WM 75 auxiliary generator blues

On your car, the alternator recharges the battery after you start it, and provides power for lights and controls.  On the GE 44 ton locomotives, this is done by an auxiliary generator.  In fact, each engine has its own auxiliary generator, regulator and associated circuits.

We have recently found that these are not working at all, and have not worked since at least 2011 Fall Color Tours.  We charge the battery with a small charger, and that's all the energy available to the locomotive for the whole day.  If somebody forgets to plug in the charger - no train!

I've been asked to take a look at that.   

Here are closeup pictures of Auxiliary Generator #1 (for engine #1).  Note that the glyptal paint is somewhat aged (not that this is necessarily a problem).  This machine actually has two separate generators in the same physical machine: the aux gen, and an exciter on the other end.  Here's the aux gen end of #1. 

You're looking at a commutator, which is how electricity gets to/from the armature (rotating part).   That is about what one should look like, though it could probably use freshening of the paint.  The crinkling of paint near the end of the armature is a little troubling, could be from overheat. 

Here is the exciter end of the same machine. 

Now let's look at auxiliary generator #2.  Here's the armature end.  Uh oh.  

Uh oh.  That white stuff suggests a problem.  It could be as simple as being connected to no load (or a bad regulator).  Because when a generator is driven like this, and is connected to no load, its voltage must increase toward infinity. That will eventually exceed its design voltage and cause a variety of problems.

Here's the exciter end of the same machine

That looks real good, almost to a fault!  Note all the red - I call that the "monkey with a spray can" look.  The armature (spinning part) should look that way - not the whole machine.  That's trouble. It's a cheap way to fake around a rather important maintenance procedure.

See, most armatures should be solid.  They should be nothing but coils, insulation and varnish.  There shouldn't be any air pockets in them, places where coil windings could vibrate, rub or have insulation fail.  There's a procedure used on a working (or repaired) armature that assures this.  The traditional method is called a "hot dip".  The armature is warmed to 125 degrees C to boil off any trapped water.  Then the armature (not the commutator) is dipped in varnish, with the idea that the varnish fills every air pocket and void in the armature.  Then it's baked at 125-150C to cure the varnish.  The trouble is, the varnish has solvents in it, which evaporate, leaving air pockets.

The modern way is called VPI. It uses an epoxy varnish which doesn't have any solvent so it fills all the space.  They set it in a tank, commutator up.  They draw a vacuum on the tank, which has a side-effect of boiling off any water in the armature (water boils at only 70 degrees in a pure vacuum.) Then they fill the tank with epoxy, remove the vacuum, and apply air pressure - this forces the epoxy into every possible void, turning the armature quite solid.  They drain off the excess epoxy (for reuse on other jobs) and turn on heat lamps.  The heat makes the epoxy cure in place.   Test, balance and paint the armature and done.

Some rebuilders don't have VPI equipment, or the volume of work needed to pay for having a huge vat of epoxy.  All they can do is whip out the spray can and hose the motor down with red insulating paint, which is "skipping the VPI altogether", a procedure not recommended by GE unless the armature is in excellent shape already and just happened to be out for light maintenance.  It impresses the customer because it looks good, but it doesn't really do anything to make the motor more reliable, which is the thing you're paying for.