METHOD FOR SHORT-CIRCUIT CURRENT PROTECTION OF ELECTRICAL INSTALLATION Russian patent published in 2001 - IPC

FIELD: protection of power transmission lines against line-to-line shorts. SUBSTANCE: electrical installation current is measured and compared with first and second reference values. Instant disconnection signal is sent when this current exceeds first reference value. When current exceeds second reference value, electrical installation current is stored through first time delay, and present-time current of installation is subtracted from this value to obtain first difference. When electrical installation current rises above second reference value, its phase current is stored through first time delay and present-time phase current is subtracted from this value through second time delay to obtain second difference. If second difference is lower than fourth reference value and first difference, lower than third reference value, disconnection signal is applied. EFFECT: enhanced sensitivity, selectivity, and reduced operating time of protective gear due to eliminating self-start currents of moving load. 4 dwg