Case Study:
Transformer Oil Sampling & Switchgear Maintenance
Scheduled Maintenance for Transformers and Switches Shows the Need for Regular Testing
Objective
- Annual Preventative Maintenance Testing of Switchgear and Transformers.
Solutions
- Tank pressure was checked; dry nitrogen was added if needed.
- Oil samples were retrieved from transformers.
- The switchgear was cleaned and then tested to NETA specifications.
- Minor miscellaneous issues, such as missing hardware, were fixed and noted.
- Recommendations were noted for issues that were unable or infeasible to be corrected during service.
- After the service, a full, detailed report was generated, highlighting issues that need to be corrected to ensure the transformer operates as expected
Results and Benefits
- Regular preventative maintenance, including minor repairs and testing, is essential to personnel safety and reliable equipment operation.
- Regular preventative maintenance allows the customer to estimate the remaining reliable service life of the equipment and make an informed decision on when it is nearing the end of life.
Challenges
The Quad Plus Testing Team made a service visit to a food manufacturing industry to perform preventative maintenance services on six oil-filled transformers and 11 medium-voltage switches. All equipment was de-energized before testing. The nitrogen pressure of the transformers was corrected if necessary, and oil samples were collected from all units. The switchgear was cleaned and tested per NETA specifications.
Key Findings From Transformer Oil Sampling Analysis
During this service call, one transformer showed nitrogen blanket displacement. This allowed oxygen and moisture intrusion, which can degrade the insulation over time and increase the risk of partial discharge. Another transformer had a defective ball valve that prevented proper oil sampling. Signs of corrosion on a temperature gauge also pointed to potential long-term moisture exposure.
Proper nitrogen levels in transformers are critical to maintaining the integrity of the insulation. Over time, transformer oil can become contaminated by moisture, dissolved gases, or other materials. The oil analysis detects dissolved gases, moisture content, and dielectric breakdown voltage–all key indicators of the insulation’s condition.
Oil filtration removes these contaminants to prevent buildup and oxidation that could compromise the insulation. Degasification eliminates dissolved gases such as methane, hydrogen, and acetylene, which indicate electrical arcing, overheating, or insulation breakdown. Regular filtration and degassing can slow insulation degradation to reduce failures and extend the operational lives of transformers.
Quad Plus Solution
The team discovered several issues during testing. One of the transformers had oxygen displacement in the nitrogen blanket, and the high-temperature level indicator on the thermometer revealed it had run hotter than expected. Another unit showed signs of corrosion on the temperature gauge. Lastly, one of the switchgear lineups had signs of severe overheating, and multiple components had loose and missing hardware.
The service team recommended leaving the transformer with oxygen displacement off until it could be repaired correctly. Once the rest of the cleaning and testing was completed, all equipment meeting NETA specifications was surrendered to the customer for service.
Switchgear Maintenance for Long-Term Equipment Efficiency
Our routine switchgear maintenance testing includes megger and ducter testing to assess insulation integrity and contact resistance, helping identify potential failure points before they escalate. During this visit, the Quad Plus team found loose and missing hardware on multiple switchgear components, which can lead to increased resistance, localized overheating, and potential system failures.
Over time, exposure to environmental factors, dust accumulation, and thermal cycling can also degrade insulation and mechanical components. Minor issues such as loose connections, worn insulations, or corroded contacts can escalate into equipment failure, resulting in power outages and equipment damage.
Implementing periodic inspections and preventive maintenance schedules will help ensure continued operation without costly downtime. Plus, well-maintained switchgear protects workers by minimizing the risk of arc flashes and equipment failures. Proper documentation of test results allows for tracking long-term trends so components can be repaired and replaced before a failure occurs.
Common Issues Found During Transformer Oil Sampling
Several common issues were identified during the transformer oil sampling. The most concerning was nitrogen displacement, which led to excessive moisture inside the transformer. Moisture accelerates insulation degradation and increases the likelihood of internal arcing. To address nitrogen displacement, leaks should be identified and repaired.
Another common issue we found was clogged or malfunctioning sample valves that prevented proper oil extraction and analysis. We also found corrosion on external components, such as temperature gauges. This can indicate prolonged exposure to moisture or environmental contaminants. Contaminants and degradation byproducts can go undetected without regular transformer testing, leading to equipment failure.
Discolored transformer oil is another common issue we found. Oil can become discolored from excessive heat exposure or dissolved gases in the transformer oil. This can indicate partial discharge activity or thermal degradation of insulation inside the transformer. When discolored oil is detected, a detailed dissolved gas analysis (DGA) should be performed to determine the source of the degradation. If excessive gas buildup is detected, oil filtration, reconditioning, or complete replacement may be required.
Lessons Learned from Conducting Annual Preventative Maintenance
Annual preventative maintenance testing is a proactive approach to electrical system reliability. This service visit highlighted the importance of regularly monitoring and servicing transformers and switchgear to find issues before they become equipment failures.
One key lesson learned was the necessity of verifying nitrogen pressure levels in transformers. Even minor leaks can introduce oxygen and moisture, compromising the integrity of the insulation. Another critical takeaway was the importance of ensuring tight and secure switchgear connections to prevent overheating and electrical faults.
Additionally, the need for clear documentation and communication between maintenance teams and facility operators is clear. Providing detailed test reports and documentation of problem areas ensures that necessary repairs are addressed quickly.
Establishing regular maintenance schedules based on industry best practices and NETA standards will enable facilities to increase the working life of their electrical equipment while maintaining operational efficiency.
Regular Maintenance Saves Time & Money
De-energizing your equipment for cleaning and testing may seem like an unnecessary hassle when all operations appear fine. However, many causes of unexpected shutdowns begin with a small issue that can be corrected during planned maintenance.
From loose and missing hardware to the first signs of rust, a few hours of work now can spare endless headaches in the future. Let our maintenance experts work with your production needs to schedule preventive maintenance today!
Frequently Asked Questions
Transformer oil should be tested at least once a year to monitor moisture levels, dissolved gases, and overall insulation integrity. More frequent testing may be necessary in high-load environments or for aging equipment.
NETA MTS (Maintenance Testing Specification) recommends preventive maintenance for switchgear every 12-60 months, depending on factors such as system voltage, environmental conditions, and criticality. Most industrial facilities test switchgear every 12-24 months for medium-voltage systems (1kV-69kV) and 3-5 years for high-voltage systems (69kV and above). More frequent testing is recommended for harsh environments and mission-critical equipment. Regular testing helps identify potential points of failure before they become critical.
Nitrogen is a dry and inert gas used in transformers to maintain a protective blanket over the insulating oil. It helps reduce oxidation and moisture contamination, which can degrade insulation and lead to premature failure. If nitrogen leaks, contamination can occur and accelerate the breakdown of insulation. The result is an increased risk of internal arcing or dielectric failure. Over time, this will compromise the performance of transformers and cause overheating, eventually leading to equipment failure.
The long-term benefits of transformer oil testing include allowing for the early detection of potential failures. Identifying conditions such as moisture contamination, gas buildup, or insulation degradation helps prevent costly damage and unexpected downtime.
Establishing baseline data and tracking trends over time allow facility managers to make informed decisions about maintenance schedules and component replacements. A proactive approach will reduce operational risks, avoid catastrophic failures, and ensure continuous and safe power distribution.
Regular maintenance significantly improved the switchgear’s performance and reliability. Cleaning and testing according to NETA standards helped identify and correct loose connections. Megger and ducter tests help ensure proper insulation resistance and contact integrity.
Replacing missing hardware and tightening connections reduced electrical resistance and minimized the risk of arcing and overheating. Preventive measures like these will increase the switchgear’s efficiency, prolong its working life, and ensure safe power distribution for the facility.
Transformer oil sampling is a diagnostic process used to assess the condition of insulating oil in transformers. It involves extracting a small amount of oil and analyzing it for contaminants, moisture content, dissolved gases, and dielectric strength.
Transformer oil sampling helps identify early warning signs of overheating, insulation breakdown, or moisture intrusion. That way, preventive repairs can be performed to reduce the risk of equipment breakdown caused by these types of failures. Regular sampling ensures that your transformers operate efficiently and extend their working life to maintain reliable power distribution in industrial and manufacturing facilities.
