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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
Quick Summary: 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.