Enamelled Milliken



The global transmission grid is undergoing significant transformation the next 30 years to accommodate future scenarios, especially driven by the increasing electricity demand and production from fluctuating renewable energy sources. A clear tendency toward higher voltage ranges and overall conductor sizes is experienced. When AC conductor size increases the efficiency of the cable decreases due to magnetic phenomena called skin effect.


Skin effect


Skin effect phenomena is the tendency of an alternating current to run at the exterior of the conductor. The AC current density in a conductor decreases exponentially from the exterior of the conductor towards the center. The phenomena is caused by the changing magnetic field internally in the conductor, inducing eddy currents opposing the current flow in the center of the conductor, and increases it at the exterior. The overall result is increasing AC resistance and inefficient use of the conductor material. The current distribution in a standard non optimized conductor is graphically illustrated in the following illustration:


In the above illustration δ (delta) is denoting skin depth. The skin effect is only substantial when conductor diameter is significantly greater than the so called skin depth δ. Skin depth can easily be approximated for various materials in the standard transmission and distribution frequency region 50-60Hz. For conventional conductor materials copper and aluminium the skin effect becomes substantial for conductor sizes over 1000mm2 and 1600mm2 respectively.


Enamelled copper conductor


The efficiency of the cable conductor can greatly be increased by introducing a more complex cable design. By dividing the conductor in segments using insulating tapes, some reduction of the skin effect is obtained. To further reduce the skin effect, each of the individual strands are insulated from one another using an enamel/varnish (known from coils). Now the conductor is not functioning as one solid conductor with a a uniform magnetic field as before, but rather as hundreds of separated and individual conductors represented by each of the wires. The complex design conductor can significantly improve the efficiency of the cable.



However, the improved utilization of the conductor material is impeded by the time consuming, unreliable and hazardous conductor preparation process. This process is to be performed prior production testing and at field installation and termination. Currently known process implies various mechanical or chemical procedures of removing the enamel where the conductor strands are split to gain sufficient access. After removal of the enamel, all strands needs to be recollected in the exact same configuration as before to avoid substantial increase of conductor size prior the actual splicing process.

ReliBond has developed an automated process using novel technology to the industry, where non of the polymers inside the conductor needs to be removed prior termination and splicing of the conductor. The solution completely removes the time consuming, unreliable and hazardous conductor preparation process currently known today.

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