Torsional Damper Detuner is the most modern anti-galloping device available today which has been specially designed for use on bundled high voltage and extra high voltage power transmission lines.
This device is the result of multi-disciplinary cooperation between the University of Liege and ESSP (Russia). The concept of a device combining the benefits of torsional damping and detuning for the optimum control of galloping on bundled overhead power lines was invented by the University of Liege and this initial concept was made into a practical device by the Dulmison Company in the UK. The development and testing of these prototypes was performed by Laborelec in Belgium. This development and testing included both laboratory and field trials, which resulted in significant improvements being made to the initial prototypes, and these have been incorporated into the final design. The galloping has been substantially reduced on all the lines where the TDD has been installed.
Galloping of overhead power transmission lines has been a problem for many years and is primarily caused by the build-up of ice and wet snow on the conductors.
The main characteristic of galloping is large amplitude motion, upto the sag of the span, predominantly in the vertical plane at a frequency of around 0.5Hz. The effects of galloping on a transmission line is dependant upon the severity and duration of the galloping event but typical problems are phase to phase flashover causing outages and arcing damage to conductors, loosening of tower bolts and damage to suspension and tension clamps, spacers and vibration dampers and, in some critical cases, structural damage to towers.
The asymmetric build-up of ice and snow on conductors forms an aerodynamic profile which causes lift forces. The increased torsional stiffness of bundled lines prevent the free rotation of the individual conductors and this leads to the build up of a very eccentric ice/wet snow profile compared to that on single conductors. Also the vertical and torsional natural frequencies of bundled conductors fitted with spacers are in the same, narrow, range. Therefore, under these conditions, a resonant vertical oscillation may be excited by a torsional oscillation which destabilises the bundle. Therefore the concept of detuning [moving the vertical and torsional frequencies apart] and torsional damping [limiting the transfer of energy from torsional to vertical movements] was evolved for the control of galloping on bundled lines.
The mechanism for galloping on single conductors is different to that for bundled lines and cannot be solved by the same method.
Systems of increased phase to phase clearances and/or offset tower crossarms involve substantial changes to tower design and are not normally applicable to solve galloping problems on existing lines. A ’retro fit’ device is therefore required to prevent galloping on existing power transmission lines.
An efficient galloping control system should prevent not only phase to phase flashover but also any large amplitude conductor motion in order to avoid damage to the tower structures and conductor fittings.
Various methods have been suggested and field trialed over the years but none has proven to be totally capable of controlling the galloping on bundled power transmission lines, until now.
The TDD is a new device, initiated by the University of Liege and developed by Laborelec, Belgium, and ESSP, Russia, which combines the properties of torsional damping with those of detuning. Theoretical analysis shows that torsional damping influences the phase relationship between the coupled torsional and vertical motions involved in many forms of galloping, reducing the ability of the conductor to extract energy from the wind. The torsional damping of the TDD increases the critical wind speed for the galloping instability to start and subsequently limits its amplitude. The detuning aspect of the TDD further enhances its effectiveness by separating the torsional and vertical frequencies, in the manner of the detuning pendulum thereby reducing the coupling between these modes.
The TDD is mounted on the conductors over a set of Armour Rods, to protect the conductors, and support the clamps. Metallic and rubber lined clamps are available, dependant upon customer choice/preference. The TDD consists of a Pendulum which drives a torsional rubber damping element. The Pendulum is supported by nylon bearings, chosen for their long fatigue performance and the damping element is housed within an aluminium alloy protective sleeve for maximum service life. The torsional stiffness and damping of the elastomeric sleeve, the moment of inertia of the pendulum about its pivot and the distance between the centre of gravity of the TDD and the centre of the bundle are the principle design parameters. A typical natural frequency of the system is 0.5 Hz. Two or three devices are normally installed per span at defined positions. The TDD has a typical mass of 20-30kg and is suitable for bundled conductors upto quad configuration. It is not suitable for single conductors.
The TDD has been tested in the Laborelec High Voltage Laboratory, in both dry and wet conditions, and was proven to be corona free at a system voltage of 400 kV.
Prototype Torsional Damper Detuners were first installed on an instrumented test line in Belgium in 1992. The TDD has also been installed on a test line by STATNETT in Norway and on operating power lines by Electrabel in Belgium and Scottish Power in the UK. The galloping has been substantially reduced on all lines where the TDD has been installed and recent field records from Belgium, see diagram, show that the system is very efficient in the control of galloping and also free of any side-effects.
The following figure shows results obtained with TDD during a galloping event that occurred at the experimental station of Villeroux (included in the 400 kV network), in Belgium
The graphic enhances the tension fluctuation at anchoring level for different phase arrangement (triple conductor, twin reference conductor, twin with pendulums and twin with TDD). Only relative change is of importance and are given in kN. A reference galloping of about 6 meters peak to peak (giving a tension variation of about 30 kN per insulator string - which means 60 kN peak to peak variation) is reduced to about 15 kN by pendulums (wind speed was about 8 to 10 m/s) and to 5 kN by the TDD.
Video 1: Overhead line under galloping - without TDD Voir
Video 2: Overhead line under galloping - with TDD Voir
Video 3: Three span without TDD modelisation using SAMCEF - Mecano. Voir
Video 4: Three span with TDD modelisation using SAMCEF - Mecano. Voir
|© All rights reserved 1998 T.D.E.E.|