Summary
Recently, electrical submersible pumps (ESPs) have become widely used in
depleting oil fields with low pressure (dead crude) and in deep wells with
marginal pressure to achieve oil production. These types of ESPs are
variable-speed drives (VSDs) and operated at variable voltages and frequencies
to optimize production. The introduction of a large amount of ESPs driven by
VSDs into an electrical power system of an offshore oil field that is
electrically weak leads to distortion of voltage and current profile beyond
acceptable limits, thereby producing harmonics. The more distortion there is in
the waveforms, the higher the harmonics.
The concept of harmonics, along with their impact and mitigation measures to
be exercised in an offshore power system, is discussed in this paper.
Furthermore, a method statement is provided for sizing the active harmonic
filter (AHF). An attempt is made to arrive at an empirical relationship for an
AHF rating in kVAR for offshore electrical power systems, but it is not yet
well documented. A case study of harmonic analysis for an integrated offshore
field in the South China Sea has been discussed.
The information contained in this paper is useful for design engineers as
well as operators handling electrical power systems for offshore oil fields
with significant amounts of nonlinear loads or VSD loads. This enables them to
predict the requirement of harmonic treatment in offshore electrical power
systems. It also helps them to take early action at the planning/design stage
to avoid probable damage to equipment or loss of power resulting from harmonics
and to conduct detailed harmonic analysis.
Introduction
A highly reliable, high-quality power supply is of paramount importance in
offshore oil and gas installations. Power outages and poor power quality have
resulted in considerable cost in these installations. Power quality is defined
in terms of voltage variation, voltage transients, and voltage waveform. One of
the power-quality characteristics lies in its waveform. It is preferred to have
a power-supply waveform as close as possible to that of a pure sine wave. In
reality, the power-supply waveform is never purely sinusoidal. The power-supply
waveform gets distorted because of nonlinear loads, rectifiers, VSDs, arc
furnaces, fluorescent tubes, discharge lamps, fan regulators, and other
power-distribution equipment. The waveform distortion is identified as a
combination of fundamental sinusoidal waveforms and harmonics.
Harmonics are pollutants and impact the quality of power and the life of the
electrical equipment. They need to be contained and can be contained by
adopting the mitigation measures discussed in this paper. It has long been
recognized that harmonic currents and voltages are highly detrimental to
electrical power equipment and systems. Their presence can damage equipment and
disrupt the production process, thereby costing the offshore oil and gas
operators tremendously.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
1 January 2005
- Revised manuscript received:
4 August 2005
- Manuscript approved:
14 August 2005
- Version of record:
20 March 2006
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