Complex sentence: The cause of the failure was human error that happened days before the blackout, when maintenance personnel incorrectly set a protective relay on one of the transmission lines between the Niagara generating station Sir Adam Beck Station No.2 in Queenston, Ontario.
Split into simpler sentences: The cause of the failure was human error that happened days before the blackout. Maintenance personnel incorrectly set a protective relay on one of the transmission lines between the Niagara generating station Sir Adam Beck Station No.2 in Queenston, Ontario.