Anna Noyd-Dryver wrote:
Marland wrote:
Anna Noyd-Dryver wrote:
Marland wrote:
bob wrote:
Graeme Wall wrote:
On 08/02/2019 10:58, Bevan Price wrote:
On 08/02/19 4:14, Recliner wrote:
The DfT remains consistent in its dislike of OHLE

https://www.thetimes.co.uk/article/battery-powered-trams-to-beat-congestion-pzz3p9jk3?shareToken=d7efc8230f20d995b8ea4bff5daae 175





As usual, the incompetent DfT only thinks about short term costs of
initial construction, not the long term running / operating costs.

Batteries have a finite life. You can recharge them, but they eventually
deteriorate, hold less charge, and have to be replaced - and they are
not cheap to replace.

Moreover, you use additional energy to convey the weight of the
batteries on every journey, instead of getting energy from fixed
overhead wires to move a vehicle that is lighter due to the absence of
batteries.

And before anyone suggests fuel cells, they also have finite lives, and
to function, they often rely on the presence of rare, expensive,
precious metals (platinum, palladium, rhodium, etc.)


Though once you've done the difficult bit of the infrastructure,
actually getting the tracks in the road, adding OLE later is a much
simpler engineering task.

It is provided you’ve done the work to properly isolate the track return
current to prevent electrolytic corrosion problems. If not, it probably
means ripping the whole lot up again.


Or use twin conductors like a trolley bus.



That would necessitate use of trolley poles, where pantographs are the
current standard fitment for new tramways.

I suppose you could have twin pantographs as fitted for 3-phase on certain
mountain railways, though you might get polarity issues on single track
sections, plus I suspect the OLE then needs to be aligned more accurately,
thus making it more intrusive.


What polarity issues would that be? Trolley buses frequently moved poles
over to the opposite set to get around an obstruction or damaged section.
DC traction motors as used in trams ,trolleys and trains have the the field
windings made from coils and are not polarity sensitive, its only on small
DC motors with permanent magnets like on model trains etc that reversing
the polarity will make the motor rotate in a different direction.

Though in the unlikely event of such an installation happening would trams
still be using DC motors nowadays?
Or like most trains electronic gubbins that can be fed all sorts of things
then send it to a AC 3phase motors.


AIUI trolleybuses are designed with both the positive and negative traction
circuits fully isolated from the vehicle. Trams OTOH have the negative
side, ie rails, connected to to the vehicle underframe and body frame ie
everything is earthed. The two-wire tram would therefore need a
non-standard wiring loom etc.

AFAIK modern trams have separate traction wiring for both polarities though
as you say they will eventually arrive at the same earth point, but there
would not be much complication if the the cable to that was connected to a
second pole and wire, just not at the same time , any idea how London’s
conduit trams were wired? The conduit supply was not electrical different
from a two wire supply except the wires have become protected live rails,
the track was not used as the return . It must have taken some good
planning on such a large system to ensure no tram could end up with the
plough turned around, and you have the added complication that after
dropping the ploughs and going to overhead on some routes then the chassis
and wheel return would then be used. Did those trams have a switch that had
to be operated to go from plough return or track?
I understand that some of the Underground’s battery locos can be switched
to third rail supply from the fourth
as there was a hope they could be hired out for engineering duties on the
National Rail 3rd rail network.
I don’t that ever came about though a pair once top and tailed a railtour
and Sarah Siddons the Met Loco was similarly modified for the tours it did
at one time to Portsmouth etc.

GH