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2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
1
Accurate Voltage
Measurement of Energized
Street Level Objects
David Kalokitis
Chief Technology Officer
Power Survey Company
Senior Member, IEEE
dkalokitis@powersurveyco.com973-344-7116
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
2
Agenda
Contact Voltage Characteristics
Goals of Measurement Process
Measurement Process
Shunt Resistor Selection
Observations
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Voltage on publicly accessible surfaces
Normally non-energized objects
Fault does not operate protection
Shock hazards may persist for long periods of time
Voltage level may vary over time
Characteristics of Contact Voltage?
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Contact Voltage can Affect Anything
Public assetsPublic assets
Other assetsOther assetsPrivate assetsPrivate assets
Utility assetsUtility assets
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Goals of Measurement Process
Is there a hazard present?
Find the fault/source of Contact Voltage
Measurement repeatability
Measurement accuracy
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Good Data Helps Everyone
Field Workforce
Utility management & decision making process
General Public & Government
Reduce Shock Hazards
Troubleshooting & Repair Process clarity
Repeatable & trusted detection processes
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
A New Type of Measurement
Typical Electrical Work
• Line voltage +/- 5%
• Access to trusted ground
• Assume faults will operate protection
Contact Voltage
• Variable voltages 1-120V+
• Select ground references
• Hi-Z faults persist beyond overload
protection
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
What is a Safe Level?
Any voltage is a sign of a possible electrical fault
Hazard is related to underlying fault, not measured voltage
Fault and corrosion will only worsen over time
~50% of Contact Voltage findings can be traced to damaged insulation on line voltage sources
Measurement and characterization are key to successful mitigation
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Ground referenceo Not energized
o Low impedance
Clean connections
Verified using shunt resistor
Ideal Field Measurement
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Where does common terminal go?
Choosing Field Grounds
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Energized Ground Reference
Hot groundsHot grounds give false readings
SolutionSolution
Verify using multiple ground references
May require longer test leads
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Very high source impedance
Cannot drive current
Voltage collapses to ~ 0V with shunt resistor applied
Capacitive Coupling & False Positive
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Maximize measurement accuracy and repeatability Remove false positives from results Ideally, ZSH >> ZC + ZG
Choice of Shunt Resistor Value
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Choose shunt resistor to eliminate capacitive coupling, but retain measurement integrity
Choose un-energized, low-Z ground references Minimize ground impedances
Shunt Value & Measurement Error
Lo-Z shunt
Good
ground &
contact
Hi-Z shunt
Good
ground &
contact
Lo-Z shunt
Bad ground
& contact
Hi-Z shunt
Bad ground &
contact
Hi-Z shunt
Bad ground &
contact
ZSHUNT 500Ω 3000Ω 500Ω 3000Ω 10,000Ω
ZS 20Ω 20Ω 20Ω 20Ω 20Ω
ZG+ZC 50Ω 50Ω 250Ω 250Ω 250Ω
VSHUNT 0.88•VOC 0.98•VOC 0.65•VOC 0.92•VOC 0.97•VOC
Error % 9% 2% 32% 8% 2%
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
No Shunt
V=97.6
500 Ω Shunt
V=0.95V
3000 Ω Shunt
V=5.4V
10000 Ω Shunt
V=16V
Fault Under Sidewalk
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Select shunt value appropriately
Recognize error sources
Select appropriate earth reference
Understand measurement circuit
Control the process
Provide adequate training
Conclusions
2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,
Canada
Questions?
Some good references
R.J. Gustafson, “Instrumentation for Stray Voltage”, Proceedings National Stray Voltage Symposium, Syracuse, NY Oct 10-12, 1984
A. Cedrone, et al “Harmonic Waveshape Analysis For Quick
Determination of Faults to Energized Conductive Objects” Jodie S. Lane Stray Voltage Detection, Mitigation & Prevention Conference, New York, NY, 2009 (www.epri.com)
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