For effective excimer laser pumping high voltage pulses with the pulse duration of 100 ns and energies from a fraction of joules to some 10 joules are necessary. For the generation of these pulses traditionally Thyratron circuits are used. The limited lifetime and repetition rates of such a device does not fulfil not the requirements of a modern excimer laser. State of the art is a solid state circuit with IGBT switches, high voltage pulse transformer and pulse compression networks. Due to the many stages, complexity is high and efficiency is moderate. To overcome this limitation a new solid state circuit for excimer laser pumping is developed. The circuit works without magnetic pulse compression. The switch is made by a stack of "off the self" MOSFETs and SiC diodes. In the presentation the general design and its calculation, diode and switch qualification and test results are presented.
The output from narrow-band high-power microwave (HPM) sources, such as the virtual cathode oscillator (vircator) and the magnetically insulated line oscillator (MILO), is strongly dependent on the voltage pulse feed. A rectangular, flat-top voltage pulse can be achieved by the use of a transmission line as a pulse-forming unit. The development in high-voltage cable technology has made them useful as parts of high-voltage and high-power generator systems. The generator is designed to deliver a 200 ns voltage pulse of 500 kV into a 10 Ω unmatched load with an electric power of 25 GW. The generator has an impedance of 2 Ω. The primary energy storage of the generator consists of a 50 kV, 20 kJ capacitor bank. The 50 kV is discharged into a transformer that charges a pulse-forming line to 550 kV. When charged, the pulse-forming line is discharged into the load via a spark gap. This paper presents results from initial testing of the generator.
Some research has been done on making the compact, portable pulse forming line. A kind of ceramic and a kind of newly developed composite polymer are both used as the dielectric of the planar pulse forming line. The ceramic's dielectric constant ranges from 200 to 600 and the composite polymer's dielectric constant ranges from 100 to 200. It is easier to manufacture the large composite polymer dielectric bulks than to manufacture the ceramic bulks. In the experiments, using the large composite polymer bulk as the dielectric, the planar Blumlein line generated the pulse up to 100 kV with duration 90 ns. Using the ceramic bulk as the dielectric, the planar line generated the voltage pulse up to 60 kV with duration 92 ns.
Charging operations of a compact Tesla transformer were experimentally investigated, in single-shot and rep-rate (50 pps for 1 s) modes, respectively. The charging limitations were also explored. The experimental results were compared and analyzed. The maximum secondary charging voltages of the Tesla transformer were measured to be 380 kV and 300 kV in single-shot and rep-rate modes, respectively. The RMS pulse-to-pulse instability of the secondary charging voltage is generally less than 10% but increases with the increasing initial voltage across the primary capacitor. Since the secondary capacitor of the Tesla transformer is a pulse forming line (PFL), continued operation is possible if there is breakdown in the PFL. Furthermore, operation can even be continued under occasional breakdown for some pulses, without the effects on the operations of subsequent pulses.
Linear transformer driver stages are designed to be used as a primary energy storage in high power pulsed generators. In this report, the design and test results of the linear transformer driver stage prototype that delivers ≈100 kA fast pulse with 133 ns FWHM into a ≈0.87 Ω resistive load are described. This stage consists of 20 (100 kV, 20 nF) storage capacitors that are arranged in 10 identical bricks located evenly around the axis of the stage. Each brick contains two capacitors, a multi-gap switch, and the output connector that transfers the energy to the resistive load. The outer diameter of the stage is ≈1.5 m, at a length of ≈20 cm. The stage is developed to demonstrate the possibility of the fast linear transformer driver technology to create high power pulsed generators.
Investigation results concerning acoustic emission signals coming from partial discharges generated by modeled sources are presented in the paper. These sources have been made using different bushing ends (without any extra elements and with a thread or a pike) situated directly in the oil, but without screens typical for partial discharge investigations in a bushing. Measurements have been carried out using own measuring acoustic emission system DEMA-COMP and - in a parallel way - computer-aided partial discharges measuring system TE 571 (produced by the firm Haefely Trench). Fundamental and advanced analysis of acoustic emission signals has been made. These signals were recorded in 20 measuring situations which need to multiple installation of acoustic emission sensors. Conclusions resultant from own originate advanced analysis of signals content description of properties revealed by defined acoustic emission descriptors.
Authors of the paper present investigation results concerning properties of ADP, ADC and ADNC descriptors which have been obtained during measurements made within three oil transformers and then tested also by other methods (electric and dissolved gas analysis ones). Methodology which makes easier an analysis and identification of acoustic emission signals generated by partial discharges is presented. Results obtained by acoustic emission method have been referred to results coming from other measuring methods.
Data processing algorithms are important parts of modern measurement systems. These algorithms are often delivered to the user as complex program and their numerical structure is not known. Therefore also influence of algorithm on processed data accuracy is not known. One of the methods to evaluate uncertainty propagation through algorithm is based on matrix form of algorithm. Coefficient matrix of algorithm represents its numerical operations and it is a basis to algorithm accuracy evaluation. The paper presents a method how to identify this coefficient matrix when algebraic form of the algorithm is known or is difficult to use. Identified matrix form of algorithm is then used to estimate uncertainty propagation through exemplary algorithms. Results are compared with experiments.
Gigawatt power switches for microsecond range applications based on an assembly of Reverse Switch-on Dynistors (RSD) and fast compact generators for nanosecond range applications based on new semiconductor devices Deep Level Dynistors (DLD) are discussed. As an example design and operation principles of 25 kV, 300 kA, 600 μs pulse duration power switch based on 76 mm diameter RSDs and 25 kV, 10 kA switch based on 16 mm diameter DLDs are described. It is possible to increase the pulse power by increasing both diameter of dynistor structure and number of devices connected in series or in parallel.
For one kind of high current diodes composed of a ceramic-metal welding vacuum interface, the electrical design was presented. For compactness, a radial type insulator and a cone-column anode crust were adopted. The shielding methods around cathode and anode region were applied to mitigate the influence of welding solder to vacuum flashover. Finite Element Analysis (FEA) simulation results indicated that by adjusting the anode outline and shielding shape, the electric fields along the ceramic were well distributed. High voltage test was conducted on a long-pulse accelerator and experimental results confirm the theoretic design: the diode can stably hold on 400 kV and 200 ns voltage pulse.
Compact high voltage subnanosecond monocycle former (MF) was tested. The device was designed on base of energy compression device and operated in a travelling wave mode. MF consists of high impedance and forming lines, which discharged for the load in parallel. As a result, the monocycle with pulse duration ∼1 ns and typical peak-to-peak amplitude ∼250 kV was formed without additional peaking of the nanosecond pulse rise time. Some pulses reached the maximum amplitude ∼270 kV. The parallel discharge circuit, and a spiral shape of forming line allowed keeping small dimensions of MF, and save enough electrical strength to operate with pulse repetition rate up to 100 pps.
This paper presents a high voltage pulse source which is able to generate ultra wideband (UWB) pulses during about 1 ns through a 16 antennas array. This UWB source is composed of a 50 kV DC voltage supply, a Tesla transformer to amplify this voltage up to 400 kV, a gaseous pressurized peaking switch and an impedance transformer (50 Ω → 3.125 Ω). This output impedance value corresponds to the input impedance value of a sixteen 50 Ω antennas array. That is why a distributor is needed in order to feed the antenna array. In this paper, the peaking switch and the capacitive line divider used to characterise the generated pulses are particularly described. The peaking switch is based on the principle of a line discharge by means of a high pressure gas switch. It is loaded with a Tesla transformer to obtain a good pulse reproducibility. The main characteristics of the output pulse waveform (amplitude and rise time) are linked to the properties of the gas switch and particularly to the gap distance, the pressure and the nature of the gas used in the switch filling. The aim is to find a good compromise between various parameters as the output pulse amplitude, the rise time and the repetition rate in order to ensure a better efficiency of the UWB source. Classical voltage measurement techniques do not allow us an estimation of the main characteristics of such an output signal. Therefore a voltage probe was designed and realised to measure both the amplitude and the rise time of the pulses delivered by the generator. This device is based on the principle of a capacitive line divider. Calibration tests (transient and frequency tests) were performed and show that the high cut-off frequency, around 2.5 GHz, is consistent with the transient response of the output high voltage waveform. The design, realisation and calibration tests are also presented.
A new pulsed power machine to be called AMPERE is currently under development at AWE. Its initial use will be as a metallic foil accelerator for the specific purpose of applying large impulses (>300 Pa s) and pressures (>450 G Pa) to a target for material property testing. The critical circuit features are described and a computer model has been written to predict the expected machine performance. Future uses of this facility for driving further hydrodynamic experimentation are also discussed.
We present in this paper the design and realisation of two autonomous, ultra wideband radiation sources consisting of a high gain broadband antenna driven by two subnanosecond pulsed power sources. Each one is made of a Marx generator and a pulse forming device based on the use of gaseous spark gap. The main pulsed source is a ten stage subnanosecond Marx generator which delivers pulses in the range of 250 kV/1.5 J, with a 300 ps rise time, subnanosecond pulse duration at a pulse repetition frequency of 350 Hz. The antenna combined with the pulsed source is a travelling wave antenna called Valentine antenna. Some mechanical modifications were made to improve the dielectric strength of this radiation element. A 3D model of the antenna, on a time domain electromagnetic software, was first performed to study the influence of these modifications on the main radiating characteristics of the antenna. Its high gain and its capability to radiate short pulses without dispersion allow us to achieve a high measured figure of merit.
The paper refers to diagnostics problems connected with the presence of partial discharges in gas-insulated substation. The basic stimulus for partial discharges generation is local, high value electric field, greater than the inception one. The numerical simulations of the electric field distribution in the part of the gas insulating system and in the vicinity of the metallic protrusion located on high voltage conductor are presented. Such defects are often present in SF₆ insulated constructions and are the cause of a local increase of the electric field. Theoretical analysis of physical mechanism of partial discharges initiation and development in the case of micro-needle type defects is described.
Emission acoustic signals, recorded in investigated power oil transformers, have been analyzed in the time, frequency and time-frequency domain. Analysis of each signal has been started by filtration within selected frequency band and subsequently the following quantities have been calculated: spectral power density, phase-time characteristic, averaging phase-time characteristic, short-time Fourier transform spectrograms, signal amplitude distributions, descriptors with acronyms ADC and ADP and thereafter maps of descriptors on lateral walls of transformers can be carried out. Frequency bands applied in order to filtration have been chosen in such a way so that signals coming from different sources (among other things from partial discharges, Barkhausen's effect, oil circulation and outer acoustic disturbances) can be differentiated. The sources have been localized using maps of descriptors calculated for selected frequency bands. The fundamental properties of obtained signals have been determined. Such properties describe: partial discharges, Barkhausen's acoustic effect and other acoustic interferences.
The original system useful for analysis of signals recorded during investigations of partial discharges within power oil transformers by means of acoustic method is presented. This method includes the basic and advanced analysis of recorded data. In the frame of basic analysis of data recorded signals undergo filtration in chosen frequency bands and next the analysis is made - in domain of time, frequency, time-frequency and discrimination threshold. In the frame of advanced analysis of data the amplitude distributions of acoustic emission signals and the acoustic emission descriptors (defined by the authors) are calculated in order to outline maps of acoustic emission descriptors on lateral walls of a transformer; it is a base for location of sources of partial discharges by means of the original method consisted in determination of advance degree of a signal. Results of this analysis, for signals recorded in two chosen transformers with identical construction (partial discharge occurred only within one of them), are presented in the paper. The source of partial discharge, situated within oil near transformer tank, was localized; the revision confirmed this result. Properties of recorded emission acoustic signals at chosen measuring points situated on the tank, in function of distance between the partial discharge source and measuring points, are presented.
Investigation results of properties characteristic for acoustic emission signals recorded in two selected power oil transformers are presented. Signals were put to the filtration, whereas components coming from partial discharges have been left. The calculations concerned: phase-time characteristics, averaging phase characteristics, averaging short time Fourier transform spectrograms, amplitude distributions of signals, values of acoustic emission descriptor with acronym ADC. On the ground of calculated basic characteristics and maps of ADC descriptor three areas have been selected on lateral walls of transformer tanks. Acoustic emission signals recorded in these areas were analyzed from the point of view how is influence of propagation path on these properties.
Investigation results of acoustic emission signals coming from partial discharges within chosen generator coil bar, in relation to measurement results of apparent charge introduced by partial discharges sources, are presented in the article. Analysis is based on amplitude distributions calculated for acoustic emission signals, ordered at different measuring points for different values of the supply voltage. In order to assign acoustic emission signal to its advance degree a descriptor named by an acronym ADP (defined by authors) is calculated for each amplitude distribution. Descriptor families describing acoustic emission signals measured at particular measuring points (for different supply voltages) are presented in relation to apparent charge introduced by acoustic emission sources. These families concerning acoustic emission signals, measured at different measuring points for identical supply voltage, enable us to locate acoustic emission sources with maximum activity.
Transformers represent one of the oldest and most mature elements in a power transmission and distribution network. The new superconducting transformers are smaller and lighter than conventional ones and they have lower power losses, too. Also, the new 2G superconducting tapes with high resistivity in the normal state allow to build transformers with high short-circuit strength. The short-circuit current limiting feature of the superconducting transformer, which is the most important benefit of replacing conventional windings by superconducting ones, provides protection and significantly reduces the wear and tear of circuit breakers and other substation power equipment. This paper describes the design and experimental investigations results of a model of a 1-phase, 8.8 kVA superconducting transformer with windings made of 2G HTS tape. A special regard is given to the ability of the device's superconducting winding to limit the short-circuit current, in particular its equivalent resistance in normal state at a temperature of 77 K (i.e. resistance of the resistive layers of the HTS tape just after transition to the non-superconducting state).
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