From: grr@cbmvax.commodore.com (George Robbins)
Newsgroups: rec.railroad
Subject: Re: Diesel vs. Electric Locomotive Maintenance
Date: 7 Oct 92 07:08:18 GMT
Reply-To: grr@cbmvax.commodore.com (George Robbins)
Organization: Commodore, West Chester, PA

In article <1992Oct6.170801.16310@engage.pko.dec.com> pierson@cimcad.enet.dec.com (Dave Pierson) writes:
> In article <35601@cbmvax.commodore.com>, grr@cbmvax.commodore.com
> (George Robbins) writes, in part:
> 
> >In article <1992Oct5.233132.27383@s1.gov> lip@s1.gov (Loren I. Petrich)
> >writes:
> 
> >> 	I have seen it claimed that electric locomotives usually need
> >> much less maintenance than diesel ones. Is there any truth to that
> >> claim?
> 	Yes, tho I haven't numbers, nor do i know off hand where to find any...
> 
> >Well, the are a couple of problems with your assertions.  First of all
> >electric locomotives aren't particularly simple.  In the case of the
> >diesel locomotive, you can regulate power output simply by changing
> >the engine speed and simple switching of the traction motor series-
> >parallel arrangements.
> 
> >An electric (we'll deal with a powerful AC one) has to in effect
> >have a power sub-station
> 	Consider that most power substations are expected to operate unmanned,
> 	24 hours a day 365 days a year.  Such subs are highly reliable.
> 	Bouncing them around a railroad will cut into that, but not a lot.

Assertion.  Substation equipment need not meet size/weight concerns
that traction equipment is subject to, operates under effectively
constant or slowly chaging load and is not subject to vibration or
impact.

> >to step down the 11-50KV power from the
> >overhead to a lower voltage ~300-600 Volts that can be used in brush
> >type DC traction motor or handed economically by solid-state rectifiers
> >and switching circuits.  In addition there either has to be fairly
> >complex switchgear for selecting different effective voltages for
> >different speeds/power outputs or fancy solid state inverter/chopper
> >circuits for newer equipment.

> 	Similar swirch gear is need on some diesels.  Many modern ones use
> 	solid state gear, just like the modern straight electrics.

Not so.  Most of the diesel gear is on the control side of things and
switches substantially less power, as opposed to  switching full power
under load.

Modern diesels use alternators and solid state rectifiers in place of
a compound wound DC traction generator.  Evaluation units have been
produced with AC traction motors, but I don't think this is standard
practice.  Even if so, they still vary engine speed and generator
excitation to control power output.

> 	                                                       .  I recently
> 	toured a "receiving terminal" for a +/- 500 KV, 500 megawatt (?) dc
> 	link (the one from Hydro-Quebesc to Littleton, MA) as part of an IEEE
> 	tour.  If memory serves, they spec less than 10 minutes a year outage
> 	for the whole thing, choppers included.  No vibration to hurt, but the
> 	voltages are higher....

Yes, but hi-reliablity/uptime is a major design constraint in the design of
such equipment.  How big was it, how much did it cost and what sort of
engineering/redundancy want into it that wouldn't be appropriate for traction
usage.

> >All of these needs to be cooled and controlled so you have quite a
> >pile of auxilliaries
> So does a diesel prime mover.  Needs rather more cooling, in fact.

Could be, not sure it's a given though.

> >Second, the maintenance requirements for diesel locomotives aren't all
> >that demanding.  The locomotive style diesel is rugged and subject to
> >periodic oil and filter changes runs (guessing a little) hundreds of
> >thousands of miles before requiring major maintenance or rebuilding.
> 
> 	Soundslike a pretty close guess, but consider that the transformer
> 	it "replaces" has NO moving parts bigger than an electron.  (OK, mild
> 	poetic license...   8)>>)  It has cooling, but so does a diesel.
> 	Call it a wash.
> 
> 	I suggest that the diesel electric and the straight electric are nearly
> 	the same except:
> 		Diesel engine has MANY more moving parts.
> 		Diesel engine dissipates more waste heat on unit.
> 		(some side issues also, not relavant to maintenance...)

Yes, but just keep in mind that the scale of the diesel locomotive is
large enough that engine wear is probably negligible compared to fuel
costs (over lifetime) and thermal efficiency isn't all that bad.

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