harmonic currents

[76nemo]

i read the product notes for the 43b and it says it can calcuate 3 phase stuff from single phase measurements. i might just save up the 8000 dollars for hte 434. the guys at work will think im nuts for spending that much money on a meter maybe ill buy a cheaper one first :wink:

Buy a thermal imager before you go spending that kind of $ on a PQA. No, really, unless you would be testing on large systems and majoring in it like brian john, the 43B will suit you just fine:wink:

 

[electricalperson]

The problem with harmonics and transformers is that if they are delta/wye transformers (most are) then the higher frequency of the harmonic currents never leaves the delta side and causes higher currents in the core causing it to heat up. if the problem is severe enough and you cannot eliminate the harmonics the use of a "K" rated transformer is recommended. In addition, as many a one neutral per phase may also be required due the the fact that the 3rd and all 3rd 3rd harmonics add in the neutral (These are called triplens).

are triplen harmonics the only ones that add up? what problems can harmonics other than triplen cause?

 

[Besoeker]

Yes, the nonlinear line to neutral loads on three phase systems can cause excessive neutral loads on the neutrals of multiwire branch circuits and feeders.
I thought you were saying that these types of loads cause excessive neutral current on single phase systems.

My point in mentioning the single-phase is that the third and other odd triple-n harmonics emanate from the single-phase non-linear loads.
As I said, I don't deal with single-phase systems much. I just get called in by other divisions of our mighty empire when there is a problem or perceived problem - usually after the event.
In the case I mentioned, it was a monumental c0ck-up that should have been spotted by the main electrical contractor at the design stage.
Unfortunately, harmonic analysis still seems to be a black art for many.

I cut my teeth mainly on variable speed drives DC, AC, Slip Recovery, Mercury Arc (aka Archaic) etc. and mostly from a few hundred kW upwards for industrial applications. People in the drives field have known about the detrimental impact of harmonics for many years - I have a copy of a 1948 paper by a Prof Reid on the subject.

With the growing proliferation of electronic devices in the domestic and commercial sectors, awareness of the problems and potential problems is growing.

Harmonic filters could become good business.....

 

[LarryFine]

are triplen harmonics the only ones that add up? what problems can harmonics other than triplen cause?

It's odd-numbered harmonics that cause the peaks of current to occur simultaneously in 3ph systems, which is why they add. Higher-numbered harmonics are weaker, so they have less effect on the system.

 

[winnie]

It's odd-numbered harmonics that cause the peaks of current to occur simultaneously in 3ph systems, which is why they add. Higher-numbered harmonics are weaker, so they have less effect on the system.

Not quite. Its the multiple of 3 harmonics that phase align and add up on three phase systems.

Most sources of harmonics produce far more odd harmonics than even harmonics and for just about any reasonable _source_ of harmonics, the lower harmonics are weaker than the higher harmonics.

If you had some strange load that produced lots of 6th harmonic, then it would cause neutral problems on a 3 phase system. This is not seen as a problem because such a load would almost have to be intentionally created.

-Jon

 

[Besoeker]

Not quite. Its the multiple of 3 harmonics that phase align and add up on three phase systems.

The odd multiples of triple-n.
3, 9, 15, 21, etc.

 

[winnie]

The odd multiples of triple-n.
3, 9, 15, 21, etc.

Please see my post above.

Non-linear devices tend to produce mostly all odd harmonics. Generally there aren't enough even harmonics to bother considering.

But if you had a source of even harmonics, then the even multiples of 3 harmonics would also add.

-Jon

 

[Besoeker]

Please see my post above.

Non-linear devices tend to produce mostly all odd harmonics. Generally there aren't enough even harmonics to bother considering.

But if you had a source of even harmonics, then the even multiples of 3 harmonics would also add.

-Jon

Yes, Maybe pedantic, but a valid point.
In several decades of making measurements, I have not seen any significant levels of even harmonics.