To go off on a complete tangent does any one know if the 3000 volt
3 phase system the Metropolitan railway considered would have been
straightfoward to install, or would that have required some tunnel
alterations.
Mention is made however of Ganz which IMU infers 3-phase but according
to Wonkypaedia :-
http://en.wikipedia.org/wiki/K%C3%A1...A1n_Kand%C3%B3
there was also a modified system using a single-phase OH supply with
conversion to 3-phase on the locomotive used in Hungary; the wlv.ac.uk
article referred to above mentions the "an overhead conductor" so the
Met. might only have wanted one piece of wet string.
No, it was two overhead wires. The following is from "A History
of London Transport" (Barker and Robbins), volume 2, pages 58
and 75. The Metropolitan and District issued a call for tenders for
electrifying their lines and hired two consultants, Sir William Preece
and Thomas Parker, to examine the tenders.
# Preece and Parker... on 9 January 1901, reported that the thought
# that Ganz's seemed the most suitable but felt that they ought to
# inspect the Ganz system before making a definite recommendation.
# They went to Budapest and reported to the joint committee on
# 7 February 1901 that they were satisfied. It was therefore
# decided to recommend the Ganz system to the two companies.
# This agreed recommendation came as a bombshell, for the Ganz
# tender was for a 3,000-volt three-phase a.c. system fed to the
# trains from two overhead wires, quite unlike anything which had
# been tried out by the underground companies so far and, indeed,
# different from anything which had been in successful commercial
# operation up to that time anywhere in the world.
...
# This had the attraction of economizing in transformer and
# converting plant but the disadvantage of requiring twin overhead
# wires with a potential difference of 3,000 volts between them
# and between each of them and earth. These overhead wires would
# be difficult to install in underground tunnels and, should either
# of them be brought down when the trains had started to run, they
# might endanger human life by fire or electric shock and would
# certainly lead to long interruptions in service. There was
# the further disadvantage that alternating current motors had
# a much poorer starting torque, a very important consideration
# on a system having numerous stations and frequent stops. And,
# most important of all, the Ganz system had not at that time been
# tried out anywhere in the world under commercial conditions,
# though it had been shown to be technically feasible on a trial
# stretch of open line about a mile long...
"Difficult to install in tunnels". That sounds to me as though
they felt there was enough clearance for 3,000-volt overhead
wiring, but only just.
Note incidentally that there was 3,000 volts between each wire and
earth as well as between the two wires. That's obviously because
the earthed running rails were to be used as the third phase, just
as they are a conductor when used with third rail (and not fourth)
or single-wire overhead. In a 3-phase system with 3 separate
conductors, they only need to be at 3,000/sqrt(3) = 1,732 volts
relative to earth to have 3,000 volts between any two of them.
The book includes a long footnote which says, among other things,
that the first use of the Ganz system in commercial service was on
the Valtellina line near Lake Como in September 1902; and that
technical details of the system and an illustration of a Valtellina
line locomotive can be found in "History of the Electric Locomotive"
(1969) by F.J.G. Haut.
--
Mark Brader, Toronto | This is Programming as a True Art Form, where style
| is more important than correctness... --Pontus Hedman
My text in this article is in the public domain.