Nomex paper covered winding wires for transformers

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Thermal Performance That Redefines Possibilities

What makes Nomex truly exceptional is its ability to maintain its electrical and mechanical properties even at extreme temperatures. We have seen test data confirming that Nomex insulation retains its integrity at temperatures up to 220°C. This means transformers wound with our Nomex paper covered wire can operate continuously at much higher temperatures than those using conventional kraft paper insulation.

The practical implications for our customers are substantial. By specifying Nomex paper covered wire, transformer manufacturers can design units with higher power density—more power in a smaller physical footprint. As one industry analysis noted, using Nomex insulation allows transformers to be designed with an operating temperature up to 180°C, requiring less conductor material and smaller cores, which reduces overall size and weight.

Mechanical and Chemical Resilience

Beyond thermal performance, Nomex offers exceptional mechanical properties that contribute to long-term reliability. The material exhibits excellent elasticity, flexibility, tear resistance, and abrasion resistance. It resists moisture absorption, maintains dimensional stability under compression, and withstands thermal shock without cracking or degrading. These characteristics ensure that transformer windings remain tight and structurally sound throughout the equipment’s service life.

We have also confirmed that Nomex is highly resistant to acids, bases, and chemical attack. It is not damaged by insects, mould, or fungi, and is compatible with all types of varnishes, adhesives, transformer liquids, lubricants, and refrigerants. This chemical stability ensures that our Nomex paper covered wire performs reliably in diverse operating environments and with various transformer fluid systems.

Critical Applications: Where Nomex Paper Covered Wire Excels

Traction Transformers for High-Speed Rail

One of the most demanding applications for Nomex paper covered winding wire is in traction transformers for high-speed trains. These transformers must deliver high power output while operating in extremely confined spaces under continuous thermal and mechanical stress. A landmark example is the Acela Express high-speed trains operating in the northeastern United States.

In this application, the traction transformer was required to deliver 5.745 MVA of power while fitting beneath the passenger cars. The design called for continuous operating temperatures reaching 160°C, with peaks up to 180°C. Traditional insulation materials could not provide the necessary 220°C safety margin. Only Nomex paper covered winding wire could meet this requirement.

The results were remarkable. By using Nomex insulation on the copper windings, along with Nomex laminates for layer insulation and cooling duct spacers, the transformer manufacturer achieved a 15% to 25% weight reduction compared to conventional designs. The transformers achieved a service life of 25 to 30 years due to Nomex’s negligible aging effect, significantly reducing lifecycle maintenance costs.

Dry-Type Transformers

Dry-type transformers represent another major application area for Nomex paper covered wire. Unlike oil-immersed transformers, dry-type units rely on air or resin for insulation and cooling, making the thermal performance of the winding insulation even more critical. We have supplied Nomex paper covered wire for many dry-type transformer projects where high temperature resistance and fire safety are paramount.

The UL recognition of insulation systems incorporating Nomex at 220°C class (Class R or 220°C rating) provides our customers with confidence that our wire meets the most stringent safety standards. For dry-type transformers used in buildings, underground installations, and other fire-sensitive locations, the non-toxic, self-extinguishing properties of Nomex are particularly valuable. Even in a fire event, Nomex does not release toxic gases, an important safety consideration for indoor installations.

High-Voltage and Extra-High-Voltage Power Transformers

At the utility scale, Nomex paper covered wire is increasingly specified for high-voltage and extra-high-voltage transformers where reliability is non-negotiable. We manufacture Nomex insulated wires for oil-immersed power transformers serving substations, grid infrastructure, and industrial facilities.

One particularly sophisticated application we have encountered is in step-shaped transposed conductors for converter transformers used in HVDC (High-Voltage Direct Current) transmission systems. These components, which are produced by combining multiple strands of Nomex paper covered wire into a transposed conductor configuration, are used in the network-side windings of converter transformers. The Nomex insulation provides thermal rating up to 180°C and significantly improves the winding’s longitudinal capacitance, enhancing the transformer’s ability to withstand impulse voltages and improving its short-circuit strength. The resulting winding has 1.5 times the overvoltage withstand capability of conventional designs.

Furnace Transformers and Industrial Equipment

Industrial applications demand equipment that can withstand harsh conditions and continuous operation. Furnace transformers, used in electric arc furnaces for steelmaking and other metallurgical processes, experience extreme thermal cycling and high fault currents. We have found that Nomex paper covered wire is ideally suited for these demanding applications.

The excellent mechanical strength and thermal stability of Nomex ensure that windings remain intact despite the thermal expansion and contraction cycles that furnace transformers experience. The material’s resistance to aging means that transformers can maintain their electrical integrity over many years of continuous service, reducing costly downtime for maintenance or rewinding.

Mobile and Pole-Mounted Transformers

For mobile transformers and pole-mounted distribution transformers, size and weight are critical factors. Nomex paper covered wire enables more compact designs that are easier to transport and install. The ability to operate at higher temperatures means less copper and core material is required for a given power rating, reducing the overall weight of the transformer.

We have supplied Nomex paper covered wire for pole-mounted transformers deployed in remote locations where reliability is paramount and maintenance access is limited. The long service life and thermal stability of Nomex provide assurance that these transformers will perform reliably for decades without intervention.

Military and Aerospace Applications

The demanding requirements of military and aerospace applications call for insulation materials that can withstand extreme conditions including high temperatures, radiation, and mechanical stress. Nomex paper covered wire is specified for these applications due to its proven radiation resistance and thermal stability. With 220°C temperature capability and UL recognition, our Nomex paper covered wire meets the stringent reliability requirements of defence and aerospace systems.

Manufacturing Considerations for Nomex Paper Covered Wire

From our manufacturing perspective, processing Nomex paper requires careful attention to detail. The material is available in various grades, most commonly Type 410, which is the standard electrical grade. We apply the Nomex tape in a spiral wrapping process with precise tension control, using various lapping configurations including self-lock overlap, half-lapped, and opposite-direction lap wrapping, depending on the insulation thickness and breakdown voltage requirements.

Our typical insulation configurations achieve breakdown voltages ranging from 600V for single-layer self-lock wrapping to 3000V for two-layer half-lapped wrapping. For customers requiring higher dielectric strength, we can apply additional layers to achieve the specified insulation thickness, with our capability extending to multiple layers as required