Oil field retrofit of ESPs to Meet Harmonic Compliance

A large Petrochemical company installed nearly 50,000 HP of electrical submersible pumps (ESP´s) at an existing midwest USA oil field. Being equipped with Adjustable Speed Drives (ASD´s) these ESP´s introduced high levels of current harmonic distortion which resulted in 14%-19% voltage harmonic distortion at the Electrical Utility supply. Initially, the Utility noticed the low power factor (PF) and had the Oil company pay for the installation of power factor correction (PFC) capacitors on their medium voltage (MV) supply. Once installed, the Utility began to have problems with these capacitors and continued to receive complaints from other customers adjacent to the oil field so they enforced harmonic limits, as defined by IEEE Std 519, at all points of common coupling. Measurements were made with a harmonic analyzer at several locations throughout the electrical system to quantify harmonics and determine the effect the ESP´s were having on the Utility distribution system. Computer simulations were performed to analyze different methods of harmonic mitigation. Ultimately, passive harmonic filters were installed on all ESP´s in phases. In addition, the PFC capacitors were permanently disconnected after determining that a power system resonance condition existed. Once all phases of the project were complete, the voltage distortion level decreased to below 5% and power factor improved to near unity without the PFC capacitors. This article will describe the effect of harmonics on the electrical distribution system caused by ASD´s, practical solutions to excessive voltage harmonic distortion, resonance issues with PFC capacitors and the challenges associated with different methods of harmonic mitigation.