Christopher Yeckel

Electrostatic Field Simulation Study of Nanoparticles Suspended in Synthetic Insulating Oil

Electrostatic field simulations have been performed to investigate the effect of barium strontium titanate (BST) nanoparticle suspensions on electric fields within synthetic oil dielectrics. We predict that by physically integrating nanoparticles of high dielectric constants into the breakdown regime, the self-break jitter in rep-rate oil switches might be reduced. The simulations show that the nanoparticle suspensions generate nonlinear and random electric field enhancements within the oil dielectric and also on the electrode surfaces. The BST nanoparticles have been modeled as perfect spheres which have an approximate dielectric constant of 2000. The oil in the simulation was given a dielectric constant of 2.33 and the electrodes are modeled as perfect electrical conductors with no field enhancements. A comparison is made between simulated electric fields on the surface of the cathode with increasing nanoparticle concentration, radius, and distance from cathode. Effects on capacitance with increasing nanoparticle concentration and radii are also investigated. All electrostatic simulations were performed with CST EM Studio. Preliminary experimental electric field breakdown data are included to validate simulation results.

Pulsed breakdown characterization of advanced liquid dielectrics for high-power high-pressure rep-rate oil switching

Several advanced oils have been identified by the Air Force Research Laboratory, Materials and Manufacturing Directorate, for characterization by MU as pressurized dielectric switching media. The oils tested were Diala AX transformer oil, a hydrogenated 1-decene polyalphaolefin, two hydrogenated 1-decene/1-dodecene polyalphaolefin mixtures, a silahydrocarbon, an ester, an alkylbenzene, and a silicone oil. Experiments on the pulsed voltage breakdown were performed to characterize the breakdown behavior of these dielectrics. A pulse generator, specifically designed for the characterization of oil breakdown strength, was implemented for this study. The pulse generator produced a voltage rise of 250-kV/µs across a 1.85-mm electrode gap. Thirty high voltage pulses were applied to each of the eight oils at five oil pressures, totaling 150 breakdown measurements per oil. The oils were pressurized to 3.45, 5.17, 6.89, 8.62, and 10.34-MPa during testing. Before each test cycle, the oil was sparged with dry nitrogen to reduce the water content, and the switch electrodes were polished. Between each of the 150 tests the oil was filtered to remove generated carbon.

SPICE analysis of an innovative solid-state Marx topology utilizing a boost regulator circuit to generate millisecond pulses with low droop

SPICE simulations indicate that a solid-state Marx modulator utilizing a novel boost circuit topology can generate a 5 ms long megawatt pulse at 10 Hz with a voltage droop of less than 1%. The boost regulator operates by charging the discharge capacitor voltage with energy stored in a boost inductor. Both the discharge and boost capacitors are charged to the same pre-pulse voltage, so a simple power supply structure is required. A feedback circuit controls the operation of the boost IGBTs, increasing the efficiency of the circuit by limiting the current through the boost inductor. Additional controls prevent overcharging of the discharge capacitor in the case of fluctuating load impedance. Techniques are introduced to mitigate the output voltage ripple generated by the switching transients.

Multistage Marx with parallel active droop compensation for long pulses

Research and development of a parallel boost network providing droop compensation for long pulse applications has reached a milestone at Stangenes Industries. The demonstration unit is capable of producing a 3.2 kV / 3.2 A pulse that persists for 3.6 ms with a stability of better than 1%. The pulse is generated by two modular stages oriented in a Marx topology with a parallel droop compensator stage. The system is meant as an integration option for an existing 30-stage, 3.8 MW Marx-modulator. The option allows for longer pulse lengths that require the reliability and flexibility inherent in solid-state switching modulators. The parallel boost stages float at the voltage of the existing Marx stages and utilize the same charging and auxiliary power networks. In this arrangement, two 30 μF boost capacitors charge in series and discharge in parallel through a 3 mH boost inductor to deliver energy to two parallel 30 μF discharge capacitors during the pulse. The maximum repetition-rate of the system is governed by the charging power available. The demonstration unit is capable of 0.25 Hz operation with the 30W charging power available; however its parent system operates reliably at up to 400 HZ with 100 μs maximum pulse lengths at 90 kV / 50 A delivering 130 kW of average power. The parent system utilizes 30 modular stages [1]. Generating voltage stability of less than 1% requires significant tuning of the feedback network located on each boost stage. Evidence suggests that the droop percentage improves with an increasing number of Marx stages if certain ripple interference strategies are implemented. Improvements to the logic on the next generation boost control card will lead to greater control over the droop parameters.

Experimental analysis of a solid-state Marx topology utilizing a boost regulator circuit to generate millisecond pulses with low droop

Continuing investigations indicate that a solid-state Marx modulator utilizing a novel boost circuit topology can generate a 4 ms long megawatt pulse at 10 Hz with a voltage droop of less than 1%. The boost regulator operates by charging the discharge capacitor with energy stored in a boost inductor. Both the discharge and boost capacitors are charged to the same pre-pulse voltage, so a single power supply voltage is required for operation. A feedback circuit controls the operation of the boost IGBTs, increasing the efficiency of the circuit by limiting the current through the boost inductor. Additional controls prevent overcharging of the discharge capacitor in the case of dynamic load impedance. Preliminary experimental data are analyzed and future system goals are stated.

Experimental analysis of an innovative solid-state Marx topology utilizing a boost regulator circuit to generate millisecond pulses with low droop

Summary form only given. High-power solid-state modulators have emerged as reliable, tunable, and cost-effective alternatives to current spark gap and thyratron technologies. The persistent improvement of the power, speed, and availability of solid-state components is generating increased commercial interest in their development. Solid state pulsed systems are optimal for technologies demanding stringent and stable pulse shapes, high repetition rates, ultra-long lifetimes, and performance redundancy. SPICE simulations show that incorporating a boost circuit in parallel with the discharge circuit of a solid-state modulator significantly improves the pulse characteristics. By supplying energy to the pulse during the discharge, the boost circuit can virtually eliminate pulse droop in long pulse applications. The boost circuit is designed to be driven by the same high voltage supply as the central Marx circuit which reduces circuit complexity compared to a parallel buck circuit. A prototype modulator has been designed and built at Stangenes Industries that produces a 6 kV, 19 A pulse that persists for 4 ms with <;1% voltage droop. The pulse repetition rate is 10Hz and the rise and fall time are 400 ns and 800 ns, respectively. The voltage ripple is held at <;1% with a pulse-to-pulse stability of 200 ppm. The function of the prototype modulator parallels the simulation results. While there is no theoretical limit to the pulse length, practicality dictates that there must be adequate recharge time through a conventional high-voltage power supply. The pulse length and power are also limited by the necessity of maintaining a reasonable efficiency. This paper provides those considerations as well as waveforms generated by the prototype modulator. Control circuitry is also briefly discussed.

Pulsed breakdown characterization of two dielectric oils with a BST nanoparticle suspension and varying filtration pore size

As more applications require high power and rep-rate capabilities, the University of Missouri-Columbia is investigating the design of liquid dielectric switches. In particular, the design and characterization of oil dielectrics is critical for optimum switch performance. Previous improvements, such as tuning of the oil pressure and flow rate, have dramatically reduced the rep-rate self-break jitter by eliminating breakdown byproducts. By introducing a suspension of Barium Strontium Titanate (BST) nanoparticles in the oil dielectric we hope to further reduce the breakdown jitter. Electrostatic simulations show that a nanoparticle suspension within the oil dielectric generates non-linear electric fields on both the electrode surfaces and in the bulk of the oil dielectric with a uniform applied electric field. These electric fields may help reduce jitter by enhancing cathode electron emission and streamer propagation across the gap. The two oils utilized in the experimental study were Hexadecene C16H32 and a synthetic oil dielectric developed by NYCO called NYCODIEL. A pulse generator, specifically designed for the characterization of oil dielectric strength, is implemented for this study. The pulse generator produces a voltage rise of 160-kV/μs across an adjustable electrode gap. Fifty voltage pulses are applied to each of the two oils at two oil pressures, totaling 100 breakdown measurements per oil. Before each test cycle, the oil is sparged with dry nitrogen to reduce the water content, and the switch electrodes are polished. The water content was measured by a K-F coulometric titrator. The oils are filtered between shots with three different filter pore sizes: 5-μm, 1-μm, and 0.45-μm. This was done to determine the optimum size filter for the system as the buildup of carbon byproducts reduces switch performance. A description of the pulse generator is provided, and the experimental procedure is described. Data for the dielectric oils is presented and analyzed, including the mean and percent standard deviation of the voltage breakdown data.

Investigation of causes leading to dielectric flashover in a laser triggered gas switch

Summary form only given. In support of Sandia pulsed power efforts, we are beginning a study of dielectric flashover in a laser triggered gas switch. The goal of this study is to determine important factors leading to flashover in a laser triggered gas switch (LTGS) filled with SF6. The University of Missouri - terawatt test stand is testing a rim fire LTGS housing to understand and improve the flashover characteristics of these switches. A rim fire LTGS was modified to mimic normal operating conditions of the trigger section of a switch tested on Z20. The modified switch was tested repeatedly over a range of pressures to acquire insulator flashover statistics. The switch was then altered and tested under various conditions to try to improve the flashover characteristics of the trigger section. The aspects of the switch that were identified for testing include, but were not limited to, geometry of the insulator, switch cleaning procedure, field shaping and type of insulator. An analysis of the findings of this study is presented

An all solid-state inductively-driven radiation-resistant modulator for fast-kicker magnet applications

Stangenes Industries has developed a solid-state inductor-driven kicker magnet pulse generator for use in a particle accelerator application. The system operates in a neutron environment which precludes the use of standard capacitor-driven systems. A 500–700 A pulse is produced by switching high-current through a large 360 μH inductor from the circuit return into a 6.5 μH kicker magnet. The DC magnetic field inside the inductor resists change in current producing a maximum 3.5 kV sinusoidal voltage pulse across the kicker magnet. A di/dt of 450 A/μs is produced in the kicker magnet and the current is maintained at a DC level until the system receives a command to end the deflection of the particle beam, whereby the switches again change state removing the kicker magnet from the source. Both the controls and the high-current DC supply are located 40 meters from the generator. The time of application and level of high-voltage across the IGBT switches is limited to a few μs and half the rated switch breakdown voltage, respectively. This topology statistically reduces the probability of a neutron-induced switch failure.

Field enhancement simulation study of nanoparticle-infused dielectric oil with roughened electrode surfaces

The Center for Physical and Power Electronics at UMC has been having experimental success in reducing the self-break jitter of a single-shot pulsed oil switch with various high-K nanoparticle-infused oil dielectrics. In support of this effort, electromagnetic simulations have been completed to quantify the observed phenomena. The simulation results presented in this paper focus on modeling the electric fields associated with the spatially random placement of both electrode enhancements and polarized high-K particles in a simulated oil gap. The simulation results show that high-K particles increase the average electric field on the surface of a rough electrode surface which contributes to the lower experimental oil breakdown strength.