CTC Insulation Types - Paper Covering

An outer covering of insulating paper is normally applied over the transposed conductors to provide mechanical and dielectric strength. The tapes are normally thermally upgraded paper, applied with a butt lap and center registered with the previous layer. The final two layers are applied with an intercalated lap of approximately 50%. All layers are wrapped in the same direction.

The thickness of the covering is expressed as the increase in cable dimensions due to applying the outer covering (i.e. twice the wall thickness). The increase in dimensions specified is a minimum and the plus tolerance of normal designs will not exceed the following allowance:

These tolerances are acceptable only when there is no limitation placed on the number of tapes or the nominal thickness of the individual tapes to achieve the specified build. 

For the insulation of CTC designed for use in oil immersed transformers only insulating paper corresponding to IEC 554-3-5 is used. Available grades of cellulose paper are described below.

For CTC used for low voltage windings special products are available. Please contact us for further details and separate product information.

Different grades of aramide paper are available for insulation of CTC for e.g. use in traction transformers at higher operation temperature.

CTC designed for cast resin transformers are covered with glass fabric tape to ensure good interconnection with the encapsulation resin used.

High density crepe papers are often recommended as outermost layers to improve mechanical strength of the insulation, thus avoiding e.g. tension problems during the winding operation. These papers are thermally upgraded.