training on power frequency electric and magnetic field ......power lines are both electric and...
TRANSCRIPT
Training on power frequency electric and
magnetic field strength prediction model
Enrica Caputo – Arpa Piemonte, Radiation Department
• Macro geographical analysis
• Exposition evaluation without measurements
• Exposition evaluation on new sources
• Past exposition evaluation
• Minimun distance from sources calculation
Electric and Magnetic field strength
prediction model
Why?
Energy Infrastructure
FOCUS: Overhead transmission power lines
Primary exposition source
Italy:70000 km HV (120-132-150 kV) and VHV (220-380 kV) transmission lines
GLOSSARY
1. Insulator.
2. Bundle of two conductors (some lines have 4).
3. Spacer to hold the two conductors apart.
4. Earth wire at top of tower or pylon.
5. The three bundles on one side of the tower make
up one electrical circuit. Most lines have two
circuits, one each side.
6. Identity plate saying which line it is and who owns
it. Also usually has a safety warning notice about
the dangers of electrocution.
7. Anti-climbing device - barbed wire to stop
unauthorised climbing
GLOSSARY
Ammarro
singoloSospensione
singola
Sospensione a V
singola
Ammarro
doppioSospensione
doppiaSospensione a V
doppia
In technical documentation :
SS; ┴ Single vertical insulator
DS; ╨ Double vertical insulator
SA; /\ Single horizontal insulator
DA; //\\ Double horizontal insulator
V \\// V-shape insulator (for 380 kV)
Conductors height
GLOSSARY
h1: conductor height on start pylon
h2: conductor height on end pylon
L: Span length
SAG: difference in level between the points of support and the lowest point on the
conductor
GC: minimum ground clearance (minimum height)
GC
h h
GLOSSARY
Conductors width is fixed by geometrichal pylons shape
Conductors height (cfr Sag and minimum Ground clearance) depends
on cables weight and length and environmental boundary conditions
GC
h h
CATENARY
T=Cable Tension (N)
H*= Horizontal Tension (N)
W= Cable Weight (N/m)
𝑧 (𝜉) =𝑘cosh (𝜉/𝑘+𝐶1) +𝐶2
k=Catenary Constant (m)
k= H/W (m)
C1, C2 calculated by h1,h2
h1 h2
z
𝜉
*the horizontal tension is assumed to be constant throughout the conductor at a given temperature
B-E CALCULATION
Power lines are both ELECTRIC and MAGNETIC FIELD sources
ELECTRIC FIELD
• VOLTAGE
• Conductors TYPE and SIZE
• Pylons geometrical SHAPE
• phase DISPOSITION
• DISTANCE by conductors
No time variations
Screened by most building
materials and by trees, hedges
etc
MAGNETIC FIELD
• CURRENT
• Pylons geometrical SHAPE
• phase DISPOSITION
• DISTANCE by conductors
Time variations (Current variation
by energy needs)
Not screened
3D MAGNETIC FIELD CALCULATION
Ampère-Laplace law
m0 air magnetic permeability constant (4p 10-7 H/m)
I current
dl element of length along the path taken by the current
r position vector of the point at which B is being determined
Γ Conductors curve shape (catenary)
3D MAGNETIC FIELD CALCULATION - Γ
Yv= minimum height in xy plane
X axis origin in x catenary minimum
V
V
Y
x
Y
x
V
Y
xcoshY)ee(
2
Y)x(Y VV
2D MAGNETIC FIELD CALCULATION
Simplified 2D models based on the Biot-Savart law.
If power line conductors satisfy a thin-wire approximation are treated as infinite
line sources positioned at a constant distance from the earth’s surface.
Thin-wire approximation: straight horizontal parallel wires with span length
>>distance between conductors
r
IB
pm
40 Biot-Savart law*
*for a simple conductor
2D MAGNETIC FIELD CALCULATION
Power lines: single or double three-phase balanced system (phase shift 120°)
-1.5
-1
-0.5
0
0.5
1
1.5
0 100 200 300 400 500 600
50 HzRS
T
2D MAGNETIC FIELD CALCULATION
Superposition principle:
Biot-Savart law to each phase + Sum as fasors (complex vectors)
0
)()(2
)()(2
22
0
22
0
zB
yyxx
xxIB
yyxx
yyIB
i ii
iiy
i ii
iix
p
m
p
m
2D MAGNETIC FIELD CALCULATION
• Rxi=
• Ryi=
• di=
• radi= k=
• Re(Bx)= (Rx1 cos rad1 + Rx2 cos rad2 + Rx3 cos rad3 )
• Im(Bx)= (Rx1 sin rad1 + Rx2 sin rad2 + Rx3 sin rad3 )
I*2
0
p
m
22 )()( ii
i
yyxx
xx
22 )()( hyxx i
ikd
p2
I*2
0
p
m
22 )()( ii
i
yyxx
yy
• Bx=
• By=
• Bz=0
• B=22 ByBx
22 )Im()Re( BxBx
22 )Im()Re( ByBy
Two three-phase balanced system :
Re(Bxi), Im(Bxi), Re(Byi), Im(Byi)
Re(Bx)=Re(Bx1)+Re(Bx2)
Im(Bx)=Im(Bx1)+Im(Bx2)
Re(By)=Re(By1)+Re(By2)
Im(By)=Im(By1)+Im(By2)
Bx=
By=
B=
22 )Im()Re( BxBx
22 )Im()Re( ByBy
22 ByBx
2D MAGNETIC FIELD CALCULATION
PROS
• Simple computation (self made)
• Few input
• Perfect for underground cables
CONS
• Overestimation near conductors
• Just for parallel wires
• Just transverse plane
2D MAGNETIC FIELD CALCULATION
https://arpapiemontenir.shinyapps.io/Single-circuit-B-calculation/
2D MAGNETIC FIELD CALCULATION
WEP APPLICATION developed by ARPA Piemonte
Developed in R CRAN environment (free and open source),
published in ARPA debian server (Linux) or in public hosting server
Based on R script (it is possible to run R scripts on local machine)
Simple two-dimensional model with one or two three-phase circuit
Calculation on section plane or at one heigt in a transverse axys
PROS
•Simple computation (self made) excel spreadsheet or other tools
2D MAGNETIC FIELD CALCULATION
Extract of R script
2D MAGNETIC FIELD CALCULATION
https://arpapiemontenir.shinyapps.io/Single-circuit-B-calculation/
2D MAGNETIC FIELD CALCULATION
https://arpapiemontenir.shinyapps.io/Single-circuit-B-calculation/
2D MAGNETIC FIELD CALCULATION
3D MAGNETIC FIELD CALCULATION
SEGMENTATION OF THE OVERHEAD POWER LINE CONDUCTORS
Ampère-Laplace law
Superposition principle
Each segment
+
Each phase
The magnetic induction at any point in space
can be numerically computed using a discrete
approximation of eq. having discretised each
conductor into elementary straight
segments,
PROS
• Calculation in complex configuration (multiple lines, power lines
intersection, …)
• Multiple output (horizontal plane, transverse plane, …)
CONS
• A lot of input
• Complex computation (commercial tools)
• Calculation time is proportional to catenary segmentation
3D MAGNETIC FIELD CALCULATION
3D MAGNETIC FIELD CALCULATION
MAGIC
394100 394150
394200 394250
394300 394350
394400 394450
394500 394550
394600 4.98198e+006 4.982e+006 4.98202e+006 4.98204e+006 4.98206e+006 4.98208e+006 4.9821e+006 4.98212e+006 4.98214e+006
230
235 240
245
250 255
260
265 270
275
asse Z (m)
asse X (m) asse Y (m)
asse Z (m)
3D MAGNETIC FIELD CALCULATION
MAGIC
3D MAGNETIC FIELD CALCULATION
MAGIC
3D MAGNETIC FIELD CALCULATION
MAGIC
Output + Geographical Information System= Simple exposition evaluation
2D-3D Model Comparison
Twin three-phase circuit 132 kV, span 242m, elevation gap 8m, catenary
constant 1079m
Percentual deviation
-2
-1.8
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0 10 20 30 40 50 60
distanza da asse linea (m)
sca
rto
%
sostegno
metà campata
Pylon
Midspan
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 10 20 30 40 50 60
distanza da asse linea (m)
sca
rto
%
sostegno
metà campata
height = 4.5m
from the ground
-0.012
-0.01
-0.008
-0.006
-0.004
-0.002
0
0.002
0 10 20 30 40 50 60
distanza da asse linea (m)
sca
rto
%
sostegno
metà campataheight = 1.5m
from the ground
Single three-phase circuit 132 kV,
triangle shape, span 210m, no
elevation gap, catenary constant
1050m
Percentual deviation
2D-3D Model Comparison
Pylon
Midspan
Pylon
Midspan
3D MAGNETIC FIELD CALCULATION
2D MODEL = TWO SYSTEMS OF PARALLEL CONDUCTORS
3D MODEL= COMPLEX WIRES CONFIGURATION
Two or more three-phase balanced system
Is calculation correct?
V1
I1
150 Hz
V1=V2=V3
Balanced line: I1=I2=I3, 1= 2= 3
Phase Voltage
Current
load angle
Three phase AC power lines: phase shifts
Phase shift between Current and Voltage is given to the load nature
Inductive load current LAGS Voltage: <0
Capacitive load current LEADING Voltage: >0
Real load?...
Three phase AC power lines: phase shifts
Three phase AC power lines: phase shifts
Phase shift in 220 kV power line (Torino city)
For single circuit lines, the choice of the reference current
phasor is arbitrary (e.g. phase a) and, under the hypothesis of
balanced conditions, the phase angle displacement of the other
two currents is simply 2/3π.
Three phase AC power lines: phase shifts
Three phase AC power lines: phase shifts
Differently, when two or more circuits are present, it is necessary to refer each current
phasor to a unique reference phasor (or to determine the relative phase angle between
the reference phasors of each circuit). It is useful to express the generic current phasor
as:
Twin three-phase AC power lines: phase shift
Three phase AC power lines: phase shifts
21221
12
2
12
(* Maurizio Albano, Roberto Benato, Roberto Turri, “DETERMINATION OF LINE CURRENT PHASE ANGLE
DISPLACEMENT FROM MAGNETIC FIELD MEASUREMENTS IN MULTIPLE-CORRIDOR POWER LINES” )
Three phase AC power lines: phase shifts
Application
Single three-phase circuit 220 kV (line 2) + Twin three-phase circuit 132 kV (line 1)
Method application trouble:
• Exact catenary status knowledge during measurement perform for
both lines (in order to separately calculate X-axis magnetic induction
contributions of each power line)
• Precision in determining measurement point in span reference system
0
0.2
0.4
0.6
0.8
1
1.2
1.4
00:00 02:24 04:48 07:12 09:36 12:00 14:24 16:48 19:12 21:36 00:00
ora
B (
µT
)
B1
B2
Bsfas
Binfase
Some results
0
5
10
15
20
25
-5.86 3.72 13.29 22.87 32.44 42.02 51.59 61.17 70.74
scarto % tra Bsfas e Binfase
Fre
qu
en
za
Mean: 37.5%
Median: 41.4%
Standard deviation:
22.1
Results
Percentual deviation between calculated B (phase shifts) and
calculated B (no phase shifts)
Conductors height in a point is given by catenary constant (weight and horizontal tension ratio) and span length.
Conductors elongation depends on material elastic properties and temperature (environmental + Joule effect current flow dissipation)
Thermal elongation:
at = thermal expansion coefficient
EDS = everyday stress (t=15°C and I=0)
Elastic elongation :
ec = elastic modulus
Sc = conductor section
Pc = conductor weight per unit length
k = catenary constant
)( EDScEDSttermico ttLL a
)(1
edscc
EDS
celastico kkP
S
LL
e
Model influence parameters
0
1
2
3
4
5
6
7
8
9
10
11
12
-100 -80 -60 -40 -20 0 20 40 60 80 100
distanza dall'asse della linea (m)
ind
uz
ion
e m
ag
ne
tic
a (
µT
)
EDS Temp
Catenary curve variation
Double three-phase circuit 220 kV side by side phase.
Aluminium-Steel conductors Span =300 m – 1 m Sag increase
Section B calculation in everyday stress condition (EDS) and real condition ( I=1000 A , Tenv 50°C) for
ground clearence level
2D ELECTRIC FIELD CALCULATIONCampo elettrico
Coulomb law
2
0rπε2
QE
Q conductor electric charge
r distance conductor- point
ε0 vacuum dielectric constant
Earth effect= Each of the overhead conductors
can be considered as a line charge near a
plane conductor.
Image technique: each conductor has specular
conductor with opposite charge (same distance from plane).
This situation is equivalent to the original setup, and so the force on the
real charge can now be calculated with Coulomb's law between two point
charges
Superposition principle
How can we calculate conductors charge Q? Or, better, linear charge density *?
VPπε2Q1
0
[P] Maxwell capacitance matrix
[V] Voltage fasors matrix
*charge in conductors core , const, for distance >>conductors radius
2D ELECTRIC FIELD CALCULATION
Thin-wire approximation: straight horizontal parallel wires with span
length >>distance between conductors
λ as fasor, λ image conductors= λ conductors (realistic hypothesis for
most of soil typology, but we can consider different conditions)
Gauss law
2D ELECTRIC FIELD CALCULATION
2D ELECTRIC FIELD CALCULATION
2D ELECTRIC FIELD CALCULATION STEP BY STEP
1. [P] Maxwell capacitance matrix
2. [P]-1 matrix inverse
3. i i’ ‘ as fasors
4.Combining i i’ for x and y
5.Ex,Ey
6.E
2D ELECTRIC FIELD CALCULATION
• E calculation is more complex than B calculation : additional step is
calculation knowing Voltage fasors (hardest part);
• Each conductor, even not in voltage, modify electric field (Earth wires );
• Conductors radius and spacing is needed (Bundle of n conductors :
equivalent radius)
2D ELECTRIC FIELD CALCULATION
Critical issues
• RMS Voltage from ground
• Equivalent radius
• Geometric data input (same as B calculation)
2D ELECTRIC FIELD CALCULATION: INPUT DATA
For each conductor (even Earth wires)
campo elettrico
0
1000
2000
3000
4000
5000
6000
-50 -40 -30 -20 -10 0 10 20 30 40 50
distanza da asse linea (m)
E (
V/m
)Example: Electric field value under different power lines typologies
tensione
220 kV
380 kV
380 kV
campo elettrico doppia terna
0
1000
2000
3000
4000
5000
6000
7000
-50 -40 -30 -20 -10 0 10 20 30 40 50
distanza da asse linea (m)
E (
V/m
)Double three-phase circuit : phase layout
240
120
0
240
120
0
240
120
0
0
120
240
NON-OPTIMIZED PHASES
OPTIMIZED PHASES
Electric field value depends on geometric conductors disposition, but also on
environmental conditions.
Investigation on:
• Temperature
• Soil electrical conductivity
• relative humidity.
ELECTRIC FIELD CALCULATION:Environmental Conditions
ELECTRIC FIELD CALCULATION:Temperature
)( EDScEDSttermico ttLL aThermal elongation:
at = thermal expansion coefficient
EDS = everyday stress (t=15°C and I=0)
TS= thermal stress (90°C :–t=50°C and I=1000)
ΔL= 70 cm
ΔE= 750 V/m
ELECTRIC FIELD CALCULATION: Soil conductivity
Image technique : soil is considered infinit plane perfectly conductive
Soil electric properties depends on water percentage in the form of
electrolytic solution, and since it depends on the soil type and on its
capacity to retain it, different type of soil has different conductivity .
Soil = complex dielectric medium
With some passages it’s possible to prove than electric field in air is given by
superposition of real conductors with charge density λ and Imagine conductors
with charge density λ’, assuming air permittivity as 1
ELECTRIC FIELD CALCULATION: Soil conductivity
ELECTRIC FIELD CALCULATION: Soil conductivity
Soil electrical conductivity: Soil type
In standard environmental conditions soil conductivity has small effect
campo elettrico E
0
1000
2000
3000
4000
5000
6000
7000
8000
0 5 10 15 20 25 30 35 40 45
distanza asse linea (m)
E (
V/m
)
RH 90% In blue: measured E
In pink: calculated E
E measure >E calculation ???
Hypotesis: Wider cable charge distribution
ELECTRIC FIELD CALCULATION: relative humidity
ELECTRIC FIELD CALCULATION: relative humidity
Hypotesis: Wider cable charge distribution
Possible solution: increase equivalent radius
ELECTRIC FIELD CALCULATION: Soil conductivity+RH
(a) Paved road (b) Low grass (c) Ground
Electric field variations
Red= HR 100% (fog), blue=HR 90%, green=HR<50%
With high RH, difference between measurements increase for conductive soils
https://arpapiemontenir.shinyapps.io/single-circuit-E-calculation/
2D ELECTRIC FIELD CALCULATION
2D ELECTRIC FIELD CALCULATION