Transfomer Loading and harmonics

[steve66]

I have a 300 KVA transformer, dry type electronic transformer.

I expect it to be heavily loaded, for long periods of time. (Maybe even 100% load for 7 days straight).

There will also be some harmonic content in the load current. I've been told 100KVA is for 6 pulse rectifiers with a 39% THD.

The other 200KVA is for low power electronics, and AC motors. I'll have to make a guess at the harmonics on this.

Is there any way I can calculate if I need a K rated transformer, and if it should be a K-4 or K-13?

Also, is there any way to figure out what temp. rise I should use? I can get a K rated transformer in a 115 deg rise, which would run cooler than the standard 150 deg rise.

I was also considering a standard, non K rated transformer with a 80 deg rise.

Any advice is appreciated.

 

[topgone]

IMO, if you are sure about that 100 kVA rectifier with 39% harmonics content, I guess a K-4 rated transformer will be fine for your application. 100 kVA is 33% of your 300 kVA supply transformer, making that 39% harmonics load just 13% of the total capacity. K-4 is designed to handle <35% harmonics (with 25% margin).