Transformer Turns / Voltage / Current / Impedance Ratio
The nameplate ratio the transformer tiles never compute directly: the turns ratio a = Np/Ns equals the voltage ratio Vp/Vs, the inverse current ratio Is/Ip, and the square root of the impedance ratio, so a secondary load Zs reflects to the primary as a^2 x Zs. A 480-to-120 V unit is 4:1; 50 A on the secondary is 12.5 A on the primary, and an 8 ohm load looks like 128 ohm to the source. That a^2 impedance transformation is exactly how a 70 V speaker line or an audio output stage matches a load. Ideal lossless ratio; the winding resistance and leakage reactance that sag real voltage under load are the transformer-voltage-regulation tile. A design aid; the nameplate governs.
Formula and source
a = Np/Ns = Vp/Vs = Is/Ip; Ip = Is/a; Zp = a^2 x Zs.
The ideal (lossless) transformer turns / voltage / current / impedance relations, first-principles; the nameplate and the manufacturer's data govern.
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