Re: Fate of 85/86 class

[John MacCallum <johnmac@lisp.com.au>]

Greg Hunter wrote:
> Not so!  The two tracks were MECHANICALLY separated by removing the span
> wires and replacing with all those shiny bits of galv steel.  Electrically
> nothing changed.  Power can only transfer between tracks at substations and
> section huts - about 4 km apart.
> 
> > 86 and 85 class
> > engines put their output in Regen back through internal resistors so
> > that very little excess current flows in the overhead.
> 
> The internal resistors are stabilising resistors to allow the motors to
> regen at a higher voltage.  They do not dissipate a lot of energy and then
> only when power is flowing into the overhead.  They are not like the
> dynamic resistors on diesels which dissipate all the regen energy.
> 
> > Any over voltage of the overhead is dissipated by resistors at the
> > substations.

Interesting Greg, when the concrete sleepers were laid (Lithgow
Enginemen) we were told that the Up and the Down were isolated
electrically. We always made me wonder how the substation handled
a train crossing from the Up to the down or visa versa. 
86's do indeed put a substantial amount of current through their
own resistor banks and when I get a chance I will find out just how
much they will do. I know that they have a upper limit of around
1950 volts in regen and that excitation is limited so that the
upper limit is not exceeded. Up to 800 amps of excitation is available.
It is not unusual to have quad 86's in Series regen with 700 or
more amps up on each unit. The main trouble with that is wheel slide
so if the rail is a bit greasy often we need to reduce it to around
300 amps. 

I was interested to read your comments about 25Kv AC verses 1.5 kv Dc.
I hadn't considered the Inductance in the Catenary before you mentioned
it.
Voltage drop ignored for the moment if I work on a constant 4.8 Mw
of power being produced by the locomotive then the 1500 V DC will
produce about 512 Kw of heat in the Overhead whilst the 25 KV Ac will
produce about 18.4 Kw using your .05 and .5 ohm impedance figures.

As less current is being drawn then heat generated from losses is less
and therefore transformers, associated wiring, contactors etc. need not
be a robust. Overall much more power can be supplied by a 25 Kv 
system because all equipment doesn't need to be so heavy duty.


Pope

Alias	John MacCallum