IEEE Electrification Magazine - September 2016 - 24

other than the return circuit. The
major effects of stray currents can be
the corrosion and subsequent damage
of metallic structures at the points
where stray currents exit. The metallic
mass dissipated onto the soil can be
estimated through the Faraday's laws
of electrolysis. For example, considering 1 A of stray current flowing continuously through a steel structure, the
metallic mass of corroded steel dissipated onto the soil is equivalent to
9.13 kg per year. There is also the risk of overheating, arcing, fire, and subsequent danger to people and equipment
both inside and outside the dc traction system.
Therefore, any provisions employed to control the
effects of stray currents shall be checked, verified, and validated according to the IEC 62128-2 standard when following the International Electrotechnical Commission (IEC)
approach. Additionally, the IEC approach is based on a negative busbar that is completely isolated (floating) in comparison to other historically adopted approaches like a
solid earthed negative busbar or a busbar earthed through

resistances, diodes, or thyristors. The
IEC 62128-2 standard also recommends that the system design be
completed sufficiently early so the
results can be taken into account in
the system parameters that influence
the stray-current effects. This way, the
stray-current control is a multidisciplinary task.
Besides the overall system design
of the traction power supply, the most
important parameters for the amount
of stray currents are
xx
the conductance per the length (S/km) of the tracks
and other parts of the return circuit
xx
the distance of the substations
xx
the longitudinal resistance of the running rails
xx
the spacing of track-to-track cross-bonds (equipotential connections among all rails of all tracks).
If the dc traction system meets the requirements and
measures of the IEC 62128-2 standard, then the system
is assumed to be acceptable from the stray-current point
of view. Figure 1 shows how the process is conducted.

The most important
influencing factor
for stray currents
is the conductance
between track
and earth.

Define the Cross Section
of Metallic Structures,
If Any

Define the Conductance per the
Length of the Tracks

Define the Conductance
per Each Fastening

Test the Fastening
Systems

Installation and Field
Tests

Test the Resistance per the
Length of the Rail

Test the Conductance per
the Length of the Tracks

Test the Continuity of the
Metallic Structures, If Any

Yes

Ok?

Maintenance of the
Rail System

No
No
Mitigation Solutions

Figure 1. A flowchart of the procedure.

24

I E E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2016

Yes
Ok?



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
IEEE Electrification Magazine - September 2016 - 4
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IEEE Electrification Magazine - September 2016 - 6
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IEEE Electrification Magazine - September 2016 - 26
IEEE Electrification Magazine - September 2016 - 27
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IEEE Electrification Magazine - September 2016 - 52
IEEE Electrification Magazine - September 2016 - Cover3
IEEE Electrification Magazine - September 2016 - Cover4
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