Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Moisture content in paper insulation in 33kV and 11kV 250kVA distribution transformers.

Moisture content in paper insulation in 33kV and 11kV 250kVA distribution transformers.

Moisture content in paper insulation in 33kV and 11kV 250kVA distribution transformers.

Dear All,
Please let me know, a general figure for the moisture content in paper(in %) for a new small distribution transformers of voltage rating 33kV or less. Ideally it seems 0.5%, but is this practically the case? Some standards mentioned less than 3% is required for transformers below 56KV. Is the moisture content as low as 0.5% for new transformers of this range.Kindly clarify.

RE: Moisture content in paper insulation in 33kV and 11kV 250kVA distribution transformers.

Rasika: The "normal" moisture content is going to be a function of how the insulation (plain Kraft paper, thermally upgraded paper, oil-impregnated paper, etc.) and whether the transformer is air-cooled or oil-filled. It will also depend on the age of the transformer - generally, a "plain" paper insulation will release moisture as it ages and a "thermally upgraded paper" will absorb moisture. The difference to the total amount of moisture in the transformer is minimal - it's more a matter of where the moisture ends up (in the insulation or intermixed with the oil).

A new power transformer is expected to have a water content in paper insulation (WCP) of less than 0.5% by weight. It is filled with mineral oil processed to have less than 10 mg/kg of water in accordance with IEEE C57.106. To put this information in perspective, a new transformer with 5000 kg of paper insulation and 20 000 kg of oil would have less than 25 kg of water in the paper and would be filled with oil containing less than 200 g of water.

It is highly desirable to keep WCP below one percent, but since water is a by-product of aging-related deterioration of paper and oil, the insulation in a transformer gradually becomes more moist. Over two or three decades, normal aging can increase the water content of the paper insulation to notebook paper’s natural moisture level of about 4–5%. If there is a leaky gasket or seal or if there is a breather with depleted desiccant, the transformer can breathe in humid air, greatly accelerating the accumulation of water in the oil/paper system. Actually, since the bottom of the transformer is normally cooler than the top, the paper insulation at the bottom of the windings becomes wetter than at the top. At or before the 4% level of WCP, a well-cared-for transformer may be subjected to a dry-out.

Converting energy to motion for more than half a century

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close