Generator theory

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Jcabrera415

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I might be overthinking the topic but I'm kind of confused.
If I have 2 identical 3phase 120/208v generators and turn both of them on. What will my meter read if I meter from phase A to phase A from one generator to the other. ???

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Jcabrera415 said:
I might be overthinking the topic but I'm kind of confused.
If I have 2 identical 3phase 120/208v generators and turn both of them on. What will my meter read if I meter from phase A to phase A from one generator to the other. ???

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Hmm...not my forte..I really wanna say 0V.

Are these parallel or series?
 
Even though the generators are identical, are they synchronized? There is not enough information about the two generators.

The more out of phase each generator is with the other will affect the results.
 
ActionDave said:
There is all the information you need in the question.
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Well, the engineer in me says that there IS a chance that the two generators will turn on in a synchronized condition, even though they are not so regulated.

Realistically it will virtually never happen, or, if it happens, it won't last long.

Also, we don't know if the generators are floating or are referenced to Earth.
 
If the two generators are not at all connected together, meaning no connected phase conductors and no connected neutral, and also no _grounding_, then ActionDave has the answer; you have two things with no closed circuit, and thus no defined voltage between them. The measured voltage would depend upon random fluctuations, static charges, etc.

If the two generators share a common reference, say because both have grounded neutrals, then you should be able to measure a definite voltage.

If the two generators (with common reference) are both running at exactly the same frequency but are not synchronized, then you would measure an AC voltage with a random value of between 0 and 240V.

If the two generators (with common reference) are both running at slightly different frequencies, then you would measure a very slowly changing AC voltage, going from 0 to 240V and back.

If the two generators (with common reference) are both running in a synchronized fashion, then the voltage between corresponding phases on the two units would be 0V.

-Jon
 


And note carefully that even though the line to line voltage on each generator is 208V, the line to line from one generator to the other could be as high as 240.

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You can do the same thing with 2 batteries. Take 2 batteries and connect your meter from the positive of one to the negative of the other. Electricity wants to return to its source. Since the batteries are not connected you should read any voltage.
 
High impedance meter may register an unstable voltage due to capacitive effects. Low impedance meter shouldn't read any voltage.
 
Jcabrera415 said:
I might be overthinking the topic but I'm kind of confused.
If I have 2 identical 3phase 120/208v generators and turn both of them on. What will my meter read if I meter from phase A to phase A from one generator to the other. ???

Sent from my SM-G892U using Tapatalk
Click to expand...
Are the star points grounded?
 
winnie said:
If the two generators are not at all connected together, meaning no connected phase conductors and no connected neutral, and also no _grounding_, then ActionDave has the answer; you have two things with no closed circuit, and thus no defined voltage between them. The measured voltage would depend upon random fluctuations, static charges, etc.

If the two generators share a common reference, say because both have grounded neutrals, then you should be able to measure a definite voltage.

If the two generators (with common reference) are both running at exactly the same frequency but are not synchronized, then you would measure an AC voltage with a random value of between 0 and 240V.

If the two generators (with common reference) are both running at slightly different frequencies, then you would measure a very slowly changing AC voltage, going from 0 to 240V and back.

If the two generators (with common reference) are both running in a synchronized fashion, then the voltage between corresponding phases on the two units would be 0V.

-Jon
Click to expand...

so now ask, if they are not sync'd per phase, will you get a V diff on meter? and can you get amps if the meter was a load?

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Jcabrera415 said:
I might be overthinking the topic but I'm kind of confused.
If I have 2 identical 3phase 120/208v generators and turn both of them on. What will my meter read if I meter from phase A to phase A from one generator to the other. ???

Sent from my SM-G892U using Tapatalk
Click to expand...

Series connected three phase generators?

That will be the day.. . . :roll:

Anytime you attempt to come up with your scheme, and get something out of it, you will be disappointed.

Usable power source generated by electro-mechanical system based on your scheme is untenable "pie-in-the-sky, wishful thinking".

I gather, you are only curious what the meter would read. You will read some voltage alright but not enough to make out something usable.

The following may be more than what you need but it will mitigate your confusion.

Because mechanically driven, combustion engine prime mover generators are fraught with nuances that no one can predict.
Running two three phase generators in parallel as suggested by other posters is something I've never heard of because of synchronization issues caused by the above.

It is possible to run an array of generators but it will involve more than meets the eye.

Running combined generators to deliver power to distant location was developed by the Europeans in early 1889.
The most noted pioneer was a Swiss engineer Rene Thury. He connected combined generators running DC that were connected in series not parallel.

These generators operate on a constant current mode and delivered to consumer. At the time there were no solid state inverters using IGBTs to invert DC to AC. Today's application uses transformers to deliver power.
Toroid transformers are common for reduced weight and smaller footprint--they are expensive however.

So, at that time power was delivered in the DC format.

In a nutshell, you can synchronize three phase AC or single phase by starting off at DC.

This was the precursor to DC distribution in most part of the world. The Pacific Intertie yet holds the largest and longest DC distribution stretching from Oregon to Southern California.

China has in its planning stage to operate at twice the Pacific Intertie capacity.

State of Texas also has their own, but still on the drawing board.
 
Generators in parallel:

I worked on a five generator 'peaker' power plant. I asked one of the engineers how they manage to take an off line generator and get it on line and in phase. He told me that the generators are first connected to the grid like motors and they 'motor up' in phase. Once they get to near max rpm, they are gradually transferred to the prime movers and the rpm is brought up to the required amount and the 'motor' becomes a generator and is perfectly in phase. Granted, these were not IC prime movers. Steam for three, land based jet turbine for the other two.
 
Unless the generators have never been installed then it is a “safe bet” that the X0 (neutral) is bonded to ground. In that sense they are indeed connected together. If this is the case you could see anything from 0 to 240 volts.
 
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