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# Transformer ratio K and voltage ratio K

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Update time : 2018-04-11 13:28:12
Transformer rated ratio K is the transformer primary voltage and secondary voltage ratio, and transformer wiring has nothing to do.
You are talking about the single-phase method is compared when the variable ratio test variable ratio, such as star-delta transformers ratio K = U1 line / U2 line, single-phase test is the phase voltage ratio of phase U1 / U2 phase, Because U1 phase = U1 line / √3, U2 phase = U2 line, U1 phase / U2 phase = U1 line / √3 / U2 line = K / √3. That is to say, when the variable ratio of the star-delta transformer is K, when the single-phase method is used to make the variable ratio test (usually, the single-phase method is more effective than the proportional bridge method), the calculated transformation ratio is K / √3.
1.    variable ratio k: refers to the transformer secondary winding potential ratio.
k = E1 / E2 = (4.44fN1Φm) / (4.44fN2Φm) = N1 / N2
Variable ratio k is equal to the turns ratio. The number of turns of a winding must meet certain conditions:U1 ≈ 4.44 f N1Φm ≈ 4.44 f N1BmS     N1≈U1 / 4.44fBmS
The value of Bm and transformer performance are closely related. Bm ≈ hot-rolled silicon steel 1.11 ~ 1.5T; cold-rolled silicon steel 1.5 ~ 1.7Tb
2.    voltage ratio K: refers to the three-phase transformer line voltage ratioIn doing three-phase transformer winding test voltage ratio K used to calculate.
K = (UAB / uab + UBC / ubc + UCA / uca) / 3