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International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3 rd-4 th June, 2009 Tutorial on International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3 rd-4 th June, 2009 Tutorial on MITIGATION TECHNIQUES OF POWER FREQUENCY MAGNETIC FIELDS ORIGINATED FROM ELECTRIC POWER SYSTEMS Programme 1 Ener Salinas General principles - Methods of assessment Strategies 2 Pedro L. Cruz Romero Conductor management - Compensation - Mitigation for T&D lines (EHV, MV, LV) 3 Jean Hoeffelman Shielding by metallic materials - Power cables 4 Ener Salinas Substations - Examples Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 1

About the working group C 4. 204 • CIGRÉ Working Group formed in 2001 About the working group C 4. 204 • CIGRÉ Working Group formed in 2001 • Motivation: Concerns from customers, utilities and researchers in relation to some alleged health risks (in particular childhood leukaemia) of long-term exposure to power frequency magnetic fields • Initial aim: To collect discuss and synthesise the available technical data referring to different existing techniques to mitigate extremely low frequency (ELF) magnetic fields • Final form: A published Technical Brochure (TB 373) Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 2

1. 1 General Principles Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF 1. 1 General Principles Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 3

Sources of power-frequency magnetic fields (PFMFs) The flow of electrical energy from the generation Sources of power-frequency magnetic fields (PFMFs) The flow of electrical energy from the generation plant to the customer. Along the way there are different types of sources of powerfrequency magnetic fields The PFMFs sources and techniques can be classified according to their origin: • Power lines • Underground cables • Complex sources (e. g. substations) Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 4

Difference between Electric and Magnetic fields ELECTRIC FIELD MAGNETIC FIELD • The electric field Difference between Electric and Magnetic fields ELECTRIC FIELD MAGNETIC FIELD • The electric field E does not penetrate the house Effect on humans • The magnetic field B penetrates the house easily • As the field reaches the walls, the electric charges (generated as a consequence of this field) are diverted to earth and recombined • Only certain materials with specific geometries or dedicated circuits could oppose to this action • Even in the case of lightning, the lightning rods connected to ground will do this diversion successfully • The purpose of designing mitigation techniques is to find out what are the most appropriate materials, geometries or circuits that achieve this action effectively Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 5

Interaction of AC magnetic fields with materials AC Source (a) Ferromagnetic enclosure (b) “Concentration” Interaction of AC magnetic fields with materials AC Source (a) Ferromagnetic enclosure (b) “Concentration” Region of interest Coil “Deviation” Ferromagnetic Plate (c) “Rejection” Magnetic fields can have different interactions with different materials The geometry and the field incidence are also important! Pure conductive Plate (d) Region of interest Some important design parameters: Skin depth Shielding Factor Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 6

1. 2 Methods of assessment of the mitigation techniques Analytical Biot-Savart formula Numerical At 1. 2 Methods of assessment of the mitigation techniques Analytical Biot-Savart formula Numerical At power frequency we use the quasistatic approximation, i. e. displacement currents are neglected Experimental Shielding experiments with busbars and conductors at normal scale Small scale experiment of a 3 -phase underground cable Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 7

1. 3 Some strategies for mitigation A relevant factor regarding the technique to use 1. 3 Some strategies for mitigation A relevant factor regarding the technique to use is the choice of the location i. e. where it is to be applied. In other words apply it to the source or to the area of interest? This is not an easy question since the definition of the area of interest is not always unambiguous. As a general rule, it may seem natural to think that it will be more cost-effective to mitigate at the source than at the area of interest. However, the choice can be different. For example in some cases where the source is rather large (e. g. long busbars); or if the purpose is to mitigate the field in a small region. The green outlines are symbolic representations – not necessarily metal plates – they could indicate a loop, an active device, or any other mitigation action within that region. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 8

International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3 rd-4 th June, 2009 Tutorial on International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3 rd-4 th June, 2009 Tutorial on MITIGATION TECHNIQUES OF POWER FREQUENCY MAGNETIC FIELDS ORIGINATED FROM ELECTRIC POWER SYSTEMS Programme 1 Ener Salinas General principles - Methods of assessment Strategies 2 Pedro L. Cruz Romero Conductor management - Compensation - Mitigation for T&D lines (EHV, MV, LV) 3 Jean Hoeffelman Shielding by metallic materials - Power cables 4 Ener Salinas Substations - Examples Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 9

2. 1 Conductor management Applied mostly to linear sources: overhead lines, underground cables, busbars, 2. 1 Conductor management Applied mostly to linear sources: overhead lines, underground cables, busbars, etc. Original configuration Layout Compaction Change of geometry of conductors keeping the same phase-to-phase clearance Keeping the same geometry reduce the phase-to-phase clearance Balanced system !! Contour curves values in T Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 10

2. 1 Conductor management Phase splitting Single-phase line Current dipole Current quadrupole Faster reduction 2. 1 Conductor management Phase splitting Single-phase line Current dipole Current quadrupole Faster reduction with distance to source !! r : Distance to centre of dipole r : Distance to centre of quadrupole Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 11

2. 1 Conductor management Phase splitting Three-phase line Two split phases Three split phases 2. 1 Conductor management Phase splitting Three-phase line Two split phases Three split phases No great improvement !! Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 12

2. 1 Conductor management Phase cancelation Multi-circuit line Super bundle Low-reactance Both circuits should 2. 1 Conductor management Phase cancelation Multi-circuit line Super bundle Low-reactance Both circuits should be equally loaded Changes in protection relays could be needed Changes in corona performance in overhead circuits Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 13

2. 2 Compensation Passive compensation Location close to the source of a loop or 2. 2 Compensation Passive compensation Location close to the source of a loop or coil. Magnetic field generated by the coil that partially compensates the original field. Induced current in the loop due to the flux linkage. Increase of effectiveness: insertion of capacitor to compensate the inductance of the loop. Design parameters: • Shape of the coil • Location of the coil • Electrical parameters of the conductor Not complete compensation !! • Number of coils Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 14

2. 2 Compensation Passive compensation Single-phase line Loop With capacitor Contour curves values in 2. 2 Compensation Passive compensation Single-phase line Loop With capacitor Contour curves values in T Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 15

2. 2 Compensation Active compensation Current in the loop generated by an external power 2. 2 Compensation Active compensation Current in the loop generated by an external power source. Current control in amplitude and phase. More sophisticated equipment is required. Costly and less reliable than the passive loop. Higher flexibility in the location of the loop. Possibility of locating it far from the source. Not complete compensation !! Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 16

2. 3 Mitigation for T&D overhead lines Techniques Increasing the height of masts Conductor 2. 3 Mitigation for T&D overhead lines Techniques Increasing the height of masts Conductor management Compensation • Low-medium cost • Medium-high cost • Low-medium reduction factor • Low-medium-high reduction factor • Medium-high reduction factor Shielding factor = reduction factor !! Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 17

2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Increasing the 2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Increasing the height of masts Reduction restricted to underneath the line. Reduction factor at x=0 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 18

2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Conductor management: 2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Conductor management: changing the geometry of conductors 380 k. V Low reduction factor close to the line Low reduction factor far from the line Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 19

2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Conductor management: 2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Conductor management: compaction Medium reduction factor 115 k. V • Lower visual impact • Reduction of line surge impedance • Difficult to maintenance perform live-line • EHV line: increase of corona effect Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 20

2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Conductor management: 2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Conductor management: phase cancellation Low reduction factor close to the line 380 k. V 1500 A Medium reduction factor far from the line Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 21

2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Conductor management: 2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Conductor management: phase splitting Medium reduction factor close to the line 380 k. V 1500 A High reduction factor far from the line Star line: complete reduction at 35 m !! Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 22

2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Passive compensation 2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Passive compensation Low reduction factor close to the line Medium reduction factor far from the line at one side High reduction factor far from the line at the other side Capacitor: nonsymmetrical reduction!! Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 23

2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Effect on 2. 3 Mitigation for T&D overhead lines EHV and HV Power lines Effect on other electrical parameters Magnetic Field Electric Field Audible Noise Radio Interference Unbalance Height increase (1) = Layout = Compaction Vertical super-bundle low-reactance (2) Phase splitting Passive/active loop = = = Method (1) Starting from certain distance (about 50 m) the effect is the opposite (2) It rises lightly from about 30 m off Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 24

2. 3 Mitigation for T&D overhead lines MV and LV Power lines Differences with 2. 3 Mitigation for T&D overhead lines MV and LV Power lines Differences with EHV and HV lines • Variation of current along the feeder • Different distribution systems different presence of zero sequence current – 3 -wire 3 -phase – 4 -wire 3 -phase – 5 -wire 3 -phase – 2 -wire – 1 -phase • Lower voltages use of covered and insulated conductors • Shorter phase-phase clearance Field mitigation only of interest near the line more effectiveness in raising the poles. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 25

2. 3 Mitigation for T&D overhead lines MV and LV Power lines Mitigation technique 2. 3 Mitigation for T&D overhead lines MV and LV Power lines Mitigation technique Reduction level (%) Installation cost Global performance over conventional Effect of unbalanced current Small compaction 25 -45 Lower Low Crossarms armless 60 Low/medium Lower Medium Tree wires 60 Medium Higher Medium Spacer cable 80 Higher High Aerial Boundle Cable 100 Very high Higher High Underground line 90 Very high Higher High Phase split 70 -80 Medium Lower High Increase clearance to ground 25 -60 Low/medium Lower Low Compensation loop 35 Medium Lower Medium Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 26

International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3 rd-4 th June, 2009 Tutorial on International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3 rd-4 th June, 2009 Tutorial on MITIGATION TECHNIQUES OF POWER FREQUENCY MAGNETIC FIELDS ORIGINATED FROM ELECTRIC POWER SYSTEMS Programme 1 Ener Salinas General principles - Methods of assessment Strategies 2 Pedro L. Cruz Romero Conductor management - Compensation - Mitigation for T&D lines (EHV, MV, LV) 3 Jean Hoeffelman Shielding by metallic materials - Power cables 4 Ener Salinas Substations - Examples Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 27

3 Shielding by metallic materials Two types of shielding materials Magnetostatic shielding Flux-shunting mechanism 3 Shielding by metallic materials Two types of shielding materials Magnetostatic shielding Flux-shunting mechanism Shielding by eddy currents Induced currents mecanism Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 28

3. 1 (pure) ferromagnetic shielding Initial Relative Permeability r, ini Maximum Relative Permeability r, 3. 1 (pure) ferromagnetic shielding Initial Relative Permeability r, ini Maximum Relative Permeability r, max Iron, 99. 8% pure 150 5000 Steel, 0. 9% C 50 100 300 - 400 2000 Ultra Low Carbon Steel (ULC) 250 1100 Hot rolled Ultra Low Carbon Steel (HR ULC) 250 2000 to 5000 Material Low Carbon Steel (LCS) Silicon steel (Si 3%) - Grain oriented (GO) 78 Permalloy (μ-material) 40, 000 8, 000 100, 000 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 29

3. 1 (pure) ferromagnetic shielding Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on 3. 1 (pure) ferromagnetic shielding Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 30

3. 1 (pure) ferromagnetic shielding Htengential continuous Bnormal continuous To be efficient at distance 3. 1 (pure) ferromagnetic shielding Htengential continuous Bnormal continuous To be efficient at distance a ferromagnetic shield needs to be closed ! Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 31

3. 1 (pure) ferromagnetic shielding To be efficient a ferromagnetic shield needs to encompass 3. 1 (pure) ferromagnetic shielding To be efficient a ferromagnetic shield needs to encompass completely the source. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 32

3. 1 (pure) ferromagnetic shielding Closed shield Closed ferromagnetic shields can have a very 3. 1 (pure) ferromagnetic shielding Closed shield Closed ferromagnetic shields can have a very high efficiency mainly when they are not too large with respect to their thickness. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 33

3. 1 (pure) ferromagnetic shielding Open shield (a) (b) (c) At distances higher than 3. 1 (pure) ferromagnetic shielding Open shield (a) (b) (c) At distances higher than the shield width, the shielding efficiency is virtually zero. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 34

3. 2 (pure) conductive shielding Closed shield a SF ~ a Good shielding materials 3. 2 (pure) conductive shielding Closed shield a SF ~ a Good shielding materials need to have a high conductivity ( ) like copper or aluminium Contrary to what happens with the pure ferromagnetic shielding, the shielding factor (SF) increases with the shape of the shield. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 35

3. 2 (pure) conductive shielding Open shield (a) (b) (c) Even at distances higher 3. 2 (pure) conductive shielding Open shield (a) (b) (c) Even at distances higher than the shield width, the shielding efficiency remains important. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 36

3. 3 actual shielding materials Metal Conductivity in MS/m Copper 59 Aluminium 36 Iron 3. 3 actual shielding materials Metal Conductivity in MS/m Copper 59 Aluminium 36 Iron 10 Steel 6 GO steel 2 Permalloy 1. 8 In ferromagnetic materials the conductivity plays also an important part in the shielding efficiency. Sometimes multilayer shield involving both high permeability material and good conductive metals are applied. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 37

3. 4 Underground cables How to mitigate the fields ? ü Acting on laying 3. 4 Underground cables How to mitigate the fields ? ü Acting on laying geometry and laying depth ü Introducing passive loops ü Allowing currents to flow in the metallic sheaths ü Shielding by conductive metallic materials ü Shielding by ferromagnetric metallic materials Independently from the shielding efficiency of each of the above solutions, the best solution strongly depends on whether the intervention must be carried out on an existing cable already in operation or on a new cable still to be laid down. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 38

3. 4 Underground cables Passive loop Tutorial on Magnetic Field Mitigation Techniques, International Colloquium 3. 4 Underground cables Passive loop Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 39

3. 4 Underground cables Passive loops (joint chamber) Double loop : SF 2 Tutorial 3. 4 Underground cables Passive loops (joint chamber) Double loop : SF 2 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 40

3. 4 Underground cables Closed ferromagnetic shielding Steel tube: SF > 50 Tutorial on 3. 4 Underground cables Closed ferromagnetic shielding Steel tube: SF > 50 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 41

3. 4 Underground cables Closed ferromagnetic shielding Raceway: SF 20 Tutorial on Magnetic Field 3. 4 Underground cables Closed ferromagnetic shielding Raceway: SF 20 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 42

3. 4 Underground cables Flat conductive shielding Copper plane shield (flat formation): SF > 3. 4 Underground cables Flat conductive shielding Copper plane shield (flat formation): SF > 7 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 43

3. 4 Underground cables Flat conductive shielding In order to be effective, the shielding 3. 4 Underground cables Flat conductive shielding In order to be effective, the shielding plates have to be welded together Aluminium may also be used but is less effective Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 44

3. 4 Underground cables Open conductive shielding Aluminium H shield (flat formation): SF > 3. 4 Underground cables Open conductive shielding Aluminium H shield (flat formation): SF > 7 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 45

3. 4 Underground cables Open conductive shielding bridge 15 0 welding 32 62 20 3. 4 Underground cables Open conductive shielding bridge 15 0 welding 32 62 20 60 Aluminium square shield (trefoil formation): SF > 7 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 46

3. 4 Underground cables Synthesis Passive loops Open ferromagnetic shielding Closed ferromagnetic shielding Conductive 3. 4 Underground cables Synthesis Passive loops Open ferromagnetic shielding Closed ferromagnetic shielding Conductive shielding Shielding factor SF 1. 5 to 4 (flat formation) depends on distance to shield ! > 15 >7 Losses low low to medium Corrosion risk / needs protection Cu: OK Al: depends on soil p. H Costs low medium high Cu: high Al: medium Maintenance easy rather easy variable rather easy Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 47

International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3 rd-4 th June, 2009 Tutorial on International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3 rd-4 th June, 2009 Tutorial on MITIGATION TECHNIQUES OF POWER FREQUENCY MAGNETIC FIELDS ORIGINATED FROM ELECTRIC POWER SYSTEMS Programme 1 Ener Salinas General principles - Methods of assessment Strategies 2 Pedro L. Cruz Romero Conductor management - Compensation - Mitigation for T&D lines (EHV, MV, LV) 3 Jean Hoeffelman Shielding by metallic materials - Power cables 4 Ener Salinas Substations - Examples Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 48

4. Substations LV SUBSTATIONS The main characteristics of these sources, and the ones that 4. Substations LV SUBSTATIONS The main characteristics of these sources, and the ones that differentiate them from power lines and underground cables, are: • • • Complexity Local concentration Proximity The list of possible sources contributing to the emitted PFMF is: • • • Busbars Transformers Low-voltage cables Low-voltage connections High-voltage cables Neutral/stray currents Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 49

Typical LV in-house substation located in the cellar of a building Tutorial on Magnetic Typical LV in-house substation located in the cellar of a building Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 50

Mitigation of PFMFs from busbars Busbars can have different shapes. Yet, longitudinal profiles are Mitigation of PFMFs from busbars Busbars can have different shapes. Yet, longitudinal profiles are often common and it can be sometimes a reasonable approximation when designing geometries and selecting shielding material Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 51

More elaborated shielding designs for busbars (a) (b) (c) Combination of 2 passive shields More elaborated shielding designs for busbars (a) (b) (c) Combination of 2 passive shields and one active loop (d) Busbars Averaged shielding factors in front of the second shield = 2 when cancellation loops are used alone Windows and apertures Narrow gaps = 4 when the 1010 -steel is used alone = 6 when the Al shield is used alone = 9 when aluminium and 1010 -steel are used larger than 20 when aluminium, 1010 -steel and loops are used Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 52

Magnetic field from transformers-1 Because of the core and cover, transformers (by themselves) emit Magnetic field from transformers-1 Because of the core and cover, transformers (by themselves) emit almost no magnetic field Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 53

Connections from the LV side The responsible for field emissions nearby transformers are often Connections from the LV side The responsible for field emissions nearby transformers are often the connections from the secondary side A possible mitigation technique is to optimize phase mixing Before phase management After phase management R ST T R S Mixing phases R S Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 T 54

Field mitigation techniques for MV/LV substations Source Strategy Technique Method Short busbars (residential) Mitigation Field mitigation techniques for MV/LV substations Source Strategy Technique Method Short busbars (residential) Mitigation at the source • Conductive shielding (e. g. aluminium) • Passive compensation -3 D-FEM or Integral methods -Lab experiments Long busbars (industrial) Mitigation at the source may not be cost efficient. Thus mitigation at the affected area may be needed • Conductive or ferromagnetic shielding • Active compensation -2 D-Numerical methods -Analytical Transformers Mitigation at the source, by optimizing the connections at the secondary side • Phase cancellation • Distance management -3 D-Numerical -Experiments with the relevant components (connections at the LV side) Mitigation at the source • Shielding with metal plates • Passive compensation with loops -Analytical -2 D-FEM Cables Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 55

Mitigation of PFMFs from HV/MV substations • In HV substations, the highest magnetic fields Mitigation of PFMFs from HV/MV substations • In HV substations, the highest magnetic fields are also registered at the secondary side • However these are located mainly between the substation limits • Some emission over the 1 -microtesla level can be registered outside the substation boundaries • A possible mitigation technique is distance management, i. e. moving the affected area or extending the fence some metres. Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 56

Examples of Implementation of Mitigation Techniques Tutorial on Magnetic Field Mitigation Techniques, International Colloquium Examples of Implementation of Mitigation Techniques Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 57

Example 1: Ferromagnetic pipes in Genoa • The three cables are enclosed inside a Example 1: Ferromagnetic pipes in Genoa • The three cables are enclosed inside a ferromagnetic tubular section, which acts as a shield trapping the magnetic flux • The material used is low carbon steel, with an external diameter of 508 mm and a thickness of 9. 5 mm • 2 km of circuit of 150 k. V 1 x 1000 mm 2 XLPE cable were shielded with this technology • Field at 1 m above the ground < 0. 2 μT Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 58

Example 2 Passive lops in Vienna Tutorial on Magnetic Field Mitigation Techniques, International Colloquium Example 2 Passive lops in Vienna Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 59

Example 3: High Magnetic Coupling Different designs Results SF = 7. 3 Source only Example 3: High Magnetic Coupling Different designs Results SF = 7. 3 Source only Configuration 1 SF = 88. 4 Configuration 2 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 60

Example 4: Castiglione Project, a case of active shielding of a HV overhead line Example 4: Castiglione Project, a case of active shielding of a HV overhead line in Italy The scope of this project was the reduction of the magnetic field - in an area of children activity - to values below 0. 2 μT as requested by the local administration. Before mitigation After mitigation operations After works, inactivated screen Before works After works, activated screen Cabin containing loop feeding devices Regulated current generator Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 61

Example 5: Shielding of busbars in a secondary substation Results After implementation of the Example 5: Shielding of busbars in a secondary substation Results After implementation of the two separated shielding plates (back of the switchboard and ceiling) The maximum value of the magnetic field in the area of interest was 0. 4 μT The average value of the magnetic field was 0. 2 μT Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 62

Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3 rd-4 th June, 2009 63