company news about How to select I²t of fuse?

        The I²t value is one of the important indicators of the selected fast fuse, that is, the fuse fusing time t is related to the size of the fusing current I, and its law is inversely proportional to the square of the current.

        All kinds of electrical equipment (including power grid) have certain overload capacity. When the overload is light, it can be allowed to operate for a long time, and when it exceeds a certain overload multiple, the fuse is required to fuse within a certain time. When selecting the fuse to protect overload and short circuit, it is necessary to understand the overload characteristics of the electrical equipment, so that this characteristic is properly within the fuse sec-ampere protection range.

        The fusing current Io is theoretically infinite, which is called the minimum melting current or critical current, that is, the melt current will not fuse if it is less than the critical value. The rated current Ie of the selected melt should be less than Io; Generally, the ratio of Io to Ie is 1.5 to 2.0, which is called melting coefficient. This coefficient reflects the different protection characteristics of the fuse when it is overloaded. If the fuse can protect small overload current, the melting coefficient should be lower; The melting coefficient should be higher to avoid melting the melt due to short time overcurrent during motor starting.

        After the current capacity of the fast fuse meets the requirements of the system short-circuit current, the fault current can be isolated in case of short-circuit fault, but the I²t value of the two must be analyzed if the semiconductor devices in series can be protected. When the I²t value of the fast fuse is less than the I²t value of the semiconductor device, it can protect the semiconductor device. In case of short circuit fault, I²t value is divided into two stages, namely, pre-arc I²t and fusing W. The transition time of molten metal from solid to liquid is the pre-arc time, about 1.0~2.0 ms, which can be considered as an adiabatic process. The time integral of the current generated by the fast fuse in this time period can be considered as a certain value, which is determined by the design. The pre-arc I²t value is the same for different materials, and it is a constant for each material. When the molten metal turns into steam, the arc starts to ignite, and the current decreases from the current limit value to zero during the arcing process. At this stage, I²t is called fusing W, which is a variable. This process mainly depends on the absorption of energy due to the corrosion of the filler.

         When designing the fast fuse, many measures should be taken to meet the continuous improvement of the rated current of semiconductor devices, rather than simply using the arithmetic method to select the fast fuse. The experiment shows that when the rated current is increased by one time, the I²t value of the fast fuse is 4 times, while the increase of the I²t value of the semiconductor device is much smaller. In order to reduce the I²t value of the fast fuse, it is more difficult to take measures in many ways, such as reasonable distribution of the melt, shortening the length of the melt, reducing the arc grid and improving the arc extinguishing ability of the arc extinguishing material.