| 摘要 |
PURPOSE:To obtain a time-limit characteristic by a protection output which is sent through comparison between the set value and the added value of an output of a data which is read out with a digital output matching the protection purpose computed from current value or the like of the electric power system as an address. CONSTITUTION:A digital data through sampling of the amount of AC current obtained from the electric power system is inputted to an arithmetic unit where the amount of current matching the protection purpose, such as effective value is computed every sampling. With the resulting digital output as the specified address, a digital data previously memorized is read out by means of a memory device 4 composed of a memory including ROM, RAM or the like and a reader. When the output read out is zero, an adder 5 clears the addition value every sample. When the output is out of the specified range, for example an accident caused in the electric power system, the addition value is added gradually. The moment the addition value exceeds the set value for a comparator 1, the comparator provides a protection output. |
