HARDWARE AND FITTINGS FOR OVERHEAD LINES

A remarkable experience in the design and manufacturing of transmission line fittings allows our company to offer a range of products largely improved by the most recent technology in full harmony with the technical evolution developed in this field during the last decade.

The high quality that has always characterized our product is due to the expertise gained in more than 70 year of activity. Our production, market oriented, represents one of the most complete achievements among the international industrial panorama.

NES fittings are designed to withstand the mechanical and electrical loads that can occur at any levels of voltage in electrical lines. They are suitable for any kind of insulators: IEC and ANSI standard sizes, glass and porcelain cap and pin, as well as composite insulators.
Horn, racket and ring guard devices offer the best protection from overvoltage and a more uniform distribution of the electrical field generated by the highest line voltages.
Steel elements of the hardware equipment are made of high graded carbon steel that is thermally treated to improve the mechanical characteristics and hot dip galvanized to provide them with the best corrosion protection.

 

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In high voltage lines the coupling between the tension string and the conductor is made by dead end clamps. The most used dead clamp is the compressed type. It is composed by a steel internal body and an aluminium alloy sleeve compressed on the conductor and on the internal body. In case of ACSR conductors, the terminal part of the internal body is compressed on the steel core of the conductor.
After compression the aluminium sleeve shall become an integral part of the conductor. Therefore the quality of this fittings is essential. The aluminium alloy used is chosen with low content of copper to avoid corrosion due to electrolytic couple and it is thermally treated to give it the necessary plasticity for a good and homogeneous compression. These clamps are connected to a jumper loop, which permits electrical continuity between adjacent spans.

The midspan joint is used to join two pieces of conductor. It is made with the same principle of compressed dead end clamp.
The compression dead end clamps and joints restore the complete conductivity and mechanical strength of the conductors on which they are used.
NES performs all mechanical and electrical tests to demonstrate the efficiency of clamps and joints supplied. Ageing tests are systematically carried out by means of a thermal cycle test stand with automatic temperature control and resistance measurements.
In lower voltage bolted dead end clamps are used. In such fittings the conductor pass through this clamp and not being cut. The bolt torque and the length of the clamp are calibrated to prevent the slipping of the conductor and avoid any damage on the utmost layer.

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NES suspension clamps are fully articulated and have low moment of inertia, in order to obtain the maximum mobility and accommodate any movement of the conductor. The materials used are suitably selected to reduce the magnetic losses. An aluminium alloy, with low copper content, is used in casting parts in contact with the conductor, to avoid galvanic corrosion. The clamps are designed to withstand static and dynamic loads of conductor, with high safety factors.
The bolt torque is calibrated to prevent the slipping of the conductor and avoid any damage on the outer layer.
The NES suspension clamps are free of defects and irregularities; they have all outside surfaces smooth and all edges and corners well rounded to allow safe handling and minimise Corona emission and radio interference (RIV).

NES can offer a complete range of suspension clamps suitable for monometallic conductor, bimetallic conductors, ground wires, and OPGW.
The NES suspension clamps are of four types:

  • Suspension clamps with single articulation for low and medium voltage distribution lines
  • Suspension clamps with multiple articulation trunnion type, for high voltage, in which the rotation axis of the clamp is in the same plane of the axis of the conductor
  • Enveloped type suspension clamp type for ultra high voltage. All the projecting parts of the clamp are internal to the body clamp
  • Armour grip suspension clamp. In these clamps the grip is evenly distributed over the length of the armour rods. There are not fixed points on the conductor, which avoid high concentrated stresses. The rubber of cushion inserts has been formulated to provide good resistance to ageing, to be electrically conductive and to have adequate resistance to the effect of ozone, ultraviolet radiation, air pollution and conductor heating, over the entire range of service temperature.
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