Single phase loads and harmonics

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Platinum

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Hey guys,

I have a 480V switchboard feeding a delta-wye transformer which feeds a 208/120V panel. The loads on this panel are mostly non-linear single phase loads connected line to neutral. Of course these loads will generate harmonics which will add in the neutral.

My question is should I use a K-rated transformer or Harmonic Mitigating Transformer? Will the harmonics even get from the load all the way up to the 480V switchboard? I thought they get trapped in the delta of the transformer?
 
Platinum said:
Hey guys,

I have a 480V switchboard feeding a delta-wye transformer which feeds a 208/120V panel. The loads on this panel are mostly non-linear single phase loads connected line to neutral. Of course these loads will generate harmonics which will add in the neutral.

My question is should I use a K-rated transformer or Harmonic Mitigating Transformer? Will the harmonics even get from the load all the way up to the 480V switchboard? I thought they get trapped in the delta of the transformer?
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Hello Platinum, Triple-n harmonics will be circulate inthe 480 V delta windings of the transformer, so they will not travel upstream.

The question of whether harmonic mitigation is necessary will need to be calculated from the harmonic spectra of the loads. I think of all the methods out there to mitigate harmonics, a K-rated transformer would be the best method for your situation if you have many small harmonic generating loads.
 
K-rated transformers do not mitigate harmonics. A k-rating means the transformer is able to tolerate an amount of harmonics and excess neutral current without overheating.
 
Thanks for your responses.

I guess my main concern was that the harmonic currents would travel upstream into the 480V switchboard. This would lead to voltage distortion on the whole electrical system. But if they are trapped in the delta and won't go into the 480V switchboard, then a K-transformer would be okay for light harmonics.

There just seems to be a lot of scare tactics out there advertising the use of HMT's because of all the electronic devices in use today. Seems like a K-transformer would be fine for these small harmonics.
 
wirenut1980 said:
Hello Platinum, Triple-n harmonics will be circulate inthe 480 V delta windings of the transformer, so they will not travel upstream.
Click to expand...
That is true for the generalization that third harmonic currents act like zero sequence currents, which most of it does. Some of it can be slightly out of phase and flow though the transformer.

Add: Caused by unbalanced currents.
 
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