Electricity + Control October 2018

CABLES + ACCESSORIES

tor length also changes leading to elongation and therefore a ‘buckling’ effect at high temperatures. The smaller the conductor, the greater this effect.

Energy has to be transported over long distances since points of generation and demand often do not overlap.

Figure 1: Example of pluggable system UM=550 kV.

Cable joints Modern cable joints ensure simple installation of the waterproof external housing as well as maxi- mum operational safety. Using a bolted connector allows the conductor to be connected with optimal contact force, without special tools. Treatment of the cable shielding can be adapted individually for cable type and customer needs.

Figure 3: Example of set-up for IEC type test.

To prevent buckling of the cable inside the termina- tion’s insulator housing, a special spring device has been integrated, as shown in Figure 3 . This allows for length compensation of the conductor inside the termination and at the same time prevents the conductor from moving off-centre, thereby also ensuring a constant field distribution, independent of temperature change. As in other terminations, the base plate is insu- lated from the cable screen, which allows a flexible earthing system according to customer require- ments. To allow quick and safe cable connection, the top bolt of the termination as well as the con- nection in the joint is equipped with a bolted con- nection that does not require any special tools. This bolted connection offers life-long contact force and assures the connection to the cable connector. A new cable clamping system has been devel- oped for both the cable connector and termination, consisting of mainly two parts; an extension cage and a cable clamp. If the system is to be used on small outer cable diameters, an additional adapt- er is available. The cable clamp is adjusted on the cable diameter to allow maximum retention force, ensuring minimal pressure on the cable. As such, even huge cable weights can be handled. At the same time, this system fulfils a centring function to ensure proper positioning of the cable within the connector-respective termination.

Figure 2: Example of cable joint UM=550 kV.

A major hurdle is the so-called Annex G test at which the joint is submersed in water at 1 bar pressure and cycled, with the number of cycles depending typically on regional specifications. Outdoor cable terminations Another key component in modern cable networks is the outdoor termination, now usually offering a water-repellent external housing made of silicone. Minimum creepage distance is 16 600 mm which covers a high pollution class of > 65 mm/kV. The stress cone of the termination is also pre-mould- ed and routine tested, which allows fast mounting time and ensures high reliability of these parts. A special centring device, unique to some types of terminations, ensures the right position of the stress cone, both in radial position and with the axial centricity of the important electrical part. A major hurdle for outdoor terminations is over- all size, resulting in a large free length of cable in- side the termination. Due to load change, conduc-

Electricity + Control

OCTOBER 2018

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