ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Harmonics can cause overloading and overheating in the transformer. That is how the K-Rating for transformers came about. Is the transformer K-Rated?
Neutral Current and Heat Generation
- Thread starter death900
- Start date
Thank you everyone for your inputs so far. We have gotten information back from the vendor on the transformer resistance and the neutral current is not contributing to any significant heat rejection.
That being said we do have around 10.5% THD. I dont have individual values for each harmonic level, but is there a calculation out there that can be used to calculate heat dissipation from harmonics?
That being said we do have around 10.5% THD. I dont have individual values for each harmonic level, but is there a calculation out there that can be used to calculate heat dissipation from harmonics?
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
That's only 90C, or only 50C above the supposed ambient of 40, should be well within the rating of the transformer. Sure, that's not cool, but what was expected?
(It would be useful to fill in the phase currents, transformer size, and maybe some other into. Have a photo of the ratings plate?)
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
As Ron mentions in post #21, this is an issue which K rated transformer were marketed to accommodate, do some research on these.
It has been some 20years since I amazed whether a K-1 versus a K-13 transformer was needed. I recall looking at some DOE and IEEE literature on this subject. After all the analysis we stayed with a standard K-1 unit.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Because you have significant neutral THD compared to the phases, I would imagine that a majority of the harmonics are triplen (Triplen harmonics are odd multiples of the third harmonic in a distorted periodic signal. They are also known as zero sequence harmonics.)
They can overload a transformer in the same way as adding 60hz loads.
I've been researching online about this and found a few articles about how to calculate this.
www.electricalaxis.com
This shows how to calculate K-factor by making a table based on all the harmonic values. I have done this on my end, and K-factor is less than 1. Can anyone see anything that i did wrong here?
Second one i found was to calculate power factor based on harmonics.
eepower.com
I have also done this one on my end. And found ~0.997 PF thd. Is there a way that i am not calculating the Neutral THD into this?
How to Determine the K- Rating of the Transformer?
This article is about the method on how to calculate the correct k- rating of the transformer due to the effect of harmonics
Second one i found was to calculate power factor based on harmonics.
Total Harmonic Distortion (THD) and Power Factor Calculation - Technical Articles
In this article, we will discuss how to measure total harmonic distortion and the power factor calculations utilized.
eepower.com
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
That is a lot less triplen harmonic (3, 9, 15) than I would have expected with so much neutral current.I've been researching online about this and found a few articles about how to calculate this.
This shows how to calculate K-factor by making a table based on all the harmonic values. I have done this on my end, and K-factor is less than 1. Can anyone see anything that i did wrong here?View attachment 2575120How to Determine the K- Rating of the Transformer?
This article is about the method on how to calculate the correct k- rating of the transformer due to the effect of harmonics
Second one i found was to calculate power factor based on harmonics.
I have also done this one on my end. And found ~0.997 PF thd. Is there a way that i am not calculating the Neutral THD into this?Total Harmonic Distortion (THD) and Power Factor Calculation - Technical Articles
In this article, we will discuss how to measure total harmonic distortion and the power factor calculations utilized.
View attachment 2575121
Clearly you have a lot of 6 pulse VFDs with high 5th and 7th.
FWIW, I've never calculated K-factor so I can't help with that.
The reading taken with the 397% THD on Neutral was taken on the 415V Transformer (PDU). The breakdown calculation of each harmonic level was taken at the upstream Medium Voltage transformer, since the meter on that is much more accurate to break down the individual harmonic levels.
Im trying to get a reading taken on the 415V transformer so i can see the individual harmonic levels, but i just really wanted to see if im doing these calculations correctly.
K-Factor calc was done on Medium Voltage transformer.
PF-thd calc was done using the reading on the 415V transformer.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
This does not surprise me at all.
The need for K-Rated transformer is extremely exaggerated. But, it is a good idea to check if your application is an outlier.