Generator Electrical Engineering Question

[Soundguy]

used to make a big difference to tv's and monitors.. but now not so much.. heck.. even a while back you got the ones that worked on 50-60cps.

soundguy

 

[mbohuntr]

This has been a very interesting thread, I learned a lot!! :thumbsup:

 

[dangier_VA]

Me Too!! Thanks to all that replied! Vast database of information and experience on this board. Keep up the great work!
David

 

[Redneck in training]

Exactly. If you ever been to a grid distribution center, the frequency fluctuates more or less, same for voltage.

Power distribution actually counts number of periods per in example a day and makes them the same every day. If the grid runs slower during the peak it will run proportionally faster during the light load to make it up. The difference is fraction of Hz.
Do you rmeber the old synchronious motor clock? they were prety much exact over long term but somewhat off during certain part of the day.

 

[mbohuntr]

I work at a power generating station, and I find it fascinating how the speed and phases are aligned to connect to the grid. Then there is power factor correction, and protective schemes to be considered. The subject seems to be endless. Tesla was a genius...

 

[Steve_Miller]

Then there is power factor correction, and protective schemes to be considered. The subject seems to be endless.

I don't like this at all, causes all sorts of weird and wonderful things that no one can prove when something happens to your equipment.

Steve

 

[dangier_VA]

Got a chance to put the generator back together and test run it on a load bank. Overall the results are pretty good.

No load---59 cycles---127.9/125.1/253 volts
5000 watt load---58.4 cycles---118.8/120.1/239.0
10000 watt load---57.3 cycles---117.6/118.4/236.2

I then went back and adjusted the rpm to check voltage at each load and got the following:

5000 watt load---58.8 cycles---121.9/123.2/246.1
10000 watt load---59.0 cycles---120.5/121.7/243.3

There is 1 volt difference in the combined voltage when I tried to maintain 59 cycles, where it is not there when I let the voltage (rpm) drift down under load. Not enough of an engineer to know what is causing that.

Although this is a 15,000 watt generator, it would not see anything in the 10,000 watt range. Doubt the tractor would support much above 12,000 watts either (L3130). Have a new APC 550 watt ups and it seemed to like it and went online. Have not checked it with the APC 1550 watts yet.

This generator is old, heavy, and seems built well. There is a flywheel affect with varying loads. The main bull gear in the speed increaser is 3" thick,14" in diameter, and is about 50 pounds. It rides through better than a Coleman 6500 watt gas generator I used a while ago. When loads started or stopped, the voltage fluctuated all over the place. The lights went bright and dim a lot. I like most old equipment over new-built to last!

All this is with the heads 180 degrees out. Oh, and with no bearing noise! Good for another 50 or so years....
Comments?
Thanks,
David

 

[Soundguy]

any way to up the governed rpm so frequency is correct?

soundguy

 

[luscsmith]

With all of this knowledge on board I have two questions.
How are all of the generators that are on the grid put and kept in phase?
What is RMS? Root means square, Root and square of what?

Many Many Thanks, Scott

 

[luscsmith]

One more thing, discussions like this are one of the reasons I do read TBN.

Scott

 

[dangier_VA]

Soundguy-I can up the rpm from the tractor to get 60 cycles. However the advice from Generac (thanks hr3), on the older generators was to let the cycles drift down a few cycles to get the voltage in a better range. At 60 cycles, I was in the 257 to 259 volt area. My no load was 253 volts this time at 59 cycles (within 10%, but still high too). This is the Niagara Power unit we discussed about 5 or so years ago.... made by Generac.
Thanks,
David

 

[Soundguy]

With all of this knowledge on board I have two questions.
How are all of the generators that are on the grid put and kept in phase?
What is RMS? Root means square, Root and square of what?

Many Many Thanks, Scott

rms is a way of measuring voltage. IE.. average, rms, peak, peak to peak.

think of rms as a way to compair to equivalent dc volts, and the work you can do.

( net exact.. but a good quickie answer without 6 pages of electrical theory )

soundguy

 

[Soundguy]

Soundguy-I can up the rpm from the tractor to get 60 cycles. However the advice from Generac (thanks hr3), on the older generators was to let the cycles drift down a few cycles to get the voltage in a better range. At 60 cycles, I was in the 257 to 259 volt area. My no load was 253 volts this time at 59 cycles (within 10%, but still high too). This is the Niagara Power unit we discussed about 5 or so years ago.... made by Generac.
Thanks,
David

wow.. that's rough.

I have a pto genset that can throw 60 cps and 239vac at the same time, under load...

actually makes cleaner power than my utility according to my graphing o scope meter with time comparison...

capacitve reg to boot...

soundguy

 

[Redneck in training]

With all of this knowledge on board I have two questions.
How are all of the generators that are on the grid put and kept in phase?
What is RMS? Root means square, Root and square of what?

Many Many Thanks, Scott

Simply speaking, the root-mean-squae (RMS) value of an alternating voltage is the quivalent d.c. voltage that can deliver the same amount of eregy to a resistive load.

All the generators are "phase locked" togeteher. It is the same principle as synchronious AC motor running at virtually constant speed regardless of the load. There is one "leader" generator in the system that maintains the frequency and the rest of generators are running in so called "droop" mode. If the grid slows down even a fraction of Hz the droop generators will increase their contribution to the grid to add more power and vice versa. In other words the droop generators are controling power not frequency.

 

[mbohuntr]

Agreed, RMS (root mean square) is a way of expressing the sine wave form of AC to a comparable DC value for power purposes. It is 70.7 percent of the peak voltage. It is what multimeters actually measure unless specifically set-up to measure peak. Wind mills are unable to generate at 60 hz, so the unstable AC is converted to DC,like any power supply. Then digitally reproduced into a AC waveform at 60 hz. Any store bought DC/AC inverter does the same thing, and a digital O-scope can actually see the stepping of the waveform and the output of the digital -analog converter reads like this.. 111111111100000000001111111111000000000011111111110000000000

The number of ones and zeros depends on the clock speed of the chip, but the cycles are 16 milliseconds. (60 hz.)

Sorry for the long winded trip down electrical/electronic theory lane, but I love this stuff.

 

[luscsmith]

I am not trying to change subject, would just like to learn.

"It is 70.7 percent of the peak voltage."

Does this percent increase with increase of frequency?

Scott

 

[BobRip]

I am not trying to change subject, would just like to learn.

"It is 70.7 percent of the peak voltage."

Does this percent increase with increase of frequency?

Scott

No. For a sinewave (and most are or close to it) it is 70.7%. It does change with the waveform shape. If it were a square wave it would be 100% of peak voltage.

 

[mbohuntr]

With all of this knowledge on board I have two questions.
How are all of the generators that are on the grid put and kept in phase?
What is RMS? Root means square, Root and square of what?

Many Many Thanks, Scott

Think of the grid as a giant nationwide electrical circuit. Some motors can also generate electricty by spinning their shafts... Here's the connection... A generator needs to be in sync with the grid, or else the grid which is much stronger than the generator will drive it instead causing damage to the turbine. Once connected, the electromagnetic field will keep it in sync.

 

[BobRip]

Think of the grid as a giant nationwide electrical circuit. Some motors can also generate electricty by spinning their shafts... Here's the connection... A generator needs to be in sync with the grid, or else the grid which is much stronger than the generator will drive it instead causing damage to the turbine. Once connected, the electromagnetic field will keep it in sync.

Right on. Basically they adjust the field of any individual generator to put out the power they want it to. Once they are synchronized they stay that way.

 

[Mock1]

Mbohunter. "the grid, which is much stronger than the generator will drive it"
and we now have a synchronous condenser, which is used for VAR support .
The story goes on...