Same load has different power factor when fed from different sources

[Joethemechanic]

Not without additional information and data.

I got called in once because a company's power quality monitor was going into alarm due to high harmonics. As I reviewed the waveforms the harmonic content, THDv was excessively high but the THDi was not a problem. I noticed the alarms triggered only on weekends.
I told the customer not to worry.

It turns out the facility was not in production on the weekend and the harmonic content of their new emergency exit light chargers were extremely noisy when their 15A was the only load on a 2000kVA transformer.

Here is how I rectify power for my high current DC needs. No harmonic distortion problems



Stores a lot of energy too. Built in the 30's and stone reliable

For some things the best way is the old school way

 

[acolella]

This isn’t a concern for us. Well, it isn’t now that we know why we had a discrepancy. We initially thought we had a measurement issue. Run test at the factory was measuring different current than what was measured in laboratory testing. The lab data we were referring to was recorded with the fans fed from a 480V delta primary 240V delta secondary 112.5 kVA transformer. The motors being run tested at the factory were fed from a single phase 1 kVA 600V/240V transformer which is why we had the discrepancy. I’m still going to get a scope on them at some point when I have time.

 

[Deltaforce]

THDv was excessively high but the THDi was not a problem.

Generally THDv very much less than THDi.
But not in your case
Something wrong

 

[synchro]

I got called in once because a company's power quality monitor was going into alarm due to high harmonics. As I reviewed the waveforms the harmonic content, THDv was excessively high but the THDi was not a problem. I noticed the alarms triggered only on weekends.
I told the customer not to worry.

It turns out the facility was not in production on the weekend and the harmonic content of their new emergency exit light chargers were extremely noisy when their 15A was the only load on a 2000kVA transformer.

Generally THDv very much less than THDi.
But not in your case
Something wrong

When Jim said THDi was not a problem when the alarms triggered during plant shutdowns on weekends, perhaps it was because even a high THDi would represent a very small level of harmonic current because THDi is expressed as a percentage of the total current (which was very low on weekends).

Also, it's possible to have THDi less than THDv, for example if you only had relatively linear, inductive loads (since the current through an inductor is proportional to the integral of the applied voltage). This would certainly be the case on the output of a VFD feeding an induction motor.

 

[Deltaforce]

it's possible to have THDi less than THDv, for example if you only had relatively linear, inductive loads (since the current through an inductor is proportional to the integral of the applied voltage). This would certainly be the case on the output of a VFD feeding an induction motor.

Jim very stiff source 2000kva transformer
The possibility of THDv greater than THDi only when resonance abnormal condition present

 

[jim dungar]

Jim very stiff source 2000kva transformer
The possibility of THDv greater than THDi only when resonance abnormal condition present

Yes the abnormal condition was an extremely lightly loaded transformer with a highly harmonic load.
This occurred more than 15 years ago, so I don't remember all of the details and they are not relevant. I brought it up as an example of how high harmonic content might not be a problem.

Remember this is a site primarily for electricians and installers in the US using the NEC. While we sometimes go off on engineering topics, I often try to keep the discussion as non-technical as possible.