Patent ID: 9478968
Filing Date: 2016-10-25
CPC Classification: G01R,H02H

Claim Text:
1. A method for detecting a short circuit on a line of a multi-phase electrical energy supply network with grounded neutral, the method comprising the following steps: recording current and voltage sampled values at a measurement point at one end of the monitored line by an electrical protection device; generating a first fault signal indicating a short circuit on the line if a fault evaluation of the current and voltage sampled values performed by the electrical protection device indicates a short circuit present on the line; and performing the following steps for fault evaluation of the current and voltage sampled values: calculating instantaneous reference voltage values for a reference point on the line from instantaneous current and voltage sampled values recorded before an occurrence of the short circuit; calculating instantaneous comparative voltage values for the reference point on the line from instantaneous current and voltage sampled values recorded before the occurrence of the short circuit and instantaneous current and voltage sampled values recorded during the short circuit; calculating a rectified reference voltage value from consecutive instantaneous reference voltage values and a rectified comparative voltage value from consecutive instantaneous comparative voltage values; comparing the rectified reference voltage value and the rectified comparative voltage value; generating the first fault signal if a difference between the equivalent comparative voltage value and the rectified reference voltage value exceeds a triggering threshold value; and calculating the rectified reference voltage value by the following equation: U ref (n)=2 Nk=n−(N2−1)n(u ref (k)) ##EQU00011## where U.sub.ref(n): rectified reference voltage value; u.sub.ref(k): instantaneous reference voltage value for the sampled value k; n: number of the sampled value after fault occurrence; N: number of sampled values per period; k: summation index; and calculating a rectified comparative voltage value in accordance with the following equation: UV(n)=2Nk=n−(N2−1) n(uV(k)) ##EQU00012## where U.sub.v(n): rectified comparative voltage value; u.sub.v(k): instantaneous comparative voltage value for the sampled value k; n: number of the sampled value after fault occurrence; N: number of sampled values per period; and k: summation index.