Hermetically Sealed Transformers

So, why does the expansion vessel have to be filled with air? Couldn't it be something nice and inert, like dry nitrogen?

with an accumulator for nitrogen (I think it is quite standard practice? )

Depending on the size of the tank, yes leave some air space. We left about 10 cm in small units, up to 50cm in large tanks. All hermetically sealed units underwent a vacuum cycle, with the larger ones including a flush/filter cycle. The vacuum/flush cycle time depended on the size of the unit. One hour to 24 hours. I don't know if there was a formula for any of this, I just did what the boss said 40 years ago. There might be some new protocols for oil type and inert gasses.

Are you a transformer manufacturer?

At Hippotronics Inc., I wound the first prototype transformer on a hand lathe back in 1964. I've built or helped to build most of thier prototypes and custom power supplies from electrostatic paint sprayer supplys to underground cable fault locaters, untill I left there in 1970. Many of these had 1/2" x 3/4" cu windings. I knew what I was doing then. Check for new protocalls.

Sorry, my question was directed at prabhugnanasekaran.

If there is enough oxygen in the air gap to cause a problem, you can use dry nitrogen, argon, or another gas that doesn't react with the oil. Another option is to include an accumulator in the transformer case. This could be a metal bellow. That way no gas resevoir is required.

Hi.

Our company is delivering hermitically sealed transformers for subsea useage. On the transformer tank we assemble (welded) an accumulator of the metallic bellow type. This type of accumulator is taking care of temprature differences during assembly, testing, transportation (-10 deg C to +60 deg C), pressure differences (atmospheric pressure to 308 bar at 3000 meter depth) and operating temprature differences. This type of accumulator has to be carefully calculated.

Atle

There are two types of hermetically sealed transformers.We had a discussion earlier in the forum.Normally where it is sealed agap of 150 mm or sutble taking expansion of oil is provide with nitrogen filled in the space and sealed.In the other type the oil is filled to brim.The radiators expand to absorb the expanded oil.First type is sealed and opening is difficult.Second type is easier to maintain.