transformer symbols 1

Hi everyone

My knowledge of electrical stuff is not the best.
Can someone explain the meaning of the following symbols used on three phase transformers, and how do you determine it:

: Z%
: Z0%
: X/R ratio

I've seen on the nameplates of some transformers just the MVA, the voltages and currents(pri. and sec.), the impedance (X%), type of cooling and the vector symbols.

Thanks

 

[mpparent]

z% = transformer impedance

z0% = transformer zero sequence impedance

x/r ratio = the ratio of reactive and resistive components of the transformer


Mike

 

Thanks Mike

1.So z% is the same thing as x% ?
2.How do you calculate z0% and the X/R Ratio? - I haven't see it on any transformer nameplate.

 

[jghrist]

Z% is the impedance, comprising both the resistance (R%) and reactance (X%). Think of the resistance and the reactance as vectors 90 degrees apart. The impedance is the vector sum of the two, so Z^2= R^2 + X^2. What you normally see on the nameplate is Z%. R% can be calculated by dividing the full-load loss by the rating and multiplying by 100.

Z0% is equal to Z% for two-winding transformers with solidly grounded neutrals. Except as seen from the delta side of a delta-wye transformer, Z0% is infinite. For three-winding transformers, you need tests of the individual winding impedances.

The X/R ratio is X% divided by R%. If you have Z% and calculate R% as above, you can calculate X% by solving the above equation for X.