Railways place unusual demands on transformers. Onboard traction transformers must deliver high power from units small and light enough to fit into a locomotive or multiple unit. Trackside transformers have to cope with frequent overloads in the confined space of a substation – often in tunnels, stations or city centres, where a fire would have severe consequences. MIDEL ester fluids are used in both applications.
Traction transformers on board
Since the move from DC to high-voltage AC supply, rolling stock relies on traction transformers that step down the catenary voltage – typically 15 kV or 25 kV – for the traction motors and auxiliary systems. MIDEL 7131 synthetic ester combines a high fire point with excellent moisture tolerance, allowing compact designs with high power output. More background in our sector profile on rolling stock transformers.
Bombardier has used MIDEL-filled equipment on rolling stock since 1996. Its TRAXX locomotives – first ordered as the BR185 series for Deutsche Bahn – run across Europe at 15 kV and 25 kV with an output of up to 5,600 kW (case study). In the USA, New Jersey Transit operates Bombardier ALP46 locomotives with ABB traction transformers filled with MIDEL 7131. Despite one of the toughest duty cycles, with frequent stops and regenerative braking, the fluid has needed no maintenance in more than ten years of service (case study).
Trackside and auxiliary transformers
For the Paris Métro, RER and tram network, RATP has used Bio-SLIM trackside transformers rated 3.3 to 5.5 MVA and filled with MIDEL ester fluid since 2008. The compact high-temperature design fits into confined trackside substations and handles frequent overloads – and, unlike the silicone liquid used before, the ester fluid is readily biodegradable (case study).
Why rail operators choose MIDEL
High fire safety in tunnels, stations and on board, a readily biodegradable fluid for sensitive track corridors, compact units with high power density and reliable operation under heavy load cycles. Talk to us about MIDEL for your rolling stock or trackside project.