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Extending the service life of transformers in a power station in Queensland

 

The problem

A power station located in the State of Queensland, Australia, has two gas turbines that provide peak demand power, each generating unit has a critical 190MVA ABB transformer with 45,000L insulating oil. The transformer was manufactured and commissioned in 1999 and the insulating oil and paper were deteriorating at a faster rate due to age. Therefore, they were after a solution to help to increase the service / operating life of their oil-filled transformers.

 

The goals

  • Slow oil ageing process down to a minimum by reducing O2 levels and therefore increase the remaining lifetime of the insulating cellulose
  • Reduce oil changes to a minimum
  • Increase safety and availability by reducing gas and moisture in oil, hence maintain/increase dielectric strength and reduce the risk of failures.

 

The solution

HYDAC has provided a Transformer Care Unit – TCU for this application.

The Transformer Care Unit TCU is a service unit that is able to extend the operating life of oil-filled transformers and reactors. The continuous degassing, dewatering and filtration of the insulating oil ensure low levels of the oxygen content, water content and particle contamination in the transformer. Plus, it ensures the increase of the breakdown voltage of the insulating oil. Therefore, as a result, the increase of the service life of the insulation also happens.

 

The initial situation before installation of the TCU:

  • The DGA (Dissolved Gas Analysis) showed approximate oxygen levels between 13,000 ppm (in 2016) to 17,500 ppm (Feb 2018). It has been proven in several studies that the presence of high levels of oxygen in oil can reduce in half the life of insulating cellulose
  • Online DGA results prior to installation of TCU showed water content of approx. 10-11 ppm.

 

Installation of the TCU:

  • The TCU was installed and put into operation on 1st March 2018 for the continuous degassing, dewatering and filtration of the insulating oil
  • The TCU was connected to the transformer via two hoses. Warm oil from the upper section of the transformer is fed to the TCU and degassed oil is returned to the lower part of the transformer
  • At the day of installation, the maximum vacuum pressure was 416 mbar, which equals approx. 8.32% of the total gas content in the oil.

 

Installation of the TCU.

The high amount of gases present in the oil is directly visible in the degassing and dewatering unit.

 

The results

The DGA sample result after almost 6 months of operating the TCU shows that the oxygen levels were reduced by 62 % to 6720 ppm hence slowing ageing process of the cellulose.

The total gas content was down to 2.2 % and the water levels reduced from approx. 11 ppm to approx. 7.5 ppm (after 5 months) – a reduction of 30 %.

Benefits and key figures:

  • The ageing rate of the oil and cellulose is reduced by a similar factor as the oxygen content ~62%
  • Lower oxygen content results in less consumption of oxidation inhibitors or similar protection groups in the oil
  • Extend remaining life of oil and insulation cellulose
  • Potential life extension of the transformer by approx. 10-15 years.

For more information on our TCU, visit:
https://www.hydac.com.au/products/condition-monitoring/transformer-care-unit-tcu/.

AUSTRALIA 1300 449 322

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