Aspects of the design, construction and testing of BRB´s Class 90 and 91 locomotive transformers

The geographical differences between Britain´s two main north/south rail routes are such that two locomotive specifications were justified. One designated the Class 90 with a design speed limit of 175 kph, would reinforce the west coast main line services. The other designated the Class 91 `Electra´ with a design speed limit of 225 kph, would mainly serve the east coast route. The performance of the two new locomotives required differing configurations of equipment layout in general and of the main transformer in particular. Hence, two locomotive transformers for BR were in design and manufacture simultaneously. The transformers have features in common. The arrangement of the main traction secondaries, the arrangement of the tertiary windings for auxiliary supplies, the electrical insulation levels, the use of Class A insulation materials, the temperature rise limits, cooling method, and the integral construction of the main transformer with its conservator and cooling system. The transformers also have features that differ. The author discusses the design, construction and testing of the two types of transformers