Search Results (15)

This paper explores the feasibility of implementing a flywheel energy storage system designed to generate voltage for the purpose of mitigating current flow through the transformer neutral path to ground, which is induced by a high-altitude electromagnetic pulse (HEMP) event. The active flywheel system presents the advantage of employing custom optimal control laws, in contrast to the conventional approach of utilizing passive blocking capacitors. A Hamiltonian-based optimal control law for energy storage is derived and integrated into models of both the transformer and the flywheel energy storage system. This Hamiltonian-based feedback control law is subsequently compared against an energy-optimal feedforward control law to validate its optimality. The analysis reveals that the required energy storage capacity is $13\mathrm{Wh}$, the necessary power output is less than $5\mathrm{kW}$ at any given time during the insult, and the required bandwidth for the controller is around $5\mathrm{Hz}$. These specifications can be met by commercially available flywheel devices. This methodology can be extended to other energy storage devices to ensure that their specifications adequately address the requirements for HEMP mitigation. Full article

Securing the power grid is of extreme concern to many nations as power infrastructure has become integral to modern life and society. A high-altitude electromagnetic pulse (HEMP) is generated by a nuclear detonation high in the atmosphere, producing a powerful electromagnetic field that can damage or destroy electronic devices over a wide area. Protecting against HEMP attacks (insults) requires knowledge of the problem’s bounds before the problem can be appropriately solved. This paper presents a collection of analyses to determine the basic requirements for controller placements on a power grid. Two primary analyses are conducted. The first is an inverted controllability analysis in which the HEMP event is treated as an unbounded control input to the system. Considering the HEMP insult as a controller, we can break down controllability to reduce its influence on the system. The analysis indicates that either all but one neutral path to ground must be protected or that all transmission lines should be secured. However, further exploration of the controllability definition suggests that fewer blocking devices are sufficient for effective HEMP mitigation. The second analysis involves observability to identify the minimum number of sensors needed for full-state feedback. The results show that only one state sensor is required to achieve full-state feedback for the system. These requirements suggest that there is room to optimize controller design and placement to minimize total controller count on a power grid to ensure HEMP mitigation. As an example, the Horton et al. system model with 15 transformers and 15 transmission lines is used to provide a baseline comparison for future optimization studies by running all permutations of neutral and transmission line blocking cases. The minimum number of neutral controllers is 8, which is approximately half of the bounding solution of 14. The minimum number of transmission line controllers is 3, which is one-fifth of the bounding solution of 15 and less than half of the required neutral controllers. Full article

This paper explores the use of a solid state transformer (SST) to mitigate the $E_{3A}$ component of a high-altitude electromagnetic pulse (HEMP) insult using external energy storage optimal control techniques. In lieu of conventional passive blocking devices or feedback-controlled energy storage devices, a novel implementation of Hamiltonian error tracking is utilized to develop a feedback control law for the variable converter ratio in an SST. The findings of the simulations performed in this paper suggest that additional energy storage is not necessary to protect an individual load from a HEMP insult. The simulations performed examine the response of a single-phase SST connected to a single voltage source on a long transmission line on the one side and a single linear resistor on the other. The control law is specifically developed for the late-time, low-frequency portion of a HEMP insult, namely the $E_{3A}$ components. The Hamiltonian error-based converter ratio control law is compared with nonlinear optimal feedforward controls to show that the HSSPFC is an external energy storage optimal controller. Full article

An intelligent approach is proposed and investigated in this paper for the detection of ultra-low-altitude sea-skimming moving targets for airborne pulse Doppler radar. Without suppressing interferences, the proposed method uses both target and multipath information for detection based on their distinguishable image features and deep learning (DL) techniques. First, the image features of the target, multipath, and sea clutter in the real-measured range-Doppler (RD) map are analyzed, based on which the target and multipath are defined together as the generalized target. Then, based on the composite electromagnetic scattering mechanism of the target and the ocean surface, a scattering-based echo generation model is established and validated to generate sufficient data for DL network training. Finally, the RD features of the generalized target are learned by training the DL-based target detector, such as you-only-look-once version 7 (YOLOv7) and Faster R-CNN. The detection results show the high performance of the proposed method on both simulated and real-measured data without suppressing interferences (e.g., clutter, jamming, and noise). In particular, even if the target is submerged in clutter, the target can still be detected by the proposed method based on the multipath feature. Full article

The Spaceborne Global Lightning Location Network (SGLLN) serves the purpose of identifying transient lightning events occurring beneath the ionosphere, playing a significant role in detecting and warning of disaster weather events. To ensure the effective functioning of the wideband electromagnetic pulse detector, which is a crucial component of the SGLLN, it must be tested and verified with specific signals. However, the inherent randomness and unpredictability of lightning occurrences pose challenges to this requirement. Consequently, a high-power electromagnetic pulse radiation system with a 20 m aperture reflector is designed. This system is capable of emitting nanosecond electromagnetic pulse signals under pre-set spatial and temporal conditions, providing a controlled environment for assessing the detection capabilities of SGLLN. In the design phase, an exponentially TEM feed antenna has been designed firstly based on the principle of high-gain radiation. The feed antenna adopts a pulser-integrated design to mitigate insulation risks, and it is equipped with an asymmetric protective loading to reduce reflected energy by 85.7%. Moreover, an innovative assessment method for gain loss, based on the principle of Love’s equivalence, is proposed to quantify the impact of feed antenna on the radiation field. During the experimental phase, a specialized E-field sensor is used in the far-field experiment at a distance of 400 m. The measurements indicate that at this distance, the signal has a peak field strength of 2.2 kV/m, a rise time of 1.9 ns, and a pulse half-width of 2.5 ns. Additionally, the beamwidth in the time domain is less than 10°. At an altitude of 500 km, the spaceborne detector records a signal with a peak field strength of approximately 10 mV/m. Particularly, this signal transformed into a nonlinear frequency-modulated signal in the microsecond range across its frequency spectrum, which is consistent with the law of radio wave propagation in the ionosphere. This study offers a stable and robust radiation source for verifying spaceborne detectors and establishes an empirical foundation for investigating the impact of the ionosphere on signal propagation characteristics. Full article

A variety of events such as high-altitude electromagnetic pulses, extreme solar storms, and coordinated cyber attacks could result in a catastrophic loss of infrastructure on a continental or global scale. The lengthy repair of critical infrastructure creates a need for alternative fuels such as wood gas. Wood gas is produced by heating wood in a low-oxygen environment and can be used to power combustion engines. This work investigates a novel wood chipper, designed as an energy-efficient tool for producing wood gas stock, wood chips, aiming to speed up the transition to alternative fuel. A prototype is built and tested to determine the energy efficiency and production rate of the device. The results suggest that the wood chipper could produce one cord of wood chips, 3.6 m³, in less than a day and is a viable alternative to other manual wood-processing methods. In addition, the global scaling up of production of the wood chipper is considered, indicating that the mass production of the wood chipper could accelerate the transition of wood gas production methods from manual to machine-driven immediately after a catastrophic event. Full article

Protection relays are important equipment used for protection, control, and metering functions in the power grid. These relays are used to protect critical and difficult-to-replace equipment, like generators, transformers, and capacitor banks. Once the protection devices are disturbed or damaged, a high risk of power generation interruption occurs. Therefore, it is important and necessary to study the relay’s immunity to electromagnetic pulse (EMP) events. As a preliminary step toward empirical experimentation on actual equipment, this manuscript outlines an economical and efficient methodology for evaluating the impact of an EMP. An impedance measurement strategy was employed to model the equipment, setting the stage for subsequent immunity analyses. These analyses included the pulse current injection (PCI) method, which utilized an injecting probe to introduce the transient, and frequency domain electromagnetic (FEKO) simulation, which integrated electromagnetic coupling effects into the transient simulation. The impedance measurement and simulation results in this paper provide a reliable basis for gauging equipment performance in the face of HEMP threats. The results obtained using the PCI and FEKO simulations demonstrated the performance of different port responses under a high-altitude EMP, indicating the requirement for some protection to ensure the reliable operation of relays. Full article

The transient surface current density reflects the external coupling of the electromagnetic pulse (EMP) to the tested device. In this paper, the generation mechanism and measurement principle of conductor surface current density are introduced, and the surface current density distribution irradiated by EMP on a typical aircraft structure is simulated and analyzed. The traditional surface current density is usually measured by B-dot antenna, but its output signal is the differential of the measured signal, so additional integrators or numerical integration of the measured data are required. In this paper, a self-integrating surface current sensor based on optical fiber transmission is designed based on the shielded loop antenna with gap structure. The output signal is the real signal waveform to be measured. Compared with coaxial cables, integrated optical fiber transmission improves the anti-interference ability of long-distance transmission signals. At the same time, the design process of the sensor is introduced in detail. The bandwidth of the sensor is 300 kHz~500 MHz, the sensitivity is calibrated at 1.23 (A·m⁻¹)/mV, and the dynamic range is ±25~1400 A·m⁻¹ (35 dB). The surface current of a metal plate is measured in a bounded wave electromagnetic pulse simulator using a detector developed in this paper. The test results show that the developed sensor has good engineering applicability. Full article

A High-Altitude Electromagnetic Pulse (HEMP) could induce very fast transient overvoltage (VFTO) with nanosecond level rise time and mega-volt amplitude, which severely threatens the electrical devices connected to the elevated transmission line. An elevated transmission line with different locations may suffer different levels of HEMP threat since the dip angle could influence the polarization of the HEMP wave. The combination of Rosenblatt Transformation and Polynomial Chaos Expansion (R-PCE) is introduced in this paper. With this method, the efficiency of calculating the overvoltage of an elevated transmission line under HEMP is improved, speeding up 24.75 times. The influence of different factors (dip angle, elevated height, and earth conductivity) on the overvoltage of elevated transmission lines applied in power systems is calculated and analyzed. The numerical result shows with 99.9% confidence that the overvoltage would be over 3.7 MV of amplitude and 6.7 × 10¹⁴ V/s of voltage derivative, which is much more rigorous than a lighting pulse. We also find that elevated transmission lines may have a larger HEMP threat in a small dip angle area. The corresponding data are shown at the end of the paper, which could be useful for relative researchers in pulse injection experiments and reliable evaluation. Full article

High power electromagnetics (HPEMs) pose a potential threatening risk to the wireless communication system, especially according to the main coupling path of the RF front-end channel. SPICE modeling of the responses coupled on the RF channel is crucial for the EM risk assessment, which helps us learn more about how the pulse conducts on the RF channel. A simplified linear RF channel with pyramid horn antenna is taken as an example by the selection of the key electronic modules of the actual wireless system. This paper proposes a system-level SPICE circuit model for the simplified RF channel according to the hybrid methods of the antenna electromagnetic simulation and SPICE modeling of the RF circuit. The equivalent circuits of the horn antenna illuminated by HPEMs are established with the Vector Fitting method based on Thevenin and Norton theorems. The short current response as the excitation files for the SPICE models are obtained by the commercial electromagnetic simulation of the horn antenna illuminated by Multiple HPEM environments. Equivalent circuits of a micro-strip bandpass filter are also derived with $\pi$ type circuit structure based on the measured admittance data. Then we analyze the HPEM risk faced by the RF channel by considering multiple HPEM environments. The norm theory is utilized to analyze the waveform characteristics from electric fields of HPEMs to the responses of the RF channel. The ratios of the responses versus electric field for each norm are computed and the EM risk degree is ranked based on those results. The results demonstrate that high power microwave is the highest threatening risk for the linear RF channel compared to the other two HPEMs such as ultra-wide band, high altitude electromagnetic pulse. Finally, the flowchart of EM risk assessment is presented based on a previous analysis, which will benefit the EMC design in engineering. Full article

In system-level high-altitude electromagnetic pulse (HEMP) illumination tests, it is common to perform the test in two orthogonal polarizations of the incident electric field. With the judgment standard of the electromagnetic norm, this paper evaluated, improved, generalized, and verified this method. The evaluated result shows that the maximum error of the maximum coupling in this method is less than 3 dB. Meanwhile, this method is improved by serving the 1.2 period of the larger coupling of the 2 illuminations as the maximum coupling. The maximum error can be controlled within 1.5 dB. Moreover, this method is generalized to non-orthogonal conditions. Expressions of the deviations of this method are strictly derived. Based on this method, the application and some extended thinking are discussed. At last, a current coupling test is designed and carried out to verify the methods and conclusions. The methods introduced in this paper can be applied to any linear system in the illumination test under approximate transverse electromagnetic (TEM) waves. Full article

In order to study the strong electromagnetic pulse effect of critically vulnerable equipment in power systems and evaluate the survivability under high-altitude electromagnetic pulses, it is necessary to study the characteristics of the transient response of metal oxide arresters to the high-altitude electromagnetic pulse by experiment. In this paper, an experimental platform for high-altitude electromagnetic pulse conduction current injection for a typical 10 kV metal oxide arrester was set up, and the key parameters such as peak value of overshoot voltage, peak value of residual voltage, action voltage and response time were obtained by the experiment. The results show that: the action voltage of this type of metal oxide arrester is 3.53 times higher than that of its rated voltage; the peak value of overshoot voltage is 2.19 times that of the peak value of residual voltage under lightning impulse current; the peak value of residual voltage is 1.57 times that under lightning impulse; and the response time varies little with the electromagnetic pulse conduction current amplitude, averaging 46.86 nanoseconds under a high-altitude electromagnetic pulse conduction environment. Full article

The study of electromagnetic sensitivity of electronic modules is crucial for the selection of a component-level pulse current injection (PCI) waveform, which will determine whether a component-level PCI test is equivalent to a system-level pulse illumination test of the system to which the electronic module belongs. For electromagnetic sensitivity analysis, the equivalence between the injection waveform and a typical high-altitude electromagnetic pulse (HEMP) conducted disturbance waveform in a component-level PCI test is studied. Based on an RF low noise amplifier (LNA) test board, component-level PCI tests were performed using 20 ns/500 ns double exponential wave and square-wave pulse with multiple pulse-widths. The damage threshold was analyzed and determined by using vector norm and its internal damage was observed and validated by optical microscopic analysis. The conclusions are demonstrated as follows: first, during square-wave PCI tests of RF LNA, the electromagnetic sensitive parameter action is divided into three regions by pulse-width range, called $\infty$-norm, 2-norm and competitive failure-dominating regions; second, the electromagnetic damage effect of the RF LNA is mainly caused by the burning of its two cascaded transistors, forming a pulse energy transmission channel with short-circuit impedance from the input port to the ground; third, the 100 ns-width square waveform can be determined as the equivalent injection waveform of a HEMP conducted waveform, and the pulse peak value of injected current is determined as the electromagnetic sensitive parameter for square-wave PCI tests of the RF LNA. The conclusions verified the feasibility of establishing the equivalence between different pulse waveforms according to the electromagnetic sensitivity analysis based on the vector norm theory and effect mechanism analysis. Full article

Nowadays in solving geological problems, the technologies of UAV-geophysics, primarily magnetic and gamma surveys, are being increasingly used. However, for the formation of the classical triad of airborne geophysics methods in the UAV version, there was not enough technology for UAV-electromagnetic sounding, which would allow studying the geological environment at depths of tens and hundreds of meters with high detail. This article describes apparently the first technology of UAV-electromagnetic sounding in the time domain (TDEM, TEM), implemented as an unmanned system based on a light multi-rotor UAV. A measuring system with an inductive sensor—an analogue of a 20 × 20 or 50 × 50 m receiving loop is towed by a UAV, and a galvanically grounded power transmitter is on the ground and connected to a pulse generator. The survey is carried out along a network of parallel lines at low altitude with a terrain draping at a speed of 7–8 m/s, the maximum distance of the UAV’s departure from the transmitter line can reach several kilometers, thus the created technology is optimal for performing detailed areal electromagnetic soundings in areas of several square kilometers. The results of the use of the unmanned system (UAS) in real conditions of the mountainous regions of Eastern Siberia are presented. Based on the obtained data, the sensitivity of the system was simulated and it was shown that the developed technology allows one to collect informative data and create geophysical sections and maps of electrical resistivity in various geological situations. According to the authors, the emergence of UAV-TEM systems in the near future will significantly affect the practice of geophysical work, as it was earlier with UAV-magnetic prospecting and gamma-ray survey. Full article

High-altitude electromagnetic pulses (HEMPs) are bursts of electromagnetic energy that result from nuclear weapon detonations at altitudes at or above 30 km. A HEMP is comprised of three components: E1, E2, and E3. E1 and E2 are instantaneous emissions that can damage electronic components, whereas E3 generates low-frequency, geomagnetically-induced currents in transmission lines and power transformers. These currents can lead to the half-cycle saturation of power transformers and increased reactive power consumption. This study assessed the impact of the E3 HEMP on Korean electric power systems. For this assessment, two publicly available E3 HEMP environments were identified. A Direct Current (DC)equivalent model of Korean power systems was developed to calculate the geomagnetically-induced currents and increased the reactive power absorption of transformers in power systems. The vulnerability assessment involved two types of analysis: Static power flow analysis and dynamic transient stability analysis. The maximum electric field limit was determined by performing a steady-state analysis. The capability of the Korean electric power systems to maintain synchronism and acceptable voltages in the transient stability time frame following an E3 HEMP event was evaluated. Furthermore, the effects of detonations at five target locations were compared. It was concluded that Korean electric power systems cannot maintain their stability when affected by an E3 HEMP. Full article