Recently Electrical Submersible Pumps (ESPs) are being widely used in the depleting oil fields with low pressure (Dead Crude) and in deep wells with marginal pressure to achieve oil production. These ESPs are variable speed drives (VSDs) and operated at varriable voltages and frequencies to optimize production. The introduction of large amount of ESP driven by VSDs into an electrical power system of an Offshore Oil Field, which is electrically weak, leads to distortion of voltage and current profile beyond acceptable limits, thereby producing harmonics. More the distortion in waveform higher are the harmonics. The concept of harmonics along with their impact and mitigation measures to be exercised in an Offshore Power System has been discussed in this paper. Further, a method statement is provided for sizing the Active Harmonic Filter (AHF). An attempt is made to arrive at empirical relationship for AHF rating in kVAR for Offshore Electrical Power System, which is not yet well documented. A case study of harmonic analysis for an integrated offshore field in South China Sea has been discussed. It is concluded that AHF is the optimum choice for an Offshore Power System in view of it's flexibility, better harmonic control, reliability, power factor improvement and least space requirement. The information contained in this paper shall be useful for design engineers as well as operators handling Electrical Power System for Offshore Oil Field with significant amount of non linear loads or variable speed drive loads. This shall enable them to predict the requirement of harmonic treatment in Offshore Electrical Power System. It will also help them to take early action at planning / design stage to avoid probable damage to equipment or loss of power due to harmonics and to conduct detailed harmonic analysis.


Highly reliable and high quality power supply is of paramount importance in Offshore Oil and Gas installations. Power outage and poor power quality cost heavily 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 power supply waveform as close as possible to that of a pure sine wave. In reality the power supply waveform is never pure sinusoidal. The power supply waveform gets distorted due to non linear loads, rectifiers, variable speed drives, arc furnaces, fluorescent tubes, discharge lamps, fan regulators, and other power distribution equipment. The waveform distortion is identified as combination of fundamental sinusoidal waveform and harmonics. Harmonics are pollution and impact quality of power and life of electrical equipment. They need to be contained and can be contained by adopting mitigation measures as discussed in this paper. It has long been recognized that harmonic currents and voltages are highly detrimental to electrical power equipment and system. Their presence can damage equipment and disrupt production process thereby costing heavily to the Offshore Oil and Gas operators.

Concept of Harmonics

The harmonics are defined as sinusoidal components of a periodic wave having a frequency that is an integral multiple of fundamental frequency.

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