Case Study
Hybrid Insulation Systems | DuPont ™ Nomex ® Insulation | DuPont USA

Hybrid Insulation Systems Solve High Overload Challenge in Rail


The rapidly growing demand for transportation in China puts a high value on the reliability of power equipment under extreme overload conditions.  Yunnan Transformer Company, which has served electric power and railway utility requirements in China since 1936, has responded to these increasing requirements by innovating with DuPont™ Nomex® brand paper and cellulosic pressboard in a range of liquid-immersed transformers with hybrid insulation systems.

Application Description

For more than 75 years, Yunnan Transformer Company has been custom designing high-quality transformers to meet a vast range of climatic and performance conditions. 

In response to increasing requirements for reliability under extreme overload conditions—such as 300% for two minutes up to 12 times per day—Yunnan Transformer Company began using hybrid insulation systems with Nomex® paper and cellulosic pressboard in its railroad track line power rectifier transformers .

These liquid-immersed transformers with hybrid insulation systems are available in two types:  Type SF4 (rated for 10 MVA to 25 MVA) and Type SF5 (rated for 16 MVA to 40 MVA).

Benefits Gained

Competitive edge:   Despite facing increased competition from around the world, Yunnan Transformer Company expects to successfully compete in the high-impact rail utility market due to the improved efficiency, reliability and operational cost of its offering made possible by the use of hybrid insulation systems with Nomex® paper and cellulosic pressboard.

Improved reliability:   Due to its exceptional mechanical strength, excellent thermal stability and proven ability to withstand electrical overloads, Nomex® insulation helps improve the reliability of these liquid-immersed transformers.

Materials Selected and Why

Yunnan Transformer Company selected Nomex® paper for use in hybrid insulation systems because it provides the thermal stability, mechanical strength and proven overload capacity required to meet the increasing reliability demands being placed on its power equipment. 

China Manufacturer Pioneers Hybrid Insulation in Transformers to Meet Growth Demands Safely and Reliably