Correct Answer - Option 3 : 26.24 kA
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
Rated symmetrical breaking current, \(({I_B} = \frac{S}{{\sqrt 3 {V_L}}} )\)IB=S3√VLIB=S3VL
Where, S = Rating of the circuit breaker in MVA
VL = Line voltage in kV
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:
Given
VL = 11kV
MVA rating, S = 500 MVA
∴ Rated symmetrical breaking current,
\((I_B= \frac{{500 \times {{10}^6}}}{{\sqrt 3 \times 11 \times {{10}^3}}} = 26.24\;kA)\)
