Generator Electrical Engineering Question

[dangier_VA]

BobRip-"If the two generators are in phase (0 degrees) then the voltages track each other. i.e. they are both positive at the same time and both negative at the times time. If you put these generators in series and they are at 0 degrees then the voltage between the two will read zero since they are at the same volts. This is like taking two D cell batteries and put the negatives together. If they are both new, then you will read very close to zero volts between the two positive terminals. What you want is 180 degrees out of phase. So when one is negative then the other is positive. This way the voltages add and you get 240 volts between the two hot legs of the generator. This is like two D cell batteries with the negative of one connected to the positive of the other. The unconnected terminals will have about 3 volts between them."

My thoughts exactly. That is why I was concerned about the armatures being "right on" each other. They are either 180 degrees from each other or 0 degrees at this point. When it was running yesterday, it was producing the high voltages under a 5000 watt load at 60 Cycles. I think I need to assume that they are at 180 degrees since they were generating power for the 250 volt load. Otherwise they would not support the load. When I get the bearings right, I plan to have the unit "scoped" to verify the sine wave. I stopped at the 5000 watt load as my old 2n would not carry the next 5000 watt load bank. I have an old heat pump indoor unit with three switchable 5000 watt heating coils and fan used for load testing and emergency heat if needed.
David

 

[Rob-D]

If your two waveforms are not in phase, your voltage and power will suffer. I would talk to a generac tech and get their input.

I Think this is about right and good advice too.

Rob

 

[firedog]

Because that is incorrect.

I dont understand exactally how it all works either, but 3-phase power lines running down the road have the 3 main wires (each phase) and then the ground. If you have 3 phase service, it requires 3 transformers.

Out here in the rural sticks, we only have single phase power. 1 Hot wire, and then the ground (neutral). I only have those two wires comming to my house, and I only have 1 transformer, but still have 240v and not the 120 as you suggest anly 1 phase would be.

True, a single phase transformer is feeding your home. 240 volts with a center grounding tap, That gives you 120v either side of the ground and 240v across the lines.

 

[CubMon]

True, a single phase transformer is feeding your home. 240 volts with a center grounding tap, That gives you 120v either side of the ground and 240v across the lines.

Yep, and if the 'neutral' has a loose connection or intermittent connection, each leg of that two leg (120VAC) voltage will increase above neutral as the other will decrease proportionately.

 

[Jimbrown]

Basic alternating current 101.

the generators produces a wave that goes positive and negative at 60cycles per second. The peak voltage is higher than the RMS voltage. Useful voltage is measured as .707 of peak this is RMS and where you would normally have your 120v.

If the two generator heads are out of phase by just a few degrees this will cause the period of peak voltage to last longer and thus the RMS will also increase. I ain't a whiz at drawing but in my picture the second generator is the red line and you can see how the peak voltage would last longer and thus cause the RMS to be higher. In three phase current the three peaks would be spaced exactly 120 degrees apart and thus cause the RMS to be considerably higher. You have the two heads slightly out of phase. Believe it or not if they were not geared together but running via separate engines the would synchronize their self.

 

[Transit]

Just thought of something else-We have a 1500 watt ups for the computer, router, and satellite equipment. The last January's power outage, the ups did not like the power from the generator and would not switch over. Had not had an extended power outage before and didn't notice that. We have extended capacity batteries and they last a day or two.
In checking the 60 cps, my meter is reading a solid 60 cps on utility power. I can run the meter all around and zero in at 60 cps easily with the rpm adjustment, so I think the meter is close enough.

We have all kinds of UPS at work [90 at my last count, 50 more to find], 120, 120/240 volt, single phase 600 va to 6,000 va, 3 phase 120/208/240 volt, 10,000 to 250,000 va with 208, 240, 480 volt 3 phase input from the utility; with 2,000+ Hp generators and all are sensitive to ground and neutral miswriting. Gas engines are the worse with spark noise confusing the UPS.:confused2:

 

[jenkinsph]

Basic alternating current 101.

the generators produces a wave that goes positive and negative at 60cycles per second. The peak voltage is higher than the RMS voltage. Useful voltage is measured as .707 of peak this is RMS and where you would normally have your 120v.

If the two generator heads are out of phase by just a few degrees this will cause the period of peak voltage to last longer and thus the RMS will also increase. I ain't a whiz at drawing but in my picture the second generator is the red line and you can see how the peak voltage would last longer and thus cause the RMS to be higher. In three phase current the three peaks would be spaced exactly 120 degrees apart and thus cause the RMS to be considerably higher. You have the two heads slightly out of phase. Believe it or not if they were not geared together but running via separate engines the would synchronize their self.

Not arguing, just interested in this last sentence, I know that the small Honda gensets such as the 2000 and 3000 inverter units tie the outputs together when you chain them together. Always thought that odd is this the same priciple?

 

[Lineman North Florida]

Because that is incorrect.

I dont understand exactally how it all works either, but 3-phase power lines running down the road have the 3 main wires (each phase) and then the ground. If you have 3 phase service, it requires 3 transformers.

Out here in the rural sticks, we only have single phase power. 1 Hot wire, and then the ground (neutral). I only have those two wires comming to my house, and I only have 1 transformer, but still have 240v and not the 120 as you suggest anly 1 phase would be.

You don't have to have 3 transformers to have a 3 phase service, 2 transformers can be banked together and wired Delta on the secondary side to give you 120/240 out of the lighting pot and 208 out of the power pot, these are used often for smaller 3 phase load such as jiffy stores or mini marts, these delta wired banks also allow you to feed a single phase customer off of them as well.

 

[jenkinsph]

No, the peak would not last longer. Across a common load, the voltages would add vectorially. This is why I brought up the 208 volt 3 phase comment as an example.



In parallel, yes. In series, no. Diesel generators that are put on-line for additional increases in power are often done this way. However, you had better make sure that they are almost in phase when they are combined.

We use to use KVAR meters for the very purpose of bringing motors on line. The older drilling rigs used EMD (train engines) and 1.5 megawatt generators and were kind of scary to add on line, had to catch the dial pointers at 12 o'clock and slam those 2500 amp breakers on by hand.

 

[Craig Clayton]

Sir
I have been reading the comments about the generator. I would let this one pass into history. My concern is if it is tied to a residence how good is the voltage regulation going to be. Fuel consumpation from a tractor is going to be high for the load. There would be no savings if you blew out our frig , furnace ,etc. I posted an article about Vehicle mounted generators and this could be used in that way to supply cord connected devices at 120 VAC.
Craig Clayton