| 摘要 |
PURPOSE:To obtain a ratio differential relay for transformer protection in which a discrimination can be made accurately between internal fault current and excitation surge current when a transformer is thrown into a system by determining ' the content of second harmonic in the basic wave of excitation surge current accurately. CONSTITUTION:Only basic wave and second harmonic are passed through first to third filters 7-13 and subtractors 14, 15. A comparator 16 then calculates the content of second harmonic with respect to the basic wave thus making a decision whether it is an excitation surge current or not. |
