Optimalt design av lineoppheng i kraftledninger

By using double jumpers, the stiffness and the eigenfrequency of the jumper increases, and then resonance with the wind will be avoided /reduced. This gives again reduced displacement of the jumper. The simulations show that the number of spacers in the double jumper has great significance to increase the stiffness, and thus reduce the displacement. The distance between the two conductors in the double jumper have less significance for the stiffness. The distance can thus be selected so the jumper can be designed as practical as possible. It is very common to splice the loop by using two clamps. The simulations show that this is an unfortunate solution, which provides significantly greater displacement than a single continuous jumper. It is recommended that jumpers with splices are designed as double jumpers. That is, each end is brought up to the dead end clamp on the opposite side and clamped there. In suspension clamps, conductors can get fracture due to fatigue when conductors vibrate. Broken strands mainly occur from the keeper edge and up to the last point of contact in both the outer and inner layer. The most critical point is at the keeper edge, which makes it difficult to detect damages by visual inspection. For span without dampers it is recommended that the ratio between the horizontal stretch and net weight per length unit (factor H/w) for the span is held under a given value. For span that is beyond the recommended limit, it is recommended to carry out a detailed calculation of the vibration level to ensure that the planned damping is sufficient to protect the span from harmful vibrations. Bolted clamps can loosen and cause fretting and fatigue in the conductor if the components deform. The problem can be reduced by designing a clamping system, which is more elastic and thus making the force reduction less. This can be achieved by using long slim bolts with high tensile strength and self-locking thread profile, thick flat washers and conical spring washers, in order to absorb dimension changes. Laboratory tests showed that the increased elasticity through the use of thick flat washers, conical spring washers and repeated compression of the conductor, can reduce the power reduction in clamps significantly. The results show that relatively simple adjustments of suspension systems' design will enhance the power line reliability. The recommended design solution provides increased redundancy, it reduces the likelihood of line breakage and makes it easier to find any strand breaks by condition control. This is because the wire break now will mainly occur in the outer wire layer, because the stiffened loop reduces the amplitude of the vibration. The recommended design with double loops, will result in marginally longer repair time. The project has thus achieved two of its three objectives, namely reducing outage costs and better opportunities for condition monitoring of critical stress points in the suspension system. The third goal of reduced repair times, is not strictly reached, but a marginal increase of repair time is regarded as acceptable in terms of the usefulness of the achieved goals. Possible economic benefit is the reduction of annual outage costs in the order of 50 to 70 million NOK.

Den overordnede ideen er å bedre kraftledningenes driftssikkerhet, som inngår i ENERGIX´s hovedmål om høy forsyningssikkerhet og internasjonalt konkurransedyktig næringsutvikling tilknyttet energisektoren. På grunnlag av nettselskapenes driftserfaringer med feil i og nær lineoppheng, at N-1 kriteriet ikke lenger er oppfylt i høylastsituasjoner samt økte utfordringer pga. mulige klimaendringer, så vil nettselskaper, konsulenter, leverandører og produsenter av elverksmateriell i dette prosjektet gå sammen om å utvikle ny teknologisk kunnskap om: * design av stress- og energidempende opphengssystem for liner. * materialegenskaper, som er korrosjon- og frettingdempende * vedlikeholdsvennlige komponenter og opphengssystem * montasjeteknikker, som ikke endrer komponentenes iboende egenskaper Løsningene har følgende mål: * Redusere andelen av KILE ved varige feil i lineoppheng med 25%, * Redusere reparasjonstiden spesielt i sentral og regionalnettet * Bedre muligheten for tilstandskontroll i kritiske stres spunkt i opphengsystemet. I tillegg vil nasjonale produsenter og konsulenter kunne styrke sin markedsposisjon og øke omsetningen i et internasjonalt perspektiv.