[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.