Talk:Insulation system

IEC and NEMA ratings

NEMA only has A, B, F and H. Those other letters may belong to an IEC standard. We should distinguish the difference. --Wtshymanski (talk) 03:33, 13 August 2011 (UTC)

Done, though it took a few references to find all the code letters. --Wtshymanski (talk) 19:33, 14 August 2011 (UTC)

Table needs to delineate for Kraft paper and thermally upgraded Kraft paper

(Previous version re-stated as follows.)

Table needs to delineate for oil-immersed (and other liquid-immersed) transformers (and other apparatus) that are based on Kraft paper (ie, Class A) and thermally upgraded Kraft (TUK) paper (ie, Class E). Normal life expectancy loading of TUK-based transformers are associated with the following limits:

• 65 C insulation rise
• 15 C hot-spot allowance

---

• 80 C Sub-total--------------------------------------------80 C Sub-total
• 30 C 24-hour average ambient----------------------40 C maximum ambient

---

• 110 C 24-h avgr for winding insulation hot-spot--120 C peak for insulation hot-spot

• 105 C max. instantaneous for top-oil.

Corresponding limits for 55 C rise Kraft paper based transformers:

• 55 C insulation rise
• 10 C hot-spot allowance

---

• 65 C Sub-total--------------------------------------------65 C Sub-total
• 30 C 24-hour average ambient----------------------40 C maximum ambient

---

• 95 C 24-h avgr for winding insulation hot-spot--105 C peak for insulation hot-spot

References:

• "Transformer Insulation Upgrading and Loading Guide Equations" sponsored by the IEEE Transformer Committee
• "Transformer Overloading and Assessment of Loss-of-Life for Liquid-Filled Transformerss" by Colorado School of Mines (CSM)

Cblambert (talk) 16:55, 4 April 2012 (UTC)

Are these standard relevant for oil-filled equipment? This discussion would be better as a separate, referenced, section instead of modifying the classes for dry insulation. --Wtshymanski (talk) 18:09, 4 April 2012 (UTC)

It is not a priority for me but essential liquid-immersed aspects of table should eventually be included. Temperature limits are the same so only separate treatment would be confusing. Class A&E insulation systems have same max. limit for both dry and paper-liquid-immersed apparatus as follows:

• -----------------24-h avge---------Max limit------------Class
• -----------------Hot spot
• Kraft paper+oil-- 95 C --------- 105 C ------------- A/105
• TUK + oil-------- 110 C --------- 120 C ------------- E/120
• Kraft paper+FR3-- 130 C --------- 145 C ------------- A/105?

Normal life expectance 24-hour average limit column should accordingly likely be added to table.

I hesitant to wade in this article just yet partly because there so many standards to consider (see below), partly because of complex of transformer loading aspects, and so on.

Some related standards:

• IEEE 1276 Guide for the Application of High-Temperature Insulation Materials in Liquid- Immersed Power Transformers
• IEEE C57.91 IEEE Guide for Loading Mineral-Oil-Immersed Transformers
• IEC 60076 Power transformers
  • IEC 60076-2, Part 2 Temperature Rise for Liquid-Immersed Transformers: section 3.18 - Normal life expectancy at least 65 000 h for 50 % retained tensile strength at 110°C in a sealed tube
  • IEC 60076-7, Part 7 Loading Guide for Oil-Immersed Power Transformers: daily average hot spot limit: a) TUK+oil -> 110 C b) Kraft paper+FR3 -> 130°C
  • IEC 60076-14, Part 14 Design and Application of Liquid-Immersed Power Transformers Using High-Temperature Insulation Materials: Table I - TUK -> Class 120 °C (old IEC 60085 Class E?)
• IEC 60085 Electrical Insulation - Thermal Evaluation and Designation
• IEC 354 Loading guide for oil-immersed power transformers

Cblambert (talk) 18:35, 5 April 2012 (UTC)

The title of the article is unfortunate because it doesn't distinguish between the code letters of the various standards, and the whole field of insulation material. I think that this article should confine itself to the IEC/NEMA code letters and leave all the stuff on design of insulation for apparatus to some other, more detailed article. --Wtshymanski (talk) 21:46, 5 April 2012 (UTC)

I sort of agree. And will think in terms of separate article, if any . . .Cblambert (talk) 23:18, 5 April 2012 (UTC)

Letters versus Actual Temperature Values

I was under the impression that the various agencies obsoleted letter classes decades ago and went directly to number classes based on the maximum temperature. So why do we still see a promotion of letters? Is there another purpose for the letter other than just a reference for temperature? If not, then why promote letters when a number gives you all the information you need? If someone tells me a letter, I have no idea what it means and must waste valuable time researching it when telling me a number gives me the information right away without any drama.65.214.124.122 (talk) 14:20, 3 June 2013 (UTC)

Possible Error in Table

It appears that in the Table for NEMA and NEMA/UL the 240 and the S are switched. The 240 should be in the NEMA column and the S in the NEMA/UL column? Yes? No? 65.214.124.122 (talk) 14:25, 3 June 2013 (UTC)