Electronic trip device comprising an improved long delay function

摘要

To perform the long delay function of an electronic trip device, a quantity (TLR1) representative of the thermal current state varies proportionally to the difference (I.sup.2 -Is.sup.2) between the square of a value (I) representative of the current flowing in a conductor to be protected and the square of a current threshold (Is). This first quantity (TLR1) is used in combination with a second value (TLR2) to produce a tripping signal when the second value exceeds a preset value (TLR2max). The second quantity preferably increases proportionally to the square (I. sup.2) of the value representative of the current, when the first quantity exceeds a preset threshold (STLR1) and decreases, preferably exponentially, when the first quantity is lower than this threshold.