Development and Qualification of a 420 kV Dry-Type Outdoor Termination

Termination. Being the dry-type terminations not yet fully covered by the existing international and domestic standards, some additional special tests have been specifically defined and carried out to deep dive on the performance of such a new product.

Cable accessory manufacturers have introduced over the last years various dry-type outdoor termination designs. However, both geometric and non-linear resistive field grading methods struggle to sufficiently lower the electric stress at the termination surface, necessitating a larger diameter. These designs also exhibit significant temperature gradients across the solid insulation, which restricts their suitability for EHV (extra high voltage) applications.

Capacitance-graded bushings, on the other hand, offer a precise control of the electric field distribution on the bushing surface, resulting in a more compact core design. Hence, this paper introduces the development and qualification of a new 420 kV dry-type termination concept, which combines established technologies from both bushing and plug-in cable termination designs.

Electrical FEM calculations have been carried out to optimize bushing and plug-in cable termination parts, as well as the interface between the two units, which is key for the correct behaviour of such dry-type termination. Thermal and mechanical analysis have been also performed, as part of the overall assessment of the product.

The official qualification of the 420 kV termination is conducted as per IEC 62067. At the time of writing this paper, the official Type Test has been already successfully completed on 2500mm2 XLPE cable with copper conductor, while the Prequalification Test is ongoing on two different XLPE cables, both with 2500mm2 cross section, with Aluminium and Copper conductors.

Although the design of such new dry-type cable termination has been optimized using state of the art simulation and calculation tools, in order to validate the design limits, laboratory testing is needed to ensure the electrical, thermal and mechanical performance under the most extreme conditions, on top of what is required by IEC 62067. Some examples of the development tests performed on this 420 kV dry-type outdoor cable termination are presented as well. The development test program has been designed according to the experience of the manufacturer and special requirements set by utilities.