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General Considerations for Test
Methods
When considering Contact Voltage
test protocols, a number of
considerations are necessary to
achieve measurable safety
performance improvements in an
efficient manor.
Where
to test
While it is desirable to know
the status of the entire system,
reductions in reported shocks
and injuries will be greatest
when test efforts are
concentrated in areas where
there is underground
infrastructure and significant
foot traffic.
Detection and Scanning
Detection methods are very
efficient in finding Contact
Voltage. Given the wide variety
of structure types found
energized in the field, a
detection scheme is required.
The selected detection methods
must; 1) work at some stand off
distance, 2) provide a sense of
direction, intensity and 3) be
agnostic toward the type of
structure. Simply making contact
measurements to utility owned
structures has been shown to
miss large numbers of energized
structures. Additionally, a
brute force contact measurement
survey working from an asset
list will by definition miss any
energized structure not
appearing on said list.
Interpretation of Findings
Voltage appearing on publicly
accessible structures must
trigger further investigation.
The measured voltage is likely a
result of abnormal system
operation such as a fault. While
the voltage reading is
important, more important is the
determination of the voltage
source, as the surface voltage
can increase.
Survey
Test Methods
Survey test methods must be
optimized for speed and
accuracy. Operating a detector
from a moving platform allows
workers to cover a broad
geographic area at a high rate
of speed. Progress can be
tracked using both GPS as well
as paper maps. When an
abnormality is detected from the
moving platform, workers must
stop the vehicle and perform a
manual investigation. This
investigation consists of
isolation of the source(s) of
high E-field using a handheld
directional E-field detector,
followed by proper voltage
measurements using suitable
grounds and shunt resistance.
Higher voltages will dictate
immediate response from repair
personnel. All dangerous sites
must be isolated from public
access.
Repair
Activity
Repair personnel should be
equipped with the same tool set
and training as the survey
personnel. Continuity of
measurement procedure is
necessary to insure the repair
personnel are able to confirm
voltage measurements and verify
repairs have effectively
eliminated voltage.
Mobile Detection Test Equipment
E-field sensing
has proven to be an effective
measure for the detection of
Contact Voltage conditions. A
mobile detection system offered
by Power Survey Company is
currently in use in a number of
US cities. The detection system,
known as the SVD 2000 is
operated by trained technicians
as part of a mobile scanning
program designed to locate
Contact Voltage conditions.
The SVD 2000 pictured below,
uses a sensitive E-field
detector to locate anomalous
changes in E-field. Energized
surfaces and structures exhibit
a pattern of electric field
lines recognized by the SVD 2000
system.
The SVD 2000 is able to detect
objects energized with as little
as 1 volt and provides effective
detection out to a distance of
30’ on either side of the
sensor. Sophisticated digital
signal processing filters out
interference from environmental
and radio frequency sources. The
system travels at approximately
20 MPH while detecting E-field.
A graphical user interface
program running on a laptop
computer allows the operator to
interact with the system and
document findings. Side looking
video cameras and a GPS system
enable pinpoint location of
energized targets.
When the SVD 2000 operator
detects a peak in E-field, the
vehicle is stopped and an
investigation is performed to
locate the source of E-field.
Hand held E-field detectors are
used in conjunction with the SVD
2000 to determine the exact
source so a voltage measurement
can be performed.
Survey
Measurement Methods
A measurement protocol,
specifically adapted to a
Contact Voltage survey protocol,
is required for fast and
accurate voltage determination.
Some key elements to procedure
design for survey measurement
methods are listed below.
Measurement ground connection
Field measurements by survey
crews will require ground
connections. While system
neutral is the preferred ground
point, survey crews rarely, if
ever, have access to system
neutral. Available grounds such
as fire hydrants, sign posts,
and other metal objects are
usable as ground points.
Selected ground points must be
tested with a hand-held E-field
detector to ensure elevated
voltage is not present on the
ground connection. |
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