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Here is a good presentation that goes into surge protection and harmonic distortion. Two different things, but both should be addressed in our modern world of electronics.

As explained, a harmonic is a component of a periodic wave with a frequency that is an integer multiple of the fundamental frequency. Whereas a surge (or transient) is a high rising voltage condition on one or more phases lasting 2 milliseconds or less.

A surge suppressor cannot correct THD because it doesn't even know it exists. A SPD works in a completely different (higher) voltage range than line voltage.

Article 230.67 of the 2020 NEC requires all services supplying dwelling units to be provided with a surge protective device (SPD), as an integral part of the equipment or located immediately adjacent. The SPD must be a Type 1 or Type 2 SPD. This requirement also applies to residential service equipment being replaced.
 

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The grid does indeed have low THD ... it puts out "clean water" (under high pressure), as the grid supplier works to keep it that way through constant monitoring at many points.

One problem the grid has is that commercial/industrial sites do throw THD back out on the grid, and cause trouble in the grid "ocean" for other customers downstream or nearby those sites. This is why the grid will punish these offending sites with chargeback fees, and is also why those sites have EE's & specialized equipment to counter the THD levels. If it is a thing on a grid, and in a commercial building's "lake", then it's a thing in our smaller "pond" (the scale changed, but not the problem).

The power comes into our pond, circulates (and some is consumed), and then returns to the source (the grid). The grid (or your gen) keeps the pressure high, so that anything consumed is replaced, but it still circulates.

Is the grid affected by our homes? A very good question, and I don't know how the grid is protected from each of us in terms of THD ... one googled explanation is:

"The proliferation of nonlinear loads and the increasing penetration of distributed energy resources in medium-voltage (MV) and low-voltage (LV) distribution grids make it more difficult to maintain the power quality levels in residential electrical grids, especially in the case of weak grids. Most household appliances contain a conventional power factor corrector (PFC) rectifier, which maximizes the load power factor (PF) but does not contribute to the regulation of the voltage total harmonic distortion (THD V ) in residential electrical grids."

I'd take this to mean the grid is good/bad in your area ... warrants more research & reading.

The other problem the grid has is "surges", and there isn't anything the grid folks can do about those ... your clean water from the grid comes with the occasional free and big surge. Inside your house, more free micro-surges are happening, to the tune of dozens, hundreds, or more. While we can block surges, I don't see how we can block THD, when almost every device in your house is contributing to it.

Linear or non-linear loads? I'll let google answer that:

"with linear loads, the voltage and the current sine waves are going to look the same. Current that is drawn from a regular motor or a light can look like the clean voltage, even if it is not in phase or a little bit leading or lagging—it depends on the power factor of the load."
"with nonlinear loads, the current is not going to look like the voltage. The more drives or the more distorted current we add—the more voltage distortion we have on the system."

And finally ...

"Times have changed. Harmonic problems are now common in not only industrial applications but in commercial buildings as well. This is due primarily to new power conversion technologies, such as the Switch-mode Power Supply (SMPS), which can be found in virtually every power electronic device (computers, servers, monitors, printers, photocopiers, telecom systems, broadcasting equipment, banking machines, etc.). The SMPS is an excellent power supply, but it is also a highly non-linear load. Their proliferation has made them a substantial portion of the total load in most commercial buildings."

So there's the kicker ... the (non-linear load) SMPS is both good and bad! It's good for the device behind it ... it's bad for any other device in the pond, unless they also have an SMPS in front of them. I have dozens, if not hundreds of SMPS "wall-warts" in operation, just walking around my house and doing a quick count. Each one is throwing THD back out on the wiring, by definition of how it works. If I had just one, I'd agree ... nothing to see, move along. But, a dozen ... a hundred? I can't do anything about these devices nor the THD, so I just let them duke it out. After 5 years, I'm still waiting for things to blow up, because THD should've been handled differently.

So, my dirty gen adds dirty water to my already dirty pond, and each SMPS is eating that dirty water, cleaning it up, and presenting clean water to the device behind it, and throwing dirty water back out. Maybe it's possible that I've lost a wall-wart or three, over the 5 years I've operated dirty gens, but I haven't lost a TV or other "sensitive" device behind those wall-warts, or that has built-in power protection. Each wall-wart is ... $10 or so. I might be one of the few that puts 1000/hrs/yr of (in my case, dirty) water into the pond from a gen.

Whereas, almost anyone can point to a single surge event (lightning, grid) and show several devices that fried right after that surge. Nobody can point to a 1000 micro-surges, which happen daily. Yet, a few SPD's later, I've protected against surges from without, and micro-surges from within. I just can't do that with THD, given all the devices in my pond, and given that there are no equivalent THD SPD's (TPD's?). And a $5k low-THD gen? If our use-case is home backup power, that's clean water for 10 hours per year (insert your own number). If the use-case is rock-band sound/audio mobile power generation, at 50 events per year, 8 hours each ... yeah, I'd throw a Honda at it, and hopefully the business income would pay for it. Food truck? Another great Honda use-case ...

I'm not sure ANYONE can point at a fried/dead device and definitively say THD did that. Maybe device manufacturers will one day add autopsy circuits to these things. Tilt this way for surge, and that way for THD.

I couldn't come up with a better metaphor than ponds/lakes/oceans, and perhaps someone will ...

You could argue the total number of electrons with me ... I can't grasp the numbers, where trillions of the little devils are running around in the system. I just see plenty of research that says that our house is a system (in a chain of small to big systems), and things in our house (like an SMPS) actually causes THD themselves (not just a gen causing/not-causing THD), and I extrapolate from there. Then I look for something practical that I can do, right now; SPD's were very practical.
 

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At the end of the day we have gone years with the conventional (non-inverter) generators with little or no reports or damage to devices and all this talk has come about since the invention of the inverter generator.... Plus manufactures wouldnt be allowed to sell generators if they caused damage to devices..

Should be fine for 50Hz.

My generator unloaded, goes to 62-63Hz. So far, my UPSs seems to tolerate it. But that's only for a short time. Once I've got most of the load up and running, the gen droops down to around 60-61Hz... totally within spec.
Just did the monthly run on my generator and the hertz goes anywhere from 49 - 53 and sometimes a 54.
 

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I know this is a generator fourm, and we like to debate stuff like this, but outside of these types of fourms nobody knows what THD is and nobody cares. I will never argue having a low THD unit is bad, but unless your running a boatload of servers off generator power 24/7, rest easy. The 3hrs every other year you actually need your generator isn't going to wreck your $300 TV.

Sent from my SM-G973W using Tapatalk
 

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At the end of the day we have gone years with the conventional (non-inverter) generators with little or no reports or damage to devices and all this talk has come about since the invention of the inverter generator.... Plus manufactures wouldnt be allowed to sell generators if they caused damage to devices..
I agree... though, with caution. It's a calculated risk. Oftentimes, you need backup power more than being OC about knowing that something might break.

I don't deny that elevated THD is bad for electronics.... like sugar drinks and soda is to the human body. But does it mean that drinking a glass of sweet beverage every now and then will affect your lifespan significantly?

Yeah, bad example I bet. I love Coke. lol

Just did the monthly run on my generator and the hertz goes anywhere from 49 - 53 and sometimes a 54.
Does it swing like that with or without load?
 

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Plus manufactures wouldnt be allowed to sell generators if they caused damage to devices..
It may be different it in the UK, but on this side of the pond it is buyer beware. Most of the manufacturers put warnings in their literature, or on their website (sometimes in the Q&A or FAQ sections) about using their >5% THD gens with sensitive electronics. If you can't find it there, call customer support and ask about it.
 

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Does it swing like that with or without load?
it does with or without, but swings less with a load, but thats only with about a 400watt load and its a 2600watt gen. So the hz might swing less with a heavier load maybe? The volts are pretty stable with a 400watt load as it hovers between 226-230v.. But Ive noticed that my UPS only corrects the voltage but not the Hertz, but I have the voltage set on the UPS at 240 not 230 and thats like 10volts out, so the UPS will correct that. But the hertz are not that far off the correct value.

Ah Ive just had a look and the UPS corrects the Hertz if it goes below 45 or above 55, so the generator is just keeping the Hertz in range.
 

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I have no idea how the UPS increases the volts to 240 from the generators round abouts 230v without using battery power, because it doesnt click over to battery mode and the UPS inverter can't increase the voltage surely?
 

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I have no idea how the UPS increases the volts to 240 from the generators round abouts 230v without using battery power, because it doesnt click over to battery mode and the UPS inverter can't increase the voltage surely?

For small corrections like that a "Line Interactive" UPS uses a multi tap transformer called an autoformer. With the use of various relays inside it senses the voltage it will switch to a different tap on the autoformer to either step up or step down the incoming voltage to keep within a given normal range. However if the voltage moves beyond what the autoformer is capable of adjusting to then it will switch to battery power.


In a double conversion UPS the onboard battery charger charges the batteries all the time, and the loads are run by the internal inverter. Such a UPS for simplicity/reliability will have a large inductor and capacitor at its input to the charger called an LC Filter to handle any high THD and then rectify it to DC. Simple circuit and it works, but it sacrifices voltage/frequency range

Take the Triplite SU2200XLCD for example. The specs say a "nominal 100V AC; 110V AC; 120V AC; 127V AC" and either 50/60hz. Nominal 120V means 108-132VAC and either 50/60hz.

On a Cyberpower 1500PFCLCD Line Interactive, constant voltage fluctuations and speed droops on a generator cause it to switch to battery power because the sensing IC circuit for choosing the different autoformer taps/switching to battery power is getting too much noise from the high THD it cannot perform its function so it defaults to battery power. Eventually this unit will fail on generator power either because the IC sensing circuit fails, relay fails from too many cycles, and/or overheating of components not designed to handle it.



I suppose we should discuss PFC circuitry a bit as depending on the design topology, it can either tolerate high THD very well or be completely crippled by it.

Passive PFC: In SMPS is simply a large capacitor/inductor. Its referred to as the Pi filter. Cap is wired across the line/neutral, and the inductor is in series with the hot. Called an LC filter. It is then rectified to DC to be used by the switchmode portion of the PSU. The main advantages are simplicity, reliability and ruggedness, insensitivity to noise and surges, no generation of high-frequency electromagnetic interface (EMI), and no high-frequency switching losses. The main disadvantage is a narrow frequency/voltage operating range, and in greater than 100 watt power applications, those LC components get large and heavy.

***IOTA Engineering makes their DLS chargers/PSUs with this type of topology. I use their 120VAC to 12VDC 90A chargers to replenish my inverter battery bank. They handle high THD of a generator no problem, and the main limitation is the input voltage range can only be between 108-132VAC and frequency between 47-63hz. They have 240VAC variants with the same range too. ***If it were an Active PFC, then you would see specs like 50/60hz 100-240VAC input.

Active PFC: This circuitry use active electronics circuits, which contain devices like MOSFETs, BJTs, and IGBTs. There are so many topologies I could make a novel on it. The two main types are boost (increasing the line voltage on the output) and Buck (decreasing the voltage) on the output. Basically they use an integrated circuit microcontroller to run the MOSFETS turning them on/off really fast in a circuit with an inductor. This precisely controls the current/voltage output.

There is still basic passive filtering before the DC to DC Buck/Boost Stage I discussed above, but it is not made to be as robust to correct power factor since that work is being on by the IC circuit. If enough harmonic distortion enters that PSU, it will heat up those passive filtering components adversely, and potentially cause that IC circuit to malfunction/fail. When that happens any loads connected to it when that IC circuit lets go, then you got cascading damage that costs BIG $$$$.


This should explain why some devices handle THD well and others over time fail. It is a factor in failures on portable generator power, but it is Surge that kills more devices than THD. Its important to look at the specs of devices, and again low THD generators are far less likley to cause all this crap we are discussing. Very informative technical knowledge, but crap to the commoner not familiar with the science.

Cheers!
 

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I have no idea how the UPS increases the volts to 240 from the generators round abouts 230v without using battery power, because it doesnt click over to battery mode and the UPS inverter can't increase the voltage surely?
For small corrections like that a "Line Interactive" UPS uses a multi tap transformer called an autoformer. With the use of various relays inside it senses the voltage it will switch to a different tap on the autoformer to either step up or step down the incoming voltage to keep within a given normal range. However if the voltage moves beyond what the autoformer is capable of adjusting to then it will switch to battery power.
Yepp... Line interactive, aka AVR/AVS in some literature. To add, It provides voltage boost and trim so the UPS can maintain nominal voltage output over minor over- and under-voltage at the input. This helps a lot in extending the life of the UPS battery as this avoids unnecessary switching to battery backup.
 

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I would say that was impossible thing todo, adding more voltage.
Mine is a Online UPS, but its setup as a Line interactive UPS just because it uses less power:) and only acts as a Online UPS when the voltage goes over/under 5%
 

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Here's my Onan 4.0 BF 4000 watt generator made in 1977. It's my backup and the first generator I used my new meter on. If I'm reading the meter correctly, the THD shows 6.0 at about 2800 watts. HZ was 60.33. Not as good as an Inverter gen, but not too bad for $100.


View attachment 13684 View attachment 13685
Looks like a generator typically installed into an RV.
 

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Onan generators especially from that era are some of the best built generators you can find. Sadly the stuff they push out these days is more crap than ever. 6% at almost 3/4 load is not bad at all. I can't imagine it rising up much further closer to full load.

Keep that dinosaur rolling, very few generators made these days comes close to that build quality.
 

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I helped the seller pull it out of a 5th wheel RV. It's surprising how little they cost. Most folks want the newer ones. This one was designed to put out 4000 watts continuously at 1800 rpm. Nest step is to convert it to natural gas.
 

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the THD shows 6.0 at about 2800 watts. HZ was 60.33. Not as good as an Inverter gen, but not too bad for $100.
Wow, that's a real bargain at $100! Not bad at 6% THD either. 👏

Nest step is to convert it to natural gas.
I would think that it should be fairly easy to do that.
 

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I would say that was impossible thing todo, adding more voltage.
Mine is a Online UPS, but its setup as a Line interactive UPS just because it uses less power:) and only acts as a Online UPS when the voltage goes over/under 5%
The AVR in an interactive UPS uses a multi-tap autotransformer. The UPS logic decides when to boost or trim the voltage so the load only gets to see nominal or near-nominal voltage coming out of the UPS. An autotransformer pretty much is a combination of both a step-up and step-down transformer in a single package. There are other distinct differences which are not relevant here.

Here's a schematic of a typical autotransformer. This design has one level for boost and one level for trim. Some UPSs or dedicated AVRs (non-UPS) have two levels for both boost and trim for a more granular voltage correction.

If the line voltage coming into the UPS is higher or lower than what the AVR can correct, it goes into battery backup mode.

Slope Line Font Parallel Rectangle
 
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