NEW DIGITAL DISTANCE-PROTECTION SYSTEM COMBINING SIGNAL-SPECTRUM ANALYSIS AND DIFFERENTIAL-EQUATION SOLUTION FOR POWER-DISTRIBUTION SYSTEMS

Normally the incoming signal data for digital distance-protection rela ys are distorted sinusoidal oscillations. To get a correct response, c onsidering upper harmonics, it is necessary to fulfill a Fast Fourier Transformation (FFT) with signal analysis. To receive a fast reply tim e of protection relays, the use of differential-equation ion solutions is demanded. A combination of spectrum analysis and differential solu tion is shown, which joins the advantages of considering upper harmoni cs and short-grading time, using digital signal processors.