accurate voltage measurement of energized street level...

2013 IEEE PES 2013 IEEE PES July, 2013 Vancouver, British Columbia,

Canada

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Accurate Voltage

Measurement of Energized

Street Level Objects

David Kalokitis

Chief Technology Officer

Power Survey Company

Senior Member, IEEE

[email protected]


Canada

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Agenda

Contact Voltage Characteristics

Goals of Measurement Process

Measurement Process

Shunt Resistor Selection

Observations


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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?


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Contact Voltage can Affect Anything

Public assetsPublic assets

Other assetsOther assetsPrivate assetsPrivate assets

Utility assetsUtility assets


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Goals of Measurement Process

Is there a hazard present?

Find the fault/source of Contact Voltage

Measurement repeatability

Measurement accuracy


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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


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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


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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


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Ground referenceo Not energized

o Low impedance

Clean connections

Verified using shunt resistor

Ideal Field Measurement


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Where does common terminal go?

Choosing Field Grounds


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Energized Ground Reference

Hot groundsHot grounds give false readings

SolutionSolution

Verify using multiple ground references

May require longer test leads


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Very high source impedance

Cannot drive current

Voltage collapses to ~ 0V with shunt resistor applied

Capacitive Coupling & False Positive


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Maximize measurement accuracy and repeatability Remove false positives from results Ideally, ZSH >> ZC + ZG

Choice of Shunt Resistor Value


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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%


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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


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Select shunt value appropriately

Recognize error sources

Select appropriate earth reference

Understand measurement circuit

Control the process

Provide adequate training

Conclusions


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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)

accurate voltage measurement of energized street level...

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