nt at King Fahd University of Petroleum & Minerals,
Dhahran, Saudi Arabia


ABSTRACT

Transmission lines are considered one of the major sources of magnetic field. In recent years
electromagnetic field (EMF) interference with buried pipelines has been of great interest in the
literature. The EMF interference on pipelines located in utility corridors is a real and serious
problem which can place both operator safety and pipeline integrity at risk.
Installing pipelines in energy utility corridors containing high-voltage AC transmission lines
subjects the pipelines to induced AC voltages. This can be caused by an imbalance in the
transmission system, and by high voltages near transmission tower grounding systems resulting
from lightning strikes and phase faults.

When a long-term induced AC voltage exists on a pipeline, it can be dangerous and potentially
life-threatening for operations personnel to touch the pipeline or appurtenances. In addition,
pipe corrosion also can result from AC discharge.

Due to the wide lands of Saudi Arabia and its long water and oil pipelines, a considerable
length of these pipelines extends along the high voltage transmission lines right-of-way. A
study was conducted in 1992 in the Eastern region to evaluate such AC voltages deposited on
buried oil pipelines from the utility transmission lines. As well as in 1998 another investigation
was conducted on a 380 KV transmission line and a parallel buried water pipeline in the West
region.

To address this problem, the pipelines must be grounded with a system that passes AC, but
blocks DC, to both mitigate the AC and maintain the cathodic protection system on the
pipeline. The paper presents the essential procedures, guidelines, needed data and cautions
when conducting such evaluations. Also, it presents the results of a case study of a 380 KV
transmission line in the Eastern region of Saudi Arabia
.


KEYWORDS

Electromagnetic Field, EMF Interference, Pipelines, EMF Interference Investigation,
Transmission Lines Interference
Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
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INTRODUCTION
The problem of EMF interference on buried pipelines has been known for well over 30 years.
However, the problem has gained widespread recognition only in the last 10 years due to
improvements in pipeline technology and the increased tendency to locate pipelines in utility
right-of-way (ROW) near high-voltage electric transmission lines. Pipelines are now frequently
being installed in electric power transmission right-of-ways (ROW). Installation of pipelines
which are considered as electric conductors near high voltage transmission lines can result in
unusual pipeline/EMF interference problems.

When steel pipelines are installed close to overhead electric transmission lines, interference can
occur between the electric lines fields and the pipeline, as seen in figure 1.1. Electric power is
transmitted in three phase systems and on one or double circuit structure; each carried on a
separate line held aloft by pylons or towers along the right of way.




Figure 1.1 Influence by inductive coupling

The voltage sequence of the power is sinusoidal AC power phase and is 120� out of phase
with the other two. If each phase is equal, the sum of the alternating currents in the three
phases and the sum of the magnetic fields resulting from the alternating current in each phase
should add up to zero in balanced three phase system. Figure 1.2 illustrates that the different
distances between the pipeline and each phase in the transmission line, along with phase
imbalance, lead to induced AC interference on the pipeline [1-2].

Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20
th

22
nd
October 2003

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Figure 1.2 Induction Affect and Different distances between the pipeline and the transmission line circuit

Coatings on pipelines are usually used to avoid and protect pipelines from the severe corrosive
effects due to the harsh environment in Saudi Arabia. Modern pipeline coating technology has
exacerbated the AC mitigation problem by creating better coatings, leaving fewer defects in
the coating for AC to go to ground. In fact, a bare pipeline would be a good answer to the
induced AC problem. Both the Fusion Bonded Epoxy coatings used in the U.S.A. and Three
Layer FBE/PE coatings used in Europe have made the problem of AC interference on
pipelines more severe. In the past, less well coated pipelines had sufficient grounding, such
that induced voltages were not a practical problem. The rapid expansion of transmission lines,
industrial plants and remote resources of discovered oil field as well as the limited water
resources in Saudi Arabia dictates the delivery of such commodities to its ports and locations
[3-4]. This means the addition of more buried pipeline routs to maintain services, life and
development in Saudi Arabia. The continuous up grade of such services, corrosive climate
requires cathodic protection (CP) to be implemented. This will make EMI evaluation studies a
vital one to assure that (CP) is actively operative and above all the electromagnetic field
interference (EMI) studies are needed for the safety of personal and assets.

BACKGROUND

EMF interference between transmission systems and buried pipelines can be of three kinds:

A.

Electrostatic or capacitive interference:

Occurs in the immediate vicinity of the overhead power lines when the pipe is laid on a
foundation that is well insulated from the ground. The pipeline picks up a voltage
relative to the soil, which is proportional to the voltage in the transmission line.


Welded pipe lengths near high voltage lines must be grounded when the nominal
voltage in the overhead lines exceeds 115 kV and the length of the welded section
exceeds more than a few hundred feet to 1,000 ft. Electrostatic coupling is of minor
consequence after construction, since even the best pipe coating will allow sufficient
leakage to earth, through defects, to effectively ground the electrostatic charge [5-6].
B.

Resistive or ohmic interference: Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20
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22
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October 2003

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Occur when lightning strikes a transmission structure, or when there is a phase-ground
fault. When this occurs, a large voltage cone is created around the pylon grounding
system. If a pipeline is located within this area, voltage can get onto the pipeline in the
area within the voltage cone through coating defects.


Anyone touching the pipeline outside the voltage cone could receive a shock from the
potential between the pipeline and the surrounding soil. Protective measures for people
are required if the contact voltage exceeds 65 V for long-term interference, or 1,000 V
for short-term interference. These measures include wearing rubber boots, insulated
gloves, or insulated protective padding. On no account, however, can there be any direct
bond between the pipeline and the pylon grounding system [6-7].


Special conditions arise if the pipeline is laid in the vicinity of a power station ground
system or a transformer installation. If a lasting or transitory connection with the
grounding installation results during a grounding fault, the grounding voltage will be
transferred to the pipeline and appear outside the voltage cone as a contact voltage.
Depending on the pipeline and its coating, the contact voltage decreases more or less
quickly at greater distances.

C.

Electromagnetic or inductive interference:

Occurs when there is extended and close parallel routing with three-phase high voltage
AC transmission lines. The voltage is due to any phase imbalance in the lines. The
likelihood of interference increases with rising operating currents in the overhead lines,
with increasing quality of the coating on the pipeline, and with the length of line parallel
to and close to the high voltage AC (HVAC) transmission lines.


Voltages are induced in the pipeline by magnetic coupling with the high-voltage lines,
and results in currents flowing in the pipeline. These currents result in a voltage
difference between the pipeline and the surrounding soil.

D.

Contact voltages:

When a long-term induced AC voltage exists on the pipeline, resulting from long
sections of parallelism with EMF tower electric transmission lines, it may not be safe to
touch the pipeline or appurtenances. This "contact" voltage, or the difference between
the line and the earth, can cause AC current to flow to ground through a person
touching the line. When a metal structure, such as a pipeline, is under the influence of
electrical fields and a person touches it, a current passes through their body to the earth.