Application

Semi-conductive cable compounds

Cable insulation for mid-voltage (MV) and high-voltage (HV)

For cables in the medium-voltage (MV) and high-voltage (HV) range, the cable insulation is surrounded by a concentric, semiconductive layer on the inside and outside. These layers serve to homogenize the electrical field in the insulation. The semiconductive layers usually consist of co-polymers based on ethylene, such as EVA, EBA or similar materials, and a high proportion of conductive materials such as soot, graphite or carbon nanotubes, which impart semiconductive properties.

Typical areas of application

Black raw mixture from semi-conductive cable compounds, manufactured with a BUSS compounder for insulating cables
Rote Kabelstücken aus halbleitenden Kabelcompounds
Querschnitt eines Kabels zur Visualisierung der aus halbleitenden Kabelcompounds bestehenden Kabelisolationsschichten
Cable section with insulation compound from semi-conducting compounds

Initially, too little importance was attached to the effect of the semiconducting layers on the insulation. However, it was soon realised that the ions contained in the semiconductors can contaminate the intermediate insulation layer and contribute to the formation of water trees.

For the category of strippable MV cables, it is possible to ensure that the outer semiconductor layer can be easily removed from the insulation by selecting suitable polymers and additives, which in certain cases facilitates the assembly of cable fittings in certain cases.

For EPR-based compounds, the ease of removal of the semiconductor remains a basic requirement, as it is difficult to remove mechanically. Volumes are increasing in line with the development and growth of polymeric MV cable insulation.

Further insights into our options for cable applications

Benefits

BUSS compounding technology offers the following specific benefits for semi-conductive cable compounds

Latest generation multi-flight BUSS compounders achieve a better mixing effect with a low overall specific energy input. This is because there is a high number of mixing cycles, optimally attuned to the respective process zone. The energy required for melting is almost exclusively introduced mechanically (dissipated) as shear energy.

The moderate shear rates of the BUSS Co-Kneader guarantee controllable shearing and low temperature profiles and demand considerably less of the structure of fibers and highly-structured fillers such as carbon black than other systems. This results in better mechanical and electrical properties, improved flow characteristics and lower consumption of expensive additives.

The BUSS technology allows high filler loadings by splitting to 2-3 feed positions, use of feed-in processes such as side feeders, gravimetric dosing units, back venting and excellent conveying efficiency. The Co-Kneader's moderate shear rates allow effortless handling of the high viscosities arising with high filler loadings.

A large number of mixing cycles is achieved with the latest multiple-flight BUSS Co-Kneaders in the compounding machinery. The unique new screw geometries enable maximized splitting and recombining of the compounds, with numerous striations and excellent mixing over a very short process length.

Uniform shear rates allow controlled mixing at lower temperatures whilst imparting only the required shear energy for the task at hand. The narrow shear rate distribution compared to alternative systems ensures uniform shear histories for every individual particle. This results in high-quality processing with reduced energy input.

Compounding requirements

from Semicon

The requirements for the compounding process of semi-conductive cable compounds are very demanding. Conductive properties must be ensured at both room temperature and elevated operating temperatures. The structure of the highly structured carbon blacks must be retained and they must be distributed extremely homogeneously to form the conductive network. The polymers used must degrade as little as possible. The surfaces of the layers co-extruded during processing must be very smooth and uniform. In most cases, peroxide-based cross-linking is required.

The BUSS Co-Kneader can fully exploit its specific strengths to meet this complex set of requirements for semiconductive cable compounds: the high proportions of conductive additives can be introduced at several feed points. The immediately initiated mixing processes at moderate shear rates lead to excellent distributive mixing results without damaging the internal structure of the conductive materials and polymers.

The design freedom of the system also makes it possible to specifically address the increasing viscosity in the processing zones with carefully selected configurations. This allows customised control and monitoring of the process conditions.

In the two-stage BUSS Co-Kneader system, the compounding and pressure build-up steps are strictly separated. This means that the compounding step is optimized for the best possible results in terms of quality and throughput, independently of the pressure build-up, filtration and shaping steps.

The modular and therefore adaptable design of the entire compounding system and BUSS's broad-based process expertise make the BUSS Co-kneader the technology leader and system of choice for almost all needs in the compounding of semi-conductive cable compounds worldwide – regardless of the installation location and the required output rate.

Typical plant layout

Typical plant layout for manufacturing semi-conductive cable compounds

COMPEO for semi-conductive cable compound production

Take a look at our typical plant layout for semi-conductive cable compounds in our COMPEO showroom.

Get to know our COMPEO compounder series

BUSS Co-Kneaders

worldwide

Our patented Co-Kneaders are used worldwide nowadays, supporting our customers in the production of plastics. Using BUSS compounding systems, our customers can master all the demanding requirements for manufacturing semi-conductive cable compounds.

World map with an overview of the Co-Kneaders used for cable compounding

Number of Co-Kneaders used for manufacturing cable compounds

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COMPEO series

We present: COMPEO, the state-of-the-art compounder that offers more versatility in its application, higher flexibility in process engineering, and increased added value in compound manufacturing.

HFFR cable compounds

Polyolefins have excellent insulation properties, but are also highly flammable and must be made flame-retardant accordingly.

XLPE insulation

Peroxidic cross-linked cable compounds are also referred to as PEX. The process was patented during the 1960s and has been used in the cable industry since then.