Transformer K-factor Method.

[EAntoun]

Hi,

I'm sizing a 1500 KVA transformer and I need some assistance to determine whether it need needs to be a K-type or not.

The MCC fed by the transformer have about 80 HP of VFD load, and around 1000 HP of linear load.

I used some excel sheet calculator to determine my K-factor for the transformer and it shows as [highlight #8AE234]1.2[/highlight] K-factor.

My question is the following:

Is there a need to get a K-4 transformer in this case? or is the k-factor too small to bump the rating to a K-type?
in other words, what is the break point before we would have to consider bumping up the rating.

Please advise if this info is shown anywhere In IEEE standards.

Thanks.

 

[sibeen]

Without knowing the harmonic content of the input currents to your VFD it's impossible to tell, but lets face it, you've got about 7% of non-linear load; I very much doubt that is ever going to be an issue.

Also, I wish Le Système international d'unités was international

 

[EAntoun]

Thank you Sibeen, I agree.

 

[meeko]

k factor of 1.0 is a linear load (no harmonics). above 1.0 begins to get non linear. can you post your calc to get 1.2

 

[jghrist]

I agree that there most likely will not be a problem unless you are loading the transformer at or near its rating. See C57.110-2008 - IEEE Recommended Practice for Establishing Liquid-Filled and Dry-Type Power and Distribution Transformer Capability When Supplying Nonsinusoidal Load Currents to evaluate the loading if you are loading close to the rating. Non-linear loads cause more heating that linear loads.

 

[LionelHutz]

I also can't see there being a problem with ~80kVA of non-linear load on a 1500kVA transformer with ~1080kVA load total. You're just over 2/3rds loaded on the transformer.