Power Quality Harmonics · VSD Remote Well Site Multi-Pulse Comparison Case Study

Harmonic Control at a Remote Oil Well: Better Than 18-Pulse Performance at 12-Pulse Cost — Mirus International

Denis Ruest, M.Sc. (Applied), P.Eng. (ret.) · IPQDF · Technical Reference Series

Source & Acknowledgment

This article is based on field data and application engineering by Mirus International Inc. (Mississauga, Ontario, Canada) — developers of the Lineator AUHF Universal Harmonic Filter. The original case study was produced in collaboration with Chevron (Peter O’Brien, Electrical Engineer). The original documentation is available at mirusinternational.com. IPQDF gratefully acknowledges Mirus International for making this field data available to the engineering community.

System at a Glance

Location	Simonette well site, far Northern Alberta
Client	Chevron Canada
Application	Submersible pump drive — remote, unmanned oil well
Service transformer	200 kVA
Drive	150 kVA, 480 V adjustable speed drive
Motor	150 HP
Load configuration	Drive is the only load on the transformer
Harmonic filter	Mirus Lineator AUHF 150 HP
Performance	Better than 18-pulse; 9% less expensive than 12-pulse drive option

01 Operating Context: Unmanned Remote Well Sites in Northern Alberta

Chevron operates adjustable speed drives on submersible pump motors at remote, unmanned oil wells across far Northern Alberta. These sites share a common electrical architecture: a single service transformer feeds a single VSD, which controls a single submersible pump motor. There is no other load on the transformer. The sites are completely unmanned — visited periodically for maintenance, monitored remotely the rest of the time.[1]

This configuration creates two distinct requirements that pull in opposite directions. The single-drive-on-transformer topology is the worst-case harmonic scenario — the drive is the only load, so there is no linear load current to dilute the harmonic content, and the current drawn from the transformer is essentially the raw harmonic spectrum of a 6-pulse rectifier. At the same time, the unmanned and remote nature of the site demands maximum reliability — a harmonic problem that causes a drive trip or a communication system failure means a well that stops producing, with no one on site to respond.

The single-drive-on-transformer problem

When a VSD is the only load on a transformer, the current THDi seen by the transformer primary is essentially the unmodified harmonic spectrum of the 6-pulse rectifier — typically 35–45% THDi depending on drive loading and DC bus capacitance. There are no linear loads to provide fundamental-frequency current that would reduce the THDi percentage. The transformer sees this distorted current through its full impedance, producing high voltage distortion on both the primary and secondary. Any control or communication equipment sharing that transformer secondary is exposed to that distortion.

Chevron’s engineering team took a proactive, preventive approach: rather than waiting for harmonic problems to manifest at well sites, they established a standard specification for harmonic mitigation on all low-voltage, single-drive well sites up to 1,000 HP. The Simonette well site represents the application of that standard.[1]

Chevron Simonette well site — remote oil well with service transformer and VSD enclosure

Fig. 1. Chevron’s Simonette well site, far Northern Alberta. The 200 kVA service transformer and 150 HP VSD enclosure are visible. Single drive, unmanned, remote. Source: Mirus International / Chevron.[1]

02 The Single-Drive Problem: Harmonics With No Dilution

2.1 Why this topology is particularly sensitive

A 6-pulse VSD draws current in characteristic pulses — the familiar double-humped waveform per half-cycle that contains predominantly 5th, 7th, 11th, and 13th harmonic components. On a large industrial bus with many loads, these harmonics mix with the fundamental-frequency currents from motors, lighting, and other linear loads, and the resulting THDi at the bus is lower than what any single drive would produce alone.

At the Simonette well site, none of this dilution exists. The transformer secondary feeds only the VSD. The transformer primary sees only the distorted VSD current. The voltage distortion on the transformer secondary — which is also the supply voltage to the drive control electronics and any communication equipment at the site — reflects the full harmonic content of the 6-pulse rectifier through the transformer impedance.[1]

2.2 Communication system vulnerability

Remote well sites rely on SCADA and telemetry systems for monitoring and control. These systems share the site electrical supply. Voltage distortion and high-frequency harmonic content can interfere with the sampling and communication circuits of SCADA equipment, causing false readings, communication dropouts, or equipment lockups. In an unmanned application, a communication failure means lost visibility into well production — a direct financial consequence with no personnel on site to diagnose or reset the system.[1]

Drive input current waveforms before and after Lineator installation, with predicted waveform

Fig. 2. Current waveforms at the Simonette well site. Left: drive input before Lineator installation — characteristic 6-pulse distortion. Centre: measured result with Lineator installed — near-sinusoidal. Right: predicted Lineator input waveform from simulation. Figures 1 and 2 supplied by Chevron.[1]

03 Multi-Pulse Drives vs. the Lineator: A Technology Comparison

Chevron’s electrical engineers were experienced users of multi-pulse drive technology. Before selecting the Lineator, they specifically evaluated 12-pulse and 18-pulse drive options against the Lineator AUHF for this application. The comparison is instructive.[1]

3.1 How multi-pulse drives work

A 12-pulse drive uses a phase-shifting transformer with two secondary windings — one wye and one delta — to feed two 6-pulse rectifier bridges in parallel. The 30° phase shift between the windings causes the 5th and 7th harmonic currents from the two bridges to cancel in the transformer primary, leaving the 11th and 13th as the dominant harmonics. An 18-pulse drive extends this to three phase-shifted secondary windings feeding three bridges, cancelling through the 13th harmonic and leaving the 17th and 19th.[2]

Both approaches reduce THDi substantially compared to a standard 6-pulse drive. But they carry specific costs and constraints that made them problematic for the Simonette application.

3.2 The comparison

Criterion	12-pulse drive	18-pulse drive	Lineator AUHF
Harmonic performance	Good — cancels 5th & 7th	Better — cancels through 13th	Better than 18-pulse (measured)
Capital cost vs. 12-pulse	Baseline	Higher	9% less than 12-pulse
Factory testing required	Yes — phase shift & load sharing	Yes — more complex	No
Installation complexity	Moderate	Higher	Plug and play
Drive supplier endorsement	Standard offering	Available	Fully tested & recommended
Performance sensitivity to load	Degrades at light load	Degrades at light load	Robust across load range

Why multi-pulse performance degrades at light load

Multi-pulse harmonic cancellation relies on the two (or three) bridge currents being equal in magnitude so their harmonic components cancel precisely. At light drive loading, the DC bus capacitors dominate the current waveform shape, and the bridge currents become unequal and more peaky — the cancellation is imperfect. The result is that a 12-pulse drive can produce higher THDi at 25% load than at 100% load, which is the opposite of what is usually assumed. The Lineator AUHF is not dependent on current cancellation between parallel bridges, so its attenuation is more consistent across the load range — an advantage in well-site applications where pump loading varies with reservoir conditions.

“Our experience was with multi-pulse drives. We have used 12-pulse drives. However, in order to achieve the harmonic limits that we need, we realized that we must either purchase 18-pulse drives or evaluate other options. Our drive supplier had fully tested and recommended Lineator as a power quality solution, and that was enough for us.” — Peter O’Brien, Electrical Engineer, Chevron

The drive supplier endorsement carries weight in this context. Chevron was not evaluating an unknown product — the Lineator had been tested by the drive manufacturer for compatibility with their specific drive platform. This eliminated the integration risk that can accompany third-party harmonic filters and was a decisive factor in the selection.[1]

04 Results: Performance as Predicted, Cost Below Alternatives

The Lineator AUHF was installed at the Simonette well site on the 150 HP, 480 V drive. Measured current waveforms confirmed the simulation predictions: the drive input current waveform was transformed from the characteristic distorted 6-pulse pattern to a near-sinusoidal shape.[1]

The measured harmonic performance exceeded 18-pulse drive specifications — the most demanding multi-pulse standard Chevron had previously used. This was achieved at a capital cost 9% below a 12-pulse drive configuration, with simpler installation (no factory pre-testing required) and full compatibility confirmation from the drive supplier.

Chevron’s two objectives — both met

Reliability: Harmonic distortion reduced to levels that protect drive electronics, control systems, and SCADA communication equipment from interference and instability. Unplanned well shutdowns due to PQ-related drive trips or communication failures eliminated.

Cost effectiveness: Better harmonic performance than 18-pulse at lower cost than 12-pulse. No factory testing costs. Plug-and-play installation. Standard solution deployable across all single-drive well sites up to 1,000 HP.

“At Chevron, we want to achieve the most harmonic reduction for our dollar.” — Peter O’Brien, Electrical Engineer, Chevron

05 The Power Quality Perspective: What This Case Study Illustrates

5.1 The single-drive-on-transformer scenario — a common field condition

Remote well sites, irrigation pump stations, small water treatment facilities, and similar single-load installations share the same electrical topology as Simonette: one transformer, one VSD, no other loads. This topology appears throughout rural infrastructure wherever a pump or compressor is the sole electrical load at a remote site.

From a utility standpoint, these single-drive installations are PQ problems waiting to develop. The transformer sees high THDi continuously, runs hot, and ages faster. If the transformer feeds any utility-side measurement equipment, communication relays, or revenue metering, harmonic distortion affects their accuracy and reliability. Chevron’s proactive approach — standard harmonic mitigation on all single-drive well sites — is the correct engineering response and produces lower lifecycle costs than reactive mitigation after failures occur.

5.2 Multi-pulse drives — when they make sense and when they don’t

Multi-pulse drives (12-pulse and 18-pulse) are effective harmonic mitigation when the application justifies their cost and complexity. They make most sense for large, high-utilization drives where the phase-shifting transformer is a minor fraction of total system cost, where load is relatively constant (avoiding the light-load performance degradation), and where the harmonic cancellation can be verified by factory testing before shipment.

They are less well-suited to small drives (the transformer cost becomes a significant fraction of drive cost), variable-load applications, and situations where field installation simplicity is valued. The Simonette well site failed all three of the conditions that favour multi-pulse — small drive, variable pump load, remote unmanned installation requiring simple maintenance. The technology comparison led directly to the correct conclusion.

Utility perspective — harmonic standards and single-point loads

IEEE 519 establishes harmonic limits at the point of common coupling (PCC) — the point where the utility and the customer systems interface. For a single-drive well site fed by a dedicated distribution transformer, the PCC is the transformer primary. If the site draws only VSD current, the harmonic current at the PCC is entirely from that one drive. The full harmonic burden falls on a single point with no diversity benefit from other loads. Meeting IEEE 519 limits at such a PCC requires effective mitigation at the drive — there is no network-level averaging to rely on.

5.3 Preventive vs. reactive harmonic management

Chevron’s decision to specify harmonic mitigation as a standard requirement across all single-drive well sites — before problems occurred — is worth noting as a management approach, not just an engineering one. The cost of a harmonic filter at installation is far lower than the cost of diagnosing and resolving harmonic problems after the fact: transformer replacement, drive repairs, SCADA system troubleshooting, and lost production during unplanned downtime. Preventive harmonic management is straightforward to justify when the single-point, high-impedance topology makes the harmonic outcome predictable from day one.

This case study concludes the IPQDF series of Mirus International case studies. Taken together — ESP motor protection, pipeline generator rightsizing, offshore vessel DP compliance, natural gas processing plant MCC mitigation, and remote well site harmonic control — they cover the major categories of generator-fed and supply-constrained harmonic applications encountered in the oil and gas, marine, and process industries. The common thread is a high source impedance that amplifies harmonic consequences beyond what utility-connected engineers typically encounter, and a passive wide-spectrum filter that addresses the problem without adding the complexity and failure modes of active or multi-pulse solutions.

References

[1] Mirus International Inc., “Case Study: Chevron’s Simonette Well Site,” Application Case Study, Mississauga, Ontario, Canada. Available: mirusinternational.com
[2] IEEE Std 519-2022, “IEEE Standard for Harmonic Control in Electric Power Systems,” IEEE, New York, NY, 2022.