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Dry-type Transformers

Dry-type transformers, ranging in size from electronic power supplies and lighting ballasts to 19MVA/35kV distribution transformers, have been benefiting from the superior performance of Nomex® paper and pressboard insulation for more than 40 years. With ventilated dry-type transformers and cast-resin transformers growing in popularity worldwide, the wide range of Nomex® papers and pressboards allow major design improvements in these types of transformers. Dry-type transformers insulated with Nomex® products offer the following advantages to end users:


There are no fluids to spill explode or burn. And most Nomex® insulation materials do not support combustion in air. In the case of a building fire, our products do not produce significant amounts of toxic smoke or dangerous particles. For this reason, Nomex® is also used extensively in honeycomb structures for aircraft interiors.

Low transmission losses

Since dry-type transformers with Nomex® insulation can be located close to their loads, inside factories, schools, hospitals and apartments, low-voltage lines can be shortened.

Reduced cost, size and weight

Transformers made with Nomex® insulation can be designed with a temperature rise up to 150°K, requiring less conductor and core steel, and resulting in lower initial cost. This reduced size creates ease of installation, especially since no vaults or catch basins are required. Smaller cores also mean lower no-load losses.

Improved capability for harmonic loading

Standard transformers typically reduce the base temperature to compensate for hot-spot temperatures. Unfortunately, this increases the size of the unit. Dry-type and cast-resin transformers designed with Nomex® insulation have a large reserve temperature capability to accommodate these hot spots, with no loss of life to the load.

Increased reserve capacity

If transformers are to be operated continuously, efficiency is of prime importance. For example, 80°K-rise VDT units insulated with Nomex® products allow these units to operate continuously at 133 percent of rated load, if needed, at a cost significantly lower than you might pay for an additional transformer.

Improved performance

Surveys published by IEEE show that failure rates of modern ventilated dry-type transformers are equivalent to conventional fluid-filled units in the same power and voltage classes. Whenever necessary, repair time for dry-type units can also be considerably shorter.

Resistance to humidity

Since the properties of densified Nomex® papers and pressboards are insensitive to moisture, transformers with Nomex® insulation perform well in the most humid environments.