| 摘要 |
<P>PROBLEM TO BE SOLVED: To eliminate erroneous determination in protection computation due to saturation of CT and prevent malfunction and inoperability just by adding a few arithmetic processing elements to an existing protection relay. <P>SOLUTION: A digital protection relay samples and converts the transformer current of an auxiliary current transformer 1 into digital data through an A-D converter 3. The relay extracts a fundamental wave component from this data through a digital filter 4 and carries out protection computation at a protection computation unit 5 based on this fundamental wave component. When it is determined that the amplitude of the digital data obtained as the result of conversion by the A-D converter includes exceeded the full scale of the A-D converter, a saturation determination processing unit 6 obtains relay operation output. The saturation determination processing unit obtains relay operation output only when the full scale of the A-D converter is exceeded both on the positive side (positive wave) and on the negative side (negative wave) during one cycle of the digital data. The saturation determination processing unit obtains relay operation output on condition that the effective value of the fundamental wave component exceeds a set value. <P>COPYRIGHT: (C)2009,JPO&INPIT |
