T-T connected transformers

[Gauss2k]

I was looking for informations about T-T connected transformers because I saw a couple of them in the last months.

I found this thread via google where it was briefly discussed: thread238-151261

Some manufacturers like "Marcus Transformers" (

http://www.marcustransformer.com),

also found with google, claim that:

"In the T-T connected transformers by Marcus, the triplen harmonics are cancelled in the magnetic circuit and do not flow in the primary windings as in competitive designs. This results in a 14% reduction in copper losses, less heat and extended transformer life."

and

"We use the T-T connection for our three phase distribution transformers to derive the inherent benefits of single phase construction: high short-circuit strength, rugged physical integrity and superior reliability. These characteristics are normally available only on pole-mounted utility-grade, oil-filled transformers where every watt lost and every hour of downtime is critical."

Anyone can give more technical informations about those claims? I was wondering the same thing as waross said in the other thread: What are the advantages and disadvantages compared to conventional transformer connections?

Is the triplen harmonics elimination one of the caracteristics of the kind of connection or is that only valid for a particular T-T transformers that this particular manufacturer make -> "[...]do not flow in the primary windings *as in competitive designs*"

 

[davidbeach]

Think Y-Y transformer and picture three windings. Now draw one winding, with a center tap, between two of the terminals; add a second winding, this one also tapped, but tapped 58% of the way from one end to the other. Connect this second winding between the third terminal and the center tap of the first winding with the tap of this winding where the neutral of the wye is, the 58% is between the terminal and the tap and the 42% is between the tap and the center tap of the other winding.

Because there is no delta winding, triplens are not trapped, but pass through the transformer. These are less expensive because they only require two windings rather than three, but the 42% of the second winding carries current for all single phase loads on the first winding. You'll often find these in smaller (9kVA and below) 3-phase transformers.