Electrical Revolution: 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.

Electrical Revolution