PROTECTIVE DEVICE FOR LOAD CIRCUIT

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PROBLEM TO BE SOLVED : To provide a protective device for a load circuit capable of detecting a temperature rise in an electric wire and completely cutting off the load circuit on the occurrence of rare short. SOLUTION : A temperature rise in the electric wire 7 is calculated based on thermal characteristics (thermal resistance and thermal capacity) of the electric wire 7 or a contact conductor when a current flowing through the load 4 rises, a temperature rise due to arc is calculated when arc occurs, and a down temperature of the electric wire 7 is calculated based on the thermal characteristics of the electric wire 7 when a current flowing through the load 4 is zero or decreases. Besides, the obtained temperature rise and down temperature are totally added to estimate a present temperature of the electric wire 7, and the load circuit is cut off when the estimated temperature exceeds a prescribed permissible temperature, thus protecting the circuit with high accuracy based on the temperature rise of the electric wire 7. COPYRIGHT : (C)2008, JPO&INPIT