Adjusting voltage on genset - The Combine Forum
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post #1 of 16 (permalink) Old 10-14-2019, 02:15 PM Thread Starter
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Adjusting voltage on genset

I have a genset that is putting out 120/208 volts. I am using single phase aeration fans off this genset and using 2 of the 3 phase legs to supply the fan with 208 volts. Trying to run 3 fans at a time each using a different 2 legs of the 3 phase to help balance the generator out.

I also use the 120 volt from the generator for providing power to a frost fighter heater.

Been using welder plugs and extension cords and they seem to fail often. Part of the problem is that on the 7.5 hp fans the amperage goes up when the voltage drops to 208 instead of the 240 that you would get on a standard yard service. The fan motors are all rated 208-230 volts.

So I am wondering if I adjust the voltage regulator on my generator so it puts out say 132/228 volts from the genset, would the 132 volts cause any problems running the frost fighter heater or any other 120 volt loads that are now getting 132 volts? I am thinking that the 228 volts to my aeration fans would be a good thing for them and that is the primary use of this genset.

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post #2 of 16 (permalink) Old 10-14-2019, 04:13 PM
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Hard to say what the heater controls will do, probably be ok as they are pretty basic. A +/-5% voltage variation for electrical equipment is basic design standards but you are talking 10% and I have seen large power transformers (like 500 kva) burn up underground at the potash mines when the underground shuts down operation on a weekend and voltage goes up from 4160 to say 4500v. It's not so much the higher voltage causes voltage to punch through insulation or flash over, rather the iron in the transformer core saturated and overheats (can literally catch fire) - even with no load on transformer. Now little control transformers may be fine, or they may be made such that they are more sensitive to voltage variations. That i don't know. Just some theory.
The voltage regulator on the genset came to mind too as something that would be operating outside a normal bandwidth but frankly they need to be built to handle generator voltages that can be all over the place for various reasons so really shouldn't be an issue.

Just so you know, here is an example of a voltage regulator I have seen used on a few units. Not expensive if it does crap out and most shops will have one on hand or a couple days away.

Https://www.americasgenerators.com/N...Regulator.aspx


Thinking a little more, your generator stator core is not much different in theory to a transformer core so perhaps best to stay at 5% over 120v. A saturated iron core starts creating a distorted sine wave so a guy would really need a scope meter to see how high you can go till problems start showing up. I would think a scope meter would be the best way to know how much is too much.


Last edited by kenmb; 10-14-2019 at 04:15 PM.
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post #3 of 16 (permalink) Old 10-16-2019, 09:21 PM
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Your genset is configured 120/208 (parallel star) and if it is a 12 lead genset it can be changed to 120/240 to what is called Series Delta

Hi-Leg. Electrician should be able to do this or a good Genset mechanic.

However with this Hi-Leg you have to be very careful on how your distribution is setup as you will have 2 legs that will be 120v to neutral and on the third leg (Hi-Leg) it will be 208v to neutral. As a note you will not be able to pull the amperage on the 120v legs like you can with the parallel star 120/208.
The max I would push out on single phase would be 130 volts unless your extension cords are lighter gauge and fairly long,then voltage drop would become a factor to the frostfighter and you can push it a bit higher.
We upgraded from 125kw to 200kw this summer and left the genset 120/208 parallel,but I pushed the AVR (regulator) up to 245 volts (no 120 volt equipment hooked to gen) as last year on the smaller genset the highest I could go was 218volt and some of the fans in warmer weather shutdown from overheat trip. They run cooler and draw less amps now.


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post #4 of 16 (permalink) Old 10-16-2019, 10:25 PM
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You need a Phase converter to use single Phase motors off a 3 Phase Genset. Talk to an electrician, I know enough to leave it alone. I wired houses when I was younger with my brother who is an electrician.

Leo

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post #5 of 16 (permalink) Old 10-16-2019, 11:52 PM
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You need a Phase converter to use single Phase motors off a 3 Phase Genset. Talk to an electrician, I know enough to leave it alone. I wired houses when I was younger with my brother who is an electrician.
That would be the other way around. 3ph gen will run anything. If you have only single phase gen or high line power, you need phase convertor or VFD to run a 3ph motor.


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post #6 of 16 (permalink) Old 10-17-2019, 12:17 AM
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You could be right

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post #7 of 16 (permalink) Old 10-17-2019, 12:42 AM Thread Starter
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If on the 120/208 generator configuration, I turned up the AVR to get 240 to 245 volts, could I find a used transformer to bring that down to 120 volts? I think the frost fighters use about 13 amps at 120 volts and I would like to run 2 of them, so not a real big load on the 120v.

Not sure if the transformers need exactly 240 volts input to get 120 volts out or if 245 volts into the transformer gives you 120 volts out?
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post #8 of 16 (permalink) Old 10-17-2019, 09:58 AM
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Transformers are strictly a ratio. If 240:120v then it is 2:1 ratio and you can figure your voltage based on that ratio. That is a good thought on reconnecting the generator, a lot of small units can be reconnected from 1 Ph to 3 Ph. There would be a connection drawing on the generator somewhere, usually on the inside of the cover you take off to access the generator connections. You will loose some current (kw) capability going to 1 Ph like maybe a 65% rated output instead of the kw output rated at 3 Ph but may be a good solution.

I would be concerned with over excitation. Couldn't find a short answer on it but there are enough engineering papers if you search the term "generator over excitation" which is what you would be doing. Heating in the stator and rotor are common concerns. A small unit may be forgiving, and the field is over excited every time a load hits it. But I notice Phil mentions his motors were tripping on overtemp with the generator over excited which could be related to what I posted earlier about the sine wave being distorted. Think about why fans were going out on over temp. What are the chances the motor was running a fan right at the motor full load amps rating? Not very likely, as the bin is filled the fan pushes less air and so less load. And if a 10% voltage increase boosts amps 3% what are the chances that fan motor is now at its full load amp rating causing the motor trigger over temp protection. Not likely. Is it possible the over temp was the result of a poor waveform from an over excited generator? You would need to see the waveform to be sure.


You can experiment and see what happens, just understand the symptoms and cause/effects you need to be watching for.
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post #9 of 16 (permalink) Old 10-17-2019, 10:06 AM
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Some transformers are multitap, dependent on size or KVA rating. Hammond C1F005XES should do the trick. Weatherproof and good for 41 amps at 120 volts. Automation Direct $557.00 USD

Hammond general purpose transformer, encapsulated core, 5 kVA, 1-phase, 190/200/208/220/240 or 380/400/416/440/480 VAC primary, 120/240 VAC secondary, 50/60 Hz, electrostatic shield, NEMA 3R, wall mount.


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post #10 of 16 (permalink) Old 10-17-2019, 10:27 AM
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Hi kenmb, hence why we went bigger and a bit newer genset for this year, 200kw vs the 125kw. The 200 has electronic fuel control and runs at a steady 60Hz vs the 125kw which was all over the map even after opening up the pump.......

Have
11 drying bins with 10hp 3ph (5 added this year along with the genset and distribution)

4 drying bins with 7.5hp 3ph
4 storage bins 10hp 3ph
3 storage bin 10hp single phase, to be upgraded as they are an ugly amp draw if not all running to balance the load.
With all fans running 525 amps load.

Cannot stress enough if you are looking at a genset go a bit bigger than what you require as we are already looking at 5 more bins for next year and another boiler.
Also as a note as voltage goes up, amperage comes down. 10hp3ph last year at 218volts were drawing 26-27 amps, this year at 240 volts a comfortable 22-23 amps and no temperature shut downs.



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Last edited by Feeder House Phil; 10-17-2019 at 10:35 AM.
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