IEEE Electrification Magazine - September 2014 - 26

that is in contact with the rail. Measures were taken to insulate the track
from the earth to reduce the straycurrent process, thus reducing the
corrosion of the base of the rails and
other grounded steel structures for
the sections of the rail that were
embedded in the ground in urban
areas. Track maintenance was also
suggested to keep vegetation out of
the tracks, keeping the tracks clean
and dirt free, dry, and free from salt to
help keep the resistivity of the rails
high and to keep them out of contact
with the earth [4], [7].
Well-drained broken-stone ballast
or gravel ballast was recommended for
use in the embedded sections for its
much higher resistance to stray current as compared to concrete. However, authorities in Germany and England held the view that the leakage of current
cannot be reduced by the roadbed construction. In the United States, it was recognized that well-drained crushed-stone
ballast had a resistance from 2 to 5 X/1,000 ft of single track.
In contrast, the resistance of solid concrete ballast in contact
with the rails and of earth roadbeds, in which the ties are
embedded, was only 0.5-1.5 X/1,000 ft of single track and
0.4 X for 1,000 ft of double track. Moreover, it was also established that the resistance in dry weather may be three or

more times higher than in wet weather
per 1,000 ft of single track [4].
Insulated negative return feeders
were widely used in the earlier constructions, especially where track bonds
could not be well maintained. Supplementary conductors were installed in
parallel with the track and connected to
the track at frequent intervals to carry
the current to the negative feeders and
to ensure the continuity of the return
circuit. However, it was soon detected
that these buried bare conductors
increase the contact area between the
return circuit and the earth, therefore
counteracting the significance of their
need [8]. Later, it was also observed that
the use of frequent substations along
the route provides a more economical
increase in the track drainage points than the use of insulated negative feeders.

The recent advances
in the stray-current
collection have also
validated the use
of a combination of
mitigation methods
and collection
techniques for
the control of
stray current.

Maximum Number of Traction Power Substations
Another stray-current mitigation technique that saw early
advancement was increasing the number of substations as
much as the budget allowed. This technique reduces the
feeding distances and the amount of current to be returned
to any one point, resulting in the reduction of track voltage
drop, thereby reducing the amount of current that will stray

800
Effect of Feeding Distance
on Stray-Current
Line Constants

700
Total Current, Station
at End of Line

Amperes in Return Circuit

600

500

Stray Current, Bus
Grounded, Station at End of Line

400

Total Current, Station at
Center of Line

300

200

Stray Current, Bus
Ungrounded, Station at End of Line

100

Station

Stray Current, Bus
Ungrounded, Station at Center of Line
2

4

6

Station
8
10
12
Distance (Thousands of Feet)

Figure 4. The effect of substation spacing on stray current [4].

26

Length: 20,000 ft, Double Track, 72-lb Rail,
Resistance: .004 Ω /1,000 ft,
Load of 40 A/1,000 ft,
Uniformly Distributed

I E E E E l e c t r i f i c ati o n M agaz ine / september 2014

14

16

18

20



Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2014

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IEEE Electrification Magazine - September 2014 - 1
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