Answer:
Delta star transformer
Secondary side
= 415 V
= 239.6 V
= Line current, = 800 A
Primary side
= Phase voltage, = 3300 V
Primary phase current = 58.08 A
= 100.6 A
Turns ratio = 83/(660·√3)
Star-star transformer
Secondary side
= 3300 V
= 1905.26 V
= Line current, = 100.6 A
Primary side
= 11000 V
= 6350.9 V
Line current, = Phase current, = 3.018 A
Turns ratio = 3/100.
Explanation:
Delta star transformer
For the star Connection to the 3-Phase load,
Secondary line voltage, = 415 V
Secondary phase voltage, = ÷ √3 = 415 ÷ √3 = 239.6 V
Secondary phase current, = Line current, = 800 A
For the primary side of the delta star transformer
Line voltage, = Phase voltage, = 3300 V
K = 415/(3300×√3) = 83/(660·√3)
Primary phase current = 83/(660·√3)× 800 A = 58.08 A
Line current, = Phase current, × √3 = 100.6 A
The turns ratio = 83/(660·√3)
For the star-star transformer, we have;
Secondary line voltage, = 3300 V
Secondary phase voltage, = ÷ √3 = 3300 ÷ √3 = 1905.26 V
Secondary phase current, = Line current, = 100.6 A
For the primary side of the star-star transformer
Line voltage, = 11000 V
Phase voltage, = 11000 V ÷ √3 = 6350.9 V
K = 3300/11000 = 3/100
Primary phase current = 3/100× 100.6 = 3.018 A
Line current, = Phase current, = 3.018 A
The turns ratio = k = 3/100.