Is there any illustration that can show this math? Sorry i am a visual learner lol
Wye VP = VL ÷ √3
Delta VL = VP
Wye VP = 7200 ÷ √3 = 4157
Delta VL = 480
4157/480 = 8.7:1
*Give me a smart idiot over a stupid genius any day*
You did nothing wrong. I do not know why are assuming that you did anything wrong. Just FYI - I am not an administrator here or at NETA. Just a regular member. I am just baffled by the confusion here that should not have existed.
The gentlemen on this thread have made all sorts of assumptions and tried their explanations. With all due respect to their efforts, I am not sure how many of these gentlemen or NETA question makers use a standard textbook definition of Turns Ratio.
For Turns Ratio - You take identical parameters. Line parameters (LL) or Phase parameters (LN). If nothing is mentioned, automatic assumption is that the values are Line parameters NOT phase. These are the first concepts of power engineering.
"Delta windings use phase to phase"
The fundamental is: In delta windings, V Line to Line or V subscript LL = V Line to Neutral or V subscript LN. So no conversion is required on Delta side.
The way I taught my guys that seemed to stick with them was to visualize all transformer ratios as single phase devices.
First off, it's important in this example to note that it's a WYE primary, which is not common and is an easy way to make a mistake.
With a line voltage 7.2kV, we divide by 1.732 to find a phase voltage ~4.16kV.
In the DELTA secondary, VL and VP are equal at 480V.
At this point you can ignore the fact that these are part of a three phase system. You have three individual transformers with primary voltage of 4,160 and secondary at 480.
4,160/480 = 8.67
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