This interrupting current is ofcourse lower than the momentary current and

This interrupting current is ofcourse lower than the

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This interrupting current is , of course, lower than the momentary current and depend on the speed of the breaker, such as 8,5,3 or 2 cycles, which is a measure of the time from the occurrence of the fault to the extinction of the arc.
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Professor Arturo Bretas | EEL 4251 - PSA The Selection of Circuit Breakers 60 Breakers are identified by nominal-voltage class, such as 69 kV. Among other factors specified are rated continuous current , rated maximum voltage , voltage range factor K , and rated short-circuit current at rated maximum kilovolts.
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Professor Arturo Bretas | EEL 4251 - PSA The Selection of Circuit Breakers 61 The rated maximum voltage of a circuit breaker is the highest rms voltage for which the circuit breaker is designed. The rated voltage range factor K is the ratio (rated maximum voltage ÷ the lower limit of the range of operating voltage). K determines the range of voltage over which the product (rated short-circuit current × operating voltage) is constant.
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Professor Arturo Bretas | EEL 4251 - PSA The Selection of Circuit Breakers 62 In the application of circuit breakers it is important not to exceed the short-circuit capabilities of the breakers. A breaker is required to have a maximum symmetrical interrupting capability equal to K × rated short-circuit current.
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Professor Arturo Bretas | EEL 4251 - PSA Example 3: 63 A 69-kV circuit breaker having a voltage range factor K of 1.21 and a continuous current rating of 1200 A has a rated short-circuit current of 19.000 A at the maximum rated voltage of 72.5 kV. Determine the maximum symmetrical interrupting capability of the breaker and explain its significance at lower operating voltages. SOLUTION : The maximum symmetrical interrupting capability is given by: This value of symmetrical interrupting current must not be exceeded. From the definition of K we have:
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Professor Arturo Bretas | EEL 4251 - PSA Example 3: 64 Hence, in the operating voltage range 72.5 -60 kV, the symmetrical interrupting current may exceed the rated short-circuit current of 19.000 A, but it is limited to 22,990 A . For example, at 66 kV the interrupting current can be: Breakers of the 115-kV class and higher have a K of 1.0.
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