Patent ID: 7640080
Filing Date: 2009-12-29
Classification: G01K,H01H,H02H

Abstract:
1. A protection device for a load circuit including a power supply, a switch and a load, comprising: a current detection device detecting and measuring a current in a conductor connected between the power supply and the load; a first temperature estimation device that estimates a rising temperature of the conductor, when the current is detected by the current detection device; a second temperature estimation device that estimates a falling temperature of the conductor when the current detection device fails to detect the current or detects that the current is being decreased, a third temperature estimation device that estimates an arc-induced rising temperature of the conductor that is induced by arcing that occurs just after the current has returned to a normal current; a fourth temperature estimation device that estimates a present temperature of the conductor based on the estimated rising, falling, and arc-induced rising temperatures; a temperature determination device that determines whether the present temperature of the conductor estimated by the fourth temperature estimation device exceeds a predetermined threshold temperature; a shutoff control device that shuts off power to the load circuit when the temperature determination device determines that the present temperature of the conductor exceeds the predetermined threshold temperature, and wherein the rising temperature is estimated based on both the current measured by the current detection device and thermal properties of the conductor; the falling temperature of the conductor is estimated based on the thermal properties of the conductor; and the arc-induced rising temperature is estimated based on the current just before the current returns to the normal current.