Analysis On The Technical Specifications For Fuse Selection Of Drop-out Type Fuse Links
1. Basic principles for fuse selection
The selection of High Voltage Fuse fuses must comply with IEC 60282-1 and GB/T 15166 standards, and the core parameters should meet the following requirements:
The rated current In of the fuse must not be less than 1.5 times the maximum continuous load current of the line to ensure matching requirements.
Time-current characteristics: The fuse ampere-second curve is below the thermal damage curve of the protected equipment
The fuse's ultimate breaking capacity (measured in kA value) should not be lower than the maximum expected short-circuit current at its installation location.
In terms of dynamic stability, the fuse must be able to withstand 150 or more thermal cycles of rated current without deterioration.
2. 、Key parameter calculation model
Rated current correction
In'=In×Kt×Kh×Kv
(Kt: temperature correction coefficient, Kh: harmonic coefficient, Kv: ventilation coefficient)
When the ambient temperature>40℃, Kt=0.92-(θ-40)×0.0038
Short-circuit current verification
Maximum breaking capacity of fuse Isc≥1.1×(√3×U×Kd/Z)
(U: system voltage, Kd: dynamic stability factor, Z: system impedance)
The blowing time of the upper fuse should not exceed 0.9 times the minimum blowing time of the lower fuse.
3. Influence of material properties
Low melting point alloy materials
Tin-silver alloy (Sn96Ag4): Fusing accuracy ±7%, suitable for circuits below 100A
Lead-antimony alloy (such as Pb92Sb8) has excellent anti-aging properties and can adapt to high temperature environments.
... Adopting copper-silver composite structure, the ratio of copper core diameter to silver layer thickness is controlled at 5:1, achieving 0.1ms fast speed Rapid gasification
... In high harmonic environment, the performance is optimized by increasing the asymmetry of the fuse cross section by 20%.
For lines with frequent start and stop, a bimetallic compensation structure is used.
4. Typical scenario selection strategy
Distribution transformer protection
The rated current In of the fuse is 1.2 to 1.5 times the rated current of the transformer.
Adopt K-type slow fuse, withstand 6 times In current for 0.5s
Device group protection
... Equipped with T-type fuse with inrush current suppression function, it can withstand 0.01s surge of 100 times In
Motor circuit
The rated current In of the fuse is 2.0 - 2.5 times the motor starting current.
Use a D-type fuse with inertia delay characteristics and set a 150ms action dead zone
... ... 5%
Aging coefficient missing: After 10 years of operation, the fusing time will be shortened by 18%~22%
VI. Model selection verification method
Thermal stability check: I²t fuse value ≤ 75% of the I²t value of the protected equipment
Dynamic resistance test: Full voltage drop ≤ 2mV/A (100A range)
Pre-arc characteristic detection: pre-breakdown time shall not be less than 0.9 times the theoretical calculated value.
Spectral analysis: Deviation of silver content on melt surface ≤0.3%
VII. Development of new fuse technology
... 8. Conclusion
Scientific fuse selection requires the establishment of a three-dimensional selection model based on system parameters, environmental conditions and material properties. It is recommended to adopt a dynamic selection method based on fault current spectrum analysis, and build a fuse life prediction system in combination with online monitoring data. Enbimei has established a fuse characteristic database and regularly conducts melt metallographic testing to ensure that the protection characteristics are upgraded in sync with the development of the power grid.
