GSU Transformer Upgrade – Tank Hot Spot
Summary
Significant localized tank cover flange heating had been observed by infrared scan on a 185 MVA GSU transformer, compromising the aimed upgrading (by 23%) of the name plate MVA rating.
The enhanced oil cooling could not cope with the localized tank hot spot. The simulation provided a good match with the measured tank temperatures.
Additional studies allowed the verification of alternative designs for the LV busbars enclosure. Thanks to the simulations the proper solution was identified!
Description
Transformer data:185 MVA single phase GSU transformer
Technical Challange

  • Aluminium shields inside the tank, mild steel tank wall and non magnetic steel cover parts had to be taken into account
  • A 3-dimensional modelling was necessary
  • Close cooperation with the manufacturer of the enclosure and quick delivery of the simulations were a must in order to identify a solution in time for the scheduled maintenance of the power plant

Results


Specific losses (original enclosure)

Temp. at 190 MVA,
tank flange hot spot = 96°C

Specific losses (new enclosure)

Temp. at 228 MVA,
tank flange hot spot = 72°C

The solution was to move the crossover shorting plate to shift flux induced currents and losses from the tank cover flange to the middle of the tank cover.
Conclusions
By means of simulations, together with the manufacturer of the enclosure, Weidmann Technology Services designed the optimized bus enclosure which allowed the transformer upgrade from 185 MVA to 228 MVA.

 


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