Patent ID: 7233470

Claim:
A distance relay apparatus comprising: a sampling element which samples an amount of electricity of a voltage and a current, which are received from an object to be protected, at regular intervals; an A/D converting element which converts the amount of electricity sampled by the sampling element into digital data; a first digital filter which filters the digital data obtained by the A/D converting element; a second digital filter which filters the digital data obtained by the A/D converting element, for a time period that is shorter than that required for filtering of the first digital filter; a first directional relay element which receives the digital data filtered by the first digital filter to perform computation to detect a fault, which occurs in the forward direction from an installing point of the relay apparatus, based on a computing equation; a zone- 1 distance relay element which receives the digital data filtered by the first digital filter to perform computation to detect a fault within a predetermined zone viewed from the installing point of the relay apparatus, based on a computing equation; a fault detecting relay element which receives the digital data filtered by the second digital filter to perform computation to detect a fault within a zone that is narrower than the predetermined zone in terms of data time length which is shorter than that used for the computation of the zone- 1 distance relay element; and a logic element which outputs a relay signal in accordance with a detecting operation of at least one of the zone- 1 distance relay element and the fault detecting relay element and a detecting operation of the first directional relay element.