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AC & DC Electrical

Interference

AC INTERFERENCE EFFECTSPIPELINES & HIGH VOLTAGE POWER

LINES

A RIGHT-OF-WAY PERSPECTIVE

By

Robert F. Allen

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IntroductionAC Interference on buried structures in JointPower Line/Pipeline Corridors

The Effects on the buried structures

Safety issues

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IntroductionA brief perspective on AC ElectromagneticInterference mechanisms

Design & Maintenance of AC Mitigation Systems

Discussion of causes and effects on the ROW

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OverviewWhat is AC Interference?Electrical Energy flow from Electric powerlines to nearby metallic structures

What Do We Hope to Learn?Understand the interference mechanisms anddetermine the most effective mitigation methods

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What Is AC Interference?Flow of Energy from electric power lines

Electromagnetic Fields

Long parallel exposures

Fault conditions

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Key WordsAC Electrical InterferenceElectromagnetic (Inductive) Coupling

Electrostatic (Capacitive) CouplingConductive CouplingLocal Earth Remote EarthSteady-state Fault Condition

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Key FactorsDistance from power conductors

Current carried by power lines

AC Mitigation System effects on the ROW

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Possible EffectsShocks to personnelAccelerated corrosion

Damage to electronic equipmentArcing across insulators or through coatingDegradation of coatingPerforation of the structureIgnition of volatile liquids

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Interference MechanismsEquipment isolated from earth

Vehicles with rubber tires

Above ground structures w/o adequate grounding

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3 Modes of ElectromagneticInterference

Electrostatic (Capacitive) Coupling

Electromagnetic (Inductive) Coupling

Conductive Coupling

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Electrostatic CouplingLong parallel exposure of buried metallicstructures to power linesConductors subject to capacitive couplinginclude:

Above ground pipelinesPipelines on skids during construction

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Electrostatic CouplingMitigation Techniques

Grounding structure to earth, via ground rods

Gradient control mat systems (Ground mats)

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Electromagnetic CouplingCurrent flow in the Electrical Conductor creates amagnetic field

This magnetic field penetrates the earth

The buried metallic structure acts as a transformer

by inducing voltage and current on to thestructure.

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Electromagnetic CouplingMitigation Techniques

More difficult to implement & maintain thanelectrostatic techniquesInstallation of low resistance grounding systemsto reduce current & voltage levelsGrounding, Bonding

Increase personnel precautions

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Conductive CouplingElectrical energy flowing directly from power lineto metallic structure

Can occur during steady-state or fault conditions

Can damage the metallic structure during a powerline fault condition

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Conductive CouplingMitigation Techniques

Increase Separation Distance No universally accepted guidelines for limitingvoltages produced on buried structuresThe following are guidelines in assessing hazardsin the pipeline industry:

CSA Guideline C22.3 No.6-1991

NACE Standard SP-01-77

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Key Factors in DeterminingStructure Voltage

Distance from power conductors

Current carried by power conductors

Resistance of soil along the joint corridorThe zone of influence grows as soil resistivityincreases

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Peak ValuesDiscontinuitiesRapid changes in directionTermination of either structureInsulating junction - Double stress voltageChange in structure characteristicsTransposition of AC line phases

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Personnel HazardsIn excess of 30 volts (rms) steady-stateOn the order of 300-400 volts during faultsPerson inadvertently grounding structure through their

bodyIncrease Separation of the UtilitiesStructure groundingInstallation of Gradient Control MatsSpecial Precautions in O & M Procedures

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Personnel Safety SuggestionsIncrease separation of the Utilities

Structure grounding

Installation of gradient control mats

Special precautions in O & M procedures

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Safety IssuesMinimum distance vs. Mitigation methods

Interference analysis to mitigate effects

Corrosion of non-cathodically protected structures

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Effective Mitigation MethodsA Function of many factorsDetermination of degree of mitigationSteady-state vs. Fault conditionsCompany personnel vs. General publicTemporary vs. PermanentEntire structure vs. above ground locations

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Mitigation MethodsGradient control wiresZinc conductorsSacrificial anodesGround rods

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Cathodic Protection IssuesWith mitigation wire installed

DC Isolation

AC Isolation

Electric Company Facilities Stray Current

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Power Line System

Power Line Right-of-Way (ROW)

Phase ConductorsShield WiresPhysical Configuration of Conductors

Phase Configuration (ABC)Phase Transpositions

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Power Line Structures

Structure Foundations

Grounding

Counterpoise

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Power SystemDisturbances

Natural Phenomena: Lightning, Wind

Electrical Fault- Station Equipment- Line Fault

- Multiple Line Breaker Operation- Single or Multiple Line-to-Ground

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Grounding Techniques

Nature of EarthElectrode

How does it work?

Electrical Safety

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Electrical Safety Shock Mechanisms,

& Guidelines

Abnormal Conditions

- Lightning Strokes- Line-to-Ground Faults

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Grounding System

A grounding system should provide a safe pathfor dissipation of the following:

Fault Currents

Lightning Strokes

Static Charges

EMI & RFI Signals

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Grounding System

A good grounding system will:Lessen the chance of injury due to faultyinsulation

Reduce likelihood of lightning damage

Improve performance of computer,communication and other sensitive

equipment

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Modeling & AnalysisCommon Facilities

Power SystemsPipeline Systems (Gas, Water, etc.)Railroad SystemsTelecommunication Systems

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Mitigation ObjectivesHuman Electrical Safety- NACE- IEEE

- CSA- IEC

Protection of the pipeline coatingProtection of the pipeline metalAC Induced Corrosion

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Mitigation MethodsRelocate pipelineLumped grounding or Brute Force MethodCancellation wiresGradient control wiresGradient control gridsIsolator/Surge Protector - DC

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Mitigation DesignGradient control grids at appurtenancesGradient control wires along pipelineInterconnection of gradient control wiresWire material: Zinc, Magnesium, Copper

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Other Issues

Casings

Electric power line facilities DC interference issueswith guy anchors & grounds.

Recommended

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RecommendedPractices

NACE standard SP0177-2000 Mitigation of ACCurrent & Lightning Effects on Metallic Structures &Corrosion Control Systems includes the following: Personnel protection Equipment protection

System testing

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AC & DC Electrical

Interference