Robust electrical contacts integrating a liquid metal bridge for mechanical switches

Intrinsic roughness of solid surfaces causes a series of inevitable shortcomings in the use of mechanical electrical contacts, among which one of the most fatal is the repulsive electrodynamic force arising from high currents. A large contact force coming from a heavy holding mechanism helps to suppress the repulsive effect whereas the mechanism consumes energy and remains to be challenging for a compact switching device. Here, a liquid metal (LM) bridge is introduced to wet solid electrodes to eliminate contact issues. Four instability patterns induced by the electromagnetic pinch effect are identified to characterize LM bridge’s response to high currents. Simulation results reveal that an inner vortex caused by uneven distributions of current density and electrodynamic volume force leads to the rupture of a necked LM bridge. With a uniform structure, a cylindrical LM bridge is proved to be robust with respect to an impulse current higher than 10 kA, exceeding a commercial compact relay by a factor of more than 10 in terms of current withstand performance. Our research facilitates compact and energy-saving switch equipment and has a potential to realize arbitrary desired levels of high current withstand without the use of a holding mechanism. This paper also offers deep insights into the high current applications of LM from the perspective of fluid related physical mechanisms.

Testing of Conductive Carbon Fiber Reinforced Polymer Composites Using Current Impulses Simulating Lightning Effects

Carbon fiber reinforced polymer (CFRP) composites are lightweight and an increasingly used material with good mechanical properties. In the aviation industry, they are also required to have specific electrical properties that guarantee resistance to the direct and indirect lightning effects. The paper is focused on the description of a test stand and development of a method used to determine the electrical characteristics of conductive CFRP laminate samples with the use of high current impulses of lightning nature. Samples of three laminates (square format with side 30 × 30 cm) with a different composition were tested on the constructed stand, confirming the possibility of characterizing this type of laminate sample in terms of electrical conductivity and resistance to the effects of lightning current. It was possible to observe the impulse current flow (with a peak value up to 15 kA and a rise time above 6 µs) from the high voltage electrode placed in the center of the sample in all directions towards the edge. The optical fiber measuring system was used to record the voltage and current time waveforms. The energy stored in the impulse current generator was sufficient to simulate the mechanical damage, such as burnout and delamination, that accompanies the direct lightning strike to structural elements made of CFRP. The influence of the matrix composition used for laminate fabrication on the test results describing the electrical properties of the tested CFRP samples was noted. The experimental setup allows the testing of specimens with a maximum width and length of 50 × 50 cm and any thickness with a peak current of up to 50 kA.

Equations of Electrodynamics

The equations of electrodynamics are presented, it is shown that plane and spherical electromagnetic waves are their solutions, while the spherical wave propagates only outward. Fields of uniformly moving charges are also solutions of equations. The question of finding a universal form of equations admitting a solution in the form of a field of an arbitrarily moving charge remains open. The question is raised about the existence of a two-parameter group of transformations of electromagnetic fields along with the well-known one-parameter group. The equation of motion of a charged particle in an electromagnetic field is considered without simplifying approximations. The principle of operation of an unconventional alternator in a constant electric field and a corresponding engine, as well as new types of generators of direct and impulse current, are described.

Transient impedance of grounding system with impulse superimposed sinewave

Investigating the transient performance of grounding systems subject to lightning (impulse or impulse superimposed sinewave) is valuable for protecting the power system and maintaining the system operation. In this work, the grounding system's impedance is computed when an impulse superimposed sinewave is applied to the grounding grid's proposed lumped circuit and grounding system can be simulated as an inductance in series with resistance, and all of them are in parallel with capacitance based on Thione's assumption. Several variables were investigated to study their effects on the grounding system's behavior. The variables were the soil resistivity, soil permittivity, main wire length, grid conductor radius, grid side length, grid configurationand its mesh number. The grounding system configuration varied between square and rectangular shapes, which connects to the protecting rod via the main wire conductor. A 3.69 kA peak of impulse current was applied to avoid soil ionization. The results indicated the performance of the grounding system when subjecting to impulse current.