Electric Railways - Direct Current (continued)

The control and lighting circuits were 32 V dc, fed from a motor generator with an ingenious in-cab rotary voltage regulator, and the air compressor was 1500 V dc, (its small commutator has proved a constant source of flashover and maintenance). However, in totality the system worked.

In the interests of safety the signal engineers in both Australian cities fitted substantial ac track circuiting in all keys areas (in Sydney, throughout the system), and to protect against signal over-run, installed trip-arm train stops at all signals. The electric trains had deadman handles, tripcocks on their automatic air brakes, and power knockout. While not novel technologies, the extent of their application, and the dividend in improved safety from this thoroughness, were notable in their time. There was, however, a very novel feature in the signalling on the Sydney City Railway: advance timed 'speed tripping' of approaches to platforms. This maximised line capacity and reduced the theoretical headway to 90 sec. In the years before the city circle was completed through Circular Quay it was possible to see in the same platform -only just -both the rear of the departing and the front of the next arriving train.

The following train was, however, still under full trip protection as the row of trip arms dropped progressively, always just in front of it. In a remarkable contrast to the record of many overseas cities (including London and New York) there has never been a rear end collision on the Sydney City Railway in almost 60 years' operation, solely because of this Australian devised fail-safe system and the integrity of its massive, antique vane type ac signal relays.

Beyond the introduction of mercury arc and later silicon rectifier substation systems (mid-1950s) there was little change of technological substance to the two suburban railways until 1960, and much old equipment remained in use through the following 15 years. In its post-war blue trains, Melbourne switched to classic low-voltage multiple unit train control equipment, and Sydney to motor cars with four motors, in both cases with standard 120 V dc controls of U.K. origin. In 1955 Sydney introduced a fleet of cars with power operated sliding doors.

The Sydney electric system also expanded into the 'interurban' electric area over the Blue Mountains to Lithgow, and the Melbourne system to the La Trobe Valley, still on 1500 V dc with 6-axle electric locomotives (regenerative braking on descents in N.S.W). The N.S.W. extensions involved a very heavy dc overhead, with triple headed trains drawing currents up to the full limit of 1500 V dc technology; this required sophisticated fault protection when discriminating between starting currents and faults.

Australian Academy of Technological Sciences and Engineering