Harmful effect on power systems from using big VFDs or tons of computers at home

[AC_Hacker]

Originally Posted by ICanHas

An old small industrial VFD or new bare-minimum built CHINA MADE VFD eBay devoid of all...

I don't know why this thread is in the Geothermal & Heat Pump area of the Forum. It has nothing to do with any of these things, or with any of the innovative and worthwhile projects and efforts that are here.

It is not project oriented, and is really just an editorial or opinion piece.

I think that this opinion thread should be re-located to the Billiards Room where it belongs.

-AC

[ICanHas]

Originally Posted by AC_Hacker

I don't know why this thread is in the Geothermal & Heat Pump area of the Forum. It has nothing to do with any of these things, or with any of the innovative and worthwhile projects and efforts that are here.

It is not project oriented, and is really just an editorial or opinion piece.
-AC

I disagree. There are YouTube videos about using surplus industrial VFD at home and discussions advocating it. I think the creator of video has good intentions, yet unaware of harmful effects when more people start doing it.

The air conditioner compressor is the largest motor that gets any significant number of hours at homes. Discussions pertaining to VFD that maybe used for this purpose is a pertinent topic. Things that are harmless when kept to a drop in a bucket don't stay that way when it becomes more concentrated.

Increased losses in the distribution system is wasted energy.

Products that induce power quality problems and require intervention by energy provider are social expenses. Straight through VFD has the lowest manufacturing cost and a fairly high device level efficiency. When some jerk hooks up a industrial 2.4kW 5kVA VFD at home on a 30kVA residential service, the demand distortion is significant. It's no biggie when you're only using them in a small quantity in an industrial setting so that the demand by VFD only adds up to a drop in a bucket. That is how it was two decades ago. Modern residential use inverter ACs do have a fairly effective harmonic mitigation. Cheap China made VFDs sold in the internets will also be the most harmful type that omits harmonic mitigation that adds to manufacturing cost.

The "green industry" is composed of significant amounts of marketing companies that thrive on getting in touch with the consumer's warm and fuzzy feeling about saving the environment using crafty numbers or emotional stimulation. Environmentally unsound projects or solutions disguised as "saving the mother earth" for financial gains and the less visible and delayed harmful effects in the bigger picture negate the benefits, the overall effect can be an environmental and social HARM.

It maybe very well intended but unaware of harmful effects or it could be sham looking for whatever reasons to create demand for products or indifferent to indirect effects or hiding them for the sake of profit. Ruthless bottom line driven green marketing that preys upon the uninformed public is dime a dozen. It's not exactly news flash that businesses hide harmful effects for the sake of protecting profit even if its a total showstopper to the benefits touted. Earlier LED light bulbs and patented, proprietary parts driven embedded systems based appliances with a fairly short factory warranty that wipes out any saving by ONE service call are some examples.

[AC_Hacker]

The thing that sets EcoRenovator apart from the majority of opinion-drivel of the web, is that people who are actually doing things, actually building and doing, are sharing their experiences and offering support and knowledge that comes from doing things.

It is the density of that valuable information, and the organization that gives EcoRenovator it's value.

This opinion drivel is a waste of space and valuable time that people could well spend by actually doing something.

This thread should be consigned to the Billiard Room where it belongs.

ICanHas, it is not lost to me that on the occasions that I have asked you to share information and photos about your projects, you have said nothing.

That says it all.

-AC

[ICanHas]

The question now, of course, is where would you find such a waveform? As it turns out, it's actually a very good waveform for a power inverter to output

It's also possible to design a generator to output trapezoidal waves, and in fact, the motor/generators in many hybrid and electric vehicles do just that.

You misunderstood the type of inverter. Of course you can make run whatever at whatever waveform in an isolated circuit that isn't interconnected. Aircraft equipment operates at 400 Hz for example. You can't just change the grid waveform or frequency to whatever you want whenever you want. If you want something different.

Look into the future where alternative energy is the norm and rectifier loads like PoL (Point of Load) VFDs are everywhere.

Oh sure. They'll continue to be around. But the movement in the near future is disallowing importation and sales of those harmful equipment without good front-end filtration in North America following the IEC directive model.
http://grouper.ieee.org/groups/harmo...cs/P1495D2.doc

Originally Posted by AC_Hacker

The thing that sets EcoRenovator apart

-AC

That's your opinion.
Feel free to not read/post if this thread isn't hands-on enough for you.

[mejunkhound]

My 2 cents worth:

EU has had harmonic requirements for over 20 years.

USA does not.

Why _ most heavy power users and high efficiency systems already have PFC circuits as part of the rectification circuitry (e.g UC3854 chip, $2); heck, even the Klimaire 1.5T inverter driven mini-split I bought 2 years ago from China has a PFC front end. Why: the typical PFC circuit boosts 120 Vac to a stable 200V vs drifting 170
vdc, or 240 Vac to 400 Vdc, which makes the inverter design simpler and more efficient, while at the same time raising PF to 95% to 99%.

I suspect that ICanHas is in the business sector that sells power factor correction circuits or else got burnt by ignoring harmonics in one of his designs?

Modern wild frequency aircraft power systems have very high harmonics - there is a BIG weight penalty for aircraft to correct all harmonics. Many vendors/suppliers overlooked the line harmonics in the specs when they built their power supplies, and the supplies went belly up in initial testing giving the incompetent designer a black eye. Perhaps icanhas is one of the design engineers who did not read the power system specs so now caterwhalls about wanting a clean power system.

Biggest impact for POCO is triplett harmonics, as those turn to heat in delta-wye distribution transformers. A high power VFD (most of which have PFC circuits anyway) usually have their own phase shift transformers - say with a straight 24 pulse rectifier, there are primarily 23rd and 25th harmonics, not divisible by 3.

Not to say there are not horror stories about harmonics, but overall economics for the user pretty much dictates PFC circuits anyway.

The EU harmonic requirements are a result of Europe having mostly government run power systems - easier for them to legislate on harmonics vs letting the free market fix the problem itself.

Example - cheap Chinese 6W LED bulbs with no PFC*, replacing 60 W incandescent. Power reduced by a factor of 10, good trade against a few mV of harmonics. If that $4 LED bulb had to add even 50 cents due to PFC circuit, the 54W generating saving would not be taken advantage of by a larger population segment.

* I have a cheap open CFL in hand, and am looking at the circuit - easy to do, one sided circuit board and no ICs. 4 diodes, small inductor, 10uF 200
v cap, 2 4124L (fets?) drivers to small transformer - saves over 50W for same 500 lumens, adds about 10 mA or less harmonics to input current waveform.

As far as DIY folks 'polluting' the grid, what a crock - there are so few DIY that use multi HP non PFC VFD that it is a teaspoon in the ocean.

[NiHaoMike]

In one video where someone installed a VFD on a central A/C, the amperage draw went down, not just the wattage. Granted that was under a specific set of conditions (no doubt including an A/C that was oversized to begin with), but that means the overall VA draw also went down.

Maybe what we need is an open source VFD targeting residential HVAC applications, able to drive 120V or 240V split phase motors (depending on components used) and 208V 3 phase motors. It can be designed with both the hardware and software open source, including high efficiency digital PFC. It could even be possible for the software to automatically tune the PFC (output voltage and cut in point) for peak efficiency at a given load condition, while maintaining a user set minimum PF or maximum amperage limit. Some advanced DIYers out there have built their own EV motor drives and chargers. A HVAC motor drive should be quite a bit simpler in comparison.

[ICanHas]

Originally Posted by mejunkhound

My 2 cents worth:

EU has had harmonic requirements for over 20 years.

USA does not.

Well, not yet at least. Did you get to take a look at the IEEE doc?

"A typical transformer rating for residential application is 25 kVA or 50 kVA with services run to between 6 and 10 homes.
"

"The U.S. distribution system is more susceptible to problems brought about by the third harmonic. Third harmonics readily pass through the wye wye connected transformers in the U.S. "

Why _ most heavy power users and high efficiency systems already have PFC circuits as part of the rectification circuitry (e.g UC3854 chip, $2); heck, even the Klimaire 1.5T inverter driven mini-split I bought 2 years ago from China has a PFC front end.

Remember that it is a mini-split specifically designed for use on residential service and global market meaning that it has to meet the regulations of target market. You'll find that many big screen TVs have a 100-240v power supply with a PFC so that the same power supply can be used regardless of destination market including where it must meet IEC directives.

Biggest impact for POCO is triplett harmonics, as those turn to heat in delta-wye distribution transformers. A high power VFD (most of which have PFC circuits anyway) usually have their own phase shift transformers - say with a straight 24 pulse rectifier, there are primarily 23rd and 25th harmonics, not divisible by 3.

IEEE report describes US residential distribution systems commonly use 7200 - 120/240 single phase transformers hooked up line to neutral.

Given the wye-wye nature, the harmonics from ever increasing non-linear loads add up in the medium voltage line 12470Y/7200 side. The harmonic current level at the substation level is much higher now than it was designed for in the era when harmonic demand from electronic loads were only present in much smaller amounts.

Not to say there are not horror stories about harmonics, but overall economics for the user pretty much dictates PFC circuits anyway.

The EU harmonic requirements are a result of Europe having mostly government run power systems - easier for them to legislate on harmonics vs letting the free market fix the problem itself.

Example - cheap Chinese 6W LED bulbs with no PFC*, replacing 60 W incandescent. Power reduced by a factor of 10, good trade against a few mV of harmonics. If that $4 LED bulb had to add even 50 cents due to PFC circuit, the 54W generating saving would not be taken advantage of by a larger population segment.

It will take 500 of those fired up simultaneously off of the same distribution transformer to equal the effect of one non-residential VFD with a 3kW input.

So, under any ordinary applications, their effect on total demand distortion applied on the distribution transformer is low. Even the IEC only applies harmonic rules to power supplies with input power over 75W. I believe they're dropping that down to 50W in the near future.

In the US, though not a direct legal mandate, "Energy Star" qualification is essential in marketing and many utility sponsored rebates require it. A straight rectifier bulk capacitor link LED product that is over five watts do not qualify for Energy Star, because power factor must be over 0.7 and this is not possible with the level of harmonics produced by the bridge/capacitor input. ( http://www.energystar.gov/ia/partner...quirements.pdf )

As far as DIY folks 'polluting' the grid, what a crock - there are so few DIY that use multi HP non PFC VFD that it is a teaspoon in the ocean.

This obviously depends on each location. The level of voltage harmonic distortion that will be produced at the point of common coupling is much more severe at a rural location.

In a rural area with a 15kVA transformer serving two homes:
3kVA of harmonic current on a 15kVA transformer serving two homes that sees an average demand of 10kVA is has a total demand distortion of 30%. At the local level, this is an ounce in a cup.

The same VFD used on a service in the city where it's fed from a 208Y/120 feeder with a 1,000kVA+ of transformer capacity, it would be a few drops in a bucket.

This can occur if one of the house is using an A/C unit modded with an industrial 3 phase 6-pulse VFD running on a single phase service, or using a bunch of computers doing "coin mining" or running a ton of electronic ballasts to grow weed. This can be fixed by putting the neighbor on a separate transformer, which is very expensive. The added standing loss from having two transformers as well as the reduction in conversion efficiency of the one serving the offending load, the effect of "power savings at load" by "skipping harmonic mitigation" is now overwhelmed.

It would be a "drop in the bucket" by the time it gets to medium voltage substation, but the impact is not at the local level. Since this will throw the voltage distortion beyond whats permissible at the PCC that is supplied to the neighbor,it can be considered "Usage of Service Detrimental to Other Customers" by tariff agreement as authorized by the PUC.

Then there's a further cost involved in the process of forcing the offending customer to pay the expense of putting his neighbor on a separate transformer or getting a court order to disconnect the harmonic load or install filtration device.

[ICanHas]

In one video... where someone installed a VFD on a central A/C, the amperage draw went down, not just the wattage. Granted that was under a specific set of conditions (no doubt including an A/C that was oversized to begin with), but that means the overall VA draw also went down.

Not all VFDs are the same. What is true to a harmonic reduced VFD do not translate to the same holding true for the stripped down bare minimum VFD one buys from Alibaba.

A 500W 1kVA load from a very lightly loaded induction motor do not produce the same level of losses in the transformer as diodes and capacitors used in computers.

Maybe we need more implementations of electromechanical pneumatic modulated technology such as the Copeland Digital modulating devoid of all this power electronics crap.

[AC_Hacker]

I'm thinking I would use one of these on my heat pump.

Think it might bring down the grid? They're pretty cheap.

[SDMCF]

Originally Posted by mejunkhound

The EU harmonic requirements are a result of Europe having mostly government run power systems - easier for them to legislate on harmonics vs letting the free market fix the problem itself.

I disagree. EU Regulations drive ever closer technical specifications in order to promote a cross-border electricity market, whilst at the same time forcing government run power systems to be privatised. I don't think there are any government run power systems left in the EU, but there are technical regulations despite that, so I don't see that these two issues are inter-dependant.
This is just the same as any other market. For example, there are EU regulations about car specifications, covering everything from emissions to lighting to safety etc, yet there are no government run car factories. You don't need things to be government run for them to be government regulated.