Conversion of a railway system from d.c. to a.c. high-voltage operation

The paper describes the conversion from the 1500 V d.c. to the 25 kV and 6-25kV a.c. 50c/s system of electrification of the British Railways Eastern Region lines between Liverpool Street, Shenfield, Chelmsford and Southend (Victoria). The history of the projects and reasons for change are set out, together with the effect of electrification of other lines in the area. An endeavour has been made to cover in a balanced manner all principal aspects of the conversion operation from planning to conclusion, power supply, substations and switching stations, supervisory control, overhead-line equipment, rolling stock, signalling and telecommunications, civil engineering and the actual change-over sequence. It was a combined operation requiring most meticulous planning if the very heavy electric services operating over the lines concerned were not to be disrupted, with great inconvenience to hundreds of thousands of regular, daily passengers. The operation was successfully completed to a very restricted time schedule within little more than a month of the original target date owing to the unsparing efforts of many on the railway, with contractors and with the electricity supply undertakings.