the complete loss of voltage (0.1 pu for IEEE standards and 0.01 pu for CENELEC standards) on one or more phase conductors for a time period between 0.5 cycles and 3 s, 3 s and 1 minute, and greater than 1 minute, respectively. The main interruption causes are circuit breaker openings, circuit breaker or switch defective operations, cut down conductors, and lack of power generation. The word blackout is also used for sustained interruptions.