Open circuit test on rated voltage
IF THE TRANSFORMER HAS IRON OR MANETIC CORE THEN WHAT YOU SAY IS CORRECT HOWEVER , WITH AIR CORED TRANSFORMER VOLTAGEDOES NOT MAKE MUCH DIFFERENCE FOR FOLLOWING REASONS:
1.THERE IS LIMIT IN FERROMAGNETIC MATERIAL TO CARRY MAGNETIC FLUX WHERE AS AIR HAS NO LIMIT..(JUST A STARTER)
2. ONE CAN CHANGE THE SO CALLED MAGNETIC FLUX (RELATED TO FLUX DENSITY x AREA)WITHIN CERTAIN BOUNDS CALLED SATURATION (MEANS A LIMIT)
3. HOW FAST THE THE SAID FLUX CHANGES, FROM ONE LEVEL (SAY NEGATIVE SATURATION) TO POSITIVE SATURATION, DECIDES THE VOLTAGE  THE VOLTAGE.
4. MEANS FASTER (HIGHER) THE CHANGE OF FLUX CHANGE, HIGHER THE VOLTAGE.
5. MEANS RATE OF CHANGE DIVIDED BY VOLTAGE REMAINS CONSTANT.
6. FOR CERTAIN A.C. VOLTAGE, THE RATE ( MEANS FREQUENCY) DECREASES THE FLUX CARRYING CAPACITY WILL REACH, KNOWN AS SATURATION (NOT DESIRABLE) AS MAGNETIZING CURRENT INCREASES, IRON (HYSTERISIS)LOSSES INCREASES.
7. SAME WOULD HAPPEN IF THE A.C. VOLTAGE INCREASES AT THE AME FREQUENCY..
HOPE I HAVE MADE IT ENOUGH COMPLICATED.
V. T. INGOLE