WM 75: Chasing the regulators

Time to trace the electrical wiring going to the auxiliary generators, to see how they interconnect with the voltage regulators.  These machines are under the cab floor (whose panels lift up) and they rest on the engine room floor.   That floor is covered with oil, grease and grime from - guess where - the leaky engines and fuel drains.  All of the fuel drains are designed with a place to put a cup under them, but no one does - contributing to a disgusting mess for anyone who has to work in those spaces.

Anyway, here is the original wiring diagram, for generator #1, straight from the schematic.  X1 is the regulator, A1 is the aux gen contactor, and RC1 detected reverse current.

Oh wait, there's more.  Notice how RC1 and A1 are interlocked through the engine start contactors.

Remember I said a lot of the regulator system had been ripped out of the locomotive before we got it.  Now, after a lot of cleanup and chasing wire connections, I was able to discover that this is the schematic of the unit as actually installed.   X1 is the regulator, now an EMD type.  The rest is gone. 

Wow, a lot simpler, huh.

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. 

WM 75 contactors

Western Maryland 75 is an electrical beast, and there are several "power contactors" which make electrical connections to the traction motors, and connect the battery to the main generator for engine start.   I was asked to take a look at these, because they had been acting up, with the result that not all traction motors were engaging.  

The red things on the top are "arc chutes". P2 is removed so you can see.  On either side are metal pieces that serve as parts of a magnet.  In the back of the contactor, the main power cable loops around a bolt a couple times. Magnetism is rated in "ampere-turns", and with these big amps, just 1 or 2 turns makes a lot of magnetism. The bolt attaches to those metal plates, which act like a magnet.  When the contactor breaks (opens), current wants to keep flowing, and will leap across the contact points in a burning arc.  The magnet's job is to bend that arc so it goes up into the arc chute and extinguishes itself.

Anyway, along the bottom of the contactors is what are called "interlocks".  All of the ones on P1 through P4 are "normally open", meaning they don't connect until the contactor does.  The GS1 and GS2 interlocks are "normally closed", meaning when the contactor operates, they disconnect.  In this case, that's to disable things that should not run while you're cranking an engine, notably auxiliary generators and traction motors.

As you can see, they are pretty irregular.  I worked on them for a couple of days to clean them up.