In industrial settings, maintaining critical machinery is essential to ensuring smooth operations and minimizing economic losses. One such crucial component is high-voltage motors, which, if compromised, can lead to significant downtime and costly repairs. In this case study, we explore how a European chemical plant leveraged partial discharge (PD) monitoring to mitigate risks associated with a heavily contaminated and aging 10 kV, 6.7 MVA motor.
The Challenge: Unexpected Contamination and Corrosion
Two months after a thorough cleaning, drying, and repainting of the motor, a routine visual inspection uncovered a concerning issue: significant dust contamination. This white, powder-like substance had accumulated on the motor’s surface, posing a potential risk of surface discharges that could lead to flashover.
Additionally, unpainted core material showed substantial corrosion, likely caused by ozone produced during discharge activity. This created a self-sustaining cycle: dust contamination led to surface discharge, which, in turn, accelerated corrosion and worsened the contamination problem. Given the short time frame since the last overhaul, this level of contamination was highly unusual and required immediate attention.
The Solution: On-line Partial Discharge Measurements
Due to the motor’s critical role in supplying power to chemical process equipment, taking it offline for extensive shop testing and repairs would have resulted in substantial financial losses. Instead, the plant opted for an on-line PD measurement approach to assess the extent of insulation degradation without halting operations.
Using the ICMsystem, engineers installed coupling capacitors and conducted PD calibration to gather real-time data on the motor’s condition. The results were alarming:
- Severe thermal aging of insulation was detected.
- Strong surface discharges were linked to dust contamination.
- Sparking or slot discharges—indicative of loose wedges and bar vibrations—were observed, particularly on phase V.
In good condition, motors of similar age and size typically exhibit discharge activity below 5 nC. However, this motor recorded surface and slot discharges up to 20 nC and 25 nC, respectively, confirming the severity of insulation degradation.
Key Findings and Recommendations
The PD measurements demonstrated that the contamination was not benign. Despite recent refurbishments, the high discharge activity suggested that mere cleaning and repainting were insufficient for long-term reliability.
Immediate Recommendations:
- Install a continuous PD monitoring system: Since the motor had to remain operational for at least seven more months, the plant opted to install an ICMmonitor portable device. This system used the existing coupling capacitors to track discharge activity in real time.
- Remote monitoring: The monitoring system allowed PD experts from Power Diagnostix to provide remote support and analysis. Alarm contacts, a 4-20 mA signal, and a Monitoring Web Server (MWS) ensured prompt alerts if discharge activity escalated.
Long-Term Recommendations:
- Plan for rewinding or replacement: A complete overhaul should be scheduled as soon as operationally feasible.
- Investigate dust sources: Identifying and mitigating the root cause of dust contamination within the cooling system was essential.
- Apply protective coatings: Any corroded material should be properly coated or painted to prevent further contamination and surface discharge.
Conclusion
This case study underscores the importance of proactive monitoring and early intervention in industrial maintenance. By leveraging on-line PD measurement techniques, the European chemical plant successfully navigated the risks associated with severe insulation degradation, avoiding unplanned downtime while formulating a long-term remediation strategy.
For industries reliant on high-voltage motors, partial discharge monitoring offers a cost-effective, real-time diagnostic tool that enhances reliability, extends equipment lifespan, and reduces financial losses due to unexpected failures.
