[Synchrodyne]

The list of UK electrical supply voltages, etc., at the rear of the Electrical Engineer’s Reference Book ninth edition, 1958 shows some locations as also having some two-phase distribution. Exeter was one example. Possibly this came about through re-use of existing three-wire DC distribution systems. In that case the neutral (common) would have been nominally undersized, although perhaps considered satisfactory for typical loads. Conversion from 3- to 2-phase was easily done with Scott tee-connected transformers.

By way of broad comparison , here in New Zealand, standardization of electrical distribution came quite early, with most conversions (from DC and non-standard AC) done in the 1920s and 1930s. But some DC systems lasted until after WWII.

The decision to standardize on 50 Hz, 3-phase, 4-wire, multiple-earth-neutral (MEN) type distribution was made in 1920. Part of the MEN system was that at each consumer switchbox, the neutral was bonded to local earth by the MEN link, so I think we avoided some of the earthing issues that have cropped up elsewhere about differences between local earth and supply earth. Shortly after that decision, the voltage was standardized at 230/400 volts. There was also early use of 11 kV for primary distribution; for example Christchurch started building a city-wide underground 11 kV network in 1913. There was also early use of direct transformation from 11 kV to 230/400 volts, without an intermediate 3.3 or 6.6 kV step. A very early such installation by Lloyd Mandeno (later of SWER fame) would have run fairly close by to where this is being written.

Even so, special-purpose DC systems were retained in Christchurch and Wellington additional to the standard AC systems until the later 1950s. These were said to be for applications such as elevators and dentist drills. Auckland though had a fairly extensive inner city DC system, 3-wire 230/460 volts. Conversion had not been completed before WWII, and something around 100 route miles still remained, with slow progress resumed after WWII. The work was finally completed in the late 1950s. Whether the three-wire distribution system was re-used for AC I don’t know. (This kind of information is not so easy to find.) There were some cases of 230/460 volt three-wire single-phase distribution in rural areas, but these were at the end of two-wire 11 kV single-phase or SWER spurs.

Notwithstanding the survival of the Auckland DC system into the 1950s, I have not found any evidence that the local setmakers offered AC-DC type radio receivers for use in the DC area in this period. Their products of this period seem to have been AC-only, and were fitted with 3-core power leads, i.e. true Class I by later terminology. Perhaps those living in the DC area used battery receivers. Post-WWII, the DC system had a known limited life, with progressive diminution, so production of special appliances was probably seen as something best avoided. Whether live chassis AC-DC equipment would have met the safety regulations of the time is debatable, and the supply authorities didn’t like them anyway, so they would not have been keen on any such receivers being retained in use after conversion to AC.


Cheers,