Simulation studies of energy saving with chopper control on the Jubilee line

The paper describes energy-consumption studies undertaken for the operation of rapid-transit services on London Transport´s new Jubilee line. The object of the studies was to provide comparative figures for the energy consumption of a chopper-controlled fleet and a conventionally equipped rheostatically-controlled fleet. The work was undertaken using a digital computer simulator in which train movement and power-network calculations are interdependent. This approach permits the evaluation of system constraints when regenerative braking is used in conjunction with the usual, plain diode, noninverting type of substation. Detailed figures are provided for various services operating on a short 5 km isolated power block section of the line and also for peak and off-peak services on the whole line. Sensitivity experiments on this 5 km section demonstrate the dependence of energy reduction on the opportunities to transfer energy between trains, on the line voltage limit and on the traction equipment specification. For whole line operation, at peak and off-peak headways, the energy savings are 15% and 9% respectively. These figures reflect the use of a low characteristic traction motor and the moderate proportion of braking energy actually available for potential regeneration (52% of total braking effort for an average loaded train).