TRANSFORMER TAP RATIOS

[duki]

Does anyone know how the primary taps ratio on a transformer work. Is a +2.5% tap apply to the full voltage accros the primary or to the number of turns on the primary? To raise the secondary voltage does one connect to the + or the (-) taps?

 

[jghrist]

The tap value is the % change in the number of primary turns. A +2.5% primary tap means that for a primary voltage 2.5% higher than the nominal, the secondary no-load voltage will be at nominal. To raise the secondary voltage, lower the primary tap.