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Generators & Electric Motors General Discussion

Total Harmonic Distortion of Portable Generators


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  #11  
Old 02-08-2018, 04:16:38 PM
GeneratorNewb GeneratorNewb is offline
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Default Re: Total Harmonic Distortion of Portable Generators

I intend on installing a 2 stage, variable speed 80% York furnace. But to the best of my knowledge, from an electrical perspective, it's identical to a high efficiency furnace, just without the secondary heat exchanger (someone correct me if I'm wrong).

Do you guys have any sort of advice of what type of generator I should buy. Like I said, I own a brand new Westinghouse wh7500e that has great reviews a few no reports of equipment failure but has a 9% thd and brush altenator. It would cost me an additional $500 to go to a Briggs and Stratton with a thd of less than 6% so I don't know if it's a worthwhile purchase. I just want to minimize my risk of damaging something.
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Old 02-08-2018, 05:25:27 PM
armandh armandh is offline
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Default Re: Total Harmonic Distortion of Portable Generators

oh fun

you may be able to remove the bond at the generator or not
a good background in electronics and the generator circuitry is necessary.
[some generators have flashing circuits that make this difficult]

yes the ground and neutral go to the same place in the main panel
BUT THEY SERVE TWO DIFFERENT FUNCTIONS.
the neutral caries the neutral load, the difference in 120V loads on the 240 legs
the earth ground keeps the generator frame at ground potential.
with the two also connected wrongly [for this use] at the generator
the ground also carries some of the neutral load
the voltage drop on the mis-combined neutral and ground wires
raises the generator frame above ground potential.
and on a dark and stormy night it might be just a slight tingle or fatal
you may be new to the forum, we prefer to see you become an old friend.
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Last edited by armandh; 02-08-2018 at 05:38:36 PM.
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  #13  
Old 02-08-2018, 07:35:27 PM
GeneratorNewb GeneratorNewb is offline
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Default Re: Total Harmonic Distortion of Portable Generators

Does it not make sense to purchase a portable generator unless it is an inverter generator for the safety of home electronics?
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Old 02-08-2018, 08:26:25 PM
Mikey NY Mikey NY is offline
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Default Re: Total Harmonic Distortion of Portable Generators

I own many generators and rarely need one to run my home. I am still a little perplexed with this new craze to have a whole house generator. How long is you power outage going to be. Mine are usually a few hours and rarely a few days. put in a wood stove instead. The only reason I could justify a whole house generator is if I had a basement that floods. And that could be run with a portable. Or maybe if you have elderly folks in the house that may need oxygen etc. I would never connect any of my electronic to ANY generator, properly connected or not. Electricity seems pretty simple, hot leg, neutral and ground. Nothing to it. NOT so, neutral bonding, grounding etc are very serious issues. Whatever you do, absolutely have it inspected by the nys electrical inspector. Don't take some local electricians word. file for the permit it may save your life.
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Old 02-08-2018, 08:33:53 PM
GeneratorNewb GeneratorNewb is offline
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Default Re: Total Harmonic Distortion of Portable Generators

I have no problem keeping tvs off etc but my chief concern is my furnace. I don't want a 9% thd generator to cause damage to the furnace or cause it to not operate. The house is relatively large so wood burning stove wouldn't suffice. Does it make sense to switch to a 6% thd generator or is it just a waste of money?
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Old 02-08-2018, 09:11:46 PM
armandh armandh is offline
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Default Re: Total Harmonic Distortion of Portable Generators

most furnaces don't give a hoot

but most furnaces were in order of operation
24V transformer
thermostat,
gas-valve [and built in pilot safety]
stack switch and blower motor,
warmth....

now days to get 80% efficient at a minimum
24V transformer
thermostat,
relay and draft motor / damper
bellows switches
glow coil ignition and flame sensor control box
stack switch and blower motor,
warmth....

more electronics coax every BTU into the house, 80% and up
leaving the furnace exhaust cool enough for plastic pipe

how the furnace gets along with the generator
depends more on the furnace than the generator.
ASK THE HVAC CONTRACTOR.

AND NO
inverter generators are not the answer
I refurbished a 1978 ONAN 6.5 KW NH for my daughters residence
even on wheels it is barely portable
NOTHING electronic save a battery charging circuit diode.
with a little TLC it will churn out the KWs
long after pacific rim screamer junk is recycled.

you will find here proponents of 70s American 1800 RPM generators
because they will happily chug along for weeks on end
while, in the same interval, the pacific rim junkerator has
launched internal parts out the aluminum casting

internet ratings not withstanding.
you can be sure if it is Westinghouse no longer applies
even [the current] ONAN put their name on and had to recall some cheap junk.
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Last edited by armandh; 02-09-2018 at 09:21:23 AM.
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Old 02-08-2018, 09:47:05 PM
DMeed DMeed is offline
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Default Re: Total Harmonic Distortion of Portable Generators

I suspect that 9% thd vs 6% thd is mostly marketing.

I also suspect that that 9% figure comes because the type of generator set (capacitor regulated) doesn't put out a perfect sine wave. It puts out a wave that is close to sine but distorted by 9%. (Thus the 9% Total Harmonic Distortion figure). The voltage is still 120 and the frequency is 60, just the exact waveform is distorted from a "perfect" sine wave. As far as 95% of the stuff in your house, it won't notice the difference. The stuff that does notice shouldn't be in critical applications, because power isn't perfect!

I personally wouldn't worry about it (I have a westinghouse 7500 set too). If it really bothers you, I'd be considering finding a used Onan JB set to replace it rather than anything from a box store. They would run 7.5Kw all day long for a year and run at 1800 rpm. This thread discusses onan waveforms https://www.smokstak.com/forum/showthread.php?t=120202 and AC THD. It links a few others too.

Also it would be _very_ interesting to research just exactly what the standard figures are for distortion on the sine wave that comes into your house from the power company after it's been through umpteen transformers, by how many big motors and industrial complexes with welders and other nasty power messer uppers, power factor corrected with capacitors, etc. Not to mention computer power supplies, cfc bulbs, led power supplies in your own home .

Can anyone speak to the THD% from the power company and how bad or good that gets??

This paper suggests:
https://www.researchgate.net/profile...CPowerLine.pdf

Application Class THD (%)
Sensitive Applications .
• Airports/Hospitals 3%
• Telecommunication Facilities . 3%
General Applications
• Office Buildings/Schools 5%
Dedicated Systems
• Factories 10%
Figure 5. IEEE 519 standards for total harmonic voltage distortion.

David (still learning) Meed

also might want to glance at this thread
https://www.smokstak.com/forum/showthread.php?t=111420

especially post 15 showing a jb waveform on a scope against ac power waveform
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  #18  
Old 02-08-2018, 10:13:36 PM
GeneratorNewb GeneratorNewb is offline
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Default Re: Total Harmonic Distortion of Portable Generators

Interesting, I won't waste money going from a 9% non-inverter generator to a 6% non-inverter generator. I had briefly considered the installation of an 11k natural gas standby but it's hard to swallow a $6k price tag for the very occasional power outage.

In your opinion, does it make sense to convert the Westinghouse wh7500e to natural gas? I know it results in a 10-20% reduction in power.
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Old 02-08-2018, 11:17:49 PM
Vanman Vanman is offline
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Default Re: Total Harmonic Distortion of Portable Generators

Imagine the "distortion" from a sine wave that is the output of a Modulated Square Wave inverter! They erroneously call it a modified sine wave, but that is pure false advertising. There is nothing sine wave about it except that it is AC. Yet, lots of stuff will run just fine with it...
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Old 02-08-2018, 11:42:33 PM
Wayne 440 Wayne 440 is online now
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Default Re: Total Harmonic Distortion of Portable Generators

Quote:
Originally Posted by GeneratorNewb View Post
...for the very occasional power outage.... does it make sense to convert the Westinghouse wh7500e to natural gas?...
You didn't ask me, but if it will get "very occasional" use, I wouldn't.
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