Harmonics in Offshore Electrical Power Systems

Abstract

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.