By Irvine Bell
All British trolleybus systems [1911 -
1972] operated at a nominal supply
voltage of about 550 Volts DC - the same as British tramway systems
which were all governed by the same legislation [the legally permitted
maximum, as measured at the substation, was 650 Volts]. My impression
is that about 550 Volts DC has been, with one or two exceptions,
like two 1,000 Volts DC lines in Switzerland, a world standard
for most of this century for both trolleybus and tramway systems.
In recent years, the seems to have been
a trend for new trolleybus and
tramway systems to operated at 750 Volts DC. The ALSTOM ONIX 800
range of trolleybus electrical equipment [as being fitted to the
96 new Van Hool trolleybuses for Athens] is designed for up to
750 Volts DC. I guess that 750 Volts DC is in effect a world standard
for new systems. I am not aware of any formal e.g. ISO, SAE, EEC,
etc., standards governing power supplies to trolleybus systems.
I assume that it is governed by national legislation.
In Britain, and I believe, elsewhere, the
convention was/is that the
conductor nearest the kerb [on the left in Britain] was grounded
[if
grounded at all] and the other conductor [the right hand in Britain]
was at
about 550 Volts.
Many British trolleybus systems 'floated'
their trolleybus overhead i.e
there was no ground connection and, theoretically, one could not
get a shock by touching either conductor and 'ground' at the same
time. In these
situations, the wire nearest the kerb [on the left in Britain]
was held at
about -300 Volts and the other wire at about +300 Volts, giving
a potential difference between the wires of about 600 Volts. The
London system did this [once the trams had gone].
This page uploaded 12 MY 1999
