K-rated transformers

[ryan_618]

It is my understanding that installing K-rated transformers with a higher K rating than is required can actually create more problems than it solves. Has anybody else ever heard of this, and if so, do you know what kind of problems are created?

 

[bphgravity]

Re: K-rated transformers

I read this in an article one time but don't remember the exact details. I believe the main concern was the significant decrease in transformer impedance from oversizing. Obviously, this allows more fault-current let-through but also decreases the transformers ability to work well and increaes the neutral to ground voltage drop.

Like you, I just know its not a good practice but don't exactly know why. I think I will pull out some of my transformer books later.

 

[templdl]

Re: K-rated transformers

As a former DTDT transformer application engineer a higher than require K-factor transformer was never an issue with regard to applications. We never had any limitations regarding the use of a K13 when a K-4 will do. They are more expense so why pay the extra bucks. Besides a 200% neutral the cores and coils K-factor transformers are designed to handle the extra heating of a given harmonic content. The only other down side is that, because the K-factor xfr is more robust to handle the extra heating the inrush current to energize the xfmr increases and is more apt to cause nuisance tripping of the pri. OCPD. You're asking for trouble if you apply an OCPD which is lower than one sized based upon the maximum as allowed for the pri. full load amps.

 

[dereckbc]

Re: K-rated transformers

Agree with Temple. Other than extra expense and proper sizing of OCPD on primary, no issues.

 

[ryan_618]

Re: K-rated transformers

Thanks guys, I appreciate it.