Mechanisms for Explosively-Formed Fuse Performance Degradation

Energies

High-voltage fuses are found in most electrical installations, where they are used for overcurrent protection and are the pieces of equipment providing the highest degree of protection for the lowest initial cost. This article focuses on the behavior of high-voltage fuses containing a fuse element entirely made of aluminum. We made high-power linear electrical circuits for experiments on these fuses under the most severe operating conditions. The article presents the construction details of the fuse element and its features, as well as various arc extinguishing media. The heating behavior and time–current characteristics were studied in comparison with fuses made of copper. We obtained the maximum instantaneous value of the current reached during interruption for a 24 kV, 50 kA, 50 A fuse, as well as the value of the minimum breaking current.

IEEE Transactions on Plasma Science, 1998

At Los Alamos, we have primarily applied Explosively Formed Fuse (EFF) techniques to high current systems. In these systems, the EFF has interrupted currents from 19 to 25 MA, thus diverting the current to low inductance loads. The magnitude of transferred current is determined by the ratio of storage inductance to load inductance, and with dynamic loads, the current has ranged from 12 to 20 MA. In a system with 18 MJ stored energy, the switch operates at a power up to 6 TW. We are now investigating the use of the EFF technique to apply high voltages to high impedance loads in systems that are more compact. In these systems, we are exploring circuits with EFF lengths from 43 to 100 cm, which have storage inductances large enough to apply 300 to 500 kV across high impedance loads. Experimental results and design considerations are presented. Using cylindrical EFF switches of 10 cm diameter and 43 cm length, currents of approximately 3 MA were interrupted producing ~200 kV. This indicates the switch had an effective resistance of ~100 m where 150-200 m was expected. To understand the lower performance, several parameters were studied, including: electrical conduction through the explosive products; current density; explosive initiation; insulator type; conductor thickness; and on. The results show a number of interesting features, most notably that the primary mechanism of switch operation is mechanical and not electrical fusing of the conductor. Switches opening on a 1 to 10 s time scale with resistances starting at 50  and increasing to perhaps 1  now seem possible to construct, using explosive charges as small as a few pounds.

IOP Conference Series: Materials Science and Engineering, 2012

Electrical needs are continously growing because of many various factors linked to increasing consumption and a green perception. This development-geographical, increasing production, growth of transport network, interconnection of continental networks, diversity of the transport technologies …-can not be dissociated from electrical safety considerations whatever the voltage level. For the three main levels of electric network-High Voltage, Middle Voltage and Low Voltage-one has to provide efficient electrical safety techniques or schemas which integrate different electrical safety apparatus. Among well-known apparatus we can cite SF 6 breakers, HV and MV switchgears (such as MV cells, MV and LV high current vacuum switchgears), and fuses. Electrical fuses are especially used in the MV and LV domains, sometimes as an additional safety device and sometimes as the main electrical safety component which is linked to the electrical current breaking function of electric fuse. In the paper, we will quickly depict the various kinds of electric fuses. We will especially focuss on the physical mechanisms-whatever the type of work, experimental, theoretical, modelling or empirical-prevailing during the pre-arcing period of the electric fuse operation.

The development of explosive generators that do not require an outside electrical power source, such as ferroelectric generators, requires novel switching components to allow for maximum transfer of the produced electrical energy. One critical component to achieve efficient operation is an effective closing switch. Typically a spark gap is used, although these systems tend to be relatively large compared to the explosive generator, require high pressure containers for reliable voltage breakdown operation, and are costly to manufacture. It may be possible to greatly simplify a closing switch by using a material which uses the explosive shockwave to switch. This can allow for a compact closing switch to be integrated into an explosive generator system. Significant research has been conducted on the change of conductivity of different solid bulk materials -insulators, semiconductors, and metals -under shock loading. A limited amount of research has also been conducted on powders. Aluminum powder has the unique characteristic of being very resistive in powder form due to the thin layer of aluminum oxide which forms on the grain surfaces. However, under shock loading it may be possible to fracture this layer allowing a highly conductive wavefront to propagate through the material. HEM Technologies and Texas Tech University researched different aluminum powder grain sizes as potential candidates for an explosive switch. Comparative results under shock loading and pulsed voltage holdoff are presented for the different aluminum grains researched.

Pre-arcing stage is the first working step in high breaking capacity (HBC) fuse operation and affects the following step, namely, the arcing step. We have performed realistic HBC fuse tests for short (<10 ms) and medium (>10 ms) pre-arcing times by varying the phase angle of the electrical fault (defined as the phase angle of the fault current once the supplied voltage is applied to the fuse) in the range from 0 • to 160 • , for two values of the power factor (cos ϕ ∼ 0.9 and cos ϕ ∼ 0.1). Experimental values of the pre-arcing time and the arcing time (t arc) are given for t prearc /t arc 1 to ∼4.2, and discussed from the energetic point of view by taking into account the inductive source term. The adiabatic assumption classically used in the modelling is also examined. The influence of the pre-arcing step on the arcing step is analysed by means of the Joule integral, the energy dissipated in the fuse and the mass and length of the fulgurite.

Annals of the University of Craiova, Electrical Engineering Series, 2021

The article presents an experimental study of high breaking capacity fuses with aluminum fusible element with and without a eutectic point, at minimum rated breaking current, preceded by experiments at maximum rated breaking current. The paper shows that in the construction with aluminum fusible element, the fuse has no problem breaking the maximum rated breaking current, but real difficulties appears when it comes to the minimum rated breaking current. The experiments were made on a homogeneous series 6-20 A, with a focus on the 36 kV, 25 kA, 16 A fuse. The fuses suffered multiple construction changes and tests with and without a eutectic point. After several tests was found an acceptable constructive solution was, but the obtained value for the minimum rated breaking current is not a commercially attractive value. It was also tested the capacity of the fuse to transfer the breaking duty to a load break switch.

Recently, owing to a high demand of and high dependence on electric power, the reliability of the distribution voltage of electric power systems has become more important. 22 kV high voltage cutout fuses have been used widely, but some melting accidents have occurred due to pollution/contamination of bushings. As the number of contaminants in bushings increases, the electric fields on the fuse element surface rise to a critical level, triggering corona discharge. A fuse element material that is more resistant to corona discharge than the Ag element is desired. A new type of current-limiting fuse made of stainless steel wires, which is low-cost and simple in design has been developed. Characteristics tests, including a blocking test with a high surge current when a voltage is applied, have been conducted. Using a model fuse, it was confirmed that this new type of fuse possesses similar performance characteristics to those with an Ag element.

IEEE Transactions on Plasma Science, 2000

Compact electroexplosive fuses (EEFs) as part of an explosively driven system are of interest for the one-time single-shot generation of high-power pulses. For instance, the transition from a very large driving current produced by an explosively driven flux compression generator (FCG), i.e., low impedance, to a large voltage spike delivered to the load, i.e., high impedance, can be done using an inductive storage system and an EEF. Typically, the EEF can be as large as, if not larger than, the current driver attached to it, thus making it one of the largest components in the system. Reduction in the size of the fuse will allow for size reductions of the entire high-power microwave (HPM) system. The goal of optimizing an EEF as an opening switch is to produce the greatest voltage multiplication possible to drive a load under physical size constraints. To optimize the fuse, several parameters are taken into account, including, but not limited to, fuse material, fuse length, fuse shape, and quenching medium. Individual optimization of these parameters will lead to complete optimization of an EEF, therefore resulting in a compact fuse capable of consistently producing maximum voltage multiplication for HPM systems.

1993

The need to reduce solid armature and launch package start-up acceleration for an inductively driven railgun necessitates an increase in the storage inductor to gun commutation time. For this purpose, a "fused," high current, explosively actuated opening switch has been designed and tested at the Electric Armaments Division, ARDEC, Picatinny Arsenal, New Jersey. The switch has been operated in the 600 kA to 1300 kA current range and has repeatedly demonstrated opening times from 720 ~s at 600 kA to 840 ps at 1000 kA. Armature jerk for an 615 gram solid armature has been reduced from 350 Megagees (MG)/sec to 38 MG/sec at the 600 kA operating point. The design premise for the thermal fusing section, operating experience and test results are presented.

IEEE Transactions on Plasma Science, 2015

The electrical explosion characteristics of partially confined square shaped aluminum foils have been investigated under vacuum down to 10 −4 mbar. In contrast to its behavior near atmospheric pressure, an anomalous rise has been observed in the current flowing through the foil after burst. The peak voltage developed across the foil, which is proportional to the dielectric strength of expanded vapor, has also been found to be decreasing under vacuum. More serious effects have been observed at vacuum levels from 100 to 0.05 mbar, where no signatures of foil explosion were detected. The effect of vacuum on the expansion rate of exploded metal plasma was estimated by measuring the velocity of a thin dielectric sheet placed over it and found to be significantly reduced in vacuum. The possible cause for this behavior appears to be the formation of a low-resistance breakdown channel parallel to metal foil, initiated by the ionization in released adsorbed gas molecules or in partially evaporated metal vapors in the presence of selfgenerated magnetic field over the heated foil surface.