Re: Boosters/Slugs (Was RE: BU1)

["Steve Palmano" <steve719@GTE.net>]

Aus loco discussion mailing list


(Possible duplicate transmission.)

Thanks Melanie.  You've answered a question that's been in my mind for a
while, namely did later  12 cylinder EEs (12CSVT Mk II & III engines) have
the generator/alternator current capacity to operate with a slug, and so
better utilize their "excess" power at lower speeds.  Sometime back I'd read
that in the 1970s, NZR had considered - but didn't pursue - using slugs with
its Dx class GE U26Cs, these having an even higher power-to-adhesive weight
ratio than the big Aussie EEs.  Hence the thought that the latter might have
benefited from slugs as well.

Also, I think that the Dx's also had performance control, as used quite a
bit in the US, which reduces the power at lower speeds, and allows units
with high power-to-adhesive weight ratios to be MU'd with those that have
lower power-to-adhesive weight ratios.  (I think in the US the main use is
in mixing 4 and 6 axle units, and not having the 4 axle units slip and/or
burn up their traction motors under lugging conditions.)  Maybe performance
control would have helped the ZA's MU with the Z's without the need for
general derating?  Although if operating speeds were mostly below that at
which performance control kicked in, it likely wouldn't make much
difference.

Had the YS idea been pursued, would the Z's equipped to work with them also
have required larger auxiliary generators?  AFAIK, the Z's and ZA's, like
many late EE designs, had all-shaft driven auxiliaries including TM blowers,
and so very likely a quite small (around 10 kW) auxiliary generator.  The YS
slug would necessarily have had motor-driven TM blowers (and I'm guessing
that these would have been original Y equipment, with +/-110 volt motors).
Unless the blowers could be powered from the traction circuit (and I don't
know if this is feasible) then they'd have to be powered at 110 V from the Z
battery/control/auxiliary circuit.  Each blower would probably draw about 10
kW, give or take.  So even one YS blower powered from an adjacent Z might
strain the auxiliary electrical system.

----- Original Message -----
From: Melanie J. Dennis <meld.asg@netspeed.com.au>
To: 'Aus loco discussion mailing list' <Ausloco@listbot.com>
Sent: February 22, 2000 08:27 PM
Subject: RE: Boosters/Slugs (Was RE: BU1)


Aus loco discussion mailing list

The 'Y' wouldn't actually MU with the 'Z'.  A Slug is not a locomotive in
the true sense.

The traction motors of the 'YS' would be connected across the output of the
'Z' alternators as an additional motor group.
Each 'Y' bogie has two traction motors - as a YS, these motors would be
electrically connected in series then each YS bogie (traction motor pair)
would be connected in parallel with the existing traction motor groups
across the alternator output on the respective 'Z' in a Z - YS - Z set-up.

Therefore, they would receive the same alternator output voltage as the
Master 'Z' class traction motor groups (3 parallel groups of two motors in
series) but the alternator would be required to supply extra current to
support the new load of 4 parallel groups of two motors in series.  There
would be some switchgear on the slug and motor blowers for cooling but the
existing body work becomes largely redundant.  The slug is not 'in circuit'
all the time, only when the locos require additional tractive effort as when
starting, or on banks.

It's a principle of utilising the residual capacity of the engine/alternator
to obtain a higher tractive effort from an extra bogie - on it's own, the
'Z' can't utilise all it's available power due to the HP/weight ratio being
out of kilter.  This is one reason why the 'ZA' class (originally 2,350hp)
were derated to match the 'Z" class (1,800hp) - they didn't have the weight
to make best use of the horsepower on tap for the local conditions.

That's why 3 x 830's (which have excellent low speed tractive effort
characteristics) will dig in and slug it out whereas 2 x 'Z' will be
slippery with the same load.  There are less axles for more horsepower (if
given axleloadings don't vary greatly between the two designs).    Hope this
clarifies.

Melanie Dennis
Australian Steam Group
meld.asg@netspeed.com.au

-----Original Message-----
From: ben scaro [SMTP:bscaro@hotmail.com]
Sent: Wednesday, 23 February, 2000 12:54 PM
To: Ausloco@listbot.com
Subject: Re: Boosters/Slugs (Was RE: BU1)

Aus loco discussion mailing list

I'm not sure of the mechanics of it, but what work would be needed to enable
a Y to mu with a Z ?

Cheers

Ben



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