IEC medium-voltage circuit-breaker interrupting ratings-unstated short-circuit considerations

International Electrotechnical Commission medium-voltage circuit-breaker interrupting ratings are reviewed using typical petrochemical examples. This paper investigates the complexity of high-magnitude X/R ratios, and short-circuit current zero-axis crossings beyond the interrupting time of the standard circuit-breaker when used for generator applications. Guidelines are provided, enabling the engineer to correctly define the circuit-breakers and switchgear for these applications.