Continuously Transposed Cable - Product Specifications

CTC Perforated Wrap

General Description
Continuously Transposed Cable (CTC) consists of a number of rectangular, film insulated conductors made into an assembly and usually over-wrapped with layers of insulating paper. The number of conductors is usually an odd number (from 5 to 83), arranged side by side in two stacks. Each conductor is transposed in turn without twist along its length and each conductor passing through every position. The length of cable (or “Transposing Lay”) for this complete cycle varies with the size and number of conductors.

Continuously Transposed Cables are arranged from several insulated wires with a rectangular cross-section, in two side by side laying stacks. A special tool alternately pushes the upper left and lower right wires onto the respective neighboring stack so that each wire takes on every possible position within one cycle in the continuously transposed cable. The length of the continuously transposed cable for one complete cycle is dependent upon the smallest diameter of the transformer winding, as well as upon the number and size of the single strip.
 The following description serves as general information. The manufacture of Continuously Transposed Cables follows the specific requirements of the customer. During the construction of the Continuously Transposed Cables, Essex is glad to assist in
 the design and development of your product request.

Essential advantage
Continuously transposed cables offer decisive advantages in the design of transformer, compared to the conventional paper-insulated rectangular wires:

  • Shortened winding time during the production of power transformers
  • Increased space factor in the winding and therefore decreased size and costs
  • Reduced electrical losses

  • Improved mechanical strength of the winding.

Furthermore, the manufacturing processes of Essex offer additional specific advantages:

  • Precise transposition enabling limited tolerances in measuring

  • Extreme flexibility through short pitches

  • Excellent windability and simple handling

Conductor Material
Cu-ETP or Cu-OF copper conductor could be used to fulfill various mechanical demands with different strengths according to DIN EN 1360

 Cu-ETP   Rp0.2    ≤110N/mm2
 CPR1   Rp0.2    ≤180N/mm2
 CPR2     Rp0.2   180N/mm2~220N/mm
 CPR3  Rp0.2  220N/mm2~260N/mm2

Please inform us if you need other types of copper or conductor materials.
For expediency the size of the single strips should lie within the following range:





























Insulation of the Individual Conductor
The enameled wire can be selected in accordance with the thermal requirements of the transformers:
  • Polyvinylacetal enameled rectangular copper wire, class 120 at IEC317-18.1990. GB/T7095.2-1995

  • Hard polyvinylacetal enameled rectangular copper wire, class 120 according to ETS3001 supplied by Essex

  • Bonded polyvinylacetal enameled rectangular copper wire, class 120 according to ETS3003 supplied by Essex.

  • Hard and bonded polyvinylacetal enameled rectangular copper wire, class 120 according to ETS3001 and ETS3003 supplied by Essex

  • Polyesterimide enameled rectangular copper wire, class 180 at IEC317-281990  GB/T7095.4-1995

If a higher mechanical strength of the transformer winding is needed, a coating of bondable epoxy can be applied, of which the increase (δ) is 0.03 to 0.05 mm.
The bonding time is dependent on the temperature:

      At  100     60h
      At  110     48h
      At  120     24h
      At  150     2 h 

Insulation of Continuously Transposed Cables
A range different insulation material is available for insulating the conductor stack:

  • Kraft paper

  • Thermally up-graded paper

  • High density paper

  • 22HCC Dennison paper

  • Paper with adhesive coating

  • DuPont Nomex® 

Special Continuously Transposed Cables

  • Paperless, Netting tape, Perforated Wrapping
    Technical feature: Ensure winding’s dimension smaller, excellent heat dissipation, and excellent insulated performance of enameled wire.


Single thickness  1.00~2.80mm
Single width  3.50~12.50mm
Quantity   5~63  
Insulation thickness  0.45~3.60mm
Layers 24  (8×3)  layers

Wrapping Method
In one working process, up to 24 layers can be applied in up to 3 groups. Normally all layers are overlapped, the width of overlapping should not be less than 2mm. The neighboring two layers’ overlapping part should be evenly staggered. According to the requirement of the customer and in order to keep the paper layers more evenly, the internal layers or all layers should be wound gapped instead of overlapping. The gapping width should not be more than 1 mm, the gapping part should be evenly staggered. And according to the requirement, we can wrap paper by the method of gapping wrapping for internal layers and interlocked wrapping for outer two layers.