The identification of risks linked to electromagnetic compatibility (EMC) in the electric railway is a major concern in identifying EMC problems and analyzing the unintentional various external disturbing sources as well as the probability of occurrence of interference, the level of interference along the railway system. The purpose of this analysis is to determine the electromagnetic interaction coupling generated by the high voltage (HV) lines located along the railway line by analyzing the voltage induced in the signaling transmission cables such as the european rail traffic management system/european train control system (ERTMS/ETCS) through the multi-conductor transmission line (MTL) theory which may have an impact on the transmitting information. Dubanton method and approximate calculation will be applied and simulated through COMSOL Multiphysics tool in order to analyze if the protection distance and coupling conditions are respected by the railway standards.
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The differential equations are written for the transmission line for each parameter line voltage and current:
{
ππ(π₯, π‘)
ππ₯
= βπΏ
ππΌ(π₯, π‘)
ππ‘
β π πΌ(π₯, π‘)
ππΌ(π₯, π‘)
ππ₯
= βπΆ
ππ(π₯, π‘)
ππ‘
β πΊπ(π₯, π‘)
(4)
In order to simplify the model under study, the voltage along one phase is given by the following relation:
ππ1
ππ₯
= βπ11 πΌ1 β π12 πΌ2βπ13 πΌ3 β π14 πΌ4 (5)
with, π11 is the impedance of one phase (phase R),
π11 = π 11 + ππ€πΏ11 (6)
and π1π is the mutual impedance between the j lines and the phase R.
π1π = π 1π + ππ€πΏ1π (7)
In a matrix format:
π[π]
ππ₯
= β[π][πΌ] (8)
The impedance matrix [π] is given below:
[π] = [
π§11 π§12 π§13 π§14
π§21
π§31
π§41
π§22
π§32
π§42
π§23
π§33
π§43
π§24
π§34
π§44
]
The coefficients πii is the impedance of the line βiβ and per unit length and the coefficients πij and to
the ground which represent the mutual impedance between the βiβ, βjβ lines related to the ground [5].
Current and Voltage vectors are given below:
[π] = [
π1
π2
π3
π4
] , [πΌ] = [
πΌ1
πΌ2
πΌ3
πΌ4
]
The current along the βiβ line is written by the following relation:
ππΌπ
ππ₯
= βπ¦π ππ β β π¦ππ(ππ β ππ)
4
π=1
, π β π (9)
with, π¦ππ is the mutual admittance between the line βiβ and the line βjβ related to the ground and π¦π is
the admittance of the βiβ line.
Matrix form is represented by the following equation:
π[πΌ]
ππ₯
= β[π][π] (10)
The admittance matrix [π] is given below:
[π] = [
π¦11 π¦12 π¦13 π¦14
π¦21
π¦31
π¦41
π¦22
π¦32
π¦42
π¦23
π¦33
π¦43
π¦24
π¦34
π¦44
]
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The coefficients π¦ij is the admittances between the βiβ and βjβ lines related to the ground and π¦ii is
the admittances per unit length [6]. The direct equivalence between the coefficients of the physical
admittances and the admittance matrix does not exist. The coefficients of the admittance matrix for only one
transmission line are given by the following equations:
{
π¦ππ = π¦π + β π¦ππ , π β π
4
π=1
π¦ππ = βπ¦ππ
(11)
All the conductors are represented of the power transmission lines and the railway signaling cable as
a multiconductor transmission which is an approximate approach when the values of the coefficients of
admittances and impedancesmatrix are known. The values of the equivalent components are difficult to
measure under practical conditions, because they depend on the parameters of the cables such as the position,
shape, conductivity and permeability, and the conductivity and permittivity of the ground.
2.2. Coefficients of the impedance matrix calculated
The impedance of each transmission line and the ground depends mainly on the external impedance [7],
the internal impedance of the conductor and the impedance of the ground are given by the following equation:
π§ππ = π§πππ‘ + π§ π + ππ€π π (12)
with, π§πππ‘ represent the internal impedance, π§ π represent the impedance of the ground of the conductor.
with, π π represent the inductance per unit length calculated with a perfect conducting ground.
π π =
Β΅0
2π
ππ (
2β
π
) (13)
with β is considered to be the height between the ground and the conductor line and π is the radius of
the conductor line.
The internal impedance π§πππ‘ of the conductor is represented by the following equation:
π§πππ‘ =
1
2
π π. π. π
ππππ. π + πππππ. π
πππβ²π. π + ππππβ² π. π
(14)
π = β π€. Β΅ π. ππ (15)
with ππ is the conductivity, π π is the resistance and Β΅ π is the permability.
And ber, bei represent Kelvin functions, berβ and beiβ represent their derivatives.
In order to have a valid result in an extended frequency band, the impedance of the ground π§ π is
represented by the Carson formula:
π§ π = ππ€
Β΅0
π
β«
πβ2βπ
. cos(ππ)
π + β π2 β πΎπ
2
. ππ
β
0
(16)
πΎπis the ground propagation constant defined by the formula:
πΎπ = β ππ€Β΅0(ππ + ππ€π0 π π) (17)
with, Β΅0 represent the permeability of the ground, π π represent the relative permittivity, π0 represent
the permittivity of vaccum and ππ represent the conductivity of the ground.
Mathematical equations of Dubantonβs method is used in this study to calculate the parameters of
the power transmission lines [8]. The eigen coefficients of the impedance matrix π§ππ is given by the following
formula:
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π§ππ = π§πππ‘ + ππ€.
Β΅0
π
ππ (
2(βπ + π)
π
) (18)
The mutual coefficients π§ππ of the impedance matrix is given otherwise through the following formula:
π§ππ = ππ€
Β΅0
π
(
1
2
ππ (β
(βπ + βπ)2 + π2
(βπ β βπ)2 + π2
) + β«
πβ2βπ
. cos(ππ)
π + β π2 β πΎπ
2
. ππ
β
0
) (19)
=> π§ππ = ππ€
Β΅0
2π
ππ (β
(βπ + βπ + 2π)2 + π₯ππ
2
(βπ β βπ)2 + π₯ππ
2 ) (20)
The complex depth is P,
π = β
π
π€Β΅0
(21)
π is the distance between the βiβ, βjβ conductors, βπ, βπ are the heights respectively of βiβ, βjβ conductors, π is
the soil resistivity, the pulsation of the inductor current π€ = 2ππ.
π₯ππ is the horizontal spacing between the two conductors, given by the following relation:
π₯ππ = β π2 β (βπββπ)2 (22)
2.3. The coefficients of the admittance matrix calculated
The admittance matrix for the high voltage power lines is given below:
[π] = ππ€[π]β1 (23)
[π] is the potential matrix.
[π] = [
π11 π12 π13 π14
π21
π31
π41
π22
π32
π42
π23
π33
π43
π24
π34
π44
]
The eigen coefficients πππ of the matrix [P] are given by the following relation:
πππ =
1
2ππ0
. (ππ (
2β
π
) + β« 2π0
2
.
πβ2βπ
. cos(ππ)
π. πΎπ
2 + π0
2
β π2 β πΎπ
2
. ππ
β
0
) (24)
πππ mutual coefficients of the matrix [P] of the two conductors related to the ground are given by
the following relation:
πππ =
1
2ππ0
. (ππ (β
(βπ + βπ)2 + π2
(βπ β βπ)2 + π2
) + β« 2π0
2
.
πβ(β π+β π)π
. cos(ππ)
π. πΎπ
2 + π0
2
β π2 β πΎπ
2
. ππ
β
0
) (25)
with,
π0
2
= Β΅0 π0 π€2
(26)
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3. ELECTROMAGNETIC INTERFERENCES CAUSED BY THE OVERHEAD POWER LINES
The Dubanton method previously described associated to the theory of MTL has been applied in
order to have a better approach which is an analytical calculation simplified with mathematical equations.
The electromagnetic field is divided into two components, the magnetic field and the electrostatic field [9].
Both fields will be analyzed separately in normal conditions and in different time instants.
3.1. Magnetic field
The magnetic coupling phenomenon caused by the impact between the high voltage power line and
the signaling cables is described in the Figure 5.
Figure 5. Magnetic induction coupling
The expression of the electromotive force induced E along each transmission line is given in
the form of the sum of all the electromotive forces induced in each section πππ. The magnetic induction will
be calculated through the approximate formula and the dubanton method.
πΈ = β πππ
π,π
(27)
The Dubanton aproach already expressed in the previous section is given through the following formula:
π§ππ = ππ€
Β΅0
2π
ππ (β
(βπ + βπ + 2π)2 + π₯ππ
2
(βπ β βπ)2 + π₯ππ
2 ) (28)
However, the approximate method is characterized by the following formula:
π§ππ = ππ€π (29)
with, M represented in ΞΌH/km, depends mainly on the value of x and it is equal to:
- For π₯ β€ 10:
π = 142 + 46π₯ β 198 ln(π₯) β 1.4π₯2 (30)
- For π₯ > 10:
π = 400π₯β2 (31)
with,
π₯ = πβ
π€Β΅0
π
(32)
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The magnetic field varies with the variations of the current flowing in the cables. It depends mainly
on the current flowing in the nearby conductor transmission lines and their geometry parameters.
In the case of our study, the magnetic field is determined by the following relation:
π΅ =
β6π ππ πΌ
10π2
(33)
with, πΌ is the current flowing in the high voltage power transmission line, π ππ is the distance between
the overhead phases, π is the distance of the field relative to the source.
3.2. Electrostatic field
Capacitive couplings are generated when two conductor lines are above the ground. Variable electric
field are created because of the variable voltage flowing in the conductor as seen in the Figure 6. Which
causes induced currents and voltages on overhead power transmission lines placed along the Catenary lines
2x25 kV system [10, 11].
Figure 6. Capacitive coupling generated between the catenary and the 3 phase lines
Capacitive coupling between the signal cables and the extra high voltage lines is considered to be
negligible in our study since they are buried under the ground. The catenary line is the only system that is
susceptible to be charged with electricity.
π0 =
π0
πΆ01
=
πΆ21 π1 + πΆ31 π2 + πΆ41 π3
πΆ21 + πΆ31 + πΆ41
(34)
The induced current πΌ0 flowing in the conductor is proportional to the capacitive coupling πΆ01 between
the ground and the catenary line, the length of parallelism l andthe induced voltage π0.
πΌ0 = π0. πΆ01. π€. π (35)
3.2. Results compared to international standard limits
The magnetic and electric fields are modeled by COMSOL Multiphysics as shown in
the Figures 7 and 8. The values of the parameters in the worst case located along the electric railway track are
listed in the Table 1 in order to calculate according to the two methods the mutual inductance listed in
the Table 2 to analyze the electric and magnetic field generated. Results are obtained after calculation of
the mutual inductance, it is noted that the results of the two methods are close.
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[9] G. Romero and V. Deniau, βImpact of the measurement methods on the characterization of transient
electromagnetic (EM) interferences above 2 GHz in a railway environment,β URSI AP-RASC, 2019.
[10] L. Liudvinavcius, βCompensation of reactive power of AC catenary,β Procedia Engineering, vol. 187, pp. 185-197, 2017.
[11] M. El Hajji, H. Mahmoudi and M. El Azzaoui, βHarmonic analysis caused by static converters of the railway high
speed train and their impact on the track circuit,β International Conference on Wireless Technologies, Embedded
and Intelligent Systems, 2019.
[12] CENELEC EN 61000-4-5, βElectromagnetic Compatibility β part 5: Testing and measurements techniques β
section 5: surge immunity test,β Nov. 2006.
[13] CENELEC EN 61000-4-6, βElectromagnetic Compatibility β part 6: Testing and measurements techniques β5:
surge immunity to conducted disturbancesn induced by radio frequency fields,β Aug. 2007.
[14] CENELEC EN 61000-4-8, βElectromagnetic Compatibility β part 4: Testing and measurements techniques β
section 8: Power frequency magnetic field immunity test,β Sep. 1993.
[15] CENELEC EN 61000-4-9, βElectromagnetic Compatibility β part 4: Testing and measurements techniques β
section 9: Pulse magnetic field immunity test,β Sep. 1993.
[16] CENELEC EN 61000-4-10, βElectromagnetic Compatibility β part 4: Testing and measurements techniques β
section 10: damped oscillatory magnetic field immunity test,β Sep.1993.
[17] CENELEC EN 61000-4-11, βElectromagnetic Compatibility β part 4: Testing and measurements techniques β
section 11: Voltage dips, short interruptions and voltage variations immunity tests,β Aug. 2004.
[18] CENELEC EN 61000-4-12, βElectromagnetic Compatibility β part 4: Testing and measurements techniques β
section 12: Ring wave immunity tests,β Dec. 2006.
[19] CENELEC EN 61000-4-13, βElectromagnetic Compatibility β part 4: Testing and measurements techniques β
section 13: Harmonics and inter-harmonics including mains signalingat ac power port, low frequency immunity
tests,β Jun. 2002.
[20] CENELEC EN 50121-1, βRailway Application: Electromagnetic Compatibility, Part 1: General,β Jul. 2006.
[21] CENELEC EN 50121-2, βRailway Application: Electromagnetic Compatibility, Part 2: Emission of the whole
railway system to the outside world,β Jul. 2006.
[22] CENELEC EN 50121-3-1, βRailway Application: Electromagnetic Compatibility, Part 3-1: Train and complete
vehicle,β Jul. 2006.
[23] CENELEC EN 50121-3-2, βRailway Application: Electromagnetic Compatibility, Part 3-2: Rolling Stock
Apparatus,β Jul. 2006.
[24] CENELEC EN 50121-4, βRailway Application: Electromagnetic Compatibility, Emission and Immunity of
signaling and telecommunication appliances,β Jul. 2006.
[25] CENELEC EN 50121-1, βRailway Application: Electromagnetic Compatibility, Part 5: Emission and immunity of
railway fixed power supply installations,β Jul. 2006.