Research On The Control Mechanism And Engineering Application Of The Melting Time Of Drop-out Type Fuse
The fusing time of High Voltage Fuse is the core parameter that characterizes its protection characteristics, and directly determines the speed of overload and short-circuit fault removal. This paper analyzes the formation mechanism of fusing time from multiple dimensions of materials science, thermodynamics and electromagnetics, and explores the optimization control strategy of time parameters in engineering applications.
1. The physical nature of the fuse time
The melting time consists of the heat accumulation stage and the arc extinction stage:
The heat accumulation stage (t1): The fault current causes the melt to heat up to the metal phase transition point, which conforms to the Joule integral law ∫i²dt=K, where the K value depends on the heat capacity of the melt material (silver alloy K=6000 A²s/mm²）
Arc stage (t2): Arc is generated after the melt breaks. The time is affected by the arc extinguishing medium (quartz sand)'s ability to adsorb ions. The typical value is in the range of 3-15ms
2. Analysis of key influencing factors
Material Properties
Inner diameter of melting tube: 28mm diameter design makes the airflow speed reach 120m/s, shortening the arc maintenance time by 30%
Narrow neck number: For each additional melt narrow neck, the dispersion of melting time is reduced by 15%
The time-current curve shows a negative exponential characteristic
Ambient temperature: For every 10°C increase in temperature, the heat dissipation efficiency of the organic composite material support decreases by 8%
... A dynamic model is established based on the energy conservation equation:
Cpmdt/dT=I²R(T)−hA(T−Ta)
Where R(T) is the melt resistance temperature coefficient (silver alloy α=3.9×10⁻³/℃), and h is the convection heat transfer coefficient (12W/m²·K). Finite element simulation shows that under a short-circuit current of 10kA, the time it takes for a 3mm diameter melt to reach the melting point is 32ms, and the error with the measured value is ≤5%.
Maintain a step difference of more than 0.3s with the upper circuit breaker to avoid overstepping tripping
The fuse on the high-voltage side of the distribution transformer should be selected according to 1.5-2 times the rated current
Impact: When the third harmonic content exceeds 15%, the melt cross-sectional area should be increased by 10%
Fuse time drift
Quartz sand is damp, which causes arc extinguishing time to be prolonged: regularly measure the moisture content of the medium (control ≤0.03%)
Contact oxidation increases contact resistance: silver plating process (thickness ≥50μm)
... ... VI. Technological development trends
... New arc extinguishing material
By filling quartz sand with boron nitride nanotubes, the arc voltage can be increased to 800V/cm, while the arc extinguishing time can be shortened by 40%.
VII. Conclusion
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