Thermal protection relay
AssigneeSchneider Electric Industries SAS
InventorBernhard Gotzig
Life of this patent
Estimating the term…
Abstract
The thermal protection relay determines a value representative of the thermal image of an apparatus to be protected according to a measured current value, to a previous value of the thermal image and to preset heating and cooling time constants. The relay takes into account a non-zero initial thermal image, determined from experimental thermal resistance curves of the apparatus. In the case of a motor, for example, this enables the cold tripping curve of the relay to be lowered without modifying the hot tripping curve, so as to bring the tripping curves of the relay closer to the thermal resistance curves of the motor.
Claims5
A thermal protection relay designed to protect an electrical apparatus, comprising means for measuring a current absorbed by the apparatus, means for determining a value representative of the thermal image of the apparatus according to the value of the measured current, to a previous value of the thermal image and to at least one preset time constant, means for determining at least one protection threshold, means for comparing the value representative of the thermal image with the protection threshold and means for producing an alarm and/or tripping signal when the value representative of the thermal image exceeds the protection threshold, a relay wherein a non-zero initial thermal image is taken into account for determining the thermal image, the value of the initial thermal image being determined from experimental thermal resistance curves of the apparatus.
Dependencies are inferred from the claim text.