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

2. Outline of Presentation
CGL ENGINEERING CO., LTD.
Outline of Presentation
Causes of AC voltages on pipelines
Problems associated AC interference
Mechanisms of AC induced voltages
Mitigation options
AC mitigation modeling

3. What is AC Interference ?
CGL ENGINEERING CO., LTD.
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

4. Shared Right of Ways (ROW)
CGL ENGINEERING CO., LTD.
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

5. Issues with Induced AC on Pipelines in Shared ROW’s
CGL ENGINEERING CO., LTD.
Issues with Induced AC on Pipelines in Shared ROW’s
Safety
Induced voltage can provide shock hazards to personnel safety
Pipeline Integrity
Coating damage
AC induced corrosion

6. CGL ENGINEERING CO., LTD.
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)

7. Touch and Step Potentials
CGL ENGINEERING CO., LTD.
Touch and Step Potentials
Step Potential
Touch Potential

8. North American Standards
CGL ENGINEERING CO., LTD.
North American Standards
NACE 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 80
Provides safety criteria related to heart fibrillation
Safety limits are inversely proportional to fault duration and directly proportional to surface resistivity

9. CGL ENGINEERING CO., LTD.
Coating Damage
Fault 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

10. CGL ENGINEERING CO., LTD.
AC Induced Corrosion
Recent 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

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

12. AC Interference Mechanism
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

13. CGL ENGINEERING CO., LTD.
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

14. Resistive Coupling (Electrolytic)
CGL ENGINEERING CO., LTD.
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

15. CGL ENGINEERING CO., LTD.
Inductive Coupling
Current 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

16. Factors Contributing to AC Interference
CGL ENGINEERING CO., LTD.
Factors Contributing to AC Interference
Soil resistivity values
Magnitude of steady state current in powerline
Separation distance and orientation
Powerline operating characteristics
Magnitude and duration of fault currents
Grounding characteristic
Pipeline coating type

17. AC Interference Mitigation
CGL ENGINEERING CO., LTD.
AC Interference Mitigation
Equipotential gradient control mats
Test stations
Main line valves
Meter stations
Casing vents
Parallel zinc ribbon grounding electrodes
Point grounding with sacrificial anodes
DC de-couplers devices
Dead front construction of test stations
Non-metallic casing vents

18. Equipotential Grounding Mat to Prevent Shock Hazards
CGL ENGINEERING CO., LTD.
Equipotential Grounding Mat to Prevent Shock Hazards
Test Station
Ground Mat
Connected to Pipe
Water Pipeline

19. CGL ENGINEERING CO., LTD.
Zinc Grounding Mats

20. Overhead AC Transmission Line Distributed Sacrificial Anodes
CGL ENGINEERING CO., LTD.
Distributed Galvanic Anodes (Point Grounding)
Overhead AC Transmission Line
Underground Pipeline
Distributed Sacrificial Anodes
Induced Voltage
Without Anodes
With Anodes
Distance

21. DC De-coupling Device Conducts AC current & blocks DC current
CGL ENGINEERING CO., LTD.
DC De-coupling Device
Conducts AC current & blocks DC current
AC current is dissipated to earth
Electronic Polarization Cell Replacements (PCR)
Power Cable Sheath
Insulating Flange

22. Double Zinc Ribbon Installation
CGL ENGINEERING CO., LTD.
Double Zinc Ribbon Installation

23. AC Interference Modeling
CGL ENGINEERING CO., LTD.
AC Interference Modeling
CDEGS Interference Analysis Software
Estimates interference due to inductive and conductive coupling
Calculates steady state voltage conditions
Define phase to ground fault condition
Predicts step and touch potentials
Determines high risk areas e.g. phase transpositions, powerline crossings of ROW
Recommends AC mitigation options

24. Input for AC Interference Modeling
CGL ENGINEERING CO., LTD.
Input for AC Interference Modeling
Soil conditions
Pipeline characteristics
Pipeline and power system alignments
Power system characteristics
Operating voltage
Fault currents
Phase transpositions
Tower configurations
Static wire
Grounding design
Substation locations

25. CGL ENGINEERING CO., LTD.

26. Touch Potentials Predictions at Valve Station Under Fault Conditions
CGL ENGINEERING CO., LTD.
Touch Potentials Predictions at Valve Station Under Fault Conditions

27. Thank You Can I answer any questions?
CGL ENGINEERING CO., LTD.
Thank You Can I answer any questions?