Analysis of Material Effects on Temperature Rise Characteristics And Breaking Capacity of High-Voltage Current-Limiting Fuses

1. Introduction

High-voltage current-limiting fuses are essential protection devices in power systems rated from 3.6 kV to 12 kV, providing overcurrent and short-circuit protection for transformers, motors, and capacitors. These fuses are characterized by high breaking capacity—typically 40 kA to 50 kA—and low power loss. The fundamental operating principle involves a fusible element that melts under fault current conditions, with the arc subsequently extinguished by the surrounding arc-quenching medium before the current reaches its peak value. The performance of these devices in terms of temperature rise and breaking capacity is critically dependent on the materials used in their construction.

2. Fusible Element Materials

The fusible element is the core component determining both steady-state temperature rise and fault-current interruption performance.

Silver remains the benchmark material for high-performance fuse elements. Pure silver exhibits exceptional electrical conductivity (≥100% IACS), thermal conductivity of 429 W/(m·K), and excellent arc erosion resistance. Silver elements provide stable fusing characteristics and reliable circuit protection. However, silver's relatively high melting point (960°C) means that under prolonged overload conditions, the element may reach elevated operating temperatures, potentially affecting fuse integrity.

Copper offers similar advantages with its low resistivity and high thermal conductivity, enabling smaller cross-sectional areas and reduced metal vapor production during arcing. The higher melting point of copper (1080°C) compared to silver presents challenges for rapid fault interruption, as larger fault currents are required to achieve timely melting.

Aluminum represents a cost-effective alternative. Research on high-breaking-capacity (HBC) fuses with 99% nickel-plated aluminum elements demonstrates that while such fuses can interrupt maximum rated breaking currents, difficulties arise at minimum rated breaking currents. Without the application of a eutectic point (typically silver-based), aluminum-element fuses cannot achieve acceptable low-current interruption performance. The M-effect—a metallurgical phenomenon utilizing low-melting-point alloys—can be employed to modify the time-current characteristics and improve low-current interruption capability.

Advanced designs employ multilayer fuse element structures, where different metal coatings with varying resistivities are applied to the ends of the metallic fuse body. This configuration creates differential current distribution, effectively controlling surface temperature rise while maintaining high power dissipation in the central section where cross-sectional area is smaller. During overcurrent events, the central portion preferentially melts, enabling precise adjustment of the time-current characteristic.

3. Arc-Quenching Media

The arc-quenching material plays a decisive role in breaking capacity and post-arc temperature behavior.

Quartz sand is the predominant arc-quenching medium in high-voltage current-limiting fuses. When the fuse element melts and an arc is initiated, the arc burns within the small cavity created by vaporized metal. The narrow gaps between quartz sand particles constrict the arc column diameter, while the cooling effect of the sand enables arc extinction before the current reaches its steady-state value. High-purity crystalline quartz sand (99.99%) is specified for applications requiring rated breaking currents of 31.5 kA to 50 kA.

The granulometric composition of quartz sand critically influences fuse performance. Research using emission spectroscopy has shown that the grain size distribution affects electrical characteristics, arc temperature, and electron density during arc extinction. Six adjacent grain-size intervals of 50 µm width have been studied, with the upper limit below 1000 µm. The dimensions of the fulgurite—the fused sand structure formed during arcing—are found to be proportional to the granulometry. Factors such as purity, grain size distribution, and settling characteristics must be carefully controlled to optimize extinction performance.

Surface-modified arc-quenching fillers represent an advanced approach, where gas-evolving materials are bound to the surfaces of pulverulent fillers (silicas, silicates, sand, mica, or quartz). These modified compositions enhance the energy absorption capability and improve interruption performance.

4. Housing and Enclosure Materials

The fuse housing must withstand both thermal stress during normal operation and the extreme conditions of fault interruption.

Ceramic housings offer superior mechanical strength and heat resistance, making them suitable for demanding applications. During fault conditions, housing internal surface temperatures can rapidly reach 300°C to 500°C, with areas closest to the fulgurite attaining maximum temperatures first. The fuse element temperature may rise to approximately 1000°C within seconds depending on fault magnitude.

Resin glass-fiber housings provide a lightweight alternative but require careful thermal management. When fuses are installed in SF₆ gas-insulated or confined switchgear, the surrounding epoxy or plastic materials must withstand internal temperatures that can reach several hundred degrees Celsius. Temperature rise tests specified in standards such as IEC 60282-1 are critical, as excessive temperatures can cause fuse encapsulation aging, contact weakening, and premature failure.

The thermal behavior is further influenced by installation orientation. Research on vertical fuse installation reveals that the temperature rise at upper and lower contacts can differ by nearly a factor of two, primarily due to variations in natural convection heat transfer coefficients along the fuse surface.

5. Temperature Rise Characteristics

Temperature rise is governed by the interplay of Joule heating, thermal conduction, convection, and radiation. The steady-state temperature rise must remain within limits specified by relevant standards, typically ≤75 K above ambient for silver-based elements under rated current conditions.

Material selection directly impacts temperature rise through:

· Electrical resistivity determining I⊃2;R losses

· Thermal conductivity affecting heat dissipation

· Contact resistance at electrical junctions

· Surface emissivity influencing radiative cooling

Studies on 10 kV fuses indicate that material defects are prevalent, with material testing failure rates reaching 88.9% and temperature rise test failure rates at 44.4%. Temperature rise hotspots are typically concentrated at sliding contact positions, screw connections, and fastener locations.

6. Breaking Capacity Considerations

Breaking capacity depends on the coordinated performance of all material components. The maximum breaking current must exceed the maximum expected short-circuit current in service.

The arc-quenching material's ability to rapidly cool and de-ionize the arc plasma determines the interrupting capability. The combination of high-purity quartz sand with properly designed element geometry enables the fuse to interrupt currents before the first current peak, thereby limiting both the magnitude and duration of fault current.

7. Conclusion

Material selection for high-voltage current-limiting fuses involves complex trade-offs between temperature rise and breaking capacity. Silver remains the preferred element material for demanding applications due to its superior conductivity and stable fusing characteristics, while copper offers a cost-performance balance. Aluminum elements, though economical, require eutectic point modifications for acceptable low-current interruption. Quartz sand granulometry must be precisely controlled to optimize arc extinction. Housing materials must withstand both steady-state thermal stress and transient fault conditions. Advanced designs utilizing multilayer element structures and surface-modified arc-quenching media continue to push the performance boundaries of these critical protection devices.