flashing 3 phase generator 6

[holo]

I'm new to the forum.
I have a Kohler 15RMY62 208V 3 phase 15 KW generator that is producing 30 VAC (rms) at 1800 rpm.

The diodes and brushes have been replaced.

I disconnected the field windings from each other and they are 0.9 ohms each. The wiring has no visible signs of burning or discoloration.

I flashed the 4 pole rotor with a 12VDC battery thru the brushes when it was not running. No change.

Any help or advice would be most appreciated!

 

[Allodola]

I took apart each relay this weekend, carefully pulling the plastic covers (with board removed in shop)Several of the contacts had green copper oxidation which I sprayed with contact cleaner. Also, note the four are NOT identical. 3 are 12V D/C coils, but one "1CR" on my unit, is a high voltage AC coil with a "normal" coil resistance of 1700 ohms. (The D/C units have coil reistance of about 100 ohms)
Just FYI. I'm in the laborious stage of reverse engineering the board now. best.

 

[holo]

Oops, I have probably reversed them. Thanks for the info.

 

[Allodola]

Sure. Here's another lesson (for me), though odds are small it has anything to do with your "issues". When I initally checked the coils I measured inside the relay box, as I had the plastic covers off, to look for contact crud. The coils measured appropriately. BUT, when one (CC) still seemd dysfunctional, I went back and checked from the circuitboard traces (after scraping off plastic coating) and lo-and-behold, continuity was broken from one coil end through the board to the trace! No end to the way things can fail.

 

[waross]

Hi folks:
Sorry for the delay getting back, but I had a great weekend.
Re., Zig-Zag connection vs. Double Delta;
On one of the pictures that was posted of your generator, there was a diagram of the zig-zag connection for single phase.
This site has a diagram of a double delta connection.

http://www.friesen.com/manuals/generator_wiring_diagrams.asp

The site also has a chart crossing the metric numbering convention to NEMA numbering convention.

I have seen a lot of various problems with a lot of generators.
I have never seen a problem that could be solved by changing from DD to ZZ or ZZ to DD.
DD is symetrical, and ZZ is not symetrical, but in practice, I have not observed any difference.
ZZ was used for years by many major manufacturers, DD is now becoming more common.
It may at first appear intuitively that the side with the two windings may have greater voltage drop, but a vector addition of the voltage drop shows it to be equal to the single side.
The main difference I see is that on an old set, with damaged or missing wire marking, the ZZ may be changed from 1 Ph. to 3 Ph. or from 3 Ph. to 1 Ph. quicker and with less chance of mistake, than the DD.
With appologies to the EU folk, virtually all the sets in the NEMA world start with three phase star connections.
If a set arrived from the factory wired for 3 Ph. delta, it may be easier to convert to DD than to ZZ.
By easier, I refer to the number of connections that have to be opened and reconnected.
respectfully

 

[waross]

Hi again:
The relays are usually for automatic starting and motor protection. Although this is important, the relays seldom affect the generator.
The exception is on old sets that may have a "flashing" relay. A flashing relay will be interconnected to the Automatic Voltage Regulator.
respectfully

 

[Allodola]

Thanks for the info. In the Kohler Holo and I are working on, one of the relays is in fact set up to flash the coil with 12V, but perhaps more importantly, the others in the start up sequence are tied in with a "shut down relay" which will disable the Voltage regulator. Of course if the SDR itself is dysfunctinal it may not provide its over voltage and other protective functions, allowing vr board chips to be damaged. I think also that increasing contact resistance and or intermitant contact/arcing might be generating voltage spikes from the relay that are capable of getting into the VR. Things are so interconnected that it would be hard, though certainly possible, to get the engine up and running AND the VR circuit properly functioning without the 5 control relays and the thermistor type "time out" switch (which has multiple functions) in working action. It's not clear it's a particularly good system.

 

[waross]

Hello holo and Allodola;
I am sorry for the delay, I've been short of time the last couple of days.
Allodola has just supplied the missing piece of the puzzle.
I am not surprised to see 30 volts out if the relay is flashing the field with 12 volts.
For some reason, your flashing relay is not transfering control to the Automatic voltage regulator.
What you are refering to as the shutdown relay is probably an AVR control relay.
In many of the older sets the AVR did not have an "Under Frequency Roll Off" feature. (UFRO)
Without the UFRO feature, the regulators would fail in a matter of a few minutes if the engine was operated at reduced speed.
It was recomended on many sets that the voltage regulator not be turned on until the engine was up to speed and that the voltage regulator be turned off before stopping the engine.
A shut-down relay connected to the AVR would not be unexpected on an old machine. The shutdown relay may be frequency dependent. if an old capacitor has failed or is failing the relay may not be functioning properly.
Note: I say may. There is not a lot of standardization from one make to another on the old generators in that size range.
AVRs with UFRO usually have a setting for 50 Hz. or 60 Hz.
Often it is jumper selectable.
I hope this helps.
respectfully

 

[Allodola]

Just an update on my experiences. Finally gave up trying to repair my rat urine damaged VR board. Did replace several relays and sockets on the seperate "buss" board with parts from Mouser. Found a helpful chap named Dennis at "ASAP" (

http://www.partsfortechs.com)

who supplied a simple but rugged aftermarket VR (208-240 in for up to 120V DC out to field) for about 300$ total. Gen Set now works fine. It does NOT have built in over voltage protection, and I am debating adding an external relay to the input of the VR board.
Also pondering the necessity of a Propane leak detector in the housing containg the Gen set, electronics and 20 year old 4 cylinder LP Wisonsin engine. Any thoughts on this?
Allodola

 

[holo]

Hi Allodola,
I have also delt with ASAP. They are very helpful and their original Kohler parts are cheaper than the dealers.

Instead of using an overvoltage relay, could you use an MOV?

http://www.digikey.com

has them for cheap.

 

[Allodola]

Hi Holo- MOV's and the like are worth considering, but they short when over volts, and even well fused I am reluctant to short out my V7-V8 winding! There are some commercial products for 35-100 dollars that have variable voltage and timing adjusts that throw a SPDT relay when sensing over voltage,that I could use to open the field winding or even turn off the engine. In the ORIGINAL iteration of my Kohler there was an overvolt sensor tied into the "SDR" shut down relay on the Voltage Reg board, but this did not exist in the (Kohler supplied) "up dated" VR that was in the set when I got it and eventually died. The newest aftermarket VR seems quite hardy and well made, but I like the idea of not toasting my well pump just when I need it most...
Am certainly open to suggestions of an easy reliable protection approach. Ciao