How PD Monitoring Found a Hidden Crack in a Critical Gas Compressor

A leading oil and gas producer in the Asia-Pacific region faced rising partial discharge (PD) levels on a business-critical compressor motor during routine maintenance. The asset supported up to one-third of total production, so the risk of failure carried an immediate commercial impact. Internal attempts to reduce PD did not resolve the issue, signaling deeper insulation distress.

What We Measured and Why It Mattered

PD monitoring and trending help detect insulation deterioration before it becomes a forced outage. In this case, sustained high PD trends prompted escalation from routine checks to a structured diagnostic workflow. The potential consequence was clear: a motor failure could remove ~33% of output until a replacement was installed.

Diagnostic Approach

The operator engaged Iris Power (a Qualitrol company) to review the PD trends and perform a focused inspection. On compressor motors like this, the typical Iris Power setup uses sensors installed on the machine—either Epoxy Mica Capacitors (EMC, 80 pF) or Stator Slot Couplers (SSC)—to capture high-frequency partial-discharge pulses while the motor is running. Those signals feed Iris Power’s monitoring and diagnostic tools.

Data can be collected in two ways, depending on how critical the asset is and how the site prefers to maintain it:

• Continuous online monitoring for high-throughput assets, using GuardII+ (or PDTracII 4208 for motors). This provides ongoing trending, alarms, and quick escalation when PD rises.
• Periodic online testing during planned checks, using the PDA-IV portable instrument connected to the installed EMC sensors, with results analyzed afterward.

In both cases, the data is interpreted in PDView, which makes it easy to compare tests over time and confirm whether the rise is persistent or transient. In this case, the trending and analysis supported a targeted visual inspection—leading the team directly to the affected area in the stator.

Findings

Inspection localized the issue to cracking insulation in a single coil at the slot exit. With the defect identified, the team moved from reactive troubleshooting to risk-informed planning based on the asset’s actual condition.

Business Response and Continuity Plan

The operator completed a risk and cost/savings analysis to quantify exposure and guide action. The outcome was a proactive spare-motor purchase to cover the production share at risk. With a spare staged, the site can swap quickly if failure occurs, protecting production and revenue. Decisions are now anchored in objective evidence rather than guesswork.

Operational Takeaways

• Trend PD on critical motors and escalate when levels persist; treat sustained PD as an insulation-health signal, not noise.
• Pair analytics with inspection to pinpoint cause and location fast (e.g., slot-exit coil issues).
• Protect throughput with spares when a single motor carries a large share of production; align actions to quantified risk.
• Plan by measured condition, not calendar intervals, to avoid avoidable outages and shorten recovery time.