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Product

IEC 60317 Continuously Transposed ConductorIEC 60317-0-2 / -12 / -295 to 85 Rectangular StrandsPVA / PEI+PAI + Epoxy

CTC Winding Conductor5 to 85-strand PVA / PEI+PAI enamelled Continuously Transposed Conductor (CTC) for

Custom-engineered Continuously Transposed Conductor (CTC) comprising 5 to 85 rectangular oxygen-free copper strands (PVA Class 120 or PEI+PAI Class 200 enamelled, optional B-stage epoxy bondcoat) Roebel-transposed and wrapped with Kraft/TUP paper or.

Oil-resistant
Flame-retardant
Approved
Order designation
CTC-35X-1.80X8.0-EI200-P20
Strand geometry
35 × (1.80 × 8.00)
Net Cu area
495.5 mm²
Overall H × W
35.6 × 18.2 mm
Bare Cu weight
4,405 kg/km
All sizes (12)
Request a quoteDatasheetWhatsApp
Engineering reply in 2 business hoursCut-to-length export drumsEN 10204 3.1 certificate per drum
Strand count
5 to 85 Strands
Odd number (or dual-bundle up to 170)
Strand size
1–3.15 × 3–15mm
Thickness × width per IEC 60317-0-2
Total Cu area
30 to 2,500 mm²
High space-factor transformer coil
Enamel class
Class 120 / 200
Oil-compatible IEC 60317-12 / -29
Short-circuit
B-Stage Epoxy
Thermo-setting bondcoat cures in coil
Outer wrap
Kraft/TUP/Net
2 to 32 paper layers or open PET net

Typical values for this cable type, based on IEC 60317-0-2 / IEC 60317-12 / IEC 60317-27 / ASTM B272 — confirmed in the datasheet and quotation for your order.

Application fit

Is CTC Winding Conductor right for your machine?

Minimises radial and axial eddy-current circulating losses and boosts mechanical radial short-circuit buckling strength in 10 MVA to 1,200 MVA power transformers.

Fixed installation

Suitable

Roebel transposition ensures every rectangular sub-conductor occupies every radial and axial position equally through the leakage flux.

Furnace, kiln & high-temp zone

Suitable

B-stage thermosetting epoxy overcoat fuses the two strand stacks into a rigid monolithic beam during transformer vapour-phase drying.

Immersion & wet locations

Suitable

Fully compatible with mineral transformer oil (IEC 60296), natural/synthetic ester fluids (synthetic ester / FR3), and SF6 gas.

Energy chain / drag chain

Not suitable

Rectangular magnet-wire bundle is designed exclusively for stationary power transformer, reactor and stator coil winding.

Use HF Litz Wire
Typical machines110 kV – 1,000 kV Grid & Generator Step-Up TransformersHVDC Converter Transformers & Smoothing ReactorsShunt Reactors & Phase-Shifting TransformersElectric Arc Furnace & Traction TransformersLarge Hydro & Turbo-Generator Stator Roebel Bars

Construction

Layer by layer

Roebel CTC geometry: N odd-numbered (5, 7, 9 … 85) rectangular OFHC/ETP copper strands (0.2–4 % Ag-alloyed optional) + Grade 1/2 PVA (Class 120) or dual-coat PEI/PAI (Class 200) enamel + optional B-stage epoxy bondcoat + central pressboard/epoxy-glass separator strip + multi-layer high-density Kraft / Thermally Upgraded Paper (TUP) or open polyester/fibreglass net outer lapping.

1234
Schematic, not to scale — generated from the layer data
#LayerMaterial & reference
1Rectangular oxygen-free / silver-bearing copper strands5 to 85 rectangular ETP or OFHC copper strips (Rp0.2 proof stress 100–260 MPa, or CuAg 0.1 % work-hardened for extreme short-circuit forces)Divides large conductor cross-sections into thin insulated laminations to suppress skin and proximity eddy losses
2PVA (Class 120) or PEI+PAI (Class 200) strand enamelPolyvinyl acetal (Formvar, IEC 60317-12 Class 120) or Polyesterimide + Polyamide-imide (IEC 60317-29 Class 200) Grade 1 or Grade 2 filmWithstands hot transformer oil hydrolysis and turn-to-turn impulse voltages
3Optional B-stage thermosetting epoxy bondcoat & central strip15–30 μm semi-cured epoxy resin over the enamel plus a 0.10–0.20 mm central diamond-dotted paper or epoxy-glass divider between the two stacksBonds all strands into a solid mechanical girder at +115–130 °C during coil drying while preventing inter-column strand crossover shorts
4Outer multi-layer Kraft / TUP paper or PET net wrapping2 to 32 butt-lapped layers of electrical Kraft paper, Thermally Upgraded Kraft (TUP), meta-aramid paper, or open-mesh polyester/glass netProvides turn-to-turn dielectric insulation and rapid oil impregnation channels

CTC-PAPER (Kraft / Thermally Upgraded Paper Wrapped)

5 to 85 PVA or PEI+PAI strands (with or without B-stage epoxy bondcoat) wrapped with 0.5 mm to 3.5 mm total radial Kraft or TUP paper insulation

CTC-NET (Open Polyester / Fibreglass Net Wrapped)

Epoxy-bondcoated strands held by a semi-open woven PET or glass-fibre net for direct oil cooling in high-current LV windings and shunt reactors

Technical data

Ratings & operating limits

Typical values: Typical values for this cable type, based on IEC 60317-0-2 / IEC 60317-12 / IEC 60317-27 / ASTM B272. Values for your order are confirmed in the datasheet and quotation.

Electrical

Strand conductivity (20 °C)
≥ 58.0–58.5 MS/m (≥ 100 % IACS annealed ETP/OFHC Cu)
Strand enamel breakdown
≥ 1,500 V to 3,000 V AC rms per strand (IEC 60317-0-2)
Transposition pitch check
100 % in-line high-frequency strand-to-strand short-circuit monitor
Eddy-current loss reduction
60 % to 85 % lower stray load loss vs parallel flat conductors

Thermal

Enamel thermal class
Class 120 (PVA, IEC 60317-12) · Class 200 (PEI+PAI, IEC 60317-29)
Outer wrap thermal class
105 °C (Kraft) · 120 °C (Thermally Upgraded TUP) · 180 °C (Meta-Aramid)
Epoxy bondcoat curing cycle
+115 °C to +135 °C for 6–12 h during coil drying

Mechanical

Number of strands (single CTC)
5, 7, 9, 11 … up to 85 odd strands (even counts on special order)
Individual strand thickness (a)
0.80 mm to 3.15 mm (± 0.010 mm precision rolled)
Individual strand width (b)
2.80 mm to 15.00 mm
Copper proof stress (Rp0.2)
Soft 90–130 MPa · Semi-hard 150–250 MPa · CuAg up to 280 MPa
Epoxy shear bond strength
≥ 12 MPa at 25 °C · ≥ 3.5 MPa in +100 °C transformer oil

Resistance

Insulating fluid compatibility
Mineral oil (IEC 60296), natural/synthetic ester oil & SF6
Hydrolysis resistance
Zero blister or delamination in sealed oil-tube aging test

Reference standards

Winding wire standards
IEC 60317-0-2 · IEC 60317-12 · IEC 60317-29 · NEMA MW 1000
Insulating paper standard
IEC 60554-2 · IEEE C57.12.00

Identification

Traceability
Continuous electronic pitch/short-circuit log & drum test report
Customs tariff (HS)
8544.11

Sizes

12 representative Continuously Transposed Conductor (CTC) power transformer builds

Every CTC is custom-manufactured to transformer coil design; below are 12 typical 11-strand to 75-strand HV and LV winding geometries.

Strand count, dimensions, Cu area & wrap
Order designationStrands × (a × b mm)Enamel & BondcoatOuter Insulation (2t)Net Cu Area
mm²		Overall H × W
mm		Bare Cu Wt
kg/km		Enquiry
HV & Regulating Winding CTC — Paper/TUP Wrapped (11 to 35 Strands)
CTC-11X-1.25X4.5-PVA-P1011 × (1.25 × 4.50)PVA 120 + Epoxy1.0 mm TUP Paper60.49.1 × 10.2537
CTC-15X-1.40X5.2-PVA-P1215 × (1.40 × 5.20)PVA 120 + Epoxy1.2 mm TUP Paper106.813.0 × 11.8950
CTC-19X-1.50X6.0-PVA-P1519 × (1.50 × 6.00)PVA 120 + Epoxy1.5 mm TUP Paper167.417.2 × 13.71,488
CTC-23X-1.60X6.5-PVA-P1623 × (1.60 × 6.50)PVA 120 + Epoxy1.6 mm TUP Paper234.621.6 × 14.82,086
CTC-29X-1.70X7.2-EI200-P1829 × (1.70 × 7.20)PEI+PAI 200 + Epoxy1.8 mm TUP Paper348.928.2 × 16.43,102
CTC-35X-1.80X8.0-EI200-P2035 × (1.80 × 8.00)PEI+PAI 200 + Epoxy2.0 mm TUP Paper495.535.6 × 18.24,405
High-Current LV, Generator Step-Up (GSU) & HVDC CTC (39 to 75 Strands)
CTC-39X-1.90X8.5-PVA-NET39 × (1.90 × 8.50)PVA 120 + Epoxy0.3 mm Open PET Net619.539.8 × 17.65,507
CTC-45X-2.00X9.0-PVA-P1245 × (2.00 × 9.00)PVA 120 + Epoxy1.2 mm TUP Paper796.548.8 × 19.47,081
CTC-53X-2.00X9.5-EI200-NET53 × (2.00 × 9.50)PEI+PAI 200 + Epoxy0.3 mm Glass/PET Net991.556.2 × 19.68,814
CTC-61X-2.10X10.0-PVA-P1561 × (2.10 × 10.0)PVA 120 + Epoxy1.5 mm TUP Paper1,262.168.5 × 21.711,220
CTC-69X-2.20X10.5-EI200-P1569 × (2.20 × 10.5)PEI+PAI 200 + Epoxy1.5 mm TUP Paper1,573.880.6 × 22.713,991
CTC-75X-2.24X11.2-EI200-NET75 × (2.24 × 11.2)PEI+PAI 200 + Epoxy0.4 mm Glass/PET Net1,858.087.8 × 23.116,518
  • Typical values for this cable type; dimensions and weights for your order are confirmed in the quotation.
  • Custom strand counts (5 to 85), silver-bearing copper (CuAg 0.1%), controlled Rp0.2 yield strengths (100–280 MPa), and laser-perforated paper wraps are manufactured to coil specification.

Quality & approvals

Testing & inspection

Routine tests on every production length, sample and type tests per batch — documented on an EN 10204 3.1 inspection certificate.

  1. ConductorClass 5 stranding
  2. Spark test100 % in-line
  3. Lay-upCores, earth, fillers
  4. SheathingInner, braid / screen, outer
  5. Electrical testsAC voltage, resistance
  6. DimensionsOD, wall thickness
  7. Inspection documents & dispatchDrum & dispatch
Testing & inspectionTest value / referenceFrequency
Routine tests
100 % continuous in-line strand-to-strand short-circuit monitoringHigh-frequency bridge monitors every individual strand against all others throughout transposition and paper lapping100 % of CTC length
Individual strand enamel breakdown, springback & Rp0.2 proof stressVerify Grade 1/2 dielectric breakdown, 0.2 % yield strength and dimensional tolerance (± 0.01 mm)Every copper cast & strand spool
Sample tests
Epoxy bondcoat curing shear-strength test in +100 °C oilVerify cured inter-strand shear bond ≥ 12 MPa (25 °C) and ≥ 3.5 MPa (+100 °C)Every epoxy batch

Inspection certificate

Issued with every drum, listing the routine test results for that length.

Product approvals

IEC 60317-0-2 / IEC 60317-12 (PVA) / IEC 60317-29 (PEI+PAI)IEC 60554-2 Electrical Kraft & Thermally Upgraded Paper

Company certificates

ISO 9001ISO 14001ISO 45001VDE marks approvalUL / cULCE · LVD / EMC

Marking & supply

Ordering & delivery

Sheath marking

TEBAOFLEX CTC [N]X[A]X[B] [PVA/EI-AI] [EPOXY] [PAPER/NET] [DRUM SN]
Delivery form
Precision layer-wound on heavy steel/wooden transformer drums in moisture-barrier bags
Quality dossier
Full strand Rp0.2 cert, enamel breakdown log, epoxy DSC cure cert & in-line short test log
Lead time
3–5 weeks ex-works

Technical documents

Downloads

PDFCTC Winding Conductor – technical datasheet12 sizes · construction, technical data, approvalsXLSXCTC Winding Conductor spec data (Excel)All 12 sizes with dimensions and data, for your BOM or quotation
Revision
2026-10-20
Updated
2026-10-20

FAQ

Questions engineers ask first

Not covered here? Send your drawing — an engineer replies within 2 business hours.

Why are Continuously Transposed Conductors (CTC) used instead of parallel flat copper wires in large power transformers?
In large MVA transformer windings, axial and radial leakage magnetic flux induces eddy currents inside thick copper conductors and circulating currents between parallel conductors that are not linked by identical flux. By dividing the conductor into 5 to 85 small enamelled rectangular strands and continuously transposing their positions in a Roebel cycle, every strand links the exact same magnetic flux, cutting stray eddy losses by 60–85 % and allowing a single winding pass instead of manually transposing dozens of individual flat wires.
How does the B-stage thermosetting epoxy bondcoat protect a transformer during an external grid short-circuit?
During a grid fault, radial electromagnetic forces try to buckle inner LV windings inward and hoop-stretch outer HV windings. When the wound transformer coil is heated to +115–135 °C during vapour-phase drying, the B-stage epoxy overcoat on each CTC strand melts and cross-links, fusing all 5 to 85 strands into a rigid I-beam with 5–8× higher bending stiffness than unbonded strands.
Why do most single CTC bundles have an odd number of strands (e.g. 15, 29, 35, 53)?
In the Roebel transposition head, the rectangular strands are arranged in two vertical stacks side by side, with one stack having (N−1)/2 strands and the other having (N+1)/2 strands. At each transposition step, the top strand of the taller column shifts sideways onto the top of the shorter column while the bottom strand shifts in the opposite direction, producing a continuous, self-locking rectangular profile.
When should PEI+PAI (Class 200) enamel be specified instead of PVA Formvar (Class 120) enamel?
Standard Polyvinyl Acetal (PVA, Class 120) has been the workhorse for mineral-oil-immersed 65 K rise transformers for decades. Specify dual-coat Polyesterimide + Polyamide-imide (PEI+PAI, Class 200) for high-temperature ester-fluid transformers, HVDC converter transformers, locomotive traction transformers, or windings with high hot-spot temperatures.

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