How N1 discovered transformers in trouble

October 26, 2023 3 min. read

As Denmark's second largest DSO the company N1 operates a large number of 60/10 kV transformers spread across half the country. Many are decades old and will soon need replacement. But some may be able to operate safely beyond expected life span. To gain more insight N1 decided to test Oktogrid technology.

As transformers age they may seem unchanged to the naked eye, but vibrations and ultrasonic sounds tell a different story. For many years, these data has not been collected and analysed, and therefore they were simply overlooked.

But now things are changing. Driven by the global energy transition DSOs like N1 are heading for increasingly complex scenarios of operating thousands of ageing transformers much closer to their physical limits and in a wider range of conditions. To defer reinvestments for as long as possible realistic estimations of remaining transformer lifespan are also becoming more important. 

So the question for N1 was: How do we extract and digitise information about our transformers to improve our asset management with reliable, predictive analytics? This called for more than traditional visual inspections and oil analysis. So instead, N1 decided to explore the potential of Oktogrid’s Data Collector in search of a more cost-efficient and scalable solution.

Complete digitalisation in minutes
For five months of 2022 ten 60/10 kV transformers were fitted with Oktogrid Data Collectors. Installation required no tooling as they came bundled with their own power source and data modem. And best of all: None of the transformers needed to be taken out of service for installation to take place. Each of them took less than ten minutes.

Three red flags
The ten transformers were selected for different reasons: Some were simply old. Others had very unusual load patterns suspected of creating a higher risk of accelerated ageing. As the data was analysed by Oktogrid’s Asset Monitor three transformers showed clear signs of malfunction:

  • One transformer was ageing 9.7 percent faster than normal due to overload.
  • Another showed moderate electromechanical stress at low load which increased drastically with higher load.
  • A third transformer showed signs of considerable electromechanical stress even at low load.

Digital result confirmed by physical analysis
To test the accuracy of the Oktogrid analysis, N1 decided to submit the transformer with accelerated ageing to on-site analysis by N1’s own transformer service specialists.

Interestingly, the oil analysis did not reveal any indications of concern. A decision was then made to perform a more extensive analysis by taking the transformer out of service and carrying out an electrical test. This confirmed what the Oktogrid analysis had already pointed out: significant deterioration of the winding insulation. 

N1 managers found the proof of concept very convincing and will continue to focus on Oktogrid technology as it can improve the company’s asset management, reduce costs of on-site oil analysis, and provide constant transformer monitoring.

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