Correct Answer - Option 1 : 20
Concept:
Plug setting multiplier is the ratio of fault current and the product of plug setting and CT ratio.
Plug setting multiplier \(= \frac{{fault\;current}}{{plug\;setting \times CT\;ratio}}\)
Calculation:
Given: Fault current is 4000 A, CT ratio is 400/5 A, Relay setting is 50%.
Plug setting = relay setting × secondary CT current
= 0.5 × 5 = 2.5
CT ratio \(= \frac{{400}}{5} = 80\)
Plug setting multiplier
\(= \frac{{4000}}{{2.5 \times 80}} = 20\)