Post on 11-Jan-2016
1
Tutorial on
MITIGATION TECHNIQUESOF POWER FREQUENCY MAGNETIC FIELDS
ORIGINATED FROM ELECTRIC POWER SYSTEMS
Programme
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3rd-4th June, 2009
1 Ener SalinasGeneral principles - Methods of assessment - Strategies
2Pedro L. Cruz Romero
Conductor management - Compensation - Mitigation for T&D lines (EHV, HV, MV, LV)
3Jean Hoeffelman
Shielding by metallic materials - Power cables
4 Ener Salinas Substations - Examples
2
About the working group C4.204
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
• 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)
3
1.1 General Principles
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
4
Sources of power-frequency magnetic fields (PFMFs)
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
The flow of electrical energy from the
generation plant to the customer.
Along the way there are different types of
sources of power-frequency magnetic
fields
The PFMFs sources and techniques can be
classified according to their origin:
•Power lines•Underground cables•Complex sources (e.g. substations)
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Difference between Electric and Magnetic fields
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
MAGNETIC FIELD
ELECTRIC FIELD
Effect on humansEffect on humans
•The electric field E does not penetrate the house
•As the field reaches the walls, the electric charges (generated as a consequence of this field) are diverted to earth and recombined
•Even in the case of lightning, the lightning rods connected to ground will do this diversion successfully
•The electric field E does not penetrate the house
•As the field reaches the walls, the electric charges (generated as a consequence of this field) are diverted to earth and recombined
•Even in the case of lightning, the lightning rods connected to ground will do this diversion successfully
•The magnetic field B penetrates the house easily
•Only certain materials with specific geometries or dedicated circuits could oppose to this action
•The purpose of designing mitigation techniques is to find out what are the most appropriate materials, geometries or circuits that achieve this action effectively
•The magnetic field B penetrates the house easily
•Only certain materials with specific geometries or dedicated circuits could oppose to this action
•The purpose of designing mitigation techniques is to find out what are the most appropriate materials, geometries or circuits that achieve this action effectively
6
Interaction of AC magnetic fields with materials
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
FerromagneticPlate
Region of interest
Region of interest
Ferromagnetic enclosure
Region of interest
Coil
AC Source
(a) (b)
(c) Pure conductivePlate
Region of interest
(d)
Magnetic fields can have different
interactions with
different materials
“Deviation”
“Rejection”
“Concentration”
f
1
Some important design parameters:
PB
PBPSF
s
0Skin depth Shielding Factor
The geometry and the field incidence are
also important!
The geometry and the field incidence are
also important!
7
1.2 Methods of assessment of the mitigation techniques
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Numerical
Biot-Savart formula
Analytical
Experimental
Small scaleexperiment of a
3-phase underground
cable
Shielding experiments with busbars and conductors at normal scale
At power frequency we use the quasi-static approximation, i.e. displacement currents are neglected
At power frequency we use the quasi-static approximation, i.e. displacement currents are neglected
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1.3 Some strategies for mitigation
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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?
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.
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?
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.
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.
This is not an easy question since the definition of the area of interest is not always unambiguous.
This is not an easy question since the definition of the area of interest is not always unambiguous.
9
Tutorial on
MITIGATION TECHNIQUESOF POWER FREQUENCY MAGNETIC FIELDS
ORIGINATED FROM ELECTRIC POWER SYSTEMS
Programme
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3rd-4th June, 2009
11 Ener SalinasEner SalinasGeneral principles - Methods of assessment - General principles - Methods of assessment - StrategiesStrategies
2Pedro L. Cruz Romero
Conductor management - Compensation - Mitigation for T&D lines (EHV, HV, MV, LV)
33Jean Jean HoeffelmanHoeffelman
Shielding by metallic materials - Power cablesShielding by metallic materials - Power cables
44 Ener SalinasEner Salinas Substations - ExamplesSubstations - Examples
10
2.1 Conductor managementApplied mostly to linear sources: overhead lines, underground cables, busbars, etc.
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Layout Compaction
Change of geometry ofconductors keeping thesame phase-to-phaseclearance
Change of geometry ofconductors keeping thesame phase-to-phaseclearance
Keeping the same geometryreduce the phase-to-phase clearance
Keeping the same geometryreduce the phase-to-phase clearance
Original configuration
Contour curves values in TContour curves values in T
Balanced system !!
11
2.1 Conductor management
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Phase splitting
Single-phase line
Current dipole Current quadrupole
2
1
rB 3
1
rB Faster
reduction with distance to source !!
r : Distance to centre of dipole r : Distance to centre of dipole
r : Distance to centre of quadrupoler : Distance to centre of quadrupole
12
2.1 Conductor management
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Phase splitting
Three-phase line
Two split phases Three split phases
3
1
rB 3
1
rB No great
improvement !!
13
2.1 Conductor management
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Phase cancelation
Multi-circuit line
Super bundle Low-reactance
2
1
rB 3
1
rB Both circuits should be equally loaded
Changes in protection relays could be needed
Changes in corona performance in overhead circuits
14
2.2 Compensation
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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.
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
• Number of coils
Design parameters:
• Shape of the coil
• Location of the coil
• Electrical parameters of the conductor
• Number of coils
Not complete compensation !
!
15
2.2 Compensation
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Passive compensation
Single-phase line
With capacitorWith capacitor
LoopLoop
Contour curves values in TContour curves values in T
16
2.2 Compensation
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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.
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 !!
17
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Techniques
Increasing the height of masts
Conductor management
Compensation
• Low-medium cost
• Low-medium reduction factor
• Low-medium cost
• Low-medium reduction factor• Medium-high cost
• Low-medium-high reduction factor
• Medium-high cost
• Low-medium-high reduction factor• Medium-high cost
• Medium-high reduction factor
• Medium-high cost
• Medium-high reduction factor
Shielding factor = reduction factor !!
18
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
EHV and HV Power lines
Increasing the height of masts
-100 -50 0 50 100
0
5
10
15
20
25
Distanza dall'asse della linea [m]
H=11.34 m
H=12 m
H=14 m
H=16 m
H=18 m
H=20 m
H=22 m
H=24 m
Indu
zion
e m
agne
tica
a 1
m d
al s
uolo
- B
eff
- [µ
T]
V = 380 kVI = 1500 A
H
Distance from line centre [m]
Brm
s 1
m a
bove
gro
und
[T
]
Reduction restricted to underneath the line.
Reduction factor at x=0
Reduction restricted to underneath the line.
Reduction factor at x=0
4
mitigated
mitigatednon
B
BRF
19
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
EHV and HV Power lines
Conductor management: changing the geometry of conductors
Low reduction factor far from the line
Low reduction factor far from the line
4.1RF
Low reduction factor close to the line
Low reduction factor close to the line
2RF
380 kV380 kV
20
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
EHV and HV Power lines
Conductor management: compaction
Medium reduction factorMedium reduction factor
4RF
• Lower visual impact
• Reduction of line surge impedance
• Difficult to perform live-line maintenance
• EHV line: increase of corona effect
• Lower visual impact
• Reduction of line surge impedance
• Difficult to perform live-line maintenance
• EHV line: increase of corona effect
115 kV115 kV
21
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
EHV and HV Power lines
Conductor management: phase cancellation
Low reduction factor close to the line
Low reduction factor close to the line
2RF
Medium reduction factor far from the line
Medium reduction factor far from the line
3RF
380 kV1500 A
380 kV1500 A
22
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
EHV and HV Power lines
Conductor management: phase splitting
Medium reduction factor close to the line
Medium reduction factor close to the line
5RF
High reduction factor far from the line
High reduction factor far from the line
6RF
380 kV1500 A
380 kV1500 A
Star line: complete reduction at 35 m !!
23
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
EHV and HV Power lines
Passive compensation
Low reduction factor close to the line
Low reduction factor close to the line
2RF
High reduction factor far from the line at the other side
High reduction factor far from the line at the other side
8RF
Medium reduction factor far from the line at one side
Medium reduction factor far from the line at one side
4RF
Capacitor: non-symmetrical reduction!!
24
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
EHV and HV Power lines
Effect on other electrical parameters
MethodMagnetic
FieldElectric
FieldAudible
NoiseRadio
InterferenceUnbalance
Height increase (1) =
Layout =
Compaction
Vertical super-bundle low-reactance (2)
Phase splitting
Passive/active loop = = =
(1) Starting from certain distance (about 50 m) the effect is the opposite
(2) It rises lightly from about 30 m off
25
2.3 Mitigation for T&D overhead 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 3rd-4th June, 2009
MV and LV Power lines
Differences with EHV and HV lines
26
2.3 Mitigation for T&D overhead lines
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
MV and LV Power lines
Mitigation techniqueReduction level (%)
Installationcost
Global performance over conventional
Effect of unbalancedcurrent
Small compaction 25-45 Low Lower Low
Crossarms armless 60 Low/medium Lower Medium
Tree wires 60 Medium Higher Medium
Spacer cable 80 High 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
27
Tutorial on
MITIGATION TECHNIQUESOF POWER FREQUENCY MAGNETIC FIELDS
ORIGINATED FROM ELECTRIC POWER SYSTEMS
Programme
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3rd-4th June, 2009
11 Ener SalinasEner SalinasGeneral principles - Methods of assessment - General principles - Methods of assessment - StrategiesStrategies
22Pedro L. Cruz Pedro L. Cruz RomeroRomero
Conductor management - Compensation Conductor management - Compensation - Mitigation for T&D lines (EHV, HV, MV, LV)- Mitigation for T&D lines (EHV, HV, MV, LV)
3Jean Hoeffelman
Shielding by metallic materials - Power cables
44 Ener SalinasEner Salinas Substations - ExamplesSubstations - Examples
28
3 Shielding by metallic materials
Two types of shielding materials
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Magnetostatic shieldingFlux-shunting mechanism
Shielding by eddy currentsInduced currents mecanism
29
3.1 (pure) ferromagnetic shielding
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
MaterialInitial Relative Permeability
r,ini
Maximum Relative
Permeability r,max
Iron, 99.8% pure 150 5000
Steel, 0.9% C 50 100
Low Carbon Steel (LCS) 300 - 400 2000
Ultra Low Carbon Steel (ULC) 250 1100
Hot rolled Ultra Low Carbon Steel (HR ULC) 250 2000 to 5000
Silicon steel (Si 3%) - Grain oriented (GO) 40,000
78 Permalloy (μ-material) 8,000 100,000
30
3.1 (pure) ferromagnetic shielding
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
31
3.1 (pure) ferromagnetic shielding
Htengential continuous
Bnormal continuous
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
To be efficient at distance a ferromagnetic shield needs to be closed !
32
3.1 (pure) ferromagnetic shielding
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
To be efficient a ferromagnetic shield needs to encompass completely the source.
33
3.1 (pure) ferromagnetic shielding
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Closed ferromagnetic shields can have a very high efficiency
mainly when they are not too large with respect to their thickness.
Closed shieldClosed shield
(c) (a) (b)
34
3.1 (pure) ferromagnetic shielding
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
At distances higher than the shield width, the shielding efficiency is virtually zero.
0.2 0.4 0.6 0.8 1.0 1.2 1.41.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
shie
ldin
g f
act
or
distance y (m)
L = 1 m, d = 0.2 m, = 1 mm
r = 100
r = 500
r = 1000
r = 10000
Open shieldOpen shield
35
3.2 (pure) conductive shielding
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
aa
SF ~ aSF ~ a
Closed shieldClosed shield
Contrary to what happens with the pure ferromagnetic shielding, the shielding factor (SF) increases with the shape of the shield.
Contrary to what happens with the pure ferromagnetic shielding, the shielding factor (SF) increases with the shape of the shield.
Good shielding materials need to have a high conductivity () like copper or aluminium
Good shielding materials need to have a high conductivity () like copper or aluminium
(c) (a) (b)
36
3.2 (pure) conductive shielding
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Even at distances higher than the shield width, the shielding efficiency remains important.
0.2 0.4 0.6 0.8 1.0 1.2 1.40
5
10
15
20
25
shie
ldin
g f
act
or
distance y (m)
L = 1 m, d = 0.2 m, = 10 mm = 1 MS/m = 5 MS/m = 10 MS/m = 50 MS/m
Open shieldOpen shield
37
3.3 actual shielding materials
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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.
Metal Conductivity in MS/m
Copper 59
Aluminium 36
Iron 10
Steel 6
GO steel 2
Permalloy 1.8
38
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Acting on laying geometry and laying depth
Introducing passive loops
Allowing currents to flow in the metallic sheaths
Shielding by conductive metallic materials
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.
How to mitigate the fields ?How to mitigate the fields ?
39
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
0 5 10 150.02
0.1
0.2
0.5
1
2
5
Distanza dal centro linea [m]
Ind
uzi
on
e m
agn
etic
a a
1 m
dal
su
olo
- B
eff
[µT
]Con loop di compensazione L = 500 m (I Loop = 77 A)
Posa senza loop di compensazione
Con loop di compensazione L = 500 m e con condensatore di ottimazione (I Loop = 134 A; C1 = 13 mF)
CL
1.6 m
0.25 m
x
h calc. = 1 m
V = 132 kVI = 250 A
Cavo/sez. trinceaConfigurazione in piano (=100 mm)
0.25 m
1 2
Passive loop
40
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Passive loops (joint chamber)
Double loop : SF 2Double loop : SF 2
41
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Closed ferromagnetic shielding
Steel tube: SF > 50Steel tube: SF > 50
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50.3
0.5
1
2
3
5
10
20
30
50
100
150I = 3000 A
I = 1500 A
I = 250 A
I = 750 A
I = 375 A
CL
pp =1m
x
h mis. = 0 m
I = 250 ÷ 3000 A
B r
ms
, 1 m
abo
ve g
roun
d -
[µT]
Distance from line centre [m]
0.01
0.02
0.03
0.05
0.1
0.2
I = 3000 A
I = 1500 A
I = 250 A
I = 750 A
I = 375 A
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
CL
pp =1m
x
h mis. = 0 m
I = 250 ÷ 3000 A
scherm o: L = 66 m; = 406 m m; s = 10 mm
B r
ms
, 1 m
abo
ve g
roun
d -
[µT]
Distance from line centre [m]
42
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Closed ferromagnetic shielding
Raceway: SF 20Raceway: SF 20
43
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Flat conductive shielding
Copper plane shield (flat formation): SF > 7 Copper plane shield (flat formation): SF > 7
Effectiveness of the shieldings calculated at 1 m above the ground
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10
Horizontal distance from the line axis (m)
Shie
ldin
g ef
fect
iven
ess
( d
)
d = 5 cm
d = 10 cm
d = 20 cm
2525100
145
0.3d
44
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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
In order to be effective, the shielding plates have to be welded together
Aluminium may also be used but is less effective
45
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Open conductive shielding
Aluminium H shield (flat formation): SF > 7 Aluminium H shield (flat formation): SF > 7
bridge welding
100
80
150
20
20
80
25
46
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Open conductive shielding
Aluminium square shield (trefoil formation): SF > 7 Aluminium square shield (trefoil formation): SF > 7
bridgewelding
150
32
20
62
60
47
3.4 Underground cables
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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 low to medium medium
Corrosion risk / needs protection
needs protection
Cu: OK
Al: depends on soil pH
Costs low medium high Cu: high
Al: medium
Maintenance easy rather easy variable rather easy
48
Tutorial on
MITIGATION TECHNIQUESOF POWER FREQUENCY MAGNETIC FIELDS
ORIGINATED FROM ELECTRIC POWER SYSTEMS
Programme
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
International Colloquium on Power-Frequency Magnetic Fields, Sarajevo 3rd-4th June, 2009
11 Ener SalinasEner SalinasGeneral principles - Methods of assessment - General principles - Methods of assessment - StrategiesStrategies
22Pedro L. Cruz Pedro L. Cruz RomeroRomero
Conductor management - Compensation Conductor management - Compensation - Mitigation for T&D lines (EHV, HV, MV, LV)- Mitigation for T&D lines (EHV, HV, MV, LV)
33Jean Jean HoeffelmanHoeffelman
Shielding by metallic materials - Power cablesShielding by metallic materials - Power cables
4 Ener Salinas Substations - Examples
49
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
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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
50
Typical LV in-house substation located in the cellar of a building
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
51
Mitigation of PFMFs from busbars
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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
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
52
More elaborated shielding designs for busbars
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
<SF> = 2 when cancellation loops are used alone
<SF> = 4 when the 1010-steel is used alone
<SF> = 6 when the Al shield is used alone
<SF> = 9 when aluminium and 1010-steel are used
<SF> larger than 20 when aluminium, 1010-steel and loops are used
<SF> = 2 when cancellation loops are used alone
<SF> = 4 when the 1010-steel is used alone
<SF> = 6 when the Al shield is used alone
<SF> = 9 when aluminium and 1010-steel are used
<SF> larger than 20 when aluminium, 1010-steel and loops are used
(a) (b)
(c) (d)
Windows and apertures
Windows and apertures
Narrow gapsNarrow gaps
Combination of 2 passive shields and one active
loop
Combination of 2 passive shields and one active
loop
Averaged shielding factors <SF> in front of the second shield
Averaged shielding factors <SF> in front of the second shield
BusbarsBusbars
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Magnetic field from transformers-1
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Because of the core and cover, transformers (by themselves) emit almost no magnetic field
Because of the core and cover, transformers (by themselves) emit almost no magnetic field
A possible mitigation technique is to optimize phase mixing
A possible mitigation technique is to optimize phase mixing
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Connections from the LV side
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
R S T R S T
Before phase management
After phase management
R S T R ST
R ST
Mixing phases
The responsible for field emissions nearby transformers are often the connections from the secondary side
The responsible for field emissions nearby transformers are often the connections from the secondary side
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Field mitigation techniques for MV/LV substations
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Source Strategy Technique Method
Short busbars (residential)
Mitigation at the source•Conductive shielding (e.g. aluminium)•Passive compensation
-3D-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
-2D-Numerical methods-Analytical
Transformers
Mitigation at the source, by optimizing the connections at the secondary side
•Phase cancellation•Distance management
-3D-Numerical-Experiments with the relevant components (connections at the LV side)
Cables Mitigation at the source
•Shielding with metal plates•Passive compensation with loops
-Analytical-2D-FEM
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Mitigation of PFMFs from HV/MV substations
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
•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.
•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.
57
Examples of Implementation of
Mitigation Techniques
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
58
Example 1: Ferromagnetic pipes in Genoa
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
•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 kV 1x1000 mm2 XLPE cable were shielded with this technology
•Field at 1m above the ground < 0.2 μT
•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 kV 1x1000 mm2 XLPE cable were shielded with this technology
•Field at 1m above the ground < 0.2 μT
59
Example 2 Passive lops in Vienna
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
60
Example 3: High Magnetic Coupling
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
Different designsDifferent designs
Configuration 1Configuration 1
ResultsResults
ShieldingCables
Sourcecables
Magnetic core
Sourcecables
Shieldingcables
o'
o
Windings
Shieldingcables
o
Sourcecables
Magnetic core
Windings
Section S1 and S3 Section S2
d=11.8 cm
(HV cable1600 mm2)
i=50 cm
Section S1 and S3 Section S2
d=11.8 cm
(HV cable1600 mm2)
i=50 cm
Jointing zone
S1S2 S3
x
y
z
x=0m x=10m x=20m x=30m
Jointing zone
S1S2 S3
x
y
z
x=0m x=10m x=20m x=30m
Configuration 2Configuration 2Source only
Source only
SF = 88.4SF = 88.4
SF = 7.3SF = 7.3
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Example 4: Castiglione Project, a case of active shielding of a HV overhead line in Italy
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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.
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 mitigationBefore mitigation
After mitigation operationsAfter mitigation operations
Cabin containing loop feeding devices Cabin containing loop feeding devices Regulated current generator
Regulated current generator
After works, inactivated screen
After works, inactivated screen Before works
Before works
After works, activated screen
After works, activated screen
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Example 5: Shielding of busbars in a secondary substation
Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009
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
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
63Tutorial on Magnetic Field Mitigation Techniques, International Colloquium on ELF EMF, Sarajevo 3rd-4th June, 2009