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Economical Goals of Life-extending Maintenance

5. Costs of the long-term reduction of the oxygen content in the oil

5.1 Passive systems

The up-grade costs can strongly vary with local conditions and with the type and size of the transformer

Economical Goals: Table E3
Method Advantages Draw-backs Up-gradeCosts
€ / MVA
Sealed-Tank Type
  • Classical, available method
  • Low operational costs
  • Only for small transformers
  • No or difficult check of proper function
?
Gas-Oil Sealed Type
  • Classical, available method
  • Low operational costs
  • High up-grade price *
  • No or difficult check of proper function
250 - 350
Automatic Inert-Gas Pressure Type
  • Classical, available method
  • Low operational costs
  • Medium up-grade price **
  • Buchholz relay alarm possible by pressure drop
150
Bag-In Tank or
Membrane-In Tank Type
  • Classical, available method
  • No operational costs
  • High up-grade price ***
  • No or difficult check of proper function
300 - 500
TRAFOSEAL
  • Low up-grade price
  • No operational costs
< 100

* The old conservator must be removed and a new- or modified one must be installed

** The automatic inert-gas pressure apparatus must be installed

*** The old conservator must be removed and a new one equipped by the bag or membrane must be installed

5.2 Active systems

In principle every small vacuum drier can be used as a active degassing device which is simply connected e.g. to the Filter Press Connectors of the main tank. The goal is to reduce the oxygen content permanently under 4000 ppm - it slows down the aging ca 4 - 5x compared to the full saturation ( O2 ~ 22 000 ppm)

Economical Goals: Table E4
Method Advantages Draw-backs Costs € / unit
Small vacuum drier
  • Low operational costs
  • No or difficult check of the degassing process
  • Dangerous high vacuum stripping off light fractions of oil
10 - 15 000.-
Vacuum separator VS-04
  • Low operational costs
  • Remote control of degassing process possible
  • No high vacuum stripping off of light fractions of oil
  • Higher price
25 000.-

5.3 Combined systems

Only four combinations of passive-active systems are possible - the following cost estimation is valid for ca 100 MVA Transformer.

The goal is to reduce the oxygen content permanently under 1 - 2000 ppm - it slows down the aging by ca min. 10x compared to the full saturation ( O2 ~ 22 000 ppm) .

Economical Goals: Table E5
Method Advantages Draw-backs Costs € / unit
Small vacuum drier & Bag-In Tank
or
Membrane-In Tank Type
  • Low operational costs
  • oxygen pemanently under 1000 ppm
  • No or difficult check of degassing process
  • Dangerous high vacuum stripping of light fractions of oil
Min. 45 000.-
max. 60 000
Vacuum separator VS-04 & Bag-In Tank
or
Membrane-In Tank Type
  • Low operational costs
  • Remote control of degassing process
  • No high vacuum stripping of light fractions of oil
  • oxygen permanently under 1000 ppm
  • Higher price
ca 65 000.-
Small vacuum drier & TRAFOSEAL
  • Low operational costs
  • oxygen permanently under 1000 ppm
  • No or difficult check of degassing process
  • Dangerous high vacuum stripping of light fractions of oil
Ca 25 - 30 000.-
Vacuum separator VS-04 & TRAFOSEAL
  • Low operational costs
  • Remote control of degassing process
  • No high vacuum stripping of light fractions of oil
  • oxygen permanently under 1000 ppm -
ca 35 000.-

Read next: 6. Costs of transformer "detoxication"