Electrical submersible pumps (ESPs) and their variable frequency drives (VFDs) are one of the most popular artificial lift techniques for oil extraction.
Historically, many ESPs are fed from generators where power quality was not necessarily considered a major issue. However, with the continuing transition to powering ESP VFDs from utilities supplies, maintaining acceptable power quality has become extremely important.
Indeed, failures of equipment adjacent and upstream of the ESP VFDs are often related to power quality problems. Therefore, utilities now apply strict rules regarding harmonic voltage distortion and power quality.
Traditional harmonic mitigation solution for ESP 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).
AFE (aka ‘low harmonic drives’) for ESPs
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, injected uncontrolled reactive power into the power system causing leading displacement power factor, which is especially problematic on oilfields supplied by generators.
RiteSine ActiveESP – Global harmonic mitigation for oilfield ESP VFDs
RiteSine ActiveESP provides ‘global’ harmonic and PQ mitigation for all ESP VFDs from a central point(s) per VFD in the field available in IP31, IP43, IP54 or IP65 (up 55 deg C) or IP20 (panel mounting). The compensation current capacity expanded if additional ESP VFDs are added to the field thus ensuring a future-proof solution.
In addition to total harmonic voltage distortion, a concern on offshore oil production platforms and FPSOs is the lack of physical space and the weight of ESP VFDs and ancillary equipment. This may limit the number of ESP VFDs (and their harmonic mitigation) installed and therefore, the production throughput.
On production platforms, FPSOs and where land-based utility networks supply the oilfields, the cost and ease of installation, performance and redundancy are all primary drivers. The harmonic mitigation focus is now shifting towards more centralized, advanced mitigation solutions such as the RiteSine ActiveESP.
RiteSine ActiveESP is an advanced, high performance active filter which offers ‘global mitigation’ for multiple ESP VFD applications as illustrated below thus saving valuable total purchase, installation and maintenance costs, space, weight yet ensuring high performance.
Patented ripple current interleaving cancellation technology
The ActiveESP harmonic filter utilises double interleaved inverter topology to ensure dynamic response time, reduced ripple current and reduced heat loss.
The high-frequency components of the two inverters’ output currents are shifted by 180 degrees in order to essentially cancel each other. As a result, the overall ripple current is reduced by 80% and the power losses decreases by 30% but without compromising both the response time and the need to increase the switching frequency.
ActiveESP basic specification
- Supply voltages available – 380V to 690V, 50/60Hz (above 690V on application).
- Maximum compensation capacity per discrete filter 100A up to 600A. Up to 10 filters can be connected in parallel (max 6000A).
- Broad spectrum of cancellation (from 2nd to 50th harmonics) to <5% THDi at rated load
- Ambient temperature – 40 deg C to 55 deg C with derating (above 55 deg C on application).
- Enclosure options – IP20, IP31, IP43, IP54 (IP65 on application)
- Harmonic mitigation and reactive power compensation as standard (3W)
- Superior filtering efficiency of no less than 97%
ActiveESP additional advanced outstanding features
- Powerful controller based on dual-DSP architecture allowing for ultra-fast and precise compensation
- Amorphous alloy reactors used for for low noise and enhanced energy efficiency
- Compensation for both integer harmonics and interharmonics (optional)
- Compensation for background harmonic voltage distortion (optional) to protect downstream loads
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