Auszug | eb - Elektrische Bahnen 10 | 2019

Nur zur eigenen Verwendung, nicht zur Veröffentlichung oder Vervielfältigung! 404 Engineering Rail Power Supply 117 (2019) Heft 10 Reducing 25 kV electrical clearances Paul Naylor, Richard Stainton, Milton Keynes (UK) Railway electrification delivery and costs have been greatly affected by the challenges of providing sufficient electrical clearances. This, sometimes, has led to bridge re-construction, lowering of the track, or both. Electrical withstand tests show that the physical clearance between the contact line and bridge structures can be reduced to 20mm for voltages equivalent to basic insulation. Verringerung elektrischer Abstände bei 25kV Notwendige Maßnahmen zur Elektrifizierung von Eisenbahnstrecken und deren Kosten wurden stark durch die Herausforderung bestimmt, die erforderlichen Luftabstände zu sichern. Dies führte mitun- ter zum Um- und Neubau von Brücken, zur Absenkung des Gleises oder beidem. Spannungsfestig- keitstests zeigen, dass der physikalische Luftabstand zwischen Oberleitung und Brückenstrukturen auf 20mm für Spannungen entsprechend dem Basisisolierungsniveau reduziert werden kann. Réduction des distances d’isolement en 25kV Les principes et les coûts des électrifications ferroviaires sont particulièrement impactés par la néces- sité d’une isolation électrique suffisante. Ceci conduit parfois à la modification voire la reconstruction d’un pont ou à l’abaissement de la plate-forme de la voie ou au deux. Les essais de tenue diélec- triques montrent que la distance d’isolement physique entre la ligne de contact et les structures du pont peuvent être réduits jusque 20mm pour les tensions correspondantes au niveau d’isolement de base. 1 Introduction The cost of electrifying a railway can be high. In Great Britain, the cost of electrification is often signi- ficantly higher when compared to European rail- ways, due to the legacy of the restricted railway gauge used when the railways in Britain were first constructed in the early 19 th century. Route clear ance works to provide the space for overhead con- tact systems and electrical clearances can make up over a third of the total project costs (Figure 1). Avoi ding or reducing these costs can considerably strengthen the business case for railway electrifica- tion. In Britain, the first option considered by overhead contact line designers is to reduce the system height by reducing the contact wire height from the nomi- nal value of 4700mm to 4165mm. When this is not sufficient to achieve the required electrical clearance, the next options are to consider is to reconstruction of the bridge or to lower the track, or both. The Great Western Electrification Project [1] came across a particularily difficult bridge in Cardiff, known as Cardiff Intersection Bridge, with significant space contraints. The cost estimates for reconstruction ran- ged between 40 to 50million GBP due to the cons- trained site and the proximity of stations and junc- tions. The alternative option of lowering the track would require the rebuilding and the lowering of the culvert carrying the water supplies to the former Bute Dock, together with significant main-line track works at a cost of approximately 15 to 20million GBP. The physical constraints above and below the mainline on the approach to Cardiff Central Station at Cardiff Intersection Bridge can be seen in Figure 2. 2 Reducing clearances To enable electrification through to Cardiff Central Station without major civil engineering works, it was recognised that the contact line conductors would other project costs overhead contact line systems route clearance works (bridges, tunnels, stations) electrical power (substations, grid connections) Figure 1: Typical electrification project costs (all Figures: authors).