High current fuses must be of the "fast break" type, which is mainly based on the core requirements of protection effectiveness, equipment safety, and prevention of catastrophic accidents. The following is a logically clear explanation:
The enormous energy release and destructive speed:
According to Joule's law (Q=I ² Rt), the heat generated when a fuse blows is proportional to the square of the current.
High current means huge energy release: when the fault current is large (such as short-circuit current, which can reach tens or even hundreds of times the normal current), the accumulated energy in the circuit will soar sharply in a very short period of time. For example, the heat generated by a current of 100A is 100 times that of a current of 10A (squared relationship).
Destruction is instantaneous: the temperature of protected equipment (such as wires, transformers, motor windings, semiconductor devices) will rise sharply in milliseconds when subjected to such a huge overcurrent. Insulation materials can quickly carbonize and melt, and conductors may melt or even vaporize, generating arcs and causing fires.
Requirements for protecting timeliness:
Slow break fuse response too slow: Slow break fuses (delay fuses) are designed to withstand short-term, moderate overload currents (such as motor starting currents). It takes a certain amount of time (seconds or even longer) to accumulate enough heat to melt.
High current faults cannot wait: Faced with huge short-circuit currents, the equipment may be completely destroyed before the slow breaking fuse starts to effectively melt. The melting time of slow breaking fuses cannot keep up with the speed of damage caused by high current faults.
Quick break is the only option: The design of a quick break fuse allows it to quickly melt in a very short time (usually milliseconds) when encountering high current overload or short circuit. This is like cutting off the source immediately at the beginning of an energy avalanche, maximizing the restriction of energy flowing into the fault point and providing effective protection for downstream equipment.
Preventing arc and fire risks:
When a conductor melts under high current, if the melting speed is not fast enough, a strong and continuous arc will be generated at the gap where it breaks.
High current arc is extremely dangerous: the arc energy generated by high current is extremely high, and the temperature can reach thousands of degrees Celsius. It can easily ignite surrounding insulation materials, plastic shells, and even metals, and is one of the main culprits causing electrical fires.
Quick break arc suppression: The special structure of the quick break fuse (such as filled with arc extinguishing quartz sand and multi-stage fuse design) not only has a fast melting speed, but more importantly, it can quickly and effectively absorb arc energy, cool and extinguish the arc, and minimize the duration and harm of the arc. Slow breaking fuses cannot effectively deal with this level of arc.
Characteristics of protected objects:
Equipment or circuits that require high current fuse protection usually have high intrinsic value or serious consequences of failure (such as main power input, high-power inverter output, battery pack protection, power distribution system).
The short-circuit withstand capacity of these devices often has strict limits (such as the Joule integral value of 'I ² t'). The core characteristic of a fast breaking fuse is its very low 'I ² t' value, which means that it consumes very little energy during the melting process, ensuring that the total energy released when it melts is lower than the safety limit that the protected equipment can withstand, thus truly playing a protective role. The 'I ² t' value of slow breaking fuses is usually much higher than the safety limit of these critical devices.
Summary and Core Logic Chain:
High current faults (especially short circuits) → Instantly releasing huge energy (I ² R) → Protected equipment will be destroyed/ignited at a millisecond rate → Protection must be completed in a shorter time → Slow breaking fuses have a much longer melting time (in seconds) than the breaking time → Protection fails → Fast breaking fuses with melting time (in milliseconds) much shorter than the breaking time must be used → Fast breaking fuses achieve rapid melting and efficient arc extinguishing through special structures → Quickly cut off fault currents, limit energy release, extinguish arcs → Effectively protect equipment and prevent fires.
Therefore, in high current application scenarios, fast breaking characteristics are a necessary condition for fuses to play their core protection function, and slow breaking fuses cannot meet the safety requirements under such extreme working conditions.