Electronic trip device that detects an imminent drop of the power system voltage and comprises a numerical processing circuit and a thermal memory

摘要

The electronic trip device with a thermal memory including a capacitor and a charging resistor arranged in parallel. In normal operation, the capacitor is permanently charged by a supply voltage supplied by the power system to be protected. The trip device includes a processing circuit which performs tripping functions after calculation of a thermal value representative of the thermal state of the power system and detects an imminent drop of the supply voltage. When such a drop is detected, the processing circuit orders discharging of the capacitor until the voltage at the terminals of the capacitor is representative of the calculated numerical value.