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Examoogle • User • info@examoogle.com • EE-2024-8821
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Breaking capacity of circuit breaker is expressed in terms of
KV
KA
MVA
MW
MVA
The breaking capacity of a circuit breaker is defined as the maximum value of fault current (measured in MVA) that the circuit breaker is capable of breaking at a specified recovery voltage · It represents the ability of the breaker to safely interrupt a short-circuit current without damage to the contact structure or failure of the insulation.
The breaking capacity of a circuit breaker is defined as the maximum value of fault current (measured in MVA) that the circuit breaker is capable of breaking at a specified recovery voltage · It represents the ability of the breaker to safely interrupt a short-circuit current without damage to the contact structure or failure of the insulation.
SMVA=3×VkV×IkA×10−3 — Formula for calculating MVA breaking capacity
During a short circuit, the massive current generates significant thermal and mechanical stress · The breaking capacity is calculated using the product of the rated voltage and the rated breaking current (symmetrical), expressed as: Sbreaking=3×Vrated×Ibreaking. This ensures the breaker can handle the instantaneous power flow during the arc-quenching phase.
Breaking capacity is the highest short-circuit current the breaker can interrupt.
It is different from 'Making Capacity', which is usually 2.55 times the breaking capacity.
Calculated at the rated voltage, hence the MVA unit (Mega-Volt-Amperes).
Prevents catastrophic damage to electrical equipment
Ensures system stability during transient faults
Higher capacity breakers are significantly more expensive
Requires complex arc extinction mechanisms (SF₆, Vacuum)
Grid protection substations
Industrial high-voltage motor control
Transmission lines
Option B (KA) refers to the rated short-circuit breaking current, but the capacity is the power rating (MVA).
Option A (KV) refers to the rated voltage of the breaker.
Option D (MW) is not used as the breaking capacity involves reactive power during fault conditions.
C is correct — The breaking capacity of a circuit breaker is expressed in MVA, representing the product of rated system voltage and the short-circuit current.
Remember that 'Making capacity' is the peak current (instantaneous) and is always larger than the 'Breaking capacity', which is usually the RMS value of the fault current.