| 摘要 |
PURPOSE:To eliminate influence of higher harmonics by providing a filter for removing specific order of higher harmonics produced in a system to be protected. CONSTITUTION:Input electrical amounts 1a, 1b, 1c of respective phases converted into digital amounts are fed to digital filters 5a, 5b, 5c in order to remove higher harmonic components. After ternary higher harmonic component is removed, the electric amount is fed to an adder 2 and zero-phase data Iof are obtained based on the sum of three-phase electrical amounts. That value is fed to an amplitude operating section 3 in order to obtain the amplitude, and a defect detecting section 3 produces an output upon detection that the amplitude is larger than a specific value K. Since tertiary higher harmonic components produced from a thyristor igniter are removed through the digital filters 5a, 5b, 5c, zero-phase component can be calculated accurately. |
