In selecting transformer insulation systems, engineers and purchasing personnel often encounter a key question: should they choose traditional diamond dotted insulation paper (DDP) or the high-end material Nomex®?
These two materials differ significantly in performance, cost, and application scenarios. This article will provide a comprehensive comparison in terms of temperature resistance, insulation performance, mechanical strength, and application scenarios to help selection personnel make the appropriate choice.
Diamond dotted insulation paper is typically composed of high-density pressed paperboard (such as kraft paper) and epoxy resin or modified polyester resin. Its name comes from the adhesive layer coated on the paperboard surface with “diamond” dots or a grid pattern.
Structure: The base material is aramid paper or cellulose paper, coated with a thermosetting adhesive.
Function: This material is mainly used for interlayer insulation of transformer coils. It melts the adhesive layer by heating, bonding adjacent coil layers into a rigid whole, improving the coil’s short-circuit withstand capability.
Nomex® is a registered trademark of DuPont’s aromatic polyamide (aramid) polymer. It is a high-temperature resistant, inherently flame-retardant insulating material widely used in the electrical industry.
Structure: It is made of 100% aramid fiber through a special papermaking process. It meets application requirements without the need for adhesive coating.
Function: Nomex® can be used in distribution transformers, dry-type transformers, traction transformers, and special transformers as primary insulation, interlayer insulation, or phase-to-phase insulation.
DDP: Class B (130℃) / Class F (155℃)
Nomex®: Class H (180℃) and above
Conclusion: Nomex® performs better in high-temperature environments.
DDP: It requires oil immersion, and has stable insulation performance.
Nomex®: It has high dielectric strength, and does not require oil immersion.
Nomex® is more suitable for dry-type transformer systems.
DDP: After heating, the resin on DDP solidifies, enhancing the integrity of the winding.
Nomex®: It has high inherent strength, but lacks adhesive properties.
DDP structure is superior in winding fixation.
DDP: Service life approximately 20–25 years under normal oil immersion conditions.
Nomex®: Service life can exceed 30 years.
For long-term, high-load operation scenarios, Nomex® is more suitable.
DDP: Low cost, high cost-effectiveness.
Nomex®: Unit price is typically 2–5 times that of DDP.
Cost difference is one of the key factors in selection.
Oil-immersed distribution transformers, conventional power systems, cost-sensitive projects, and medium-to-low temperature operating environments.
Dry-type transformers, data centers, hospitals, high-temperature or harsh environments, and new energy (wind power, photovoltaic) fields.
Its bonding process enhances the short-circuit withstand capability of ordinary paper insulation and is currently the mainstream solution for distribution transformers in China.
Although its unit price is higher than DDP paper, it possesses characteristics such as high temperature resistance (220°C), inherent flame retardancy, hydrolysis resistance, and long-term electrical stability. It can ensure the stable operation of critical power systems (such as data centers, hospitals, and rail transit).
DDP paper and Nomex® insulation paper each have their technical advantages and application ranges. Correct selection not only affects the transformer’s factory performance but also directly relates to its operating costs and reliability throughout its entire life cycle.
Different transformers have different design conditions, cost budgets, and certification requirements. As a professional supplier of transformer insulation materials, we offer free samples, customized cutting services, and technical support.
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