| 摘要 |
PURPOSE:Not to react a relay unnecessarily in a simple accident by determining it as system oscillation that the variation width of system current shows more than the predetermined value provided that the gradient is more than the predetermined value and it has continued for the predetermined time. CONSTITUTION:When oscillation occurs to a power system, the current fluctuates slowly at a constant oscillation cycle. Thus the oscillation of electric system can correctly be detected by a comparison means 14 in which the output is turned ON when the difference between the maximum value calculation means 12 and the minimum value calculation means 13 is greater than the designated value and the output is turned OFF when the said difference is the less, a gradient calculation means 15 which calculates the gradient of the change of current value, a comparison means 16 in which the output is turned ON when the gradient is greater than the designated value and the output is turned OFF when the gradient is the less, and an operation continuation verification means 17 in which the output is turned ON when it continues for a designated time and the output is turned OFF when it discontinues. In this way, in a simple accident, a relay can be prevented from being operated unnecessarily. |
