Reading to Basingstoke: non-standard ‘150’ No 150001
approaches Mortimer on 30 March 2017. Ken BruntPan Up Ian Walmsley
42 Modern Railways April 2019 http://www.modern-railways.com
increasingly rare for all lines and track
workers are trained to be risk averse.CUTTING YOUR LOSSES
While even a standard, lossy, steel
conductor rail is much more efficient
than hydrogen or batteries, there
is a problem with resistive losses.
These are not too serious where
traffic is light, but if a solution could
be found it could eventually be
rolled out across the system.
It is always tempting to feed a
branch from the live end connection,
which you can do on 25kV, but losses
mean you are struggling to feed
more than a few miles of third rail.
When the Central Line went east from
Epping to Ongar it was said that you
could put a short circuit bar down atOngar and the breakers would stay
in, the rail resistance being so high.
As mentioned above, losses are
proportional to the square of the
current, so if you halve the current,
you quarter the losses. Now, since we
have a safe system of work around
the third rail, why not increase
the voltage? Technically it is quite
possible to double the voltage to
1,500 Volts on a newly-electrified line,
but of course existing trains couldn’t
then use it and we can’t convert
the whole network overnight.RADICAL INNOVATION
I mentioned earlier how the system
was built for single power car units,
but most modern trains have two or
more. If we were to build new trainsfor ‘new’ third rail lines, three-car
sets would probably be preferred
with a power car each end and a
trailer in the middle. If we assume a
1,500V extension to, say, Salisbury,
these trains would connect their
power cars in series on the ‘new’ line,
so each power pack receives 750V,
as standard. When you come in to
Basingstoke they are switched from
series to parallel connections – so
they are now standard 750V kit
and off they go to London.
Any unit with an even number of
power cars could be converted, but
that would be more expensive than
new build and some good maths
would have to be done on a business
case. Like old Christmas tree lights, if
one pack failed when in series theyare both out, so a dropper resistor
might be needed for emergency use –
but traction kit is now very reliable,
and another train is usually close
behind, so it might not be worth it.
Many lines in the south are
struggling to get enough power, so
this double voltage (2XV) system
would help solve that where it was
installed, as well as cutting losses
by 75%. Alternatively, assuming no
performance boost was necessary,
a 2XV line would need half the
substations of a standard one. In
my Salisbury example I calculate
four substations instead of eight,
and remember, no bridge lifting,
gantry moving, station awning
removal, visual intrusion etc.25KV AC VERSUS 2XV DC
Make no mistake, in a world where
sensible clearances can be used
and costs are controlled I am still
very much in favour of 25kV for
the whole UK railway. But the old
Southern Region could relatively
easily be made all electric if the ORR
changed its stance and Network Rail
was committed to the project. Third
rail is not ideal, but it is a lot better
than the alternatives being looked
at now. Also remember the reason
the Southern went for it nearly
100 years ago: it is cheap to install. DC
units also do not need a transformer,
thus saving cost and weight.
You have to conclude that for
relatively low demand railways
(the high demand ones are already
done) and where speeds are under
100mph, third rail is the way to
remove diesels. Just for fun, if we
imagine the residual Southern dieselDiesel on the third rail: No 165114 at Wokingham with a Gatwick to Reading service on
28 April 2018. GWR plans to introduce dual-voltage bi-mode Class 769s on this route that will be
able to take advantage of the stretches of third rail that already exist on it. Ken Brunt040-043_MR_Apr 2019_pan up 1.indd 42 12/03/2019 15:04