Transformers Turn Ratios

[cruzy]

If all we are looking for is the turns ratio, then are these the basic rules:

1. For 3 phase transformers, use line to line ratios.

2. For 1 phase transformers, use line to neutral ratios.

This question comes in reference to NCEES #506, where they use the line to neutral ratios. But in other questions, we use the line to line ratios to transfer currents, voltages, etc...

Thanks,

C

 

[vinnius]

If all we are looking for is the turns ratio, then are these the basic rules:
1. For 3 phase transformers, use line to line ratios.

2. For 1 phase transformers, use line to neutral ratios.

This question comes in reference to NCEES #506, where they use the line to neutral ratios. But in other questions, we use the line to line ratios to transfer currents, voltages, etc...

Thanks,

C

i think in this case, it depends. the fact that the LV side needs the sqrt(3) applied is because its in Y config. when you connect the lines on an actual drawn out 3 phase config, the voltage on the Delta measures the V phase while that across the Y would be across the two lines.

I think a key is just to realize that this problem was way too easy to just apply a simple ratio calculation.

 

[Flyer_PE]

The only time you will care about the turns ratio of the individual transformers in a 3-phase bank is for a question just like this one. If all you are dealing with are values external to the transformer, all you care about is the 115kV:24kV 3-phase voltage ratio for the transformer. However, since they are asking you a question about the transformer internals, you have to account account for the configuration of the windings. One thing to remember is that any 3-phase transformer consists of three single-phase transformers connected in some combination of delta and wye.