Frequency and harmonics

P

Pinnie

Senior Member
Location
Ohio
Occupation
Commercial Electrician
Say you have voltage distortion at your service due to nonlinear loads down the line( neighbors) Does that have to be from their line to line loads only or can it be from line to neutral loads. I’m thinking it would have to be line to line only.
 
Typically harmonics shouldn't disturb the neighbors just due to the nature of it. As the waveform's peak gets larger (higher current, higher voltage) the effect of harmonics is reduced. That is why it is usually expressed as a percent of the service transformer's size. Especially when we talk about their impact on the transformer rather than their impact on the high side. If they are on the same secondary side of a transformer then maybe they could have some kind of increased effective heating but it should effect the person creating the harmonics more. A transformer oversized to the load should have enough spare "space" to accommodate the heating effects of the harmonic distortions.

It can be line to line or line to neutral.

This pdf, chapter 3 and chapter 5 should help.

 
I should add that most utilities have a harmonic requirement in their service manual or quote IEEE 519.

I always assumed it was to protect the life of the utility equipment. I don't know if they are worried about the effects of harmonics on nearby services.
 
single phase rectification right off the line make plenty of harmonics.

famous cases in the 80s when many offices started having a computer at every desk. most of the early computers simply had a full wave bridge off the line (nearly all have PFC front ends now)
Many office buildings supplied by delta-wye transformers. delta-wye short out triplett harmonics (they are in phase on the delta primary so all the triplett currents dirculate in the delta)

Many delta-wye transformers burnt up on the first hot day of the year due to primaries overheating.

so to answer OP query, either single or 3 phase loads cause harmonics.
 
Elect117 said:
I should add that most utilities have a harmonic requirement in their service manual or quote IEEE 519.

I always assumed it was to protect the life of the utility equipment. I don't know if they are worried about the effects of harmonics on nearby services.
Click to expand...
IEEE519 is a two way street in that the Utility must ensure that YOU, the customer, does not receive more than 5% THD-V at the service terminals, then YOU are required to not EXPORT the same. The utility is not CREATING the harmonic distortion, so the only way they can ensure compliance on their side is to control what their customers export. So yes, the utility can and will call out a customer who is creating excessive harmonics because it will travel on their lines and through their transformers to your neighbors. But how much makes it through is mitigated by a number of factors, so often times you can get away with it, sometimes for years, because nobody nearby has complained. In general though, when you apply for a new or significantly changed service, they will want an sssessment of your THD.

Single phase power supplies, VFDs, UPS etc. can produce significant THD, especially odd orders, because the triplets don’t cancel each other on a single phase service. But at the same time, most smaller single phase electronics have some mitigation built in so it depends a lot on what is involved.
 
Lots of things generate harmonics. Linear loads don't. So let's list the linear [across the 60Hz. waveform] loads in Homer Simpson's new house:
  1. Lighting. Err, it's LED with pcm power supplies for dimming.
  2. HVAC. Well that variable speed compressor is driven by a VFD.
  3. Washer: See 2
  4. Dryer: Err, it's a heatpump so....
  5. Stove: It's induction and ...
  6. ...
I am amazed that more pole-pigs don't get so hot the paint burns off of them.

The computer power supplies, desktop & laptop, have an EU PF/harmonics spec that they have to meet. The world of computing is so international that means every country benefits from that.
 
Pinnie said:
Say you have voltage distortion at your service due to nonlinear loads down the line( neighbors) Does that have to be from their line to line loads only or can it be from line to neutral loads. I’m thinking it would have to be line to line only.
Click to expand...

Did you mean disturbance? Generally, it's not harmonics, but the load operating pattern that causes complaints, such thing as welder duty cycle or excessive starts per hour of large motors. Zero cross/full wave cycle controls on wrong algorithm is much more likely to cause more complaints even if it doesn't cause any waveform distortion.

See: https://libratherm.com/phase-angle-control-vs-zero-crossover-control/

Say you have 200A 240v service. Set it up with two sets of 24kW 120kW heating elements.
Set it up to create 7 1/2 Hz flicker by putting it on 1 cycle (16.667mS) on, 7 cycles off (116.667mS).

You can get a total integrated average of 3kW by running 120v 200A 24kW element on 1 cycle on, 7 cycle off, which will produce a 7 1/2 Hz flicker, which is approaching the most annoying interval.

Run the left side pool heater on this cycle for 13.333 seconds on L1-N. Run the right side pool heater on L2-N for 13.3333sec, in alternating pattern.
The thermal mass of pool is big enough that it will respond as if you have a 120v 1.5kW heater running on a 20A circuit on each side of the pool running continuously. However set it up like this with zero cross power controller and there's a very high chance someone will complain to PoCo about half the house flickering for 13 seconds, another half of house flickering for 13 seconds even though harmonic distortion is none and you will likely get a corrections order from the utility.
 
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