A number of SBB locomotives Re 4/4 II and Re 4/4 III equipped with a two-speed ventilation system were retrofitted with an optimised control of the utilisation of the two speeds. The device is based on a simple computer calculating a hypothetical excess temperature in the traction motors on the basis of recorded currents and a measurement device for the oil temperature in the transformer. Threshold values automatically select one of the two ventilation speeds. As a result, full ventilation is used much less, leading to substantial energy savings.
The savings per locomotive and year add up to 70 MWh (all 294 engines approx. 21 GWh). The modification costs are CHF 5200.-- per locomotive. The order for modification of all 273 engines Re 4/4 II and 21 Re 4/4 III was placed. The first 73 engines were rebuilt until 04/30/2000. Each year further 30 engines will follow.