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The rated breaking capacity (MVA) of a breaker is equal to
Product of rated voltage (kV) and rated breaking current (kA)
Product of rated voltage (kV) and rated symmetrical breaking current (kA)
Product of breaking current (kA) and fault voltage (kV)
Twice the value of rated voltage (kV) and rated current (kA)
Product of rated voltage (kV) and rated symmetrical breaking current (kA)
The rated breaking capacity of a circuit breaker is defined as the maximum short-circuit current that the breaker can safely interrupt at a given rated voltage. It is expressed in MVA to represent the product of the rated system voltage and the rated symmetrical breaking current, indicating the maximum power the breaker can handle during fault isolation.
The rated breaking capacity of a circuit breaker is defined as the maximum short-circuit current that the breaker can safely interrupt at a given rated voltage. It is expressed in MVA to represent the product of the rated system voltage and the rated symmetrical breaking current, indicating the maximum power the breaker can handle during fault isolation.
Breaking┬аCapacity┬а(MVA)=3тАЛ├ЧVLтАЛ├ЧIsymтАЛ
MVAтЙИVkVтАЛ├ЧIkAтАЛ
When a fault occurs, a massive amount of energy is released. The circuit breaker must be able to extinguish the electric arc formed between the contacts while interrupting the symmetrical fault current. The MVA rating provides a standardized measure of the breaker's ability to handle this energy, which is proportional to the product of the line-to-line voltage and the symmetrical short-circuit current.
Breaking capacity is always defined at the rated voltage of the breaker.
It refers to the root-mean-square (RMS) value of the symmetrical component of the fault current.
The transient DC component is not included in the symmetrical breaking capacity calculation.
Exceeding this value can lead to severe damage to the breaker or failure to quench the arc.
Provides a quick safety margin assessment for power system protection.
Standardized unit allows easy comparison between different breaker models.
Does not account for the asymmetry factor of the initial fault current.
Requires derating if applied at a voltage lower than the rated voltage.
High-voltage and Medium-voltage switchgear selection.
Substation fault analysis and protection coordination.
The breaking capacity is typically tested by interrupting a specified short-circuit current under controlled conditions.
Option A is incorrect because it lacks the 'symmetrical' specification essential for standardization.
Option C is imprecise as it uses 'fault voltage' which is not a standard definition.
Option D is mathematically incorrect as no factor of 2 is involved in the standard definition.
B is correct тАФ The rated breaking capacity is measured as the product of the rated voltage and the rated symmetrical breaking current, commonly expressed in MVA.
Always remember that breaking capacity is defined by the symmetrical RMS current; if the asymmetrical current is considered, the 'Making Capacity' (which is 2.55 times the symmetrical breaking current) must be used instead.