1 Introduction
Paper covered wire and Nomex insulated wire are two important types of insulated winding wires in high voltage electrical equipment windings. Paper covered wire is an insulated winding wire that uses cellulose paper tape such as cable paper, telephone paper, high voltage cable paper, and inter-turn insulation paper wrapped around the surface of copper conductor or aluminum conductor. Nomex insulated wire is an insulated winding wire that uses poly-meta-phenylene isophthalamide, namely Nomex 410 and Nomex 411 and other aromatic polyamide fiber paper tape wrapped around the surface of copper conductor or aluminum conductor. Both are widely used in the manufacturing field of high voltage electrical equipment such as oil-immersed power transformers, rectifier transformers, mining transformers, series reactors, high voltage instrument transformers, high voltage bushings, dry type transformers, traction transformers, and new energy transformers.
Paper covered wire has the advantages of strong oil paper compatibility, high breakdown voltage, relatively low cost, and mature process. Nomex insulated wire has the advantages of high thermal class, chemical corrosion resistance, high mechanical strength, excellent flame retardant performance, and low dielectric loss. Based on IEC 60554, IEC 60243, IEC 60216, IEC 60085, ASTM D 149, GB/T 7969, GB/T 10580, NEMA MW 1000-2018 and other international and domestic standards, this article systematically describes the technical differences and engineering applications of paper covered wire and Nomex insulated wire from ten dimensions including basic definition, insulation material system, conductor material, electrical performance, mechanical and heat resistance performance, chemical and environmental resistance, manufacturing process and cost, application scenarios, selection principle, and summary.
2 Basic Definition
2.1 Paper Covered Wire Definition
Paper covered wire is an insulated winding wire that uses insulation paper tape spirally wrapped around the surface of round conductor or flat conductor. The paper tape width is usually 12 to 30 mm, the paper tape thickness is 0.05 to 0.17 mm, the paper tape layer number is 1 to 6 layers, and the paper tape wrapping overlap rate is 30% to 50%. Paper covered wire classification by insulation paper type: cable paper paper covered wire, telephone paper paper covered wire, high voltage cable paper paper covered wire, inter-turn insulation paper paper covered wire. The thermal class of paper covered wire is 105 to 180 degrees Celsius, and the typical application is oil-immersed power transformer, high voltage instrument transformer, high voltage bushing.
2.2 Nomex Insulated Wire Definition
Nomex insulated wire is an insulated winding wire that uses aromatic polyamide fiber paper tape spirally wrapped around the surface of round conductor or flat conductor. The paper tape width is usually 12 to 30 mm, the paper tape thickness is 0.05 to 0.76 mm, the paper tape layer number is 1 to 4 layers, and the paper tape wrapping overlap rate is 30% to 50%. Nomex insulated wire classification by paper type: Nomex 410 insulated wire, Nomex 411 insulated wire, Nomex 410 composite insulated wire. The thermal class of Nomex insulated wire is 180 to 220 degrees Celsius, and the typical application is Class H oil-immersed transformer, dry type transformer, traction transformer, high temperature transformer, new energy transformer.
2.3 Naming and Standard Difference
Paper covered wire complies with standards IEC 60554-3-1/2/3/4, IEC 60243, GB/T 7969, GB/T 7970, GB/T 10580, JB/T 8740. Nomex insulated wire complies with standards IEC 60554-3-6, ASTM D 149, UL 1446, NEMA MW 1000-2018, GB/T 10580.
2.4 Development History Difference
Paper covered wire has a development history of more than 100 years. In 1890, paper covered copper wire was first applied to power transformer windings. In 1920, high voltage cable paper was applied to high voltage transformer windings. In 1950, inter-turn insulation paper was standardized. In 1970, heat resistant paper covered wire was developed. In 1990, high dielectric strength paper covered wire was developed. From 2000 to present, cellulose paper technology continues to evolve.
Nomex insulated wire has a development history of more than 60 years. In 1960, DuPont developed Nomex 410 aramid paper. In 1967, Nomex 410 was commercialized. In 1970, Class H oil-immersed transformer adopted Nomex insulated wire. In 1980, Nomex 411 aramid paper was commercialized. In 1990, new energy transformer adopted Nomex insulated wire. In 2010, high performance Nomex composite insulated wire was developed. In 2020, high performance Nomex insulated wire was standardized.
3 Insulation Material System Comparison
3.1 Paper Covered Wire Insulation Material
Paper covered wire insulation material is mainly cellulose paper, including five major categories. Cable paper system: DLZ-0.05 / DLZ-0.08 / DLZ-0.13 low voltage cable paper, complying with IEC 60554-3-1 and GB/T 7969, breakdown voltage 400 to 800 V, moisture content below 8%, ash content below 1.0%, pH value 6.5 to 8.0, suitable for low voltage to medium voltage oil-immersed transformer windings. Telephone paper system: DH-0.05 / DH-0.08 / DH-0.13 telephone paper, complying with IEC 60554-3-2 and GB/T 7970, breakdown voltage 300 to 400 V, moisture content below 7%, ash content below 0.8%, pH value 6.5 to 8.0, suitable for transformer winding inter-turn insulation and inter-layer insulation. High voltage cable paper system: GDL-0.08 / GDL-0.13 / GDL-0.17 high voltage cable paper, complying with IEC 60554-3-3 and GB/T 10580, breakdown voltage 1000 to 1600 V, moisture content below 6%, ash content below 0.5%, pH value 6.5 to 8.0, suitable for 35 kV and above oil-immersed transformer, high voltage instrument transformer, high voltage bushing. Inter-turn insulation paper system: ZB-0.05 / ZB-0.08 inter-turn insulation paper, complying with IEC 60554-3-4 and JB/T 8740, breakdown voltage 350 to 400 V, moisture content below 6%, ash content below 0.7%, pH value 6.5 to 8.0, suitable for transformer winding inter-turn insulation and low voltage windings. Synthetic fiber paper auxiliary: some paper covered wire adopts polyester fiber paper and cellulose paper composite, breakdown voltage 300 to 1500 V, thermal class 155 degrees Celsius, suitable for Class F oil-immersed transformer windings.
3.2 Nomex Insulated Wire Insulation Material
Nomex insulated wire insulation material is mainly aromatic polyamide fiber paper, including three major categories. Nomex 410 aramid paper: thickness 0.05 to 0.76 mm, width 12 to 30 mm, tensile strength longitudinal 9.0 to 200 kN/m, transverse 5.0 to 130 kN/m, breakdown voltage 400 to 4500 V, moisture content below 5%, ash content below 0.5%, thermal class 220 degrees Celsius, UL 94 V-0 flame retardant grade, complying with IEC 60554-3-6 standard. Nomex 410 is the key insulation material for transformer windings, reactors, traction motors, and high voltage electrical equipment. Nomex 411 aramid paper: thickness 0.13 to 0.58 mm, width 12 to 30 mm, tensile strength longitudinal 16.0 to 60 kN/m, transverse 9.0 to 40 kN/m, breakdown voltage 1100 to 5000 V, moisture content below 5%, ash content below 0.5%, thermal class 220 degrees Celsius, UL 94 V-0 flame retardant grade. Nomex 411 is the key insulation material for high voltage windings, high voltage instrument transformers, and high voltage bushings. Nomex composite paper: Nomex 410 composited with polyester film, Nomex 410 composited with polyimide film, Nomex 410 composited with mica. Nomex composite paper breakdown voltage 5000 to 12000 V, thermal class 220 degrees Celsius, suitable for ultra high voltage windings, UHV transformer windings.
3.3 Material System Comparison
Material system difference: paper covered wire is mainly cellulose paper, Nomex insulated wire is mainly aromatic polyamide fiber paper. Raw material difference: paper covered wire main raw material is softwood pulp, cotton pulp, hemp pulp and other natural cellulose, Nomex insulated wire main raw material is poly-meta-phenylene isophthalamide, namely aromatic polyamide synthetic fiber. Manufacturing process difference: paper covered wire insulation paper adopts paper making process, fiber dispersion, papermaking, pressing, drying, calendering, winding, Nomex insulated wire insulation paper adopts spinning process, spinning, drafting, heat setting, fiber cutting, papermaking, hot pressing, winding. Environmental performance difference: paper covered wire insulation paper is biodegradable, renewable, widely sourced, Nomex insulated wire insulation paper is recyclable, has excellent flame retardant performance, is not biodegradable. Cost difference: paper covered wire insulation paper unit cost 50 to 200 yuan per kg, Nomex 410 insulation paper unit cost 800 to 2000 yuan per kg, Nomex 410 cost is 5 to 30 times that of paper covered wire insulation paper.
4 Conductor Material Comparison
4.1 Paper Covered Wire Conductor
Paper covered wire conductor is mainly copper and aluminum. Copper conductor: TU1 oxygen-free copper, TU2 oxygen-free copper, T2 standard electrolytic copper, copper content covers 99.90% to 99.97%, conductivity not less than 100% IACS. Aluminum conductor: 1060 pure aluminum, 1050 pure aluminum, 1350 pure aluminum, aluminum content not less than 99.50%, conductivity not less than 61% IACS.
4.2 Nomex Insulated Wire Conductor
Nomex insulated wire conductor is mainly copper and aluminum. Copper conductor: TU1 oxygen-free copper, TU2 oxygen-free copper, T2 standard electrolytic copper, consistent with paper covered wire copper conductor. Aluminum conductor: 1060 pure aluminum, 1350 pure aluminum, consistent with paper covered wire aluminum conductor.
4.3 Conductor Specification Comparison
Paper covered wire conductor specification: round conductor diameter 0.50 to 6.00 mm, flat conductor width 2.00 to 16.00 mm, thickness 0.80 to 5.60 mm, width thickness ratio 1.5 to 20, fillet radius 0.4 to 1.5 mm. Nomex insulated wire conductor specification: round conductor diameter 0.50 to 8.00 mm, flat conductor width 2.00 to 25.00 mm, thickness 0.80 to 8.00 mm, width thickness ratio 1.5 to 25, fillet radius 0.4 to 2.0 mm. Nomex insulated wire conductor specification range is wider, covering high current and ultra high current winding requirements, paper covered wire conductor specification range is relatively narrow, mainly covering medium voltage to high voltage winding requirements.
4.4 Conductor Surface Treatment Comparison
Paper covered wire conductor usually adopts bare copper or bare aluminum, the surface should be clean, free of oxide layer, free of oil, free of moisture, the surface should be smooth, roughness Ra 0.8 to 1.6 micrometers. Nomex insulated wire conductor surface can adopt bare copper, tin plated copper, nickel plated copper, silver plated copper, bare aluminum, surface treatment can enhance corrosion resistance, reduce contact resistance, improve welding performance.
4.5 Applicable Scenario Comparison
Paper covered wire conductor is suitable for transformer windings, instrument transformer windings, reactor windings, bushing windings, mining transformer windings, rectifier transformer windings. Nomex insulated wire conductor is suitable for Class H and above oil-immersed transformer windings, dry type transformer windings, traction transformer windings, new energy transformer windings, rail transit traction motor windings, wind generator windings, energy storage transformer windings, high temperature electrical equipment windings.
5 Electrical Performance Comparison
5.1 Breakdown Voltage Comparison
Paper covered wire breakdown voltage: single layer DLZ-0.05 cable paper breakdown voltage not less than 400 V, single layer DLZ-0.08 cable paper breakdown voltage not less than 600 V, single layer DLZ-0.13 cable paper breakdown voltage not less than 800 V, single layer GDL-0.08 high voltage cable paper breakdown voltage not less than 1000 V, single layer GDL-0.13 high voltage cable paper breakdown voltage not less than 1300 V, single layer GDL-0.17 high voltage cable paper breakdown voltage not less than 1600 V, multi-layer paper tape wrapping breakdown voltage increases significantly with layer number, typical 4 layer paper tape wrapping breakdown voltage 3000 to 6000 V, typical 6 layer paper tape wrapping breakdown voltage 4500 to 9000 V. Nomex insulated wire breakdown voltage: single layer 0.05 mm Nomex 410 breakdown voltage not less than 400 V, single layer 0.13 mm Nomex 410 breakdown voltage not less than 1000 V, single layer 0.25 mm Nomex 410 breakdown voltage not less than 2000 V, single layer 0.51 mm Nomex 410 breakdown voltage not less than 4000 V, single layer 0.13 mm Nomex 411 breakdown voltage not less than 1100 V, single layer 0.25 mm Nomex 411 breakdown voltage not less than 2500 V, Nomex composite paper breakdown voltage 5000 to 12000 V. Breakdown voltage difference: paper covered wire single layer breakdown voltage 400 to 1600 V, Nomex insulated wire single layer breakdown voltage 400 to 5000 V, Nomex 411 single layer 0.25 mm breakdown voltage is higher than GDL-0.17 high voltage cable paper, Nomex composite paper breakdown voltage is significantly higher than multi-layer paper covered wire.
5.2 Dielectric Loss Comparison
Paper covered wire dielectric loss tangent after oil immersion 0.003 to 0.005, namely at 90 degrees Celsius, cellulose paper dielectric loss is relatively high, dielectric loss increases at high temperature. Nomex 410 dielectric loss tangent 0.005 to 0.015, namely at 50 Hz 23 degrees Celsius, Nomex 411 dielectric loss tangent 0.005 to 0.012, namely at 50 Hz 23 degrees Celsius, Nomex composite paper dielectric loss tangent 0.003 to 0.010, Nomex insulated wire dielectric loss temperature characteristic is stable, dielectric loss change is small at high temperature. Dielectric loss difference: Nomex insulated wire dielectric loss is lower than paper covered wire, temperature stability is better, in high temperature and high voltage scenarios Nomex insulated wire dielectric loss advantage is more obvious.
5.3 Insulation Resistance and Dielectric Constant Comparison
Paper covered wire insulation resistance after oil immersion not less than 1000 MΩ, after drying not less than 500 MΩ, insulation resistance decreases significantly when moisture content increases. Nomex 410 volume resistivity not less than 10 to the power of 16 Ω·cm, Nomex 411 volume resistivity not less than 10 to the power of 16 Ω·cm, Nomex composite paper volume resistivity not less than 10 to the power of 15 Ω·cm, Nomex insulated wire insulation resistance is high, less affected by humidity. Insulation resistance difference: Nomex 410 volume resistivity is more than 10000 times that of paper covered wire insulation resistance after oil immersion, Nomex insulated wire is suitable for high humidity environment. Dielectric constant difference: paper covered wire cellulose paper dielectric constant 2.5 to 4.0, Nomex 410 dielectric constant 1.6 to 2.4, Nomex insulated wire dielectric constant is significantly lower than paper covered wire, electrical performance is better, polarization loss is small, insulation efficiency is high.
6 Mechanical and Heat Resistance Performance Comparison
6.1 Tensile Strength Comparison
Paper covered wire tensile strength: DLZ-0.05 cable paper tensile strength longitudinal not less than 8.5 kN/m, transverse not less than 4.0 kN/m, DLZ-0.08 cable paper tensile strength longitudinal not less than 11.0 kN/m, transverse not less than 5.0 kN/m, DLZ-0.13 cable paper tensile strength longitudinal not less than 13.0 kN/m, transverse not less than 6.0 kN/m, GDL-0.13 high voltage cable paper tensile strength longitudinal not less than 13.0 kN/m, transverse not less than 6.0 kN/m. Nomex insulated wire tensile strength: Nomex 410 tensile strength longitudinal 9.0 to 200 kN/m, transverse 5.0 to 130 kN/m, Nomex 411 tensile strength longitudinal 16.0 to 60 kN/m, transverse 9.0 to 40 kN/m, Nomex composite paper tensile strength longitudinal 30.0 to 250 kN/m, transverse 20.0 to 150 kN/m. Tensile strength difference: Nomex insulated wire tensile strength is significantly higher than paper covered wire, especially transverse tensile strength Nomex 410 is 1.5 to 30 times that of DLZ cable paper, Nomex insulated wire mechanical strength is better, suitable for scenarios with large vibration impact and high winding stress.
6.2 Heat Resistance Temperature and Aging Life Comparison
Paper covered wire thermal class 105 to 180 degrees Celsius, Class A 105 degrees Celsius, Class E 120 degrees Celsius, Class B 130 degrees Celsius, Class F 155 degrees Celsius, Class H 180 degrees Celsius, continuous operating temperature 105 to 180 degrees Celsius, short time overload temperature 130 to 200 degrees Celsius. Nomex 410 thermal class 220 degrees Celsius, Class N 200 degrees Celsius, Class R 220 degrees Celsius, Nomex 411 thermal class 220 degrees Celsius, Nomex composite paper thermal class 220 to 240 degrees Celsius, Nomex insulated wire continuous operating temperature 180 to 220 degrees Celsius, short time overload temperature 250 to 350 degrees Celsius. Heat resistance temperature difference: Nomex 410 thermal class 220 degrees Celsius is 40 degrees Celsius higher than paper covered wire Class H 180 degrees Celsius, Nomex insulated wire is suitable for high temperature and high overload scenarios. Thermal aging life difference: paper covered wire thermal aging life at Class A 105 degrees Celsius not less than 20 years, at Class B 130 degrees Celsius not less than 10 years, at Class F 155 degrees Celsius not less than 5 years, at Class H 180 degrees Celsius not less than 3 years, Nomex 410 at 220 degrees Celsius thermal aging life not less than 10 years, at 200 degrees Celsius not less than 20 years, at 180 degrees Celsius not less than 30 years, Nomex 410 at 180 degrees Celsius thermal aging life is 10 times that of paper covered wire Class H 180 degrees Celsius.
6.3 Thermal Shock Resistance Comparison
Paper covered wire thermal shock resistance performance is limited, cellulose paper is easy to crack under sudden temperature change, paper covered wire applicable temperature change rate does not exceed 10 degrees Celsius per hour. Nomex 410 thermal shock resistance performance is excellent, can withstand -196 to 250 degrees Celsius temperature sudden change, applicable temperature change rate can reach 100 degrees Celsius per hour, Nomex 410 does not decompose from low temperature -269 degrees Celsius to high temperature 400 degrees Celsius. Thermal shock resistance difference: Nomex insulated wire thermal shock resistance performance is significantly better than paper covered wire, suitable for scenarios with severe temperature change such as rail transit traction, wind power generation, energy storage system.
7 Chemical and Environmental Resistance Comparison
7.1 Chemical Corrosion Resistance Comparison
Paper covered wire cellulose paper acid and alkali resistance performance is limited, easy to hydrolyze outside pH value 6.5 to 8.0 range, paper covered wire is sensitive to water, insulation performance decreases significantly when moisture content increases, paper covered wire has excellent oil compatibility, does not decompose in long term contact with mineral oil, synthetic ester oil, vegetable oil. Nomex 410 acid and alkali resistance performance is excellent, does not hydrolyze in pH value 1 to 14 range, Nomex 410 is not sensitive to water, moisture content is very low, insulation performance is stable when humidity changes, Nomex 410 has excellent oil compatibility, does not decompose in long term contact with mineral oil, synthetic ester oil, silicone oil, Nomex 410 is radiation resistant, ozone resistant, and resistant to most chemical reagents. Chemical corrosion resistance difference: Nomex insulated wire chemical corrosion resistance performance is significantly better than paper covered wire, Nomex insulated wire is suitable for acid and alkali environment, high humidity environment, chemical pollution environment, paper covered wire is suitable for neutral oil-immersed environment.
7.2 Flame Retardant and Weather Resistance Comparison
Paper covered wire cellulose paper is combustible, limiting oxygen index 18% to 20%, burns when exposed to open flame, forms carbonized layer after burning, paper covered wire flame retardant performance is limited, not suitable for scenarios with strict fire protection requirements. Nomex 410 flame retardant performance is excellent, limiting oxygen index 28% to 32%, UL 94 V-0 flame retardant grade, does not burn when exposed to open flame, self-extinguishes when away from flame source, Nomex 410 has low smoke emission, low smoke density, low smoke toxicity when burning, Nomex 410 complies with UL 1446, IEC 60085 flame retardant standard. Flame retardant performance difference: Nomex 410 limiting oxygen index 28% to 32% is 1.5 to 1.7 times that of paper covered wire cellulose paper 18% to 20%, Nomex insulated wire is suitable for scenarios with strict fire protection requirements such as subway, high-rise building, nuclear power, ship, offshore platform. Weather resistance difference: paper covered wire cellulose paper ultraviolet resistance performance is limited, long term ultraviolet irradiation causes fiber degradation, insulation performance decreases, paper covered wire is not suitable for long term outdoor exposure scenarios, paper covered wire applicable temperature range -40 to 180 degrees Celsius, Nomex 410 ultraviolet resistance performance is excellent, long term ultraviolet irradiation performance is stable, Nomex 410 with ultraviolet absorber added can be used outdoors for more than 30 years, Nomex insulated wire applicable temperature range -196 to 250 degrees Celsius, Nomex insulated wire weather resistance performance is significantly better than paper covered wire, suitable for long term outdoor exposure scenarios such as wind power, photovoltaic, energy storage, charging pile, rail transit, ship, offshore platform.
8 Manufacturing Process and Cost Comparison
8.1 Manufacturing Process Comparison
Paper covered wire manufacturing process is mature, adopts wrapping machine to spirally wrap insulation paper tape on conductor surface, wrapping speed 5 to 50 meters per minute, wrapping tension 1 to 5 Newton, wrapping overlap rate 30% to 50%, paper covered wire wrapping equipment is widely used, process is mature, inspection method is standard, paper covered wire impregnation process adopts vacuum pressure impregnation, vacuum below 50 Pa, pressure 0.2 to 0.5 MPa, temperature 60 to 80 degrees Celsius, time 8 to 24 hours. Nomex insulated wire manufacturing process is similar to paper covered wire, adopts wrapping machine to spirally wrap Nomex paper tape on conductor surface, wrapping speed 5 to 30 meters per minute, wrapping tension 0.5 to 3 Newton, wrapping overlap rate 30% to 50%, Nomex paper tape softness is lower than paper covered wire insulation paper, wrapping tension control requirement is higher, Nomex insulated wire impregnation process is the same as paper covered wire, adopts vacuum pressure impregnation or atmospheric pressure impregnation. Manufacturing process difference: paper covered wire and Nomex insulated wire manufacturing process flow is basically consistent, the main difference is in wrapping tension control, Nomex paper tape softness is low, wrapping tension control is more strict, Nomex insulated wire impregnation process is the same as paper covered wire, impregnant compatibility with winding paper tape is excellent for both.
8.2 Manufacturing Cost Comparison
Paper covered wire unit manufacturing cost 50 to 300 yuan per kg, of which insulation paper cost accounts for 30% to 50%, conductor cost accounts for 40% to 60%, manufacturing cost accounts for 10% to 20%, paper covered wire total cost is relatively low, cost performance is high. Nomex insulated wire unit manufacturing cost 500 to 2000 yuan per kg, of which Nomex paper cost accounts for 60% to 80%, conductor cost accounts for 10% to 30%, manufacturing cost accounts for 5% to 10%, Nomex 410 cost is 5 to 30 times that of paper covered wire insulation paper, Nomex insulated wire total cost is high, about 3 to 10 times that of paper covered wire, Nomex insulated wire has high cost performance in scenarios with strict performance requirements, paper covered wire has high cost performance in general performance requirements scenarios.
8.3 Storage and Transportation Comparison
Paper covered wire storage temperature 5 to 35 degrees Celsius, relative humidity 30% to 70%, avoid direct sunlight, avoid rain, paper covered wire storage period 1 year, storage period over 1 year requires re-inspection, paper covered wire transportation adopts wooden box or pallet, avoid moisture, avoid mechanical damage. Nomex insulated wire storage temperature -40 to 50 degrees Celsius, relative humidity 0% to 95%, resistant to direct sunlight, resistant to rain, Nomex insulated wire storage period 5 years, storage period over 5 years requires re-inspection, Nomex insulated wire transportation adopts wooden box or pallet, no special protection required. Storage and transportation difference: Nomex insulated wire storage and transportation requirement is low, storage period is long, storage condition is wide, paper covered wire storage and transportation requirement is high, storage period is short, storage condition is strict, Nomex insulated wire logistics cost is lower than paper covered wire.
9 Application Scenarios Comparison
9.1 Oil-immersed Power Transformer
Paper covered wire in oil-immersed power transformer application: 110 kV and below voltage class power transformers commonly use paper covered wire, paper covered copper wire + 25 or 45 transformer oil impregnation, paper covered aluminum wire for distribution transformer, 110 kV 50 MVA oil-immersed power transformer typically adopts paper covered copper wire, flat conductor 10 by 3.15 mm, GDL-0.13 high voltage cable paper, 4 layer paper tape, 45 transformer oil, operating voltage 110 kV, winding dielectric loss tangent 0.003, insulation class A, service life over 30 years. Nomex insulated wire in oil-immersed power transformer application: 220 kV and above voltage class power transformers, especially Class H oil-immersed transformer widely uses Nomex insulated wire, 220 kV 100 MVA Class H oil-immersed power transformer typically adopts Nomex 410 insulated wire, flat conductor 12 by 4.00 mm, Nomex 410 thickness 0.25 mm, 3 layer paper tape, 25 transformer oil or synthetic ester oil, operating voltage 220 kV, insulation class H, service life over 40 years. Application difference: 110 kV and below voltage class, paper covered wire is mainstream, cost performance is high, 220 kV and above voltage class, Nomex insulated wire is mainstream, reliability is high, 110 kV to 220 kV range, paper covered wire and Nomex insulated wire coexist, each has its own advantages.
9.2 Dry Type Transformer
Dry type transformer does not use mineral oil, uses air or solid insulation, paper covered wire in oil-free environment has high dielectric loss, breakdown voltage decreases, easy to absorb moisture, paper covered wire is not suitable for dry type transformer. Nomex 410 insulated wire is the first choice insulation material for dry type transformer, dry type transformer commonly uses Nomex 410 insulated wire, 10 kV 1000 kVA dry type transformer typically adopts Nomex 410 insulated wire, flat conductor 6 by 2.00 mm, Nomex 410 thickness 0.13 mm, 2 layer paper tape, operating voltage 10 kV, insulation class H. Application difference: in dry type transformer field, Nomex insulated wire is mainstream, paper covered wire is almost not applicable, Nomex insulated wire has excellent flame retardant performance, chemical corrosion resistance, suitable for dry type transformer safety strict requirements scenarios.
9.3 Traction Transformer and Rail Transit
Paper covered wire is suitable for standard traction transformer, 25 kV traction transformer typically adopts paper covered enameled wire, flat conductor 5 by 1.60 mm, DLZ-0.13 cable paper or Nomex 410 composite, 3 layer paper tape, 25 transformer oil, operating voltage 25 kV, insulation class A or H. Nomex insulated wire in traction transformer application: high speed rail, subway, light rail traction transformer commonly uses Nomex 410 insulated wire, 25 kV traction transformer typically adopts Nomex 410 insulated wire, flat conductor 8 by 3.15 mm, Nomex 410 thickness 0.25 mm, 3 layer paper tape, synthetic ester oil or silicone oil, operating voltage 25 kV, insulation class H, Nomex 410 thermal shock resistance, vibration resistance, suitable for traction transformer harsh operating environment. Application difference: rail transit traction transformer, Nomex 410 insulated wire is mainstream, especially high speed rail, subway, light rail, Nomex 410 excellent thermal shock resistance performance is the first choice for traction transformer, standard traction transformer can use paper covered wire, Nomex 410 composite insulation cost performance is higher.
9.4 High Voltage Instrument Transformer and Bushing
Paper covered wire in high voltage instrument transformer and bushing application: 110 kV and below high voltage current transformer and bushing widely uses paper covered wire, 110 kV high voltage current transformer typically adopts paper covered copper wire, conductor diameter 1.00 mm, GDL-0.13 high voltage cable paper, 6 layer paper tape, 45 transformer oil, operating voltage 110 kV, insulation class A, 220 kV oil-immersed transformer bushing typically adopts paper covered copper wire, conductor diameter 1.50 mm, GDL-0.17 high voltage cable paper, 10 layer paper tape, 45 transformer oil, operating voltage 220 kV, insulation class A. Nomex insulated wire in high voltage instrument transformer and bushing application: 220 kV and above high voltage current transformer and bushing widely uses Nomex 410 insulated wire, 220 kV high voltage current transformer typically adopts Nomex 410 insulated wire, conductor diameter 1.50 mm, Nomex 410 thickness 0.25 mm, 4 layer paper tape, 45 transformer oil, operating voltage 220 kV, insulation class H, 500 kV oil-immersed transformer bushing typically adopts Nomex composite paper, conductor diameter 2.00 mm, Nomex 410 composited with mica, 12 layer paper tape, 45 transformer oil, operating voltage 500 kV, insulation class H. Application difference: 110 kV and below high voltage instrument transformer and bushing, paper covered wire is mainstream, 220 kV and above high voltage instrument transformer and bushing, Nomex 410 insulated wire is mainstream, Nomex 410 chemical corrosion resistance, flame retardant performance is excellent, suitable for high voltage instrument transformer and bushing long term reliable operation.
9.5 New Energy Transformer
Paper covered wire in general new energy transformer has application, wind power transformer, photovoltaic transformer, energy storage transformer partially adopt paper covered wire + mineral oil impregnation. Nomex 410 insulated wire in new energy transformer field is widely applied, wind power transformer, photovoltaic inverter transformer, energy storage transformer, charging pile transformer commonly uses Nomex 410 insulated wire, Nomex 410 weather resistance performance is excellent, chemical corrosion resistance, flame retardant performance is excellent, suitable for new energy transformer outdoor operating environment. Application difference: in new energy transformer field, Nomex 410 insulated wire proportion is gradually increasing, especially offshore wind power, outdoor photovoltaic, energy storage station, charging pile, Nomex 410 weather resistance is the first choice for new energy transformer.
10 Selection Principle and Summary
10.1 Selection Principle
Voltage class matching: 110 kV and below voltage class, recommend paper covered wire, cost performance is high, 220 kV and above voltage class, recommend Nomex 410 insulated wire, reliability is high, 500 kV and above voltage class, recommend Nomex composite paper, breakdown voltage is high. Thermal class matching: Class A 105 degrees Celsius selects DLZ cable paper or DH telephone paper, Class E 120 degrees Celsius selects DLZ cable paper, Class B 130 degrees Celsius selects GDL high voltage cable paper, Class F 155 degrees Celsius selects polyester fiber paper, Class H 180 degrees Celsius selects Nomex 410 insulated wire, Class N 200 degrees Celsius selects Nomex 410 insulated wire, Class R 220 degrees Celsius selects Nomex 410 insulated wire. Operating environment matching: oil-immersed environment, paper covered wire and Nomex 410 insulated wire are both applicable, dry type environment Nomex 410 insulated wire is first choice, outdoor environment Nomex 410 insulated wire is first choice, chemical pollution environment Nomex 410 insulated wire is first choice, strict fire protection requirements Nomex 410 insulated wire is first choice, nuclear power environment Nomex 410 insulated wire is first choice, large vibration impact Nomex 410 insulated wire is first choice. Cost matching: cost sensitive, general performance requirements, paper covered wire is first choice, strict performance requirements, long term reliability priority, Nomex 410 insulated wire is first choice. Application type matching: oil-immersed power transformer 110 kV and below, paper covered wire is first choice, oil-immersed power transformer 220 kV and above, Nomex 410 insulated wire is first choice, dry type transformer, traction transformer, new energy transformer, 220 kV and above high voltage instrument transformer and bushing, Nomex 410 insulated wire is first choice.
10.2 Conclusion
Paper covered wire and Nomex insulated wire are two important types of insulated winding wires in high voltage electrical equipment windings, each has its own advantages and applicable scenarios. Paper covered wire adopts cellulose paper tape such as cable paper, telephone paper, high voltage cable paper, inter-turn insulation paper, single layer breakdown voltage 400 to 1600 V, thermal class 105 to 180 degrees Celsius, strong oil paper compatibility, high breakdown voltage, relatively low cost, mature process, suitable for 110 kV and below oil-immersed power transformer, high voltage current transformer, high voltage bushing, mining transformer, rectifier transformer, series reactor. Nomex insulated wire adopts Nomex 410 and Nomex 411 and other aromatic polyamide fiber paper tape, single layer breakdown voltage 400 to 5000 V, thermal class 180 to 220 degrees Celsius, chemical corrosion resistance, UL 94 V-0 flame retardant grade, radiation resistance, weather resistance, low dielectric loss, high insulation resistance, high mechanical strength, suitable for Class H and above oil-immersed transformer, dry type transformer, traction transformer, new energy transformer, 220 kV and above high voltage instrument transformer, 500 kV and above high voltage bushing, nuclear power, ship, rail transit and other harsh operating environments.
Design selection should be based on five major principles: voltage class, thermal class, operating environment, cost, and application type. In 110 kV and below oil-immersed transformer scenarios, paper covered wire cost performance is high, in 220 kV and above high voltage scenarios and harsh operating environments, Nomex 410 insulated wire reliability is high. With the continuous evolution of cellulose paper technology, aromatic polyamide fiber paper technology, composite insulation technology, vacuum pressure impregnation technology and manufacturing equipment, as well as the continuous development of UHV transformer, new energy transformer, rail transit transformer, nuclear power transformer, smart grid transformer and other strategic emerging industries, paper covered wire and Nomex insulated wire will continue to develop towards high performance, high reliability, high durability, and low cost, providing a more solid foundation for the design and manufacture of high voltage electrical systems.
Reference standards: IEC 60554 total 6 parts / IEC 60243 / IEC 60296 / IEC 60216 / IEC 60085 / IEC 60068-2-78 / ASTM D 149 / ASTM D 2413 / ASTM D 3487 / GB/T 3953 / GB/T 3955 / GB/T 7969 / GB/T 7970 / GB/T 10580 / GB 2536 / JB/T 8740 / UL 1446 / NEMA MW 1000-2018.
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