Parameters of Self Restoring Fuses
Parameters of self restoring fuses
1.Rated voltage
Rated voltage refers to the high voltage that can be withstood after the self recovery fuse is disconnected. The voltage borne by both ends of a self restoring fuse during the connection period is far less than its rated voltage. When selecting a self restoring fuse, it is generally required that its rated voltage be greater than the effective circuit voltage.
2. Rated current
The rated current is the high current that a self restoring fuse can operate for a long time. Assuming the protection current is Ir and the rated current of the self recovery fuse should be In, both should meet the following conditions: In=Ir/(fo * f1), where fo is the reduction rate for self recovery fuses of different specifications. For self recovery fuses of ICE specifications, no reduction rate can be added, that is, fo=1. For self recovery fuses of UL specifications, the reduction rate is fo=0.75. To consider the reduction rate after considering temperature, the higher the ambient temperature, the hotter and shorter the lifespan of the self recovery fuse when it operates. It should be emphasized here that the air temperature surrounding the self recovery fuse should not be confused with room temperature. Whether it is UL or ICE specifications, the requirements for self restoring fuses are formulated at room temperature of 25℃, so there is no need to consider a certain reduction rate. Obviously, the reduction rate of self recovery fuses varies depending on the ambient temperature. The following figure shows the reduction rate of self-healing fuses with different characteristics at different temperatures. Curve A corresponds to a glass tube self-healing fuse (full fuse: low resolution), Curve B ceramic tube self-recovery fuse (ultra fast fuse, fast fuse self recovery fuse, and spiral wound self-recovery fuse: high resolution) Curve C corresponds to polymer self recovery self recovery fuse (PPTC plastic polymer made self-recovery fuse).
Fig.1
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