# Numerical - Primary & secondary voltages of transformer for given autotransformer

Q.  If a two winding transformer is converted into an autotransformer  by applying additive polarity and subtractive polarity which results in the secondary voltages of 1840 and 1810 volts. Then the primary and secondary voltages of transformer are
- Published on 30 Oct 15

a. 1800V, 50V
b. 1810V, 40V
c. 1820V, 30V
d. 1825V, 15V

#### Discussion

• Manashi kalita   -Posted on 18 Mar 19
Let V1= primary voltage of transformer.
And, V2= secondary voltage of the transformer.
Now, case1,
V1+V2 = 1840volt.... equ (i)
where, 1840 is the secondary voltage of autotransformer during additive polarity.

SUBTRACTIVE:
V1-V2= 1810volt....equ (ii)
Where, 1810 is the secondary voltage of the autotransformer during subtractive polarity.
NOW, (i)+(ii)=> V1+V2=1840
V1-V2=1810

So, 2V1= 3650
=> V1= 1825 volt.
Now putting the value of V1 in eun (i),
=>1825+V2= 1840
=>V2=1840-1825
=> V2= 15volt

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