{"id":3082,"date":"2026-09-23T10:00:00","date_gmt":"2026-09-23T02:00:00","guid":{"rendered":"https:\/\/anwellelectric.com\/?p=3082"},"modified":"2026-09-23T10:00:00","modified_gmt":"2026-09-23T02:00:00","slug":"dry-type-vs-oil-immersed-transformer-insulation","status":"publish","type":"post","link":"https:\/\/anwellelectric.com\/es\/dry-type-vs-oil-immersed-transformer-insulation\/","title":{"rendered":"Transformadores de tipo seco frente a transformadores sumergidos en aceite: diferencias en el sistema de aislamiento"},"content":{"rendered":"<p>The choice between a <strong>dry-type (cast-resin)<\/strong> and an <strong>oil-immersed<\/strong> transformer is usually made on safety, fire risk, and siting. But it also dictates a completely different insulation system. The materials that keep a dry-type unit alive are not the same as those inside an oil unit \u2014 and specifying for one while thinking of the other is a common, costly mistake. This guide contrasts the two insulation systems so you can specify the right materials for each.<\/p>\n<h2>Two Technologies, Two Cooling Media<\/h2>\n<p>A dry-type transformer cools and insulates with air and solid resin; an oil-immersed unit cools and insulates with mineral or ester oil. That single difference reshapes every insulation material in the active stack.<\/p>\n<h2>Dry-Type (Cast-Resin) Insulation System<\/h2>\n<p>Dry-type units rely on solid, air-cooled insulation \u2014 no flammable liquid.<\/p>\n<ul>\n<li><strong>Slot and phase insulation:<\/strong> flexible composites \u2014 <a href=\"https:\/\/anwellelectric.com\/es\/producto\/dmd-dmd100\/\">DMD<\/a> for standard Class B\/F duty, <a href=\"https:\/\/anwellelectric.com\/es\/producto\/nmn-ama-ymy\/\">NMN<\/a> where thermal and tear margins matter, and <a href=\"https:\/\/anwellelectric.com\/es\/producto\/nhn\/\">NHN<\/a> for the hottest, hardest-cycling designs.<\/li>\n<li><strong>Coil interlayer and end insulation:<\/strong> <a href=\"https:\/\/anwellelectric.com\/es\/producto\/dmd-prepreg\/\">DMD prepreg<\/a> \u2014 a resin-preimpregnated composite that bonds the LV coil layers during cure, eliminating voids.<\/li>\n<li><strong>Encapsulation:<\/strong> the whole active part is cast in epoxy resin, which also serves as the primary dielectric. No oil means no leak risk, so dry-types suit indoors, basements, and high-fire-risk sites.<\/li>\n<\/ul>\n<p>The system is &#8220;solid&#8221; end to end: composites for structure, prepreg for coil bonding, resin for encapsulation.<\/p>\n<h2>Oil-Immersed Insulation System<\/h2>\n<p>Oil units insulate and cool with the oil itself, so the solid materials are paper-based and designed to be saturated.<\/p>\n<ul>\n<li><strong>Coil conductor insulation:<\/strong> <a href=\"https:\/\/anwellelectric.com\/es\/producto\/cable-paper\/\">papel de cable<\/a> \u2014 high-purity cellulose wound directly on the conductor, impregnated by oil to form the turn-to-turn dielectric.<\/li>\n<li><strong>Lead and connection wrapping:<\/strong> <a href=\"https:\/\/anwellelectric.com\/es\/producto\/crepe-paper\/\">papel crep\u00e9<\/a> \u2014 stretchable, conformable, ideal for terminations and leads leaving the tank.<\/li>\n<li><strong>Coil interlayer bonding:<\/strong> <a href=\"https:\/\/anwellelectric.com\/es\/producto\/diamond-dotted-paper-ddp\/\">diamond dotted paper (DDP)<\/a> \u2014 resin-dotted paper that cures to glue adjacent layers together once the coil is dried and oil-impregnated.<\/li>\n<li><strong>The oil is the dielectric:<\/strong> it fills every void, carries heat, and provides the bulk insulation between live parts and ground.<\/li>\n<\/ul>\n<p>Here the system is &#8220;paper plus oil&#8221;: the cellulose does the structural insulating, the oil does the cooling and void-filling.<\/p>\n<h2>Side-by-Side<\/h2>\n<table>\n<thead>\n<tr>\n<th>Aspect<\/th>\n<th>Dry-type (cast-resin)<\/th>\n<th>Oil-immersed<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Cooling \/ dielectric medium<\/td>\n<td>Air + solid resin<\/td>\n<td>Oil (mineral or ester)<\/td>\n<\/tr>\n<tr>\n<td>Main solid insulation<\/td>\n<td>Flexible composites (DMD\/NMN\/NHN), prepreg<\/td>\n<td>Cellulose paper (cable, crepe, DDP)<\/td>\n<\/tr>\n<tr>\n<td>Coil bonding<\/td>\n<td>DMD prepreg, epoxy cast<\/td>\n<td>Diamond dotted paper, oil impregnation<\/td>\n<\/tr>\n<tr>\n<td>Fire \/ leak risk<\/td>\n<td>Low (no liquid)<\/td>\n<td>Higher (contains oil)<\/td>\n<\/tr>\n<tr>\n<td>Typical thermal class<\/td>\n<td>B\/F\/H by composite<\/td>\n<td>Class A (105\u00b0C) paper, raised by oil cooling<\/td>\n<\/tr>\n<tr>\n<td>Common siting<\/td>\n<td>Indoor, urban, fire-sensitive<\/td>\n<td>Substations, outdoor, high-power<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>How to Choose the Materials<\/h2>\n<ol>\n<li><strong>The transformer type is decided first<\/strong> \u2014 by fire risk, siting, and power level, not by the insulation. Once the type is set, the material system follows.<\/li>\n<li><strong>For dry-type, build from composites.<\/strong> Pick DMD\/NMN\/NHN by the hottest-spot temperature, and use DMD prepreg for coil interlayer and end insulation. See the <a href=\"https:\/\/anwellelectric.com\/es\/insulation-materials-for-dry-type-transformers-a-complete-selection-guide\/\">dry-type selection guide<\/a> for the full mapping.<\/li>\n<li><strong>For oil-immersed, build from paper.<\/strong> Specify cable paper for the conductor, crepe for leads, and DDP for interlayer bonding \u2014 all saturated by the oil. Browse the <a href=\"https:\/\/anwellelectric.com\/es\/categoria-producto\/insulating-paper\/\">Insulating Paper category<\/a> for grades.<\/li>\n<\/ol>\n<h2>Common Mistakes<\/h2>\n<ul>\n<li><strong>Using paper in a dry-type unit.<\/strong> Cellulose paper is designed to be oil-saturated; in air it loses its dielectric role and the coil is left under-insulated.<\/li>\n<li><strong>Using composites unimpregnated in oil.<\/strong> A dry-type composite is not the right turn insulation for an oil unit, where cable paper plus oil is the proven system.<\/li>\n<li><strong>Mixing thermal classes across one assembly.<\/strong> A Class H composite behind a Class A paper sleeve creates the weak link. Keep the whole insulation system at one verified class.<\/li>\n<\/ul>\n<h2>Conclusi\u00f3n<\/h2>\n<p>Dry-type and oil-immersed transformers solve the same problem with different chemistry: a dry-type unit is a solid system of composites, prepreg, and resin; an oil unit is a cellulose-and-oil system. Specify to the type, then to the temperature class, and the materials fall into place. For the dry-type side, start from our <a href=\"https:\/\/anwellelectric.com\/es\/categoria-producto\/flexible-composite-insulation\/\">Categor\u00eda de aislamiento compuesto flexible<\/a>; for the oil side, from <a href=\"https:\/\/anwellelectric.com\/es\/categoria-producto\/insulating-paper\/\">Papel aislante<\/a>.<\/p>\n<p>Planning a transformer build and not sure which system \u2014 or which materials \u2014 fit? <a href=\"https:\/\/anwellelectric.com\/es\/contact\/\">Contacta con nuestro equipo<\/a> with your type, rating, and duty, and we will map the insulation scheme to your spec.<\/p>\n<hr\/>\n<p><strong>Lectura relacionada:<\/strong> <a href=\"https:\/\/anwellelectric.com\/es\/insulation-materials-for-dry-type-transformers-a-complete-selection-guide\/\">Materiales aislantes para transformadores de tipo seco: Gu\u00eda completa de selecci\u00f3n<\/a><\/p>\n<p><strong>Browse flexible composites:<\/strong> <a href=\"https:\/\/anwellelectric.com\/es\/categoria-producto\/flexible-composite-insulation\/\">Categor\u00eda de aislamiento compuesto flexible<\/a><\/p>\n<p><strong>Browse insulating paper:<\/strong> <a href=\"https:\/\/anwellelectric.com\/es\/categoria-producto\/insulating-paper\/\">Insulating Paper category<\/a><\/p>","protected":false},"excerpt":{"rendered":"<p>\u00bfTransformador seco o sumergido en aceite? Comprenda las diferencias en el sistema de aislamiento (materiales compuestos y preimpregnados para los de tipo seco, papel para los de tipo sumergido en aceite) y qu\u00e9 caracter\u00edsticas debe especificar.<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[1],"tags":[],"class_list":["post-3082","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/posts\/3082","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/comments?post=3082"}],"version-history":[{"count":1,"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/posts\/3082\/revisions"}],"predecessor-version":[{"id":3087,"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/posts\/3082\/revisions\/3087"}],"wp:attachment":[{"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/media?parent=3082"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/categories?post=3082"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/anwellelectric.com\/es\/wp-json\/wp\/v2\/tags?post=3082"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}