The term damping system applies to the complex of the damping units suitably correlated and designed to reduce the vibration and in general the effect of the wind action on the conductors. The wind-induced motions ca be extremely dangerous for the integrity of the conductors. For this reason, it is very important that the damping systems are designed with great care.
The most suitable solution to the wind-induced vibration problems can vary according to the characteristics of the line and several factors must be taken into account case by case.
DAMPING SYSTEMS
Warning: preg_match(): Compilation failed: invalid range in character class at offset 12 in /home/customer/www/nesspa.it/public_html/wp-content/plugins/js_composer/include/classes/shortcodes/vc-basic-grid.php on line 151
For single conductors and shield wires, NES proposes a damping system based on vibration dampers of Stockbridge type. For extra high voltage and ultra high voltage lines equipped with bundles of two, three, four, six and eight conductors spaced from 200 mm to above 1000 mm, NES can supply a wide range of spacer dampers and flexible spacers covering all the possible bundle configurations.
NES can also offer specific solutions to the wind-generated problems including subspan oscillations and galloping. Using computer programs and the expertise of the technical staff, the most suitable and economic solution to reduce the vibration levels within safety limits can be found for any specific application.
The materials used by NES for they spacers and dampers are duly selected to withstand the most severe environmental conditions and maintain their mechanical characteristics for the whole expected lifetime of the line, without the need of maintenance.
It is well known that, neither spacers nor vibration dampers can control the conductor galloping phenomenon. It is due to the simultaneous presence of transversal winds at high speed and asymmetric ice deposit on the conductors and is not very frequent on the transmission lines.
However, when it starts it can not be controlled and may lead to severe damages to the line structures. In any case, even light galloping events limited in time and amplitude can provoke unwanted uotage of the line as a consequence of short circuits between the line phases.
In the second half of the 80’, NES has designed, in collaboration with ENEL, a complete range of antigalloping devices based on the detuning pendula principle, already largely experimented in Canada. These devices are directly installed on the conductors in case of single conductor lines and incorporated into the spacer dampers in ca se of bundled conductors.
During the last 15 years, NES has supplied more than 5000 spacer dampers equipped with detuning pendula for several transmission lines in Italy, which had shown sensitivity to the phenomenon. After the installation of these devices, the phenomenon disappeared from the lines.
Nes vibration dampers, of Stockbridge type, have been designed more than thirty-five years ago and have a remarkable service experience. The design and the technology have been continuously improved to satisfy the increasing requirements of the modern conductors and shield wires.
NES can offer a set of vibration dampers, for the complete range of cables used on overhead transmission lines, capable to control, within the safety limits recommended by IEEE and CIGRE, the aeolian vibration of the conductors, for the whole life of the line without the need of maintenance.
The vibration dampers have four resonances well distributed within the frequency range of the aeolian vibration. The single bolt clamp is designed to maintain a permanent grip in the whole temperature range. The steel messenger cable has 19 strands and is specifically produced to provide the maximum damping effect. The counterweights are made in zinc aluminium alloy directly cast on the messenger cable or in forged steel, which are instead compressed on the messenger cable.
NES vibration dampers are extensively tested in a test stand equipped with a shaker and a 45m test span fully instrumented. The stand is totally controlled by computer which software has been developed to perform automatically all the tests on vibration dampers required by the national and international, such as:
- Dynamic response curves at constant velocity or constant displacement.
- Effectiveness tests on the test span, in accordance with IEC and CIGRE recommendations.
- Fatigue tests
Moreover, NES Design Department disposes of computer programs able to anticipate the vibration behaviour of any transmission line conductor with and without additional damping and to define the quantity and optimum positioning of the vibration damper units per span.
NES vibration dampers are fully in accordance with IEC 61897 Standards and with the main Utilities’ Specifications. Besides, they are specifically designed to make the installation on the line easy and univocal considering the difficult working conditions of the linemen along the overhead conductors.
The NES vibration dampers 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 and RIV. NES vibration damper components are made of materials conforming to the requirements of IEC 61284. NES provides the Clients with a clear and complete description of the installation procedure and the in-span location of the vibration dampers.
NES flexible spacers can be used to maintain the nominal separation between subconductors. Their flexibility is designed to easily accommodates relative movements (longitudinal, vertical, transversal and conical) between the subconductors, under all normal service conditions. Since they have little damping capacity, when it is necessary to control the levels of aeolian vibration, additional vibration dampers should be installed at span extremities.
In that configuration, the NES flexible spacers provide a suitable performance as they are light and flexible enough to avoid the so-called “subspan effect” i.e. the entrapment of aeolian vibration inside the subspans.
The distribution scheme of the NES flexible spacers considers a staggered positioning optimized for the control of the subspan oscillation. Moreover, the end subspans are kept short enough to increase the torsional stability of the bundle, which strongly contribute to the restoration of the bundle rest position in case of short circuit, galloping and ice drop.
NES Design Department disposes of computer programs able to anticipate the vibration behaviour of any transmission line conductor bundle and to define the quantity and optimum positioning of the spacer units and, if necessary, of the vibration dampers.
NES provides the Clients with a clear and complete description of the installation procedure and the in-span location of the flexible dampers. NES flexible spacers are designed to withstand short circuit forces generated by fault currents of up to 50 kA.
The spacer clamps are rubber lined and designed to provide firm but gentle and permanent grip while protecting the subconductors against the local static and dynamic stresses occurring during normal operation conditions for the whole expected life of the line.
The clamps can be installed without disassembling of any part and individual components are secured against becoming loose in service.
The clamp grip is sufficient to restrain the sub-conductor from slipping and rotating inside the clamp during the normal operating conditions.
The fastening system contains a single bolt equipped with a captive nut and washers, made of the same material (galvanized steel). Moreover, it incorporates a suitable locking an energy storing elements. This is the so-called “Belleville washer”; a conical spring washer made of galvanized spring steel, which suitably protects the clamps against the loosening effect of conductor vibrations and oscillations.
The materials used for NES flexible spacer components have been carefully selected to meet service life requirements and to withstand environmental attack, without the need of maintenance.
Elastomers have 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.
The first spacer damper designed in Italy, and one of the first in the world, is the RIGANTI spacer damper. It was developed more than 35 years ago, and, since then, widely used in Italy and abroad. Its exclusive and ingenious articulation, world patented, allow the rubber components to work in full compression, developing the maximum damping effect with practically limitless fatigue endurance.
After NES took over the RIGANTI Fitting Department, the spacer damper design has been continuously updated taking advantage of the new technologies and materials. The shape and the weight have been improved to meet to the increasingly stringent requirements of the transmission line. However, the core of the design: the damping articulation, still remains unchanged in its principles.
To date, NES can offer a modern spacer dampers, well proven on the field, capable to control, within the safety limits recommended by IEEE and CIGRE, the aeolian vibration and the subspan oscillation of the conductor bundles, while maintaining their elastic and damping characteristics practically constant for the whole life of the line. Moreover, NES Design Department disposes of computer programs able to anticipate the vibration behaviour of any transmission line conductor bundle and to define the quantity and optimum positioning of the spacer damper units.
The distribution scheme of the NES spacers dampers considers a staggered positioning optimized for the control of the subspan oscillation. Moreover, the end subspans are kept short enough to increase the torsional stability of the bundle, which strongly contribute to the restoration of the bundle rest position in case of short circuit, galloping and ice drop.
NES provides the Clients with a clear and complete description of the installation procedure and the in-span location of the spacers dampers for any span length.
NES spacer dampers are fully in accordance with IEC 61854 Standards and with the main Utilities’ Specifications. Besides, they are specifically designed to make the installation on the line easy and univocal considering the difficult working conditions of the linemen along the overhead conductors.
The spacer damper clamps can be of four different types:
- Nut cracker bolted clamp
- Cantilever bolted clamp
- Cantilever rubber lined clamp
- Open clamp with armour rods
The central frame is dimensioned and shaped to provide a suitable inertial effect and to protect the articulations during short circuits.
The NES spacer dampers are designed to withstand tension and compression forces developed by short circuit currents up to 50 kA.
The NES spacer dampers 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 spacer damper components are made of materials conforming to the requirements of IEC 61284 and having an excellent corrosion resistance that is maintained for the whole expected conductor lifetime, without the need of maintenance. Elastomers, used in the articulations as damping elements, have 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.