HMTs and K-rated Transformers

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AlexanderRC

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Hello everyone, if this is the incorrect place to post this question I apologize, it's my first post. But I wanted to know more about the differences between HMTs and k-rated transformers, as in where one would be better used than the other, advantages, disadvantages, etc.

From some quick searches I've done so far, my understanding is that k-rated are basically just oversized transformers as to be able to handle the heat from harmonics where the HMTs actually address the harmonics issue. What does this mean for the supplying system or the connected loads. Obviously I'm oversimplifying but if someone could elaborate for me I would greatly appreciate it.
 
Yes, I'd say you have it right.

And it means nothing to the load, only to the supply our source upstream of the transformer. The load and the branch circuits to the load will continue to draw whatever harmonics they would normally draw.

With a HMT transformer, the harmonics tend to cancel in the primary, so the source upstream doesn't see as many harmonics.

But I might add that a standard delta - wye transformer also tends to cancel out odd harmonics in the primary. And odd harmonics are the most common ones typically caused by non-linear loads. So personally, I have no idea when one might actually need a HMT.
 
You have it right.

An HMT (harmonic mitigating transformer) will have a low pass or band pass filter to shunt certain frequencies to ground that you don't want the load to draw or to come back on the neutral such as 180hz (the first triplen) if that one is your problem.

It is tough to guess what frequency would be your problem until the install is complete because system impedances and cancellations among different loads will likely reduce or eliminate the need to worry about harmonic problems in an average situation. Even in most new data centers (I know there will be a poster that says every data center they work in has them, but your mileage may vary), we don't use HMTs, just k-rated transformers to handle the harmonics until they cancel upstream via the delta winding or mixing / diluting with other loads.
 
Thank you for the replies!

I see, so in essence they both work fine and there aren't any real advantages or disadvantages to either one? But there has to be a difference in efficiency and power loss I assume?
 
AlexanderRC said:
Thank you for the replies!

I see, so in essence they both work fine and there aren't any real advantages or disadvantages to either one? But there has to be a difference in efficiency and power loss I assume?
Click to expand...

I'm not sure. I don't see any published data that compare the two, but they will both meet DOE standards. Here are some good square d links you might like;

http://static.schneider-electric.us...ansformers/Harmonic Mitigating/7400DB0301.pdf

http://download.schneider-electric....File_Id=3329121899&p_File_Name=7400CT1001.pdf

http://ecatalog.squared.com/pubs/El...ormers/Harmonic Mitigating/7400CT0301R708.pdf
 
AlexanderRC said:
I see, so in essence they both work fine and there aren't any real advantages or disadvantages to either one? But there has to be a difference in efficiency and power loss I assume?
Click to expand...
K-rated transformer does not improve power quality. HMT improves power quality and so reduces line losses associated with harmonics.
 
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