{"id":38807,"date":"2026-10-19T12:48:00","date_gmt":"2026-10-19T12:48:00","guid":{"rendered":"https:\/\/dinghongtransformer.com\/?p=38807"},"modified":"2026-10-16T04:49:30","modified_gmt":"2026-10-16T04:49:30","slug":"onan-vs-onaf-transformer","status":"publish","type":"post","link":"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/","title":{"rendered":"ONAN vs ONAF Transformer Cooling: Key Differences, Capacity Ratings &amp; Buyer&#8217;s Guide"},"content":{"rendered":"\n<p class=\"wp-block-wd-paragraph wd-670d6080\">Choosing between an ONAN and ONAF transformer is not simply a question of whether a transformer has cooling fans.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-22027736\">The cooling method affects rated capacity, temperature rise, operating flexibility, maintenance requirements, noise, and long-term reliability.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-7e15299a\">For industrial substations, renewable energy projects, utility networks, and power distribution systems in Ukraine, Ethiopia, Vietnam, Thailand, Myanmar, Uzbekistan, Russia, and Nigeria, selecting the correct cooling arrangement can also influence equipment performance under local environmental conditions.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-8adc6584\">A transformer designed for a hot industrial site in Thailand may require different thermal considerations from one installed in a cold region of Russia or Uzbekistan.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-7d8cd4d1\">This guide explains how ONAN and ONAF cooling work, when forced-air cooling is worth specifying, and which technical details buyers should confirm before ordering an oil-immersed transformer.<\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_88 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#1_What_Does_ONAN_Mean_in_a_Transformer\" >1. What Does ONAN Mean in a Transformer?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#2_What_Does_ONAF_Mean_in_a_Transformer\" >2. What Does ONAF Mean in a Transformer?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#3_ONAN_vs_ONAF_Transformer_Technical_Comparison\" >3. ONAN vs ONAF Transformer: Technical Comparison<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#4_How_Much_Additional_Capacity_Can_ONAF_Provide\" >4. How Much Additional Capacity Can ONAF Provide?<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#Why_the_Capacity_Difference_Matters\" >Why the Capacity Difference Matters<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#5_Real_DHDL_Project_ONANONAF_Transformer_in_Uzbekistan\" >5. Real DHDL Project: ONAN\/ONAF Transformer in Uzbekistan<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#6_ONAN_vs_ONAF_for_Eight_Target_Markets\" >6. ONAN vs ONAF for Eight Target Markets<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#Hot-Climate_Projects_Thailand_Vietnam_Ethiopia_and_Nigeria\" >Hot-Climate Projects: Thailand, Vietnam, Ethiopia and Nigeria<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#Cold-Climate_Projects_Russia_Ukraine_and_Uzbekistan\" >Cold-Climate Projects: Russia, Ukraine and Uzbekistan<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#Grid_and_Maintenance_Considerations_Myanmar_and_Nigeria\" >Grid and Maintenance Considerations: Myanmar and Nigeria<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#7_Hidden_Costs_of_ONAF_Transformers\" >7. Hidden Costs of ONAF Transformers<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#8_Factory_Testing_and_Cooling-System_Verification\" >8. Factory Testing and Cooling-System Verification<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#9_ONAN_vs_ONAF_Transformer_RFQ_Checklist\" >9. ONAN vs ONAF Transformer RFQ Checklist<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#Recommended_RFQ_Attachments\" >Recommended RFQ Attachments<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/dinghongtransformer.com\/ru\/blog\/onan-vs-onaf-transformer\/#10_Choose_the_Right_Cooling_Method_with_DHDL\" >10. Choose the Right Cooling Method with DHDL<\/a><\/li><\/ul><\/nav><\/div>\n<h2 class=\"wp-block-wd-title title wd-a7a845cf\"><span class=\"ez-toc-section\" id=\"1_What_Does_ONAN_Mean_in_a_Transformer\"><\/span>1. What Does ONAN Mean in a Transformer?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-c0876b95\">ONAN stands for Oil Natural Air Natural.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-0e4a75d5\">It is a common cooling method for<strong> <a href=\"https:\/\/dinghongtransformer.com\/product\/66kv-high-voltage-oil-immersed-power-transformer\/\" data-type=\"product\" data-id=\"37438\">oil-immersed transformers<\/a><\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-56489dee\">The transformer uses natural oil circulation inside the tank and natural air movement around the external cooling surfaces.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-8a3a1118\">Heat generated by the core and windings is transferred into the insulating oil. As the oil warms, it circulates through the transformer and radiators, where heat is released to the surrounding air.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-1b911126\">The cooling process does not require electrically driven radiator fans or oil pumps.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-e41c54bf\">Key characteristics include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Natural oil circulation<\/li>\n\n\n\n<li>Natural air cooling<\/li>\n\n\n\n<li>No radiator fan operation required<\/li>\n\n\n\n<li>Relatively simple cooling equipment<\/li>\n\n\n\n<li>Lower auxiliary cooling power consumption<\/li>\n\n\n\n<li>Fewer mechanical cooling components to maintain<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-03a0b6a9\">ONAN cooling is commonly considered for distribution transformers and power transformers where natural cooling provides sufficient thermal capacity.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-a929884f\">For industrial projects in Vietnam, Myanmar, Ethiopia, and Nigeria, ONAN can be a practical option when the transformer rating, site temperature, and operating load are properly matched.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-c24bf522\">However, natural cooling does not eliminate the need for adequate ventilation and radiator clearance.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-f8983217\"><span class=\"ez-toc-section\" id=\"2_What_Does_ONAF_Mean_in_a_Transformer\"><\/span>2. What Does ONAF Mean in a Transformer?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-bbe7b944\">ONAF stands for Oil Natural Air Forced.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-ba104b52\">Like ONAN, the transformer uses natural circulation of insulating oil.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-8f1a3190\">The difference is that electrically driven fans force air across the radiators or cooling surfaces.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-e5ce859b\">This increases heat transfer and can allow a suitably designed transformer to carry a higher load under its specified ONAF rating.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-697f5fa1\">Key characteristics include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Natural oil circulation<\/li>\n\n\n\n<li>Forced-air cooling using fans<\/li>\n\n\n\n<li>Higher cooling capability when fans operate<\/li>\n\n\n\n<li>Potentially higher rated capacity<\/li>\n\n\n\n<li>Additional fan motors and control equipment<\/li>\n\n\n\n<li>Auxiliary power requirements<\/li>\n\n\n\n<li>More maintenance points than a basic ONAN arrangement<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-729136ef\">ONAF cooling is commonly used where additional thermal capacity or operating flexibility is required.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-0ae9f98c\">For example, a power transformer may have separate ONAN and ONAF ratings, allowing it to operate at a lower rating without fans and a higher rating when the cooling fans are available.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-707d2d67\">Important: ONAF does not automatically increase every transformer&#8217;s capacity by a fixed percentage. The actual ratings must be established by the transformer design, temperature-rise limits, and applicable standards.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-8aa529d1\"><span class=\"ez-toc-section\" id=\"3_ONAN_vs_ONAF_Transformer_Technical_Comparison\"><\/span>3. ONAN vs ONAF Transformer: Technical Comparison<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Parameter<\/th><th>ONAN Transformer<\/th><th>ONAF Transformer<\/th><\/tr><tr><td>Full Name<\/td><td>Oil Natural Air Natural<\/td><td>Oil Natural Air Forced<\/td><\/tr><tr><td>Oil Circulation<\/td><td>Natural<\/td><td>Natural<\/td><\/tr><tr><td>Air Cooling<\/td><td>Natural<\/td><td>Forced by Fans<\/td><\/tr><tr><td>Cooling Fans<\/td><td>Not Required<\/td><td>Required for ONAF Rating<\/td><\/tr><tr><td>Oil Pumps<\/td><td>Not Required<\/td><td>Not Required<\/td><\/tr><tr><td>Cooling Capacity<\/td><td>Natural Cooling Design<\/td><td>Enhanced Air-Side Cooling<\/td><\/tr><tr><td>Auxiliary Power<\/td><td>Minimal for Cooling<\/td><td>Fan Power Required<\/td><\/tr><tr><td>Maintenance<\/td><td>Simpler Cooling Arrangement<\/td><td>Fan and Control Maintenance<\/td><\/tr><tr><td>Noise<\/td><td>No Cooling Fan Noise<\/td><td>Additional Fan Noise<\/td><\/tr><tr><td>Capacity Rating<\/td><td>ONAN Rating<\/td><td>ONAF Rating<\/td><\/tr><tr><td>Common Application<\/td><td>Distribution and Power Transformers<\/td><td>Power Transformers and Higher-Load Applications<\/td><\/tr><tr><td>Main Procurement Concern<\/td><td>Ambient Temperature and Thermal Margin<\/td><td>Fan Reliability, Controls and Rated Capacity<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-4386c8ac\">Both cooling methods can provide reliable service when the transformer is correctly designed and maintained.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-f8d27e16\">The better choice depends on the project&#8217;s loading requirements, environment, and operating strategy.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-f431762a\"><span class=\"ez-toc-section\" id=\"4_How_Much_Additional_Capacity_Can_ONAF_Provide\"><\/span>4. How Much Additional Capacity Can ONAF Provide?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-1d3ce82c\">This is one of the most important questions buyers ask when comparing ONAN and ONAF transformer specifications.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-45e6058b\">Some transformers are designed with multiple cooling ratings.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-001cc72a\">For example, consider an illustrative transformer with:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Parameter<\/th><th>Example Value<\/th><\/tr><tr><td>Rated Voltage<\/td><td>110\/35kV<\/td><\/tr><tr><td>Frequency<\/td><td>50Hz<\/td><\/tr><tr><td>ONAN Capacity<\/td><td>30MVA<\/td><\/tr><tr><td>ONAF Capacity<\/td><td>40MVA<\/td><\/tr><tr><td>Cooling Arrangement<\/td><td>ONAN\/ONAF<\/td><\/tr><tr><td>Fan Control<\/td><td>Automatic \/ Manual<\/td><\/tr><tr><td>Installation<\/td><td>Outdoor Substation<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-09e7d6cc\">In this example, the ONAF rating is approximately 33.3% higher than the ONAN rating.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-6ca97710\">However, this is only a calculation example, not a universal capacity increase or a confirmed DHDL product specification.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-6e293ec3\">A transformer must be specifically designed, tested, and rated for the stated ONAN and ONAF capacities.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-fcfc269b\">Simply adding fans to an existing transformer does not guarantee that its permissible loading can be increased.<\/p>\n\n\n\n<h3 class=\"wp-block-wd-title title wd-2b754899\"><span class=\"ez-toc-section\" id=\"Why_the_Capacity_Difference_Matters\"><\/span>Why the Capacity Difference Matters<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-5166bf01\">Suppose an industrial substation normally operates at 25MVA but experiences periodic demand peaks approaching 35MVA.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-3be7b91a\">A transformer with appropriately engineered ONAN\/ONAF ratings may provide additional operating flexibility.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-65b0c492\">However, buyers must confirm:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Maximum continuous loading<\/li>\n\n\n\n<li>Duration and frequency of peak demand<\/li>\n\n\n\n<li>Ambient temperature<\/li>\n\n\n\n<li>Top-oil temperature limits<\/li>\n\n\n\n<li>Winding hot-spot temperature limits<\/li>\n\n\n\n<li>Fan starting and stopping settings<\/li>\n\n\n\n<li>Available auxiliary power<\/li>\n\n\n\n<li>Required capacity if the fans fail<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-44cb89de\">Hidden procurement risk: A transformer rated 40MVA under ONAF conditions may not be capable of carrying 40MVA continuously if its fans are unavailable.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-21822d32\">The protection and operating strategy should reflect this limitation.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-262b2b1b\"><span class=\"ez-toc-section\" id=\"5_Real_DHDL_Project_ONANONAF_Transformer_in_Uzbekistan\"><\/span>5. Real DHDL Project: <a href=\"https:\/\/dinghongtransformer.com\/project\/uzbekistan-tashkent-textile-industrial-park-substation-expansion-project\/\" data-type=\"page\" data-id=\"37341\">ONAN\/ONAF Transformer in Uzbekistan<\/a><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-e0ab90e2\">DHDL&#8217;s published Uzbekistan textile industrial park project provides a relevant example of why cooling selection matters.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-5709e693\">The industrial park required additional substation capacity to support spinning workshops, weaving production lines, and future industrial expansion.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-68017d12\">The project involved a high-voltage power transformer with ONAN\/ONAF cooling. DHDL&#8217;s homepage identifies a 45MVA S-45000\/110 unit, while the detailed Tashkent project page describes a 40MVA OSFZ-40000\/110 unit. Both sources identify ONAN\/ONAF cooling, but the capacity discrepancy should be resolved before using one rating in formal project marketing.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Project Parameter<\/th><th>Published Information<\/th><\/tr><tr><td>Country<\/td><td>Uzbekistan<\/td><\/tr><tr><td>Application<\/td><td>Textile Industrial Park<\/td><\/tr><tr><td>Voltage<\/td><td>110\/35kV<\/td><\/tr><tr><td>Cooling Method<\/td><td>ONAN\/ONAF<\/td><\/tr><tr><td>Tap Changer<\/td><td>On-Load Tap Changer<\/td><\/tr><tr><td>Site Conditions<\/td><td>High Temperature and Dust<\/td><\/tr><tr><td>Main Challenge<\/td><td>Industrial Expansion and Continuous Loading<\/td><\/tr><tr><td>Detailed Project Page Production Period<\/td><td>62 Days<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-d6dad325\">According to the detailed project description, summer temperatures at the site can reach approximately 45\u00b0C.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-5ff8f63a\">DHDL addressed the thermal requirements through cooling-system design, winding optimization, heat-dissipation measures, and environmental protection.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-b6d5e412\"><a href=\"https:\/\/dinghongtransformer.com\/blog\/transformer-cooling-methods-explained-onan-onaf-ofaf-ofwf-dinghong-transformer\/\" data-type=\"post\" data-id=\"37969\"><strong>The project demonstrates why ONAN\/ONAF selection should be connected to actual loading and ambient temperature rather than specified as a generic accessory.<\/strong><\/a><\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-d1404282\">For buyers in Uzbekistan, Thailand, Nigeria, and Ethiopia, this is especially relevant when industrial substations must operate under high ambient temperatures.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-b6c064e7\"><span class=\"ez-toc-section\" id=\"6_ONAN_vs_ONAF_for_Eight_Target_Markets\"><\/span>6. ONAN vs ONAF for Eight Target Markets<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-0cd51522\">Environmental conditions can influence cooling-system selection, but they do not automatically determine whether ONAN or ONAF is required.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-dbefa732\">The following table provides practical engineering considerations for DHDL&#8217;s target markets.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>Country<\/th><th>Cooling and Procurement Considerations<\/th><\/tr><tr><td>Ukraine<\/td><td>Winter operating conditions, temperature variation, load continuity and auxiliary supply<\/td><\/tr><tr><td>Ethiopia<\/td><td>Site altitude, outdoor temperatures, dust exposure and ventilation<\/td><\/tr><tr><td>Vietnam<\/td><td>Humidity, industrial load growth, corrosion exposure and radiator maintenance<\/td><\/tr><tr><td>Thailand<\/td><td>High ambient temperature, humidity and sustained industrial loading<\/td><\/tr><tr><td>Myanmar<\/td><td>Site-specific grid reliability, fan auxiliary power and maintenance access<\/td><\/tr><tr><td>Uzbekistan<\/td><td>Hot summers, dust, temperature variation and industrial expansion<\/td><\/tr><tr><td>Russia<\/td><td>Low-temperature operation, oil suitability, fan controls and condensation<\/td><\/tr><tr><td>Nigeria<\/td><td>High ambient temperature, dust, power quality and auxiliary supply reliability<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-b2ff18f6\">These are regional planning considerations, not uniform technical requirements across entire countries.<\/p>\n\n\n\n<h3 class=\"wp-block-wd-title title wd-a7eb6599\"><span class=\"ez-toc-section\" id=\"Hot-Climate_Projects_Thailand_Vietnam_Ethiopia_and_Nigeria\"><\/span>Hot-Climate Projects: Thailand, Vietnam, Ethiopia and Nigeria<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-154b6688\">For industrial projects in Thailand, Vietnam, Ethiopia, and Nigeria, the engineering team should assess the maximum ambient temperature and expected load duration.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-dfcb3c03\">ONAF may provide useful additional cooling capacity when the transformer is specifically designed for a higher forced-air rating.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-c6335bc5\">However, forced-air cooling does not eliminate the effects of high ambient temperature.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-2a6eafae\">A transformer rated under standard reference conditions may require a project-specific thermal review when installed at a hotter site.<\/p>\n\n\n\n<h3 class=\"wp-block-wd-title title wd-c802b2dd\"><span class=\"ez-toc-section\" id=\"Cold-Climate_Projects_Russia_Ukraine_and_Uzbekistan\"><\/span>Cold-Climate Projects: Russia, Ukraine and Uzbekistan<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-3866fbb7\">For projects in Russia, Ukraine, and Uzbekistan, buyers should consider minimum operating temperature, insulating-oil properties, condensation, and the performance of cooling accessories.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-3d7756be\">Cold weather does not automatically remove the need for forced-air cooling.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-c799c7ee\">The required arrangement depends on transformer loading, seasonal operating conditions, and the manufacturer&#8217;s approved ratings.<\/p>\n\n\n\n<h3 class=\"wp-block-wd-title title wd-fc2f5ddc\"><span class=\"ez-toc-section\" id=\"Grid_and_Maintenance_Considerations_Myanmar_and_Nigeria\"><\/span>Grid and Maintenance Considerations: Myanmar and Nigeria<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-b88b5a7d\">For projects in Myanmar and Nigeria, buyers should evaluate the reliability of the auxiliary electrical supply used by cooling fans.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-b969d179\">If the transformer relies on ONAF cooling to carry its required load, fan supply interruptions can reduce the available continuous capacity.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-79123557\">The specification should define how the transformer operates when one fan group or the complete forced-air cooling system becomes unavailable.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-a2f8b07e\"><span class=\"ez-toc-section\" id=\"7_Hidden_Costs_of_ONAF_Transformers\"><\/span>7. Hidden Costs of ONAF Transformers<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-57a0b999\">A common purchasing mistake is comparing an ONAN transformer and an ONAF transformer only by purchase price.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-db7c9bba\">An ONAF system can introduce additional components and operating costs.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-87cf60c4\">These may include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Cooling fan motors<\/li>\n\n\n\n<li>Fan control cabinets<\/li>\n\n\n\n<li>Temperature sensors<\/li>\n\n\n\n<li>Auxiliary electrical supply<\/li>\n\n\n\n<li>Control wiring<\/li>\n\n\n\n<li>Fan alarms<\/li>\n\n\n\n<li>Spare fan assemblies<\/li>\n\n\n\n<li>Inspection and maintenance<\/li>\n\n\n\n<li>Additional operating noise<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-a5976c32\">For example, consider an illustrative ONAF transformer with six cooling fans rated at 250W each.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-f1e3d13b\">Total fan power:<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-a1ffdb96\">\\[ 6\\times250=1{,}500\\text{ W}=1.5\\text{ kW} \\]<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-dd712726\">If all six fans operate for 4,000 hours annually:<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-d33b26ed\">\\[ 1.5\\times4{,}000=6{,}000\\text{ kWh\/year} \\]<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-05efa580\">At an illustrative electricity cost of $0.10\/kWh, annual fan energy cost would be approximately $600.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-00794877\">This example excludes control-system consumption, maintenance, and replacement costs.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-2965437f\">It also does not mean ONAF is less efficient overall. Transformer losses, loading, cooling-stage operation, and thermal performance must be evaluated together.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-bf055962\">Hidden buyer tip: Request guaranteed transformer losses and estimated cooling auxiliary power separately so that supplier quotations can be compared on a consistent basis.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-9559640b\"><span class=\"ez-toc-section\" id=\"8_Factory_Testing_and_Cooling-System_Verification\"><\/span>8. Factory Testing and Cooling-System Verification<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-0d3b17a3\">For transformers with ONAN\/ONAF ratings, buyers should request evidence supporting both cooling stages.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-0a315b56\">Relevant factory documentation may include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Rated capacity for each cooling stage<\/li>\n\n\n\n<li>Temperature-rise test results<\/li>\n\n\n\n<li>No-load and load-loss test reports<\/li>\n\n\n\n<li>Winding resistance measurements<\/li>\n\n\n\n<li>Insulation test reports<\/li>\n\n\n\n<li>Fan motor specifications<\/li>\n\n\n\n<li>Fan control schematic<\/li>\n\n\n\n<li>Automatic cooling-stage operation<\/li>\n\n\n\n<li>Alarm and failure indication<\/li>\n\n\n\n<li>Temperature monitoring configuration<\/li>\n\n\n\n<li>Cooling-system inspection records<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-bd174e10\">IEC 60076-2 addresses temperature rise for liquid-immersed transformers, including relevant thermal performance and test requirements.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-58b285c2\">For projects in Ukraine, Ethiopia, Vietnam, Thailand, Myanmar, Uzbekistan, Russia, and Nigeria, additional tests or documentation may be required by the utility, EPC contractor, or local technical specification.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-1859c732\">The final testing scope should be agreed upon before manufacturing.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-4fe203cc\"><span class=\"ez-toc-section\" id=\"9_ONAN_vs_ONAF_Transformer_RFQ_Checklist\"><\/span>9. ONAN vs ONAF Transformer RFQ Checklist<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-ee87c4ef\">Before requesting a quotation, provide the following information.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><th>RFQ Item<\/th><th>Buyer Input<\/th><\/tr><tr><td>Destination Country<\/td><td>__________<\/td><\/tr><tr><td>Application<\/td><td>Industrial \/ Utility \/ Renewable Energy<\/td><\/tr><tr><td>Rated Capacity<\/td><td>_____ MVA \/ kVA<\/td><\/tr><tr><td>Required ONAN Rating<\/td><td>_____ MVA<\/td><\/tr><tr><td>Required ONAF Rating<\/td><td>_____ MVA<\/td><\/tr><tr><td>Primary Voltage<\/td><td>_____ kV<\/td><\/tr><tr><td>Secondary Voltage<\/td><td>_____ kV<\/td><\/tr><tr><td>Frequency<\/td><td>50 \/ 60Hz<\/td><\/tr><tr><td>Vector Group<\/td><td>__________<\/td><\/tr><tr><td>Short-Circuit Impedance<\/td><td>_____ %<\/td><\/tr><tr><td>Tap Changer<\/td><td>OCTC \/ OLTC<\/td><\/tr><tr><td>Cooling Method<\/td><td>ONAN \/ ONAF \/ ONAN-ONAF<\/td><\/tr><tr><td>Maximum Ambient Temperature<\/td><td>_____ \u00b0C<\/td><\/tr><tr><td>Minimum Ambient Temperature<\/td><td>_____ \u00b0C<\/td><\/tr><tr><td>Installation Altitude<\/td><td>_____ m<\/td><\/tr><tr><td>Load Profile<\/td><td>Continuous \/ Variable \/ Peak<\/td><\/tr><tr><td>Fan Control<\/td><td>Automatic \/ Manual<\/td><\/tr><tr><td>Auxiliary Supply Voltage<\/td><td>_____ V<\/td><\/tr><tr><td>Fan Failure Requirement<\/td><td>__________<\/td><\/tr><tr><td>Temperature Monitoring<\/td><td>__________<\/td><\/tr><tr><td>Noise Limit<\/td><td>_____ dB(A), with measurement conditions<\/td><\/tr><tr><td>Applicable Standard<\/td><td>IEC \/ ANSI \/ IEEE \/ Local<\/td><\/tr><tr><td>Factory Testing<\/td><td>__________<\/td><\/tr><tr><td>Quantity<\/td><td>_____ Units<\/td><\/tr><tr><td>Delivery Destination<\/td><td>__________<\/td><\/tr><tr><td>Required Delivery Date<\/td><td>__________<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-wd-title title wd-b996a0af\"><span class=\"ez-toc-section\" id=\"Recommended_RFQ_Attachments\"><\/span><a href=\"https:\/\/dinghongtransformer.com\/blog\/transformer-rfq-checklist-specifications-buyers-must-provide-for-an-accurate-quote\/\" data-type=\"post\" data-id=\"38577\">Recommended RFQ Attachments<\/a><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Single-Line Diagram (SLD)<\/li>\n\n\n\n<li>Transformer technical specification<\/li>\n\n\n\n<li>Daily and seasonal load profile<\/li>\n\n\n\n<li>Maximum ambient temperature data<\/li>\n\n\n\n<li>Installation altitude<\/li>\n\n\n\n<li>Existing transformer nameplate, if applicable<\/li>\n\n\n\n<li>Substation layout<\/li>\n\n\n\n<li>Cooling-system requirements<\/li>\n\n\n\n<li>Auxiliary power specification<\/li>\n\n\n\n<li>Protection and monitoring requirements<\/li>\n\n\n\n<li>Applicable testing standards<\/li>\n\n\n\n<li>Required delivery schedule<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-453a7cca\">Providing this information allows the manufacturer to evaluate whether ONAN, ONAF, or a multi-stage cooling arrangement is appropriate.<\/p>\n\n\n\n<h2 class=\"wp-block-wd-title title wd-59af2aac\"><span class=\"ez-toc-section\" id=\"10_Choose_the_Right_Cooling_Method_with_DHDL\"><\/span>10. Choose the Right Cooling Method with DHDL<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-f513eb7e\">DHDL manufactures oil-immersed distribution transformers, high-voltage power transformers, and customized transformer solutions for industrial, utility, renewable-energy, and infrastructure applications.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-12ea6892\">Its product and project information includes ONAN and ONAF cooling options, with technical configurations depending on transformer capacity, voltage class, site conditions, and operating requirements.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-cf6806ba\">For transformer procurement in Ukraine, Ethiopia, Vietnam, Thailand, Myanmar, Uzbekistan, Russia, and Nigeria, DHDL can review cooling requirements alongside capacity, voltage, impedance, winding materials, and environmental specifications.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-7a2e6687\">For an accurate technical proposal, send:<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-dd12a02c\">Transformer Capacity + HV\/LV Voltage + ONAN\/ONAF Rating + Load Profile + Ambient Temperature + Site Conditions + Destination<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-f9670b72\">The best cooling arrangement is not necessarily the most complex one.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-c865af3a\">It is the configuration that delivers the required continuous capacity, acceptable temperature rise, maintainability, and lifecycle performance under actual operating conditions.<\/p>\n\n\n\n<p class=\"wp-block-wd-paragraph wd-46280709\">DHDL \u2014 Customized Oil-Immersed Transformer Solutions for Global Power Projects.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Compare ONAN vs ONAF transformer cooling, capacity ratings, fan requirements, thermal performance and costs. Includes a real project case and RFQ checklist.<\/p>","protected":false},"author":1,"featured_media":38808,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-38807","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.1 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>ONAN vs ONAF Transformer Cooling: Key Differences, Capacity Ratings &amp; Buyer&#039;s Guide - Dinghongtransformer<\/title>\n<meta name=\"description\" content=\"Compare ONAN vs ONAF transformer cooling, capacity ratings, fan requirements, thermal performance and costs. 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