| 摘要 |
PURPOSE:To achieve a higher accuracy of a protection relay, by a method wherein AC quantity of a power system is detected depending on a sampling frequency given as integral factor of a reference frequency and data of the AC amount is held so that three data is selected to meet a corresponding relationship from the data held to derive a specified function value of the AC quantity. CONSTITUTION:At the processing step 22, an arithmetic processing section 9 reads in current data Ai (or voltage data Bi) as AC data from an A/D converter as each sampling is done to hold it into a memory 17. The current data Ai (or voltage data Bi) in this case is that detected in terms of current (or voltage) in the power system depending on the sampling frequency given as integral factor of a reference frequency, for example, 60 deg. each in the electrical angle. At the processing step 23, current data Ai, Ai-2 and Ai-4 are read out from the memory 17 as data of AC quantity in the power system to execute computation of (Ai+Ai-4)/(2Ai-2) and the results are memorized 17 as data alphai, wherein (i) represents the reference frequency of the power system to be measured 30 deg. each step and alphai a specified frequency function.
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