| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent full-scale-over while satisfying a protective calculation precision specification during large changes in an input current range, for protective calculation based on an input current using an auxiliary current transformer. <P>SOLUTION: Related to A/D convertors 4A, 4B, 6A, and 6B, a pair of A/D convertors having different conversion gains from each other constitutes single auxiliary current transformers 3A and 3B. Ratio differential relays 5 and 7 are composed of a pair of protective relays which protectively calculate from the outputs of the pair of A/D convertors. A switch 8 takes, as a protective output, the output of the relay 5 which takes, as an input, the outputs of the A/D convertors 4A and 4B having low conversion gains if the input of the auxiliary current transformer is within a large current region, while it takes, as the protective output, the output of the relay 7 which takes, as the input, the outputs of the A/D convertors 6A and 6B having high conversion gains if the input of the auxiliary current transformer is in a small current region. <P>COPYRIGHT: (C)2003,JPO |
