt spacing
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X: min 20 cm
Y: max 10 cm
Intensity of induced currents depends on the shield extension, less on its thickness
Eddy currents concentrated at the edges → no endings of shield close to exposure positions
Too small dimension boundary effects (no shielding effect anymore!)
• Eddy currents concentrated at the edges → no endings of shield close to exposure positions
• Rule of thumb: 10 cm larger in horizontal and vertical direction of LV-panel
Shielding - shape
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• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb49/54
Chapter 3: Mitigation possibilities
Shield efficiency depends almost linearly on the shield thickness, if smaller than the skin depth δ• δCu: ~ 9 mm @ 50 Hz
• δAl: ~ 12 mm @ 50 Hz
Al: 2 mm < thickness ≤ 5 mm
Shield thickness
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• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb51/54
Chapter 3: Mitigation possibilities
Shield - position
Shielding performance increases as the distance between shield and sources is reduced
Conducting plates compensate mainly the normalcomponent of the field → source orientation is a major factor in determining the shield effectiveness.
Ferromagnetic material: as close as possible to the zone that has to be protected
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• Distance as the most important parameter
• Active/Passive shielding
• Passive shieldingMaterial
Shape
Thickness
Position
→ Rules of thumb53/54
Chapter 3: Mitigation possibilities
Passive shielding
o Close to adjacent sensitive dwellings
o Aluminium (flat surface, multi-layer, assembled)
o 2 mm < thickness < 5 mm
o Minimum overlap: 20 cm
o Maximum distance between bolts: 10 cm
Rules of thumb
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