Maintenance Technology October 2016 - 42


SOLUTION FOCUS

shift. Maintaining accurate records was
the job of a second thermographer.
A typical shift began 60 minutes before
the anticipated start of the scanning
window. After agreeing on the work plan
for the shift, the thermographers and
transit engineers would meet the work
train at the designated tunnel platform.
As the work train approached a target
area, the train engineer would reduce
its speed to a crawl. The thermographer
working with the imager on the front
platform would begin scanning. Data
collected at each location included the
highest and lowest cable temperatures
and a thermogram and control photograph of detected anomalies.
In a conventional setting, a thermographer has unlimited time to obtain
temperatures and adjust the thermal
imager controls to record the best
infrared image possible. That wasn't
possible on this project, given the fact
the work train could not stop in a subject
area. Instead, it would have to crawl
through it. Moreover, on many occasions,
it was ordered to speed up or clear the
track before all data could be collected. In
these situations, the location was noted
so that the train could return to the same
spot as soon as possible to complete data
collection. Again, accurate documentation by the thermography crew was the
key to ensuring complete coverage.

Scope and findings
The subway's survey included equipment
located in 30 tunnels. At the start of
the project, blueprints indicated 327
manholes and/or electrical cabinets to be
inspected. As it progressed, unlabeled or
"added" manholes were found.
Additional time was called for whenever the thermographers encountered
new locations. In these situations, thermographers and transit engineers would
have to create a name for the new site that
would fit into the system's nomenclature
and allow the area to be quickly located
by anyone assigned to repair problems
or conduct future infrared inspections.
These newly discovered areas were then
added to system blueprints for future
reference.
During the infrared survey, 394

42 |

MAINTENANCE TECHNOLOGY

specific sites-each encompassing
multiple cables, splices, connections,
and terminations-were inspected.
The system's electrified third rail was
also monitored. Overall, a total of 41
thermal anomalies or problems were
located and documented. Identified
problems included loose connections

This thermogram shows a typical thirdrail problem. At the time this image was
taken, there was a 41 C temperature
differential between rail sections.

at cable terminations, unbalanced loads
(including some with very high temperature differentials), and damaged splices,
as well as hot spots on the third rail.
Note that the cable in a mass transit
system is measured in millions of feet.
Possible problems in this type of cable
system include frayed strands, failed
splices, overloads, or poor terminations.
Since it isn't practical for subway
personnel to inspect all of the system's
cables by hand, one goal of the infrared
project was to identify cables that
did call for further investigation. The
thermographers surveyed miles of cable
located on and near the tracks. In the
process, they detected thermal anomalies
indicative of each of the previously
referenced problems. Because the
system's transit engineers were working
alongside the thermographers, they were
able to quickly generate work orders

for immediate investigation of the most
serious issues.

Results
Proper planning and work performed
by experienced thermographers allowed
the subway to meet its electrical-system
inspection goals. All work was performed

This thermogram shows a cable entering
a junction box. Since it was not possible to
do further investigation at the time of the
survey, actual temperatures within the box
might be higher than shown on the cable.

without system disruption.
The final report included detailed
descriptions needed for follow-up and
provided a basis for future studies. To
assist with a baseline and help with future
studies, high and low cable temperatures
were recorded at each manhole. Most
important, the infrared survey identified
many problems that, left unaddressed,
could have resulted in equipment failure
or safety issues.
The entire project was completed and
the final report delivered in less than
four weeks, enabling the subway system's
engineers to schedule repairs and corrective actions. MT
Jersey Infrared Consultants (Burlington,
NJ) has been providing infrared inspection
services for commercial and industrial
facilities around the world since 1984. For
more information, visit jerseyir.com.
OCTOBER 2016
http://www.jerseyir.com
Table of Contents for the Digital Edition of Maintenance Technology October 2016
