Current - Time Characteristic of Fuse

Current – Time Characteristics

• The fast acting fuse is used to protect semi conductor device. 
• The fuse is connected in series with semi conductor device and it open when the current exceeds its rated value. 
• When fuse is not used in the circuit, the fault current increases up to point B. As the fuse current increases, the temperature also increases.
• When fuse is used in the circuit, the fault current increases up to time t = t_m. There is sperk across fuse when it opens at time t = t_m. 
• The fault current increases up to point A and it is called as Peak through let current. The peak through let current is shown in the figure point C.

• The arc resistance increases at point C therefore the fault current decreases. 
• The arc diminishes at point D and fault current becomes zero at that time. The fault clearing time (t_c) is sum of melting time (t_m) and arcing time (t_a) of the fuse.

          t_c = t_m + t_a

• The voltage across fuse during arcing time is known as Recovery voltage or Arcing voltage. 
• It should be noted that the I²t rating of the fuse always less than the I²t rating of the SCR. The low rating SCR is protected by circuit breaker.

Current – time Curve

• The current time characteristic of the semi conductor device is shown in the figure B. 
• The RMS current rating of the fuse is always less than the RMS current rating of the semi conductor device in the low power converter protection.

    

FUSE - TIME CHARACTERISTICS.PDF

PROTECTION OF SEMICONDUCTOR BY FUSE.PDF

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