1 Mr. Dusit Thongjun Managing Director CGL Engineering Co., Ltd. CGL ENGINEERING CO., LTD. Mitigation of AC Induced Voltage On Buried Metallic Pipelines.

1

Mr. Dusit ThongjunManaging Director

CGL Engineering Co., Ltd.

CGL ENGINEERING CO., LTD.

Mitigation of AC Induced VoltageMitigation of AC Induced VoltageOn Buried Metallic PipelinesOn Buried Metallic Pipelines

Outline of Presentation

Causes of AC voltages on pipelines

Problems associated AC interference

Mechanisms of AC induced voltages

Mitigation options

AC mitigation modeling


What is AC Interference ? Electrical currents and electromagnetic fields

from the powerline in close proximity of a pipeline can produce AC voltages on pipelines

The magnitude and location of induced AC on a pipeline is a function of numerous conditions and is difficult to predict

The induced voltages can exist during normal

or abnormal operation of the powerline


Shared Right of Ways (ROW)Clear / unoccupied

Right-of-Way's are difficult to obtain for new pipelines

An attractive option is for new pipelines to a share an existing ROW with an overhead electric power transmission systems


Issues with Induced AC on Pipelines in Shared ROW’s

Safety Induced voltage can provide shock hazards

to personnel safety

Pipeline Integrity Coating damageAC induced corrosion


Personnel Safety

Safety standards for personnel are based on Touch and Step potentials which can result in shock hazards.

Step potential is the voltage difference measured between two points on the earth separated by a distance of 1 pace (1 meter)

Touch potential is the voltage difference between a metallic structure and a point on the earth separated by a distance of the normal reach of human (1 m)


Touch and Step Potentials

Touch Potential Step Potential


North American StandardsNACE RP0177

Considers AC step potentials >15 volts to be a potential shock hazard. Voltages above that level require mitigation or evidence that a potential shock hazard does not exist.

ANSI / IEEE 80Provides safety criteria related to heart

fibrillationSafety limits are inversely proportional to

fault duration and directly proportional to surface resistivity


Coating DamageFault currents from powerlines

can be collected and discharged from pipelines at coating holidays

Coating damage can occur when voltage exceed the dielectric strength of the coating

Arching stresses may damage the pipeline


AC Induced CorrosionRecent finding indicate that AC current can

cause 2% of the equivalent DC electrolysis problems on steel pipelines

AC induced corrosion is primarily a function of current density on steel structures. The general likelihood of AC induced corrosion is:

Current density < than 30A/m² : no or low

Current > than 30A/m² < 100 A/m² :medium

Current density > than 100A/m² : very high


Example of AC Induced Corrosion CGL ENGINEERING CO., LTD.

AC Interference Mechanism

Generation of AC induced voltages on a pipeline typically occur by one of the following mechanisms:

Capacitive coupling Resistive coupling (electrolytic) Inductive coupling


Capacitive Coupling

Caused by accumulation of electrostatic charge resulting in capacitive coupling between the powerline and a coated pipeline

Typically occurs during construction when coated and ungrounded sections of pipe are near a HV powerline

Unlikely on buried pipeline because the of the low pipe-to-earth capacitance


Resistive Coupling (Electrolytic) Unbalance phase to phase or phase

to ground faults of a powerline may cause current flow through the earth

Underground metallic structures in the vicinity may conduct some of the current

Typical occurs during abnormal operating conditions of the powerline


Inductive CouplingCurrent flow in the powerline creates an

electromagnetic field surrounding the conductors

An AC voltage can be induced on a metallic structure positioned in the magnetic field

Occurs during normal operating conditions of the powerline

The induced potential on the affected pipeline can reach 100’s of volts and present shock hazards

Pipelines within 350m to a HV powerline should be investigated


Factors Contributing to AC Interference

Soil resistivity valuesMagnitude of steady state current in powerline Separation distance and orientation Powerline operating characteristicsMagnitude and duration of fault currents Grounding characteristic Pipeline coating type


AC Interference MitigationEquipotential gradient control mats

Test stationsMain line valvesMeter stationsCasing vents

Parallel zinc ribbon grounding electrodes Point grounding with sacrificial anodesDC de-couplers devicesDead front construction of test stationsNon-metallic casing vents


Ground Mat Connected to Pipe

Test Station

Water Pipeline

Equipotential Grounding Mat to Prevent Shock Hazards


Zinc Grounding MatsCGL ENGINEERING CO., LTD.

Distributed Galvanic Anodes (Point Grounding)

Overhead AC Transmission Line

Underground Pipeline

Distributed Sacrificial Anodes

Induced VoltageWithout Anodes

With Anodes

Distance


DC De-coupling DeviceConducts AC current & blocks

DC currentAC current is dissipated to

earth Electronic Polarization Cell

Replacements (PCR)

Power Cable Sheath

Insulating Flange


Double Zinc Ribbon Installation CGL ENGINEERING CO., LTD.

AC Interference Modeling

CDEGS Interference Analysis Software

Estimates interference due to inductive and conductive coupling

Calculates steady state voltage conditionsDefine phase to ground fault conditionPredicts step and touch potentials Determines high risk areas e.g. phase

transpositions, powerline crossings of ROWRecommends AC mitigation options


Input for AC Interference ModelingSoil conditionsPipeline characteristicsPipeline and power system

alignmentsPower system characteristics

Operating voltageFault currentsPhase transpositionsTower configurationsStatic wireGrounding designSubstation locations


STEADY STATE PIPE TO EARTH VOLTAGE

15-Volt Maximum

0

30

60

90

120

0 20 40 60 80 100 120 140 160

CONSTRUCTION MILEPOST

VO

LT

S

No MitigationSingle Ribbon MitigationDouble Ribbon Mitigation15-Volt Maximum

RIGHT OF WAY SCHEMATIC

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 20 40 60 80 100 120 140 160

AC Circuit 3 - 115KV AC Circuit 7 - 500KV

AC Circuit 2 - 230KV AC Circuit 6 - 500KVAC Circuit 1 - 500KV AC Circuit 5 - 115KV

Cypress Pipeline AC Circuit 4 - 230KVCrossings not shown for clarity


Touch Potentials Predictions at Valve Station Under Fault Conditions


Thank You

Can I answer any questions?


1 Mr. Dusit Thongjun Managing Director CGL Engineering Co., Ltd. CGL ENGINEERING CO., LTD. Mitigation of AC Induced Voltage On Buried Metallic Pipelines.

Documents

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