Characteristics of fuses

Main features of fuse

1) After the fault is blown, the fuse must be replaced.

2) The protection function is single, with only one overcurrent inverse time characteristic, which is used for overload, short circuit and ground fault protection.

3) When one-phase fuse occurs, the three-phase motor will cause adverse consequences of two-phase operation. Of course, a fuse with an alarm signal can be used to make up for it, and one-phase fuse can disconnect the three-phase.

4) The remote control cannot be realized, and it needs to be combined with the electric knife switch and switch.

Fuse Characteristics

The action of the fuse is realized by the melting of the melt. The fuse has a very obvious characteristic, that is, the ampere-second characteristic. For the melt, its operating current and operating time characteristics are the ampere-second characteristics of the fuse, which are also called inverse time delay characteristics, that is: when the overload current is small, the fusing time is long; when the overload current is large, the fusing time is short.

To understand the ampere-second characteristics, we can see from Joule’s law that in the series circuit, the R value of the fuse is basically unchanged, and the calorific value is proportional to the square of the current I, and proportional to the heating time T, that is: when the current When it is larger, the time required for the melt to blow is shorter. When the current is small, the time required for the melt to fuse is longer, and even if the rate of heat accumulation is less than the rate of thermal diffusion, the temperature of the fuse will not rise to the melting point, and the fuse will not even blow. Therefore, within a certain overload current range, when the current returns to normal, the fuse will not blow and can continue to be used.

Therefore, each melt has a minimum melting current. Corresponding to different temperatures, the minimum melting current is also different. Although the current is affected by the external environment, it can be ignored in practical applications. Generally, the ratio of the minimum melting current of the melt to the rated current of the melt is the minimum melting coefficient. The melting coefficient of the commonly used melt is greater than 1.25, that is to say, the melt with a rated current of 10 amps will not fuse when the current is below 12.5 amps. .

It can be seen from this that the short-circuit protection performance of the fuse is excellent, and the overload protection performance is average. If it is really necessary to use it in overload protection, it is necessary to carefully match the line overload current with the rated current of the fuse. For example: 8-amp melt is used in a 10-amp circuit for short-circuit protection and overload protection, but the overload protection characteristics at this time are not ideal.