DY turns ratio / Spin-up #3-60

[countrytoad]

For a D-Y (Delta-Wye) transformer, does turns ratio refer to the actual turns ratio (and VLL-to-VLN), or to VLL-to-VLL ("apparent turns ratio")?

The problem requires a calculation of low-side voltage, through a D-Y transformer with 10:1 turn ratio. High-side voltage is 4600 Volts.

The solutions shows Vs-LL = 4600*(1/10). For my solution I calculate Vs-LN = 4600*(1/10), then Vs-LL = Vs-LN*1.7.

 

[Ship Wreck PE]

The ratio is for L to L on the primary and L to L on the secondary. The delta source has no L to N.

if the problem said 3 single phase transformers, the source is delta so it would be L to L but the load is Wye so it could be L to N.

 

[countrytoad]

The ratio is for L to L on the primary and L to L on the secondary. The delta source has no L to N.

Even if the secondary is Wye (L-to-N)?

So the ratio is not actually a ratio of turns, but only the ratio of VLL/VLL???

 

[countrytoad]

So I am now assuming that (1) for a D-Y transformer bank N1/N2 = VLL1/VLL1, whereas (2) for 3 single-phase transformers (in a D-Y configuration) N1/N2 = VLL1/VLN2.

Can someone briefly explain the reasons for (1)? Is the intention of "ratio" to calculate VLL/VLL, rather than actual turns ratio? Or is there something about the structure that I don't understand (and N1/N2 IS actually the ratio of turns)?

 

[countrytoad]

I found this:

""

In a three-phase bank, the delta/wye connections are internal to the bank, and are already accounted for in the voltage ratings (i.e. the sqrt(3) is built into the nameplate data on the bank). If you are hooking up three single-phase transformers you have to take the delta/wye (and sqrt(3)) connections into account yourself. In either case, if rated voltage is applied across one set of terminals of the transformer, it is going to produce rated voltage on the other set of terminals. In the case of a single-phase bank, you have to be careful to determine if line-line or line-neutral voltage is being applied on each set of terminals.

""

 

[iahim]

countrytoad,

Do you have Stevenson/Grainger? I can't remember exactly where, but they have a nice table that shows the different 3 phase transformer configurations with their associated turns ratios and voltages.

 

[knight1fox3]

countrytoad,

Do you have Stevenson/Grainger? I can't remember exactly where, but they have a nice table that shows the different 3 phase transformer configurations with their associated turns ratios and voltages.

Refer to Table 2.1 on page 62. I had that page flagged for when I took the exam.

 

[iahim]

Refer to Table 2.1 on page 62. I had that page flagged for when I took the exam.

Thanks! I made a copy of that page and stuck it my Ga Tech binder. That's my primary reference.