Winpower transformer controlled excitation

[veronikafth]

Hi everyone, first time posting. I have been reading this site for a while but never had a reason to post until now... This isn't an ST generator question, but there is another thread for the transformer controlled excitation type of generators, so I thought maybe this was the proper place to put it.

I have a Winpower GR15W4 generator that I am restoring to working order, and maybe updating it a bit while I'm at it. It has this transformer controlled excitation system that is mentioned in another thread, and I'm looking for perhaps a bit of help from some of you guys who know more about this than I do. 

I picked it up for a couple hundred dollars from an acquaintance. It's in good shape for being in a barn for decades. The Wisconsin V4 motor runs like a top, but the generator controller box had rodents move into it and was full of hay, and from years of people splicing into the wiring, it was a mess.

Anyway, I am restoring it. I ripped out the old system of relays with the rat's nest of wiring (and the mouse nests of hay) and am blasting and repainting parts.

I was going to replace the transformers with an AVR, but after reading about how good this type of excitation system is at starting motors I'm thinking about keeping it. I do want to replace the old-school relays and switches with a more modern controller.

The problem is this: I can figure out how to hook up most of the excitation system as it was largely separate from the controller circuit. But there is one line that runs from the controller circuit to the excitation circuit.. and it has a variable resistor on it. I'm assuming that this is to fine tune the power to the field somehow... but I'm not sure. I'm eliminating the controller circuit and replacing it, so I need to find out exactly what this does, so I can figure out some other way to make this work.. I'll attach the schematic so you can see what I mean.

In the schematic I posted, the excitation circuit with the transformers is on the left, controller circuit on the right. I ripped out all the controller stuff that you see on the right side. The battery charging transformer has been eliminated too. But on the right side you can see the line that says "To F1", which has the fuse and variable resistor, then runs to F1 on the left.

Am I correct in thinking that this is to adjust the field a bit?

I'm not an electronics expert as you can tell. 

Any help you guys would be able to offer me would be greatly appreciated!

Thanks!

Veronika

[mobile_bob]

i don't see the wire, resistor or fuse your refer to

do you have more schematics for this machine?

one with the relays and everything?

built in 1977 tells me there ought to be a lot of info still available for this machine.

if it were me, i would research and find the original schematic and rebuild the panel to original specs, then tune up the transformers to get the voltage regulation working  properly. the result will be much more robust than any avr is likely to ever be, and less costly.

from what you describe it sounds like someone added the resistor to the field circuit to adjust the voltage as you assume, however i doubt that the oem used this resistor because the transformer air gap and iirc taps set both the voltage no load and at full load.  its possible the used the resistor if there are no taps on the transformers.

whatever you do retain those transformers, this generator really needs them to do what it was intended to fully do. replacing them with an avr will result in a generator with much lower surge capacity.

bob g

[veronikafth]

Thanks for the reply...

This is the only schematic that is provided on Winco/Winpower's website for this model... I'll try and contact them and see if they have any more information on it. I have found a few service bulletins that have been helpful, such as the thyrector being replaced with varistors.

The part I am talking about is, on the right, where it says "To F1". This line comes out of the circuit on the right, through some kind of diode bridge/rectifier, a fuse, and that variable resistor shown right there, then I guess is supposed to go to F1 on the left.  I circled it, I'll attach it.

There are no air gaps on this transformer. It's just a big honking transformer with the line 1 and line 2 going through it, and then the secondaries coming out. There are four secondary wires coming out  but two of them are joined together, like they are two pairs connected in series.

[veronikafth]

Here's a pic of The big honking transformer and reactor from the schematic... No way of adjusting it from what I can see...

This is before I cleaned them up... they look much better now! And I tested them for shorts... all seems to be good..

[mobile_bob]

my bad!

i didn't see the scroll bar on my screen shot, so i didn't see the complete schematic

now after seeing your arrow, and went down and saw the scroll bar

and wallaaaa, now see the  right half of the schematic

anyways, yes it appears that the resistor is coming off of the right side rectifier
which provides primary power to the field

the big honking transformer powers the left side rectifier because it is a compound transformer, the more current that goes through the primary, additional boost current is induced in the secondary and is fed to the field coil via the left side rectifier.

the transformer is adjusted by altering the airgap, but i would not mess with that as of yet.  when it is time to do so, you loosen the frame bolts and move the I core in relation to the E core of that transformer lamination stack, to provide some additional air gap or to reduce the gap, this alters the boost current so that there will be additional field under heavy loading, this picks up the generators output voltage under load, instead of the voltage drooping under load it can actually climb.

i would do everything i could to clean up those transformers and reuse them if at all possible, maybe take them to a motor shop and see if they have any idea how to clean the mouse pee out of them and redip them?

having the complete schematic for this machine, along with all the original parts is a huge bonus for you, even though they are in bad shape i would think it is restoreable.

if you can't find anyone to clean up those transformers, i would consider soaking them in distilled water, warm distilled water with a bit of dish washing detergent. maybe in an old sauce pan with some heat to get the crap out of them, change the water often.

then blow dry them as best you can, and bake them dry at very low heat. then take them in and have them vacuum dipped in motor varnish.  if all else fails you could rewind them, or have them rewound.

rewinding them would not be as daunting a task as a normal E/I core transformer, because the E and I laminations are not interleaved. all the E's are all stacked together as are all the I's, this means you rewind on a bobbin core and slip it over the E stack and cap it with the I stack and then bolt it back together.

it just depends if there is enough mouse urine in there to have corroded up the windings, i can't tell from the pictures other than they look to have some issues with corrosion.

basically in my opinion, if this machine could be restored to original condition, using the original schematic and design, i think you will have a very good machine and be much happier with it that converted to an AVR excitation system.

having said that, i suppose it can't hurt to convert it to an AVR machine while you are restoring the original system?  whatever the case, don't throw away any of those parts as they are probably very hard to replace. someday you may want to restore the machine or someone else might want to or have a need for the parts.

thank you very much for the schematic, it adds more to our database of control systems.

as good as modern excitation systems are, there is still something to be said for old school methods, some of those are about as bullet proof as can be had, and in my opinion this is one of the best examples of this design.

bob g

ps. i just reread your response, if the transformers look good, you might still want to have them vacuum dipped?

[mobile_bob]

sorry about my manners,

welcome to the forum!

hope you like it here, and find this place as useful as we do.

thanks
bob g

[BruceM]

OK, I'll bite, Bob.  While this transformer regulated design is a nice old design, I don't see why this should provide any better motor starting capability than an AVR.  My ST-3 can be operated on either the harmonic or AVR with the flip of a switch, and I don't see motor starting benefits from using the harmonic.

The only place the harmonic works better for me is when I was trying to drive a grossly low PF load, as my homebrew AVR does not do true RMS voltage regulation.

[mobile_bob]

Bruce
it appears this particular unit uses 24vdc excitation and is supported by the harmonic excitation scheme as well,

where the transformer controlled system shines is in its ability to boost the field much harder than is typical of either an avr or a purely harmonic winding excitation scheme.

for this system to work the field winding has to be robust enough to take the added current during hard to start inductive loads, loads that the transformer controlled generator was designed to provide improved service to.

i am not sure a standard st head's field could take the additional current, however i am not sure it couldn't either. usually this boost is short term lasting only several seconds.

it would be interesting to measure the current going to the field under normal loads with this unit and then also measure under starting a heavy inductive load.

i think a good stout avr probably could replace the transformer control excitation system, however i wouldn't know what to suggest to replace it with without first learning the operating parameters of the oem system.

having done a bit of research on this design, the big advantage of the transformer control system vs the AVR system is one of durability. the transformer design is very rugged and darn near impossible to kill, vs some of the AVR's being a bit more delicate and subject to failure from abuse.

i guess at this point i would really like to see the OP get the unit running in stock condition so that we might see just how good the system really is.  voltage regulation is reportedly quite good with these systems, it would be nice to see that first hand on a generator in the size near what we might be using.

just my thinking anyway

bob g

[veronikafth]

Thanks for the welcome Bob! I have in fact learned a lot by just reading through this forum. Hopefully I'll contribute some useful information as time progresses. Once it's back together, I will in fact post some numbers that I come up with during testing. I've got a 240v air compressor, and of course air conditioners, and some various space heaters and things to really put a load on it. This unit is very beefy, I'm sure it's been underrated.

It is actually a three phase, 15kw 120/208Y gen head that I'm going to connect zig-zag for split phase power. This generator was available in three versions... The one I have, plus the split phase 120/240 version (that I posted the schematic here for), then a three phase, three wire delta version. The only difference between them is the armature.. this is a statically excited alternator with the field poles on the stator, power is taken from the armature via slip rings.. The transformers are the same between the models, just hooked up a bit differently in the schematic.

I did in fact clean up the transformers. Since they were pretty well sealed on the top, nothing got into the windings. So I wound up just cleaning the rust off of it, degreasing the outside with contact cleaner, and spraying them with clear electrical lacquer to seal them. I can't seem to find the picture I took after i cleaned them, but they look a lot better.

Although those transformers looked bad, the overall condition of the generator is quite good considering. The brushes look like new. There is very little rust anywhere else, just some surface rust. I'll attach a few before and afters where I'm at now with it if anyone is interested. Pictures are always nice in my opinion. 

I see what you mean about the air gap on the transformer now... the gap between the top and the body of the transformer. There is indeed a spacer there between those two parts. Makes it a lot easier to rewind, as you mentioned.

I sent this schematic to a friend of mine (an electrical engineer) and just finally got a response. Supposedly the line coming from the controller circuit on the right provides a small amount of voltage to the field when the run/start switch is engaged to help the field build up, then once the field builds up the transformers take over the excitement. It's almost kind of like flashing the field I guess, just gives it a little boost to help it get going.

The diodes on the right prevent power from the field circuit from backfeeding into the controller circuit. The variable resistor is there to fine tune the voltage so that it doesn't affect the field once the field voltage builds itself up, and it's not needed anymore.. I'm guessing if this isn't set correctly, then when the generator is unloaded, it could feed extra unneeded power into the field circuit, and affect the voltage.

Supposedly this works similarly to an alternator idiot light on the dashboard of an old car, but hooked up with a lightbulb in the circuit. Turn the key on and it's feeding the field, light is on. Start the car and the field builds itself up in the alternator, this circuit stops feeding power into the field anymore, and the light goes out. If the field gets weak, this circuit feeds more power into it and the light starts to glow... indicating a possible charging problem.

I did save most of the original parts, some were missing when I got it. I do want to keep the transformer system for excitation, but I want to replace the controller and battery charging circuit with something more modern, or at least rewire it and replace the old Potter-Brumfield relays with something more common and easier to find... Something from the automotive world probably.

If worse comes to worse, I have a cheapy chinese AVR sitting here that I can use to get it going temporarily. Maybe I'll do some comparison testing between the two, Then we can see exactly how much better the transformer is. Well, at least how much better is it than a cheap chinese AVR. 

Some pictures attached for your entertainment.

[veronikafth]

Some more pics... plus the reactor coil after I cleaned and sealed it.

[BruceM]

Thanks for the explaination, Bob.  Given the size of this generator, the voltage boost from the transformer under a surge load might exceed the mains voltage, so it makes sense to me.  Most of the AVRs will bang the field with the peak of the 240VAC, so for smaller generators, that's plenty of power for motor starts.

[Thob]

Veronika,

I agree with your electrical engineer friend.  Switch SW1A, contacts 2&3, is part of the start switch.  When engage the start switch, this provides 24VDC from the battery, thru the diode, fuse, resistor, to the wire labelled "to F1".  This provides an initial flash to the field.  Once you let off the start switch, no more flash.  You could easily leave this out and use a manual flash as needed; or even connect a separate momentary contact switch in place of SW1A.  Engine running, no AC power?  Try a short flash.

[rl71459]

That is one nice old genset! Your refurbishing looks great so far.

Rob

[mobile_bob]

it would appear the field is ~120vdc, and is boosted by the compound transformer

its going to be interesting getting some reports as to what the various voltages are and how this thing functions under various loads

bob g

[veronikafth]

That is one nice old genset! Your refurbishing looks great so far.

Rob

Thanks Rob! It's a part time effort, so it's a bit slow going.  On lunch breaks at work I have been going into the shop and cleaning, blasting, painting things, as I don't have a blast cabinet at home. The generator housing does not fit into the blast cabinet so I have stopped that until I decide how I want to get that cleaned up. But I have the engine running now after cleaning the magneto breaker points. Video here:

http://www.youtube.com/watch?v=qYhKVk2wO0c

Notice the little pieces flying out all over.. those are little pieces of an evergreen shrub that this generator must have been sitting close to or something, because there are little pieces of it in the cooling fins. When I shut it down it smelled a bit like pine needles. How very Christmas-y!

Runs really well and has good compression. I'm just not really happy about the bits of rust I found inside the crankcase, but from sitting that's to be expected. The connecting rods have a little rust/pitting on them, and the tapered crankshaft bearing at the rear of the engine has etching from sitting in one position for so long. I may just replace the bearing cup (fairly easy) and hope it lasts for a while, because I'm not taking it apart right now.

I've cleaned and sealed the armature and the field poles with electrical varnish.. It's almost ready to go back together and be wired up for testing.

Veronika,

I agree with your electrical engineer friend.  Switch SW1A, contacts 2&3, is part of the start switch.  When engage the start switch, this provides 24VDC from the battery, thru the diode, fuse, resistor, to the wire labelled "to F1".  This provides an initial flash to the field.  Once you let off the start switch, no more flash.  You could easily leave this out and use a manual flash as needed; or even connect a separate momentary contact switch in place of SW1A.  Engine running, no AC power?  Try a short flash.

Oh this is a good idea, and easy to do...  I think I'll just put a push button momentary switch in there for now. I may not even need to flash the field anyway depending on how much residual magnetism there is after each run.

As soon as I get it set up I'll run some tests with a 240v compressor, space heaters,  and a 240v buzz box welder, and see how much the voltage boosts or drops. Then I'll hook up the el cheapo chinese AVR and rerun the tests and see the difference. I don't have a high quality AVR, so unless someone wants to send one to me I can't prove for sure that this is an indication of how an AVR would work in general, only how mine works.

V