Identifying and fixing a broken sine wave filter in electric submersible pumps

Unexpected harmonics and voltage imbalance in an ESP drive

A customer faced recurring issues with one of its electric submersible pump (ESP) installations. SAM4 detected irregular harmonic patterns and voltage imbalance on the ESP- anomalies not seen on other ESPs operating under similar conditions. Specifically:

• Current phase mismatch: Phases 1 and 3 showed significant harmonic distortion, while Phase 2 remained relatively clean.
• Unusual harmonics: Even harmonics (e.g., 2X, 4X, 6X) were present – atypical for balanced three-phase systems.
• Voltage imbalance: Detected discrepancies pointed to potential issues in the drive train—likely post-VFD (Variable Frequency Drive).

These anomalies compromised power quality and risked long-term damage to the motor or downstream components, but the root cause remained unclear.

Layered troubleshooting to isolate the harmonic source

The customer, working closely with Samotics, initiated a targeted diagnostic approach:

• Powertrain segmentation: Analyzed electrical signatures at each key segment: the VFD output, the sine wave filter output, and the step-up transformer VT output.
• Hypothesis validation:
  • Checked for VFD modulation faults like dead-time distortion.
  • Investigated the sine wave filter for asymmetrical component degradation.
• Harmonic comparison: Benchmarked the ESP’s voltage and current harmonics against similar ESPs. This confirmed the issue was isolated to the ESP and not systemic.

Through harmonic analysis and comparative data, the team narrowed the fault to a likely degradation in the sine wave filter components, which were no longer symmetrically conditioning the VFD output.

Filter issue fixed to avoid lost production hours

By identifying the sine wave filter as the root cause, the customer replaced the failed component and resolved the core issue behind the ESP’s irregular power signals:

• Restored voltage balance and symmetrical current flow across all phases, bringing power delivery back within expected operating ranges.
• Eliminated abnormal even harmonics, which significantly reduced the risk of electrical stress and long-term degradation in the ESP motor.
• Prevented premature motor wear by reestablishing clean, consistent power output from the VFD through the step-up transformer.

But the impact didn’t stop at the technical level.

This fix helped the customer avoid premature ESP failure with possible liability claims. Preventing suspended production time that often follows unexplained ESP faults. With the ESP unit back online faster and operating more reliably, they avoided the typical consequences of downtime: lost output, emergency repair costs, and missed production targets.

Even more importantly, the investigation led to a repeatable diagnostic workflow for future sine wave filter issues – empowering the team to tackle similar faults in hours, not days. That means fewer delays, more predictable maintenance, and a faster path from detection to resolution.