The fuse is very easy for our electrician to handle. For small power applications, we use thin copper wires, while for larger loads, thick copper wires are used. If it blows, it's simply replaced with a higher-rated one. In recent years, our textile mill has reduced the number of fuses used, and now we rely more on circuit breakers. In the high-voltage distribution room, we use RN2 0.5A fuses for voltage transformers and 3.15A RN2 fuses for 30KVA transformers. On the low-voltage side, we have 1A RT14 fuses for control circuits and 50/63A fuses for capacitor protection. In the workshop, we use RT0 200A fuses in the distribution panel and 2-10A RT14 fuses for secondary control. We also use quick-break fuses for transistor protection in HY492 inverters. Most other fuses have been replaced by vacuum circuit breakers for high voltage and high-performance low-voltage circuit breakers ranging from 100A to 3200A, as well as miniature circuit breakers from 1A to 32A.
Figure 4 shows the inverse time characteristic curve of a fuse. Each fuse element has a minimum melting current, which varies depending on temperature. Although this value can be influenced by environmental factors, it is usually negligible in practical applications. The minimum melting coefficient is the ratio of the minimum melting current to the rated current of the fuse. For standard fuses, this coefficient typically ranges between 1.1 and 1.5. It’s generally considered that if the coefficient is above 1.25, then a 10A fuse will not blow unless the current exceeds 12.5A.
6.2 Selection Method
The rated current of a fuse should be selected based on the application:
(1) For circuits with smooth load without starting current, such as lighting or resistive loads, the fuse rating should be slightly higher than or equal to the load current.
(2) When protecting a single motor running continuously, the fuse rating can be calculated using the maximum starting current. A common formula is: Ir ≥ (1.5~2.5) * ie, where Ir is the fuse rating and ie is the motor’s rated current. If the motor starts frequently, the coefficient can be increased to 3~3.5, depending on the actual situation.
(3) For multiple motors on a single power line, the formula becomes: Ir ≥ (1.5~2.5) * ie max + Σie, where ie max is the largest motor’s rated current, and Σie is the sum of the others. To prevent over-level tripping and minimize the impact of faults, the upper-level fuse should have a rated current about 1.6 times that of the lower-level fuse.
7. Conclusion
I’ve come to fully understand the characteristics of fuses, even though I wasn’t familiar with them at first. Now, I can apply this knowledge effectively to ensure better and more reliable performance in our systems.
Degrees Of Freedom Platform,Wave Simulation Platform,Shipboard Motion Simulation Bench,flight sim motion platform
Suzhou Johnson Automation Technology Co., Ltd. , https://www.cn-johnson.com