The transformer oil pumps in Austrian national railway company ÖBB’s Taurus high-performance locomotives are being equipped with NKE hybrid bearings to prevent passage of electrical currents. NKE AUSTRIA outperformed with fast proposal of technical solutions, cost effectiveness, and short delivery time.
Taurus high-performance locomotive
The Taurus high-performance locomotive is one of Austrian railway operator ÖBB’s flagships. Assembled by ÖBB-Technische Services GmbH (TS) – a subsidiary of ÖBB – in the Taurus Center in the Austrian city of Linz, the Taurus is currently “Europe’s most powerful and fastest high-performance locomotive”, according to ÖBB sources.
The 1016 and 1116 series two-system high-performance locomotives are used mainly for main-line passenger and for heavy goods transports. Thanks to its newly developed high-speed bogeys with their performance drivetrain and brake shaft (HAB), the Taurus reaches top speeds of 230 km/h (140 mph). Each of the locomotive’s bogeys is supplied by one current converter. An oil-cooled transformer arranged under floor supplies the current converters with the required propulsion power. Each of the transformer’s cooling circuits contains two oil pumps that keep the oil circulating. An auxiliary consumer converter supplies the oil pumps with electrical energy.
NKE hybrid bearings prevents passage of electrical currents
Especially during starting, the simultaneous operation of auxiliary converter and oil pump can cause an excessive current flow through the pump’s bearings. This problem was identified by maintenance contractors ÖBB-Technische Services and was confirmed by the experienced engineers from the bearing supplier NKE. To prevent the adverse current passage, the oil pumps were to be fitted with different bearings with ceramic rolling elements that provided a complete electrical isolation.
NKE impressed with technical competence and promptness
The choice fell on hybrid bearings from Austrian-based bearing manufacturer NKE AUSTRIA GmbH. NKE impressed right from the start, with its fast submission of an offer and model selection, and the provision of samples for technical trials. The short delivery time and cost effectiveness were also the decisive advantages. In the course of routine maintenance work on the 332 locomotives at the Taurus-Center in Linz and the other ÖBB Service locations, the oil pumps are removed and their existing bearings replaced with electrically insulating angular contact ball bearings and deep groove ball bearings from NKE. The rolling elements of the new bearings are made from insulating oxide ceramic material. Ceramic rolling elements have a theoretically infinite electrical resistance and therefore effectively prevent any current passage.
Other applications for electrically insulated bearings
Beside hybrid bearings – bearings with ceramic rolling elements – electrically insulated bearings are also available with an oxide ceramic insulating layer on the bearing’s outer race. The ceramic layer is applied to the outer race through thin-film plasma spraying. The insulation has a guaranteed dielectric strength of at least 1000 V direct or alternating voltage.
Electrically insulated ball bearings are also used in other applications, for example in traction motors. NKE supplies electrically insulated bearings in standard sizes with outer diameters from 80 to 400 mm as well as custom sizes to order. The electrically insulated bearings are available in a range of designs. As their load ratings, key dimensions and tolerances are identical with those of the normal bearings, they can be easily substituted for the standard bearings in existing installations or new designs. Electrically insulating bearings provide excellent protection from bearing damage through flashover and are therefore much more reliable in operation than their conventional counterparts.