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Is there a Typical THD

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waltppiva

Member
Hello everyone,
I am gathering information for a power study on different UPS manufacturers and the one issue that many will list in their documentation is output current THD. Is there any figure, or reference value that states what the typical THD should be with 100% non-linear load, other than the lower the better? I understand what harmonics are and what causes them. And the way I see it, a UPS can control the input current and voltage harmonic (by way of the efficiency of the rectifier and input filter) and the output voltage harmonic (efficiency of the inverter), but the output current harmonic will be affected by the load equipment.

So, is there a good number to use as a reference?
 
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dave_asdf

Member
Location
tampa florida
Re: Is there a Typical THD

a good number depends on a few things, mostly the size and style of UPS, 200-300 KVA unit should be between 3-5% RMS THD at 100% non-linear. what sizes are you looking at?
 
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waltppiva

Member
Re: Is there a Typical THD

Thanks for the reply. I'm not looking at specific sizes yet, although I have field data from two 40kVA units comparing Liebert with Mitsubishi. They each had approximately 20% load on them, so I know the field data will not match the numbers in their documentation. Some UPSs come standard with an input filter while others it is an option, and then others will have a filter but it will not engage until the load is over a certain percentage. I was just trying to get a little more input.

Thanks
 
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