| 摘要 |
PURPOSE:To make it possible to detect internal faults with high sensitivity and high speed by permitting the saturation of analog/digital conversion means in setting only for external faults where the maximum input current occurs among the external faults of transformers. CONSTITUTION:An input current transformer 1023 has an ordinary load current within A/D full scale at least at the system secondary current, but the system secondary current during an external fault on tertiary side is set to a conversion ratio exceeding the A/D full scale. Instantaneous data of differential current are obtained from digital data D1, D2 and D3, but the instantaneous data of the differential current is set to '0' when D3 is larger than a predetermined value. Because of this, an internal fault of a transformer 100 can be judged at a high speed by using the differential current. Also, an external fault on the secondary side of the transformer 100 can correctly be judged, and erroneous operation can be prevented even for the external fault on the tertiary side. That is, the dynamic range of current input is made small so that the internal fault can be detected with a high sensitivity. |
