The difference between DC fuses and AC fuses, with the increasing demand for DC fuses in industry and rail transit and new energy vehicles, how to correctly choose DC fuses for effective protection is a problem that users and manufacturers should take seriously. When choosing DC fuses, they cannot simply copy the electrical specifications and structural dimensions of AC fuses, because there are many between the two Different technical specifications and design concepts are related to the comprehensive consideration of whether the fault current can be broken safely and reliably and without accidents.
1, because the DC current does not have the zero crossing of the current, so when the fault current is broken, it can only rely on the arc under the action of forced cooling of the quartz sand filler to quickly quench the breaking, which is much more difficult than the breaking of the AC arc. The reasonable design and welding method of the fuse, the purity and particle size ratio of the quartz sand, the melting point, the curing method and other factors determine the DC arc Efficacy and effect of forced extinguishing.
2, under the same rated voltage, the DC arc arc energy is more than 2 times the AC arc energy, in order to ensure that each section of the arc can be limited within a controllable distance at the same time quickly extinguished, there will be no section of the arc direct series conduction into a huge energy collection, resulting in the continuous arc ignition time is too long the fuse burst accident, the tube body of the DC fuse It is generally longer than the AC fuse, otherwise the size difference that cannot be seen during normal use will have serious consequences when the fault current appears.
3, according to the recommended data of the international fuse technical Organization, every 150V increase in DC voltage, the length of the fuse tube should be increased by 10mm, and by analogy, when the DC voltage is 1000V, the length of the tube should be 70mm, when the DC voltage is as high as 10KV-12KV When, the length of the tube body should be at least 600-700mm, even if the fuse is bent, the length of the tube body should be ensured to be about 300mm, otherwise the threat of series arc still exists. Today's AC 10-12KV fuses at home and abroad generally use 292-442mm tube length, DC fuses in Europe and the United States at 2000V DC, the round tube body is 127-190mm, square large current tube body is 170-200mm, are based on the scientific choice that must ensure safe and reliable breaking.
4, when the fuse is used in the DC circuit, the complex influence of inductance and capacitor energy must be considered, so the time constant L/R is an important parameter that can not be ignored, and it should be accurately evaluated according to the short-circuit fault current occurrence and attenuation rate of the specific line system, not randomly selected large or small. Because the DC fuse time constant L/R size determines the breaking arc energy and breaking time and allow voltage, so the thickness and length of the tube body must be reasonable and safe to choose and use, some manufacturers limited to the size of the existing porcelain tube or to reduce costs, blindly using low strength porcelain or short tube body to produce DC high voltage fuse practice, is not responsible and desirable.
5, some manufacturers because there is no own system of DC fuse products, use AC fuse instead of use, from a practical point of view is feasible, but based on the above safety reasons, when the AC fuse is used in the DC circuit, it should be used. For example, Siemens' 1000V AC fast melting is limited to 440V DC circuit, and the AC 700V fuse of EATON's BUSSMANN in the United States also follows a voltage reduction factor of 1.3-1.4 when used for DC, and is only used in 500V DC circuit, which is a safety standard recognized by the international electrical industry.
The difference between DC fuses and AC fuses is here, and I hope to help you. Finally, I would like to say that although there is no difference between DC fuses and AC fuses that we know before, or only the difference between current size and voltage level, we still need to learn more new knowledge and understand some new fuse technology.