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Non-hosted
This work describes a new approach for designing large accumulative resonant cavities of high power microwave pulse compressors by replacing a fixed shape (cylinder, sphere, prism) microwave compressor resonator with a variable geometry accumulative resonant system. Such a system is designed based on the standard structure element made as one mode or moderately multimode waveguide section whose ends are limited with two waveguide tees or their analogues. One arm of each limiting tee or an analogue is connected to the section; another arm is closed-circuited, and the third arm is open. The accumulative system is formed as extended linear or compact planar and voluminal structures or their compositions by alignment of standard elements through open arms of tees. The proposed approach to the accumulative system design allows adapting the system geometry according to the assembly place and integrates the microwave compressor into the working unit with saving or minimizing its dimensions.
This work provides specific schemes of possible microwave pulse compression system variants with a variable geometry of the accumulative system. The authors show that a specific architecture of accumulative system accompanied by the relevant distribution of energy output equipment may allow making microwave compressors with output pulse parameters that are discretely controlled over wide range. It is also shown that the variable geometry of the accumulative resonant cavity will enable design of compact compression cascade systems with multiplied power of the resonant cavity travelling wave. The work also demonstrates the first results of experimental study of the microwave pulse compression systems with planar accumulative resonant cavities.
Screamer was developed to solve a wide range circuits with a focus on pulsed-power systems. Screamer is a highly optimized code written in Fortran 77. We will describe the mathematical foundations of Screamer and show how Screamer uses a wide range of pulsed power circuit elements. Screamer incorporates many physics-based models such as lossy transmission lines, dynamic loads, gas switching, water switching, oil switching, magnetic switching, and magnetically insulated transmission lines, which are important to the high-voltage, pulsed-power community. Additional circuit models or modifications to existing models can be readily implemented in Screamer. Screamer is openly available to the community without restrictions. Screamer runs on the Macintosh, LINUX, and Windows platforms.
*Work supported by Sandia National Laboratories under Purchase Order #1518167.
Non-hosted
With the development and implementation of dc based power systems, dc arc fault protection becomes an inevitable challenge for the safe operation in various applications. This paper presents a brief review of dc arc fault modeling and detection methods. The goal is to examine state-of-the-art technologies and to identify future research and development needs of dc arc fault protection in modern dc networks. For dc arc modeling, the focus is given to external characteristic equation which models the arc with electrical parameters. This type of model, normally in the form of V-I equations, can be used to simulate and analyze the impact of an arc fault to the dc network. Moreover, models of the random high frequency components in arc current and their applications will be reviewed and discussed. Then, selected dc arc fault detection techniques based on time, frequency, and time-frequency domain analysis are reviewed and compared.
It is crucial to differentiate high-impedance, series dc arc faults from normal operating conditions such as load changes or switching-related noise. Thus, preliminary results from a robustness study of a wavelet based detection algorithm under noisy environments is presented. The noises studied include wideband noise, impulse noise from system transients, and frequency specific noises such as harmonics and switching-related noise, all of which are commonly seen in dc power systems. Current industry standards on dc arc detection are more focused on photovoltaic systems for terrestrial applications. The status of a draft SAE standard being developed on 270 Vdc arc fault detection and validation tests for aircraft is briefly discussed.
This paper describes the design of a high performance solid-state pulsed power modulator for long pulse applications. Output specifications of the proposed modulator are as follows: variable output pulse voltage, 1-40 kV; width, 1-300 us; pulse repetition rate, 1-200 pps; and average output power, 50 kW. Based on the structure of solid-state Marx modulator, the proposed modulator mainly consists of high-voltage capacitor charger and IGBT stack. For simultaneous charging of energy storage capacitors, a high efficiency LCC resonant inverter is proposed with multi-stage transformer and rectifier. The IGBT stack is designed based on power cell structure that provides voltage balancing between each semiconductor device and allows reliable operation against arc condition. In addition, a novel gate driving circuit is proposed not only for applying pulse to the load but also for discharging the stored energy from the capacitive load. This active pull-down function removes additional pull-down resistor and provides fast falling time with enhanced system efficiency.
The experimental results of developed capacitor charger shows 95% and 0.96 of maximum efficiency and power factor, respectively. Finally, the performance of the developed solid state modulator is experimentally verified including rated operation (40 kV, 20 A, 300 us, 200 Hz, 2.5% Droop), active pull-down operation, and reliable arc protection.
20 minute talk, 10 minute Q&A
Moderated Discussion
n/a
In high voltage applications that require a resistive load or shunt, one must turn to non-traditional resistor construction techniques to satisfy electrical power absorption and load matching requirements, handle thermal loads, and resist distortion and destruction due to generated Lorentz forces. A readily available material that meets these requirements is 304L stainless steel. Pipes constructed of 304L stainless are available in multiple diameters and lengths which allow one to satisfy electrical design considerations; in a coaxial configuration that minimizes the electromagnetic fields exterior to the shunt. Because of Ohmic heating during high current operation of the shunt, it is important to thoroughly analyze and evaluate the structure’s temperature distribution relative to system integration and operational requirements. In addition, while electromagnetic fields are constrained to the interior of such a shunt, these fields give rise to very strong Lorentz forces on the inner and outer conductors. These forces must be evaluated from a safety and fatigue perspective to make sure that system operation with such shunts does not endanger the system or personnel.
In this presentation, the author proposes a readily constructed, resistive, coaxial shunt from commonly available 304L stainless steel and yellow brass. This shunt is fed by multiple 350 MCM coaxial cables and is amenable to quarter symmetry analysis for numerical efficiency and to reduce computational runtime. The shunt is modeled in a commercially available multiphysics package and excited by current sources that drive each coaxial cable equally. Analysis of the thermal and electromagnetic loading will be presented. Modifications to the shunt to extend operation to higher current levels or duty cycle operation will be discussed.
This paper presents an investigation of the influence of different operating conditions of HVDC convertors on partial discharge behavior occurring within cables on the DC side of an HVDC system. Cables at the DC side undergo different stresses due to transients and harmonics, which affect their insulation integrity and may result in an intensified level of partial discharge (PD) activity. Most DC schemes, nowadays, are bidirectional with the valve firing angles at the heart of power conversion and power flow control. Depending on the mode of converter operation and the properties of the interconnected AC systems, varying levels of harmonics, either characteristic or non-characteristic, appear on the DC side. By reproducing a down-scaled version of the DC output of conventional HVDC converters under controlled laboratory conditions, PD signals occurring under an HVDC applied voltage generated at different converter firing angles have be measured. PD was produced using a range of insulation samples containing known defects and measured using an HFCT sensor with a bandwidth of 19 MHz. Characteristics of the acquired PD signals have been analyzed using statistical methods with the aim of finding a promising condition monitoring tool to identify the influence of the generated harmonics on PD activity. The results will aid HVDC network operators in identifying incipient cable faults by contributing to diagnostic knowledge rules for interpretation of PD parameters under known operating conditions.