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Breaking MVA and making kA (800 A, 33 kV)

Short answer

Breaking capacity = √3 × 33 kV × 25 kA = 1429 MVA. Making capacity = 2.55 × 25 = 63.75 kA peak.

Calculate breaking capacity in MVA and making capacity in kA of a 3 phase circuit breaker with following parameters: Rated current = 800 A; Rated voltage = 33 kV; Ibsym = 25 kA.

Breaking capacity is the MVA corresponding to the symmetrical breaking current at rated voltage, and making capacity is the peak current the CB can close onto, taken as 2.55 times the symmetrical breaking current.

Given

Rated current = 800 A (normal current, not used for these values), V = 33 kV, I_b(sym) = 25 kA.

Breaking capacity

Breaking MVA = √3 × V × I_b
             = √3 × 33 kV × 25 kA
             = 1428.9 MVA

Making capacity

I_making = 1.8 × √2 × I_b = 2.55 × I_b
         = 2.55 × 25
         = 63.75 kA (peak)

Answer: Breaking capacity ≈ 1429 MVA; making capacity = 63.75 kA (peak).

✓ Answer checked by Claude Opus 5.5 (high effort)

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