Wherever there's a need for electrical insulation, there's usually a product of NOMEX aramid to fill it. In it's various forms --primarily papers and pressboards-- NOMEX products have the right balance of properties for use in transformers, motors, generators and other electrical equipment. This unique balance of properties has been providing reliability to users for over 25 years.
NOMEX is a synthetic aromatic polyamide polymer that provides high levels of electrical, chemical and mechanical integrity, when converted into its various sheet forms. Used properly, NOMEX products can extend the life of electrical equipment, reduce premature failures and repairs, and act as a safeguard in unforseen electrical stress situations.
NOMEX products have characteristics which make them ideally suited for electrical insulation application. These characteristics may vary slightly in the different forms and types of NOMEX.
A Unique Combination Of Properties Gives NOMEX Superior Characteristics
Inherent dielectric Strength
In densified form, NOMEX aramid products withstand short-term electrical stresses of 450 to 1000 V/mil (18 to 40 kV/mm) depending on product type and thickness, with no need for further treatment with varnishes or resins.
Mechanical Toughness
Densified NOMEX products are strong, resilient and (in the thinner grades) flexible, with good resistance to tearing and abrasion.
Thermal Stability
Temperatures up to 200 C (390 F) have little or no effect on the electrical and mechanical properties of NOMEX products, and useful values are retained at considerably higher temperatures. Furthermore, these useful properties are maintained for at least 10 years of continuous exposure at 220 C (430 F).
Chemical Compatibility
NOMEX is essentially unaffected by most solvents, and is unusually resistant to attack by acids and alkalies. It is compatible with all classes of varnishes and adhesives, transformer fluids, lubricating oils, and refrigerants. Since NOMEX products are not digestible, they are not attacked by insects, fungi or molds.
Cryogenic Capabilities
NOMEX has found acceptance in a variety of cryogenic applications due to its unique polymeric structure. At the boiling point of nitrogen (77 0K), NOMEX Type 410 paper as well as Type 993 and Type 994 pressboard have tensile strengths in excess of room temperature values.
Moisture Insensitivity
In equilibrium at 95 percent relative humidity densified NOMEX papers and pressboards maintain 90 percent of their bone-dry dielectric strength while many mechanical properties are actually improved.
Radiation Resistant
NOMEX is essentially unaffected by 800 megarads of ionizing radiation (which causes polyester laminates to crumble), and still retains useful mechanical and electrical properties after eight times this exposure.
Non-Toxic/Flame Resistant
NOMEX products will not produce any known toxic reactions in humans or animals, or melt or support combustion in air. NOMEX products are available which meet UL94V-0 requirements.
NOMEX Papers and Pressboards Provide Short and Long-Term Benefits in Transformers
Transformers of all types can benefit from the superior performance of NOMEX aramid papers and pressboards. These include open ventilated dry-types, cast coil and liquid filled, in sizes from lighting ballasts up to 62.5-MVA, 35kVA mobile substations.
NOMEX Offers Improved Performance in Open Ventilated Dry Type Transformers
Open ventilated dry type (OVTD) transformers are growing in popularity worldwide. NOMEX aramid papers and pressboards permit major design improvements in this type of transformer. OVDT designs with NOMEX offer the following advantages.
Enhanced Safety
There are no liquids to spill, explode or burn, and NOMEX does not support combustion in air. In the case of a building fire, NOMEX products do not produce significant amounts of toxic smoke or dangerous particles. (For this reason, among others, NOMEX is used extensively in honeycomb structures for aircraft interiors).
Low Transmission Losses
Since dry type transformers insulated with NOMEX can be located close to their loads - inside factories, schools, hospitals and apartments - low-voltage lines can be shortened.
Reduced Cost, Size and Weight
150 C-rise units insulated with NOMEX require less conductor and core steel, resulting in lower initial cost. This reduced size and weight contributes to ease of installation, especially since no vaults or catch basins are required. Smaller cores also mean lower no-load losses.
Increased Reserve Capacity
If transformers are to be operated continuously at or near their rated loads, efficiency is of prime importance. In this case, one could select 80 C-rise units insulated with NOMEX, allowing these units to operate continuously at 133 percent of rated load (if needed, for example, due to unplanned expansions) at a much lower cost (in increased load loss) than that associated with adding an additional transformer.
Improved Reliability
Surveys published by IEEE show failure rates of modern open ventilated dry type transformers equivalent to conventional liquid-filled units in the same power and voltage classes. Repair time for dry type units is also considerably shorter.
Resistance to Humidity
Since the properties of densified NOMEX papers and pressboards are insensitive to moisture, open ventilated transformers insulated with NOMEX perform satisfactorily in the most humid environments. This allows the placement of OVDT units in many locations not considered in the past.
NOMEX Offers Improved Performance in Liquid-Filled Transformers
NOMEX aramid papers and pressboards in liquid-filled transformers offer some of the same advantages as in OVDT designs. These advantages can be realized either when building new units or repairing existing ones.
Improved Reliability
Insulation systems based on NOMEX maintain excellent electrical and mechanical characteristics over the transformer's service life. Negligible aging, resistance to shrinkage and compression, and the superior resilience of NOMEX help to assure coil structures will remain tight and able to withstand short circuit forces, even after years of service.
Increased Reserve Capacity
Transformers insulated with NOMEX have extra power capacity for emergency peak load situations and unanticipated expansions. This can result in substantial savings in redundancy planning.
Reduced Size and Weight
While maintaining top oil temperatures at constant levels, with only modest increases in average oil temperature, the weight of the transformer can be reduced up to 25 percent for a given kVA output. Conversely, the kVA rating can be increased up to 50 percent for a given size and weight.? Use of a high-temperature liquid like silicone oil permits even greater savings in size and weight.
This weight reduction allows mobile substations, for example to be designed with operating capabilities larger than ever before.
Manufacturing Economies
The mechanical toughness of NOMEX papers and pressboards reduces shop failures and repairs. Use of a single, versatile insulation for all types and classes of transformers can reduce inventory costs. The use of NOMEX versus other insulating materials has significantly reduced dry-out time prior to oil impregnation in several cases.
Specific Applications Where NOMEX is used in Transformers
Conductor wrap
Layer and barrier insulation
Coil end filler
Core tubes
Section or phase insulation
Lead and tap insulation
Case insulation
Radial and axial spacers and spacer sticks
Other Applications of NOMEX Products
Other electrical applications include fire-resistant wrapper and marker tapes for cables, appliance switch covers, shields for printed circuit boards, thermal and static barriers, and speaker coils. |
