On Jan 17, 7:55*pm, Tom Anderson wrote:
On Thu, 17 Jan 2008, D7666 wrote:
On Jan 17, 9:42 am, John B wrote:

Of course, the ELL ones will have pantograph spaces and will be
electronically capable of AC/DC operation, like all new 3rd rail stock.

Indeed, this is a key point for all present generation EMU.

Although in the general case of all types (i.e. beyond the 378s being
discussed above) it might be more than just a pantograph tp be added -
some existing classes would need - or might need in future if ordered
without - a transformer to be needed as well.

And a rectifier, i assume. Or do modern DC trains work by inverting the DC
into a low-voltage AC at the same frequency as an OHLE supply and using
that to work a motor?


Modern EMUs use three phase traction motors and both AC and DC line
voltages need to be converted for the three phase power electronics.

You say 'some' - does that mean there are trains which have a transformer
but no pantograph? It makes sense to build a system to which the AC bits
could be added later, and to leave room for a transformer etc, but
installing a transformer which will just sit there being dead weight seems
a bit crazy.


The class 375/6 are dual voltage units, delivered complete with
pantographs, but have never used the AC equipment in anger (except
maybe for some tests, I don't know) and several have had the
pantographs removed.
I think that quite a few of the other 375 and 377 subclasses also at
least the transformer fitted, the heaviest coaches in the units are
the driving coaches and an extra tonne or four in the trailers won't
make much difference to performance!! All the four car units have
three motor coaches and so outperform the units that they replace, I
don't think that weight was an important part of the design process.
Captain Deltic's description for the new generation of units is 'power
hungry lardbutts'