IEEE Electrification Magazine - September 2014 - 25

Overhead Caternary (or Third Rail)
(+)

Train

Substation
(-)

Stray Current
Leaves Pipe
and Enters Anode Region
Substation

(Rail Used for
Return Path)

Rail Current
Return Path

Soil Current Return Path

Stray Current Enters Pipeline

Soil

Cathode Region

Pipe/Utility Line
Corrosion
Figure 2. The stray-current corrosion path for a dc transit system.

on the mitigation methods and later published a report in
1921. This report included detailed stray-current mitigation
techniques and construction methods
based on their study of the transit systems functional at that time in Europe
and America.

Historical Development:
1890-1950

that welded joints provide conductivity equal to or greater
than the continuous rail and are less subject to failure compared with other forms of rail joints.
Thermit welds were the most common
kind of welds used by the transit agencies during those times. The welding of
rail lengths thus became the standard
form of construction, especially in
embedded rails within light-rail transit
systems, and has not only been instrumental in the reduction of stray current
but has also improved the performance
of rails.
Cross-bonding between the rails of a
single track and parallel tracks was
installed to ensure rail connectivity and
to equalize the current flow between
the rails, thus reducing voltage drop. In
the United States, cross-bonding was
placed at a distance of 500 ft (152 m) on
urban and 1,000-2,000 ft (305-610 m) on suburban railways,
whereas in Germany, cross bonds were provided every 328 ft
(100 m). In France, they were placed every 160-328 feet (50-
100 m) and in England, every 120 ft (36.6 m) [4].

Corrosion is normally
defined as the
deterioration of a
material, commonly
referred to as
rusting, because of
its interaction with
the environment:
air, water, or soil.

Numerous studies were conducted by
corrosion committees and the engineering community during this time to
address the problems and to provide
the best mitigation options possible.
Many of those recommendations were
implemented on the newer designs at
that time, with varying results, including some adverse effects on the nearby
utility lines, thus making it necessary
to conduct further studies. Some of the
measures that were successfully developed to control straycurrent leakage and corrosion [4] include the use of
xx
properly bonded joints (welded joints), cross-bonding,
and heavy rails for good track conductivity
xx
high electrical roadbed resistance to earth and insulated negative return feeders
xx
a maximum number of traction power substations to
reduce the return current distance, consistent with
system economy
xx
a three-wire traction power system.
In the following sections, these four mitigation and
control techniques are described in further detail, based
on the literature.

Resistance to Earth and Insulation
of Negative Return Feeders
The resistance of the ground immediately in contact with
the rail depends primarily on the type of ground material

RP
Train
IT

Bonded Joints, Cross-Bonding, and Heavy Rails
The use of heavy rail sections and suitably bonded rail joints
was one of the earliest implemented mitigation methods for
the control of stray current. With time, rail sections have
been improved in cross section, length, and the method of
joining the two sections of rail. With joints being the weak
link in the track system, various methods of connecting the
rail lengths were experimented with before it was concluded

IL
RL

VGL

Substation
+
VS
-

IT
RN
VN

IN
IS
VGS

Figure 3. A simple circuit model illustrates the stray-current components [7]. For a list of symbols used, see "Notation."
IEEE Elec trific ation Magazine / s ep t em be r 2 0 1 4

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