The rated current of the fuse is not equivalent to the rated current of the melt. The selection of the rated current for the melt depends on the load current of the protected equipment. In coordination with the main electrical equipment, the rated current of the fuse needs to be greater than the rated current of the melt. It is crucial to ensure that the generated content is based on the original text information and refrain from using a conversation style approach like ChapGPT. Instead, focus on generating completely different ways of presenting the information using a language model.
The composition of a fuse primarily consists of three components: the melt, the shell, and the support. The key factor in controlling the fuse's fusing characteristics lies in the melt. The fusing characteristics are determined by the material, size, and shape of the melt. Melt materials are categorized into low melting point and high melting point materials. Substances like lead and lead alloys, falling under the low melting point category, easily fuse due to their low melting points. However, their large resistivity requires a larger cross-sectional size for the melt, resulting in the generation of more metal vapor during fusing. Hence, they are suitable for fuses with low breaking capacity. On the other hand, high melting point materials such as copper and silver have a higher melting point, making them more resistant to melting. Nevertheless, their low resistivity allows them to be formed into smaller cross-sectional dimensions compared to low melting point melts. Consequently, less metal vapor is produced during fusing, making them suitable for high breaking capacity fuses. The shape of the melt can be categorized as filament or ribbon. Altering the shape of the variable section can significantly impact the fusing characteristics of the fuse. This enables the availability of various fusing characteristic curves that can fulfill the requirements of different types of protection objects.
Ampere-second characteristics:
The melting of the melt is how the fuse carries out its action. An important feature of the fuse is its ampere-second characteristic. It is crucial to rearrange the original content while ensuring that the generated content is highly similar and based on the given information, rather than follow the conversational manner of generating content.
The ampere-second characteristics of the fuse, also known as inverse time delay characteristics, determine the operating current and operating time of the fuse during a melt. These characteristics depict that when the overload current is small, the fuse takes a longer time to fuse, whereas when the overload current is large, the fuse fuses quickly. To summarize, the fuse's fusing time varies inversely with the magnitude of the overload current.
The ampere-second characteristics can be explained through Joule's law, as Q=I2*R*T. In a series circuit, the fuse's R value remains relatively stable, and the amount of heat generated is directly proportional to the square of the current I and the heating time T. This means that when the current is higher, the fuse will blow faster, and when the current is lower, the fuse will take longer to blow. If the heating rate is slower than the diffusing rate, the fuse's temperature won't rise to the melting point, and it won't blow. Hence, within a specific range of overload currents, the fuse won't blow when the current returns to normal and can be used again.
Hence, it is important to note that every melt possesses a minimum melting current, which varies according to different temperatures. Although external factors may influence the current, they are typically disregarded in practical applications. In general, the minimum melting coefficient is determined by the ratio of the minimum melting current to the rated current of the melt. Commonly used melts exhibit a melting coefficient greater than 1.25, meaning that a melt with a rated current of 10A will not melt unless the current exceeds 12.5A.
The fuse demonstrates excellent performance in terms of short-circuit protection, while its performance in overload protection is average. If there is a need to rely on it for overload protection, it becomes crucial to carefully match the line's overload current with the fuse's rated current. For instance, in a 10A circuit, using an 8A fuse for both short-circuit and overload protection may not yield the desired results in terms of overload protection characteristics.
The selection of a fuse primarily depends on the load's protection characteristics and the magnitude of the short-circuit current. It is essential to choose a fuse type accordingly. In the case of small-capacity motors and lighting branch lines, fuses are commonly utilized for overload and short-circuit protection. Consequently, it is preferable to have a fuse with a relatively low melting coefficient. The RQA series fuses with lead-tin alloy melts are typically recommended for such applications. On the other hand, when dealing with larger-capacity motors and lighting trunks, one must also consider factors like short-circuit protection and breaking capacity. In such scenarios, fuses from the RM10 and RL1 series, offering higher breaking capacity, are usually chosen. Additionally, if the short-circuit current is of significant magnitude, fuses from the RT0 and RTl2 series, which provide current limiting features, should be used.