A power transmission line feeds input power at 2300V to a step down transformer with its primary windings having 4000 turns. What should be the number of turns in the secondary in order to get the output power at 230V? For an efficiency of 0.70, calculate the rms value of the primary current when rms value of the secondary current is 5A.

Explanation

`v_(prms)=2300V,N_(p)=4000,N_(s)=?v_(srms)=230V`
By definition, transformer turns ratio,
`T=(N_(s))/(N_(p))=(v_(s))/(v_(p))`
`N_(s)=(230xx4000)/(2300)=400`
`therefore` Number of turns = 400
Efficiency, `eta=(v_(s)i_(s))/(v_(p)i_(p))xx100`
i.e., `0.7=(230xx5)/(2300xxi_(p))`
Thus `i_(p)=(230xx5)/(2300xx0.7)=0.714A`