IEEE Electrification Magazine - September 2016 - 21

102

10-1
10-2
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000

10-3

101
100
10-1
10-2
10-3

0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000

Voltage (V)

100
Voltage (V)

Frequency (Hz)
Cable 1 km

Frequency (Hz)

Cable 2 km

Cable 3 km

Cable 4 km

Figure 5. The normalized induced voltage for 1 A of return current versus cable length, for low
(above, 30 X) and high (below, 1,200 X) cable termination impedance and for two relative positions with respect to impedance bonds (four cables, all starting at an IB, solid line, and at an intermediate position between two IBs, dashed line).

Psophometric Voltage
Psophometric calculations are required to be satisfactorily accurate and conservatively safe, so the CCITT
method is the best choice, especially when several
parameters required by more accurate Multiconductor
Transmission Line methods are not available. In any
case, the restrictive limits (around 1 mV) and the very
weak signals almost always make experimental verification compulsory to prevent overestimating the
assumptions of the models. Psophometric voltage
is measured with a normalized loading impedance of
600 W, larger than the longitudinal impedance for most
cable lengths and almost corresponding to an open circuit voltage condition.
A series of tests was performed on a metro system
using a sample telephone cable of 1,300 m length (loop
resistance was 53 X/km). Tests performed with both
ends of the cable shield earthed gave Vp = 0.82 mV and
0.86 mV for acceleration and braking conditions, respectively; for the shield earthed at one end, only Vp
increased to 1.92 mV and 1.87 mV, respectively. Comparison confirms the cable shield's magnetic screening factor is approximately 0.4, or 8 dB, corresponding well to
known values indicated by CCITT and confirmed by
testing the cable samples.

outside the right-of-way, as typically occurs in metro and
light rail transit systems. Adequate system design and
early design evaluation, as well as hypothetical insulation defect assessment, can be achieved with the help of
simulation tools, in particular those integrating track and
soil electrical characteristics and allowing for the verification of different traffic patterns. Punctual defects of
insulation, if not properly monitored and detected, can
significantly impair the efficiency of stray current provisions and design (see Figure 7). Traffic has a significant
influence on the average rail potential and on the consequential average stray current and also on predicting
favorable or unfavorable configurations of trains along
the track absorbing power from substations and

Magnetic Field: First Equipotential Bonding at 57.919 km
(Right Side)
14
12
10
Vertical Axis (m)

configuration in Figure 3) and
intermediately between two IBs
(position II).
At higher frequency, above the
first system resonance, voltage
curves stay in a simple band, with
an approximately inductive
behavior compared with frequency; for large loading impedance,
the curves preserve the monotone
behavior with respect to cable
length. At the main system resonance, around 1,800 Hz, the coupled voltage increases above the
projec-tion of the band by even an
order of magnitude in some cases.

Magnetic Field Emissions
Magnetic field emissions may be satisfactorily simulated
by using straight conductors for each section and with
acceptable approximations on track parameters, such as
track conductance to earth and current lost into soil.
An example is shown in Figure 6 for a 1 × 25 kV system
using an earth rope located on poles at the same height
of the contact wire.

6
4
2
0
-2
-5

50

Stray Current
Stray current has a significant impact in the case of viaducts and tunnels and when there is a high concentration of concrete structures inside and immediately

8

0

55

5

10
15
20
Horizontal Axis (m)

60

65
70
Position (km)

NS

ESS

25

75

30

80

Train

Figure 6. An example of magnetic field distribution for a 1 × 25 kV
system [catenary conductors (circle), earth rope (diamond), rails
(square)], with the train at the right of the neutral section.

	

IEEE Elec trific ation Magazine / S EP T EM BE R 2 0 1 6

21



Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2016

IEEE Electrification Magazine - September 2016 - Cover1
IEEE Electrification Magazine - September 2016 - Cover2
IEEE Electrification Magazine - September 2016 - 1
IEEE Electrification Magazine - September 2016 - 2
IEEE Electrification Magazine - September 2016 - 3
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IEEE Electrification Magazine - September 2016 - Cover3
IEEE Electrification Magazine - September 2016 - Cover4
https://www.nxtbook.com/nxtbooks/pes/electrification_december2022
https://www.nxtbook.com/nxtbooks/pes/electrification_september2022
https://www.nxtbook.com/nxtbooks/pes/electrification_june2022
https://www.nxtbook.com/nxtbooks/pes/electrification_march2022
https://www.nxtbook.com/nxtbooks/pes/electrification_december2021
https://www.nxtbook.com/nxtbooks/pes/electrification_september2021
https://www.nxtbook.com/nxtbooks/pes/electrification_june2021
https://www.nxtbook.com/nxtbooks/pes/electrification_march2021
https://www.nxtbook.com/nxtbooks/pes/electrification_december2020
https://www.nxtbook.com/nxtbooks/pes/electrification_september2020
https://www.nxtbook.com/nxtbooks/pes/electrification_june2020
https://www.nxtbook.com/nxtbooks/pes/electrification_march2020
https://www.nxtbook.com/nxtbooks/pes/electrification_december2019
https://www.nxtbook.com/nxtbooks/pes/electrification_september2019
https://www.nxtbook.com/nxtbooks/pes/electrification_june2019
https://www.nxtbook.com/nxtbooks/pes/electrification_march2019
https://www.nxtbook.com/nxtbooks/pes/electrification_december2018
https://www.nxtbook.com/nxtbooks/pes/electrification_september2018
https://www.nxtbook.com/nxtbooks/pes/electrification_june2018
https://www.nxtbook.com/nxtbooks/pes/electrification_december2017
https://www.nxtbook.com/nxtbooks/pes/electrification_september2017
https://www.nxtbook.com/nxtbooks/pes/electrification_march2018
https://www.nxtbook.com/nxtbooks/pes/electrification_june2017
https://www.nxtbook.com/nxtbooks/pes/electrification_march2017
https://www.nxtbook.com/nxtbooks/pes/electrification_june2016
https://www.nxtbook.com/nxtbooks/pes/electrification_december2016
https://www.nxtbook.com/nxtbooks/pes/electrification_september2016
https://www.nxtbook.com/nxtbooks/pes/electrification_december2015
https://www.nxtbook.com/nxtbooks/pes/electrification_march2016
https://www.nxtbook.com/nxtbooks/pes/electrification_march2015
https://www.nxtbook.com/nxtbooks/pes/electrification_june2015
https://www.nxtbook.com/nxtbooks/pes/electrification_september2015
https://www.nxtbook.com/nxtbooks/pes/electrification_march2014
https://www.nxtbook.com/nxtbooks/pes/electrification_june2014
https://www.nxtbook.com/nxtbooks/pes/electrification_september2014
https://www.nxtbook.com/nxtbooks/pes/electrification_december2014
https://www.nxtbook.com/nxtbooks/pes/electrification_december2013
https://www.nxtbook.com/nxtbooks/pes/electrification_september2013
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