How to calculate VA for autotransformer from a control or isolating transformer

[elanshul]

Dear Friends, can anyone guide me how can we calculate stepup autotransformer va from a control or isolating transformer va. here is a example to calculate step down autotransformer va from a control or isolating transformer va.
Power of a normal transformer P=(Fq / B)² where Fq = core area in cm² B = magnetic induction T or wb/m²
P auto transformer = P normal transformer / {1-(U2/U1)} where U2 input voltage and U1 output voltage
more explanation is as follows if ca = 11.52 cm² and B = 1.3 wb/m² U2 = 110Volt and U1 = 110 volt Then
Power of a normal transformer P=(11.52 / 1.3)² = 78.5W
P auto transformer = 78.5W / {1-(110/220)} = 157W


can anyone help me this type of formula for A step up autotransformer. i will be highly obliged.

 

[irfan ahmad]

V input X I input = VA input
and
Vout x I out = VA out

 

[zuisti]

The correct equation is:
P_auto_transformer = P_normal_transformer * {1-(U2/U1)} ; U2 the output voltage and U1 the input voltage

So, for transformation ratio = 2, the size of the auto transformer would be approximately 50% of the corresponding size of two winding transformer.

 

[elanshul]

Dear Zuisti sir,
request you to kindly please carefully read my question i am not asking for transformer physical size. i am asking how to calculate power for autotransformer from a control or isolating transformer if u are having any formula as i describe for step down transformer.