| 摘要 |
<p>A method and system for protecting an electricity network against restriking earth faults, which electricity network comprises one or more feeders (F1 and F2) going out from a supply point (S) and is preferably a three-phase (L1, L2 and L3) network, the method comprising the steps of: detecting an earth contact related to an earth fault in the electricity network, identifying the feeder (F2) on which the earth contact occurs by means of current pulses or current pulses and voltage values related to the earth contact, a current value being interpreted as a current pulse at the moment the instantaneous value of the current divided by the effective value of the current exceeds a predetermined limit, whereby the number of detected earth contacts is calculated per each feeder (F1 and F2), and it is identified that there is a restriking earth fault on the feeder (F1 or F2) if the number of the detected earth contacts per said feeder exceeds a predetermined number during a predetermined period, or if the number of the detected earth contacts per said feeder exceeds a predetermined number while the voltage between the star point of the electricity network and the earth, i.e. the zero voltage, remains above a predetermined limit. <IMAGE></p> |
