{"id":3079,"date":"2026-09-16T10:00:00","date_gmt":"2026-09-16T02:00:00","guid":{"rendered":"https:\/\/anwellelectric.com\/?p=3079"},"modified":"2026-09-16T10:00:00","modified_gmt":"2026-09-16T02:00:00","slug":"transformer-insulation-temperature-classes-b-f-h","status":"publish","type":"post","link":"https:\/\/anwellelectric.com\/es\/transformer-insulation-temperature-classes-b-f-h\/","title":{"rendered":"Explicaci\u00f3n de las clases de temperatura de aislamiento de los transformadores: Clases B, F, H y c\u00f3mo especificarlas."},"content":{"rendered":"

If you have ever read a transformer nameplate, you have seen the letters: Class B, Class F, Class H<\/strong>. They look like a single number you either meet or miss. In practice they are the single most important lever in insulation selection \u2014 get the class wrong and you either overspend on margin you never use or quietly shorten the life of the unit. This guide explains what the classes actually mean, where the “hotspot” comes from, and how to map a temperature class to a real insulation material.<\/p>\n

What a Thermal Class Actually Is<\/h2>\n

A thermal class is the temperature at which an insulating material is expected to retain its required properties for its rated service life \u2014 commonly defined as about 20,000 hours (roughly 3 years of continuous duty). The standard classes most relevant to transformers are:<\/p>\n\n\n\n\n\n\n\n\n\n
Class<\/th>\nMax temp (\u00b0C)<\/th>\nTypical materials<\/th>\n<\/tr>\n<\/thead>\n
A<\/td>\n105<\/td>\nimpregnated paper, cotton<\/td>\n<\/tr>\n
B<\/td>\n130<\/td>\nDMD (polyester-based composites)<\/td>\n<\/tr>\n
F<\/td>\n155<\/td>\nNMN, F-grade DMD, prepreg<\/td>\n<\/tr>\n
H<\/td>\n180<\/td>\nNHN, silicone-bonded materials<\/td>\n<\/tr>\n
N \/ C<\/td>\n200 \/ 220+<\/td>\npolyimide-based (NHN top tier)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The number is not the surface temperature you feel \u2014 it is the hottest-spot temperature<\/strong> the material is allowed to reach.<\/p>\n

The Hotspot: Why the Number Is Not the Room<\/h2>\n

A winding does not heat evenly. The temperature at the hottest point inside the coil is higher than the average by a margin the standards call the *hotspot increment*. The usual reference basis is:<\/p>\n

Hottest-spot temp = Ambient (40\u00b0C) + Winding temperature rise + Hotspot increment (\u224810\u00b0C)<\/strong><\/p>\n

So when a designer says “Class F,” they mean the hottest spot must stay at or below 155\u00b0C under a 40\u00b0C ambient. The average winding rise is therefore allowed to be about 105 K for a Class F design.<\/p>\n

A common and useful trick: build with Class F materials but limit the temperature rise to Class B<\/strong> (an “F\/B” design). You get the thermal headroom of F-grade materials while running cooler, which extends service life substantially. This is why many modern dry-type transformers are sold as “F\/B.”<\/p>\n

Mapping Temperature Class to Material<\/h2>\n

Once you know the allowable hottest-spot temperature, the material choice follows:<\/p>\n