IEEE Electrification Magazine - September 2016 - 17

Rails

into account by an equivalent
value of the screening coefficient
Substation
with acceptable approximations.
Oblique exposure and crossings
may be readily evaluated with corPipeline
rections, as suggested in CCITT.
Area with Enhanced
The reason for choosing the
Corrosion Risk
simplified CCITT method is that it
is normative and calculations can
Potential
all be cross-checked, allowing for
+ Potential of Pipeline
a complete formal review. Eviwith Interference
dence of correct use, validation,
Area of Cathodic
and, in some cases, experimental
Interference
Area of Anodic
Potential of
results will be given for other
Interference
Pipeline
modeling methods.
Without
Potential of Rails
Interference
The traction current flowing in
Length
the catenary system and in the
return circuit causes induction as
part of normal rolling stock opera- Figure 1. The principles of anodic and cathodic interference from EN 50162.
tions, especially when several units
in the same supply section cause
interference evaluation must include track symmetry, rail
acceleration and contemporary loading. Induction intensileakage to earth (permanently loading the rail-to-rail difty is far more relevant when transient fault conditions are
ferential circuit and reducing sensitivity), rail attenuation,
considered because the flowing current may be an order
propagation delay, and possible resonances. In all cases,
of magnitude larger than that during overloading. In this
the quantities of interest are the current flowing in the
case, time duration is extremely important to establish
rail or leaving the rail to the rest of infrastructure and the
compliance with a series of amplitude-time limit curves,
soil, and the voltage between rails, between rail and soil,
established by CENELEC EN 50122-1 and ITU-T recomor impressed on surrounding conductive parts (Figure 1).
mendation K.33.
The psophometric voltage (and, correspondingly, the
Assessing Compliance
equivalent psophometric source current) is a thorough
Broadly speaking, calculation and simulation, test and
performance index. It is a weighted sum of spectrum
measurement, or a combination can be used to assess
components over a frequency interval that cover mostly
compliance. For all coupling phenomena, limits may be
analog and digital telephone applications and, by extendefined based on standards or on the specific susceptibilision, some data networks.
ty of victim equipment. Parameters that determine sysConductive Coupling and Stray Current
tem response and coupling should be measured or
Return current flows from the rolling stock back to supply
assumed, practically defined in terms of transfer function;
substations, flowing into the running rails through the
disturbance source represents and characterizes the
wheel-rail contact and then spreading to other return-cirinput. When, instead of being assigned known and concuit conductors, including soil. The return current specstant values, parameters and input quantities are variable
trum extends from the fundamental supply to audio
over admissible ranges, the problem assumes a further
frequency components and, even at higher frequency, is
dimension: measurement uncertainty due to, for example,
generally caused by high-order switching components
measurement repeatability, knowledge of system status
and transients of on-board static converters. Affected sysand environmental conditions, or variability following a
tems and devices are those purposely or accidentally
sensitivity analysis to the most variable parameters and
sharing a conductive path with the running rails and the
conditions (e.g., system aging, temperature, and humidity).
return circuit; the most relevant examples are track cirLimit compliance can be demonstrated taking into
cuits at power and audio frequency and conductive and
account the statistical nature and spread of experimental
concrete elements exposed to dc and low-frequency stray
or simulation results; depending on the impact on and the
current as part of the infrastructure or located nearby
relationship with safety, it may be necessary to identify
beneath the soil. Track circuits detect a train occupying a
and adopt worst-case configurations. Safety analysis may
given track section by transmitting a complex signal,
indeed require exploring unlike or even extreme configuusing the track as a bifilar line and sensing the drop in
rations for increased confidence and as an additional marrail-to-rail voltage at the receiver caused by the short cirgin. To this end, simulation models are useful for realizing
cuit introduced by train axles. In the interest of safety,
worst-case parameter combinations that are hardly met
IEEE Elec trific ation Magazine / S EP T EM BE R 2 0 1 6

17



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
IEEE Electrification Magazine - September 2016 - 5
IEEE Electrification Magazine - September 2016 - 6
IEEE Electrification Magazine - September 2016 - 7
IEEE Electrification Magazine - September 2016 - 8
IEEE Electrification Magazine - September 2016 - 9
IEEE Electrification Magazine - September 2016 - 10
IEEE Electrification Magazine - September 2016 - 11
IEEE Electrification Magazine - September 2016 - 12
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IEEE Electrification Magazine - September 2016 - 14
IEEE Electrification Magazine - September 2016 - 15
IEEE Electrification Magazine - September 2016 - 16
IEEE Electrification Magazine - September 2016 - 17
IEEE Electrification Magazine - September 2016 - 18
IEEE Electrification Magazine - September 2016 - 19
IEEE Electrification Magazine - September 2016 - 20
IEEE Electrification Magazine - September 2016 - 21
IEEE Electrification Magazine - September 2016 - 22
IEEE Electrification Magazine - September 2016 - 23
IEEE Electrification Magazine - September 2016 - 24
IEEE Electrification Magazine - September 2016 - 25
IEEE Electrification Magazine - September 2016 - 26
IEEE Electrification Magazine - September 2016 - 27
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IEEE Electrification Magazine - September 2016 - 36
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IEEE Electrification Magazine - September 2016 - 41
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IEEE Electrification Magazine - September 2016 - 46
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IEEE Electrification Magazine - September 2016 - 48
IEEE Electrification Magazine - September 2016 - 49
IEEE Electrification Magazine - September 2016 - 50
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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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