Correct Answer - Option 1 : 1,200 MVA
Concept:
Breaking current: It expresses the highest number of short-circuit currents that the breakers are capable of breaking under specified conditions of transient recovery voltage and power frequency voltage. It is expressed in kA (RMS) at contact separation. The breaking capacities are divided into two types.
- Symmetrical breaking capacity of a circuit breaker
- Asymmetrical breaking capacity of a circuit breaker
Symmetrical breaking capacity \(= \sqrt 3 {V_{L}}{I_{B}}\)
Rated symmetrical breaking current \({I_B} = \frac{S}{{\sqrt 3 {V_L}}} \)
Making current of a circuit breaker is the peak value of the maximum current loop during sub transient condition including the DC component when the breaker closes.
Symmetrical making current = 2.55 × symmetrical breaking current
Calculation:
From the given data,
MVA rating = 1200 MVA
Symmetrical breaking capacity = 1200 MVA