Electrical submersible pumps (ESPs), sucker rod pumps and their variable frequency drives (VFDs) are the most popular artificial lift techniques for oil extraction.
Sucker rod pumps on multi-well pads, still very popular in many countries, have over 920,000 pumps in operation around the world. Their use in oilfields goes back more than 150 years!
Historically, many sucker rod pumps and ESPs are still fed from generators where power quality was not necessarily a major consideration. However, with the continuing transition to powering ESPs and sucker rod pump VFDs from utility supplies, maintaining acceptable power quality has become extremely important.
Indeed, failures of equipment adjacent and upstream of the ESP and sucker rod pump VFDs is often related to power quality problems. Therefore, utilities now apply strict rules regarding harmonic voltage distortion and power quality.
Traditional harmonic mitigation for ESP and Sucker Rod Pump VFDs Series passive harmonic filters
Series passive harmonic filters are installed with each 6 pulse ESP VFD. They are very rugged electrically and environmentally, cost-effective and have acceptable performance (<5% to 8% at rated load).
Please note : Harmonic Solutions Oil & Gas also supply a complete range of series passive harmonics filters for oilfield applications from 5.5HP to 3500HP/2625kW in enclosures from IP00 to IP55 and ambient temperatures up to 55 deg C. For more information click here.
AFE (aka ‘low harmonic drives’) for ESP and Sucker Rod Pump Applications
Currently, a number of ESP VFD vendors are promoting active front end (AFE) VFDs for ESP applications. These are essentially a series active filter, DC bus and a PWM IGBT output inverter (as per a 6 pulse VFD). This technology requires the use of an LCL filter at the input which, at reduced loading, inject uncontrolled reactive power into the power system causing leading displacement power factor, which is especially problematic on oilfields supplied by generators.
MOSAF Oilfield Active Filters for ESP and sucker rod pump VFDs
MOSAF provides economical ‘global’ harmonic and PQ mitigation for ESP or sucker rod pumps VFDs from a central point (e.g., a container or switchroom) in compensation current of up to 500A per cabinet at voltages to 690V. Enclosures options available include IP20 for panel mounting and IP54 at ambient temperature up to 55 deg C. However, if required, ‘one to one’ mitigation (i.e. one filter per ESP VFD or sucker rod pump VFD), adjacent to the well site, can also be supplied.
The compensation current capacity can be expanded to 2500A if additional VFDs are added to the field, thus ensuring a future-proof solution.
A concern on offshore oil production platforms and FPSOs is often the lack of physical space and the weight of ESP VFDs and harmonic mitigation (including 24 pulse VFDs). This may limit the number of ESP VFDs (and their harmonic mitigation) installed and therefore, the production throughput.
MOSAF is an advanced, high performance active filter which offers economical ‘global mitigation’ for multiple ESP VFD applications as illustrated below. It is more cost effective when installation, maintenance, space, weight are considered, yet ensuring high performance.
For further information on MOSAF active filter for oilfield and offshore applications click here.
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