| 摘要 |
PURPOSE:To achieve a reduction in the size and cost of the equipment by directly measuring the time between the zero points of voltage and current to enable the fast detection of phase. CONSTITUTION:Current and voltage in the power system are introduced into a filter 3 through a current transformer 1 and a transformer 2 to extract a fundamental wave component and after the removal of unnecessary harmonic components, they are inputted into an A/D converter 4. A central processing unit 5 reads the output of the A/D converter 4 according to a program stored in a memory 6 to detect the zero point of the voltage input checking to ensure that the voltage input shifts from the positive to negative value. Likewise, the zero point of the current input is detected and the time T between the zero points detected is measured. Then, the time thus obtained is compared with a specified time value to judge the phase relationship. The results of the judgement are outputted outside through an output unit 7.
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