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The partial discharge inception voltage (PDIV) of low-voltage induction motor turn-turn insulation analogy is investigated for variable relative humidity (RH) of the surrounding air (temperature and pressure are kept constant close to their ambient values). Three materials, perfluoralkoxy alkane, sealed and unsealed alumina (UA), are employed as the dielectric coating (insulation) of test samples. Each material's dielectric properties change differently with RH—of these, relative permittivity is regarded as the most crucial, as it was previously proven to be, along with the coating's thickness, the key factor in determining the PDIV in dry air conditions. To further vary the value of permittivity and thus provide larger data sets for the verification study, the frequency of the excitation voltage is also varied between 1 Hz and 50 kHz. The obtained experimental data are compared against the PDIV predictions obtained by a breakdown model based on the reduced thickness of the coating (ratio of the coating thickness to its relative permittivity). Satisfying agreement between the measured and predicted PDIV are obtained for the first two materials, whereas significant discrepancies are seen for the UA material. For this case, surface conductivity is introduced into the prediction model and much better fits to the experimental data are obtained for a suitable value of surface resistance. It is hence demonstrated that the model is able to satisfactorily predict the PDIV for three substantially different materials when the RH of the surrounding air is varied between 10 % – 80 % . [ABSTRACT FROM AUTHOR]

A pressure scaling law for the partial discharge inception voltage (PDIV) of wedge-shaped, dielectric-bounded gas gaps is derived and experimentally validated. The investigated prototypical electrode geometry is of relevance in a number of practical applications, such as contacting enameled wires in electric motors or transformers. The derived pressure scaling law is of particular interest for electric propulsion in aviation systems. The results show that the PDIV can be accurately parametrized from first principles as a function of the scaling parameter p ⋅ s / ε r , where p is the gas pressure, s is the thickness of the insulating coating and ɛ r its relative dielectric permittivity. Previously published empirical relationships between the PDIV and pressure are shown to be local approximations of the presented general scaling law. In particular, the often assumed linear relation of PDIV with pressure is shown to not be generally valid. [ABSTRACT FROM AUTHOR]

A custom-made modular high-precision dielectric spectrometer for quantifying aging-induced molecular changes in (sub-)picofarad polymeric samples is presented. Validation and characterization of the setup's performance is obtained by quantifying the change in the dielectric response of an epoxy polymer following the exposure to thermal, hygrothermal and ultraviolet radiation stress. It is shown that the observed changes in the dielectric spectra can be resolved with a relative precision better than 5·10−5 and are in line with previous studies employing commercial instruments on samples of higher capacitance. This setup is intended to serve as a blueprint for a sensitive and extensible (because modular) measurement tool for studying the pre-breakdown dynamics in low-capacitance recessed or disc-shaped specimens as used, e.g., in high-voltage insulation testing. [ABSTRACT FROM AUTHOR]

Recently it was shown that it is possible to predict the breakdown voltages of arbitrary electrode configurations under standard voltage applications for electron attaching gases with a stepped leader model originally proposed for SF6. In this contribution this model was applied to the hydrofluoroolefin HFO1234ze. The parameters, which are necessary for the modeling, are derived from measurement of statistical and formative time lags in an electrode configuration with a homogeneous background field with a small protrusion. The parameters are used to predict the breakdown voltage for technical relevant geometries and standard voltage wave shapes. To verify these predictions, breakdown experiments in nearly homogeneous and strongly inhomogeneous field configurations with AC and lightning impulse voltage application of both polarities were performed. The hydrofluoroolefin exhibits insulation properties which are quite similar to those of SF6. Therefore it could be considered as admixture for high voltage gaseous insulations or as replacement in medium voltage equipment. For applications using the pure gas the temperature and pressure range has to be limited to prevent liquefaction. The good match between the simulations and the experiments gives evidence that the model can be applied to a broad range of other novel electron attaching gases as well. [ABSTRACT FROM AUTHOR]

In this contribution, a new procedure to systematically identify and quantify novel molecular gases with low global warming potential for application in high voltage insulation as gas mixtures is presented. The attention is focused on highly efficient procedures to be able to scan a large number of candidate gases. To identify new molecules, we derived an empirical correlation between the electric strength of a gas and certain molecular properties, like polarizability or dipole moment, which can be calculated by means of density functional theory. The swarm parameters of these pre-selected molecules in mixtures with buffer gases is then quantified, using a newly set-up Pulsed Townsend experiment. The setup operates with a high degree of automation to enable systematic evaluation of gas mixtures not to miss possible synergistic effects. Key element of this PT setup is a new photocathode that works with a high quantum efficiency and long lifetime even when exposed to reactive species during the measurements. Moreover, for an automated operation it is important to know precisely in which range the experiment can be operated, i.e. for example to know up to which electron density space charge effects can be neglected. Finally, the measured swarm parameters need to be translated into breakdown voltage strengths of different electrode arrangements and different applied voltage wave shapes. For this, a model of the the streamer to leader transition in SF6 will be applied to other strong electronegative gases in future studies to test if the model is universally valid. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Electric utilities are looking for novel methods to increase the transmission capacity of existing transmission lines. The conversion of conventional AC towers to hybrid AC/DC lines allows for significantly more power and reduces the need for new rights of way. Still, due to the fixed geometry, there will be coupling effects between the AC and DC systems. Corona effects, such as audible noise, which are crucial for public acceptance, must be controlled to obtain crucial public acceptance. An outdoor test setup is used to investigate the corona audible noise and partial discharges of parallel AC and DC bundles. The effect of a DC bias on the AC corona as well as an AC ripple on DC corona are studied for varying surface gradients and weather conditions. The AC and DC audible noise clearly increased for most cases of a DC bias or AC ripple, respectively. The relative increase was found higher if the conductor was only slightly above corona as it happens in dry conditions with light pollution. Still, the highest level of AC audible noise was observed during wet weather and for DC during dry conditions. [ABSTRACT FROM AUTHOR]

A newly built pulsed Townsend experimental setup which allows one to measure both electron and ion currents is presented. The principle of pulsed Townsend measurements itself is well established to obtain swarm parameters such as the effective ionization rate coefficient, the density-reduced mobility, and the density-normalized longitudinal diffusion coefficient. The main novelty of the present contribution is a detailed and comprehensive analysis of the entire measurement and evaluation chain with respect to accuracy, precision, and reproducibility. The influence of the input parameters (gap distance, applied voltage, measured pressure, and temperature) is analyzed in detail. An overall accuracy of ±0.5% in the density reduced electric field (E/N) is achieved, which is close to the theoretically possible limit using the chosen components. The precision of the experimental results is higher than the accuracy. Through an extensive measurement campaign, the repeatability of our measurements proved to be high and similar to the precision. The reproducibility of results at identical (E/N) is similar to the precision for different distances but decreases for varying pressures. For benchmark purposes, measurements for Ar, CO2, and N2 are presented and compared with our previous experimental setup, simulations, and other experimental references. [ABSTRACT FROM AUTHOR]

A positive synergy in the electric strength was observed in a previous study in SF6/HFO1234ze(E) mixtures which was shown to result from a strong electron energy moderation capability of HFO1234ze(E) combined with thermal electron attachment of SF6 (Egüz et al 2022 J. Phys. D: Appl. Phys. 55 315203). In the present work, the electron energy moderation properties of compounds with a similar C=C−C backbone are investigated. Swarm and breakdown measurements are performed in pure gases and in mixtures with SF6. Compounds with a trifluoromethyl group (−CF3) showed lower characteristic energy and as a consequence a positive synergism with SF6. Descriptors related to electron energy moderation are identified and computed; a clear trend is found from the analysis of descriptors related to inelastic processes which suggest(s) that vibrational excitations may be the main source of electron energy loss in the compounds showing positive synergy. [ABSTRACT FROM AUTHOR]

We probe the electron attachment in hexafluoropropylene oxide (HFPO), C3F6O, a gas widely used in plasma technologies. We determine the absolute electron attachment cross section using two completely different experimental approaches: (i) a crossed-beam experiment at single collision conditions (local pressures of 5 × 10−4 mbar) and (ii) a pulsed Townsend experiment at pressures of 20–100 mbar. In the latter method, the cross sections are unfolded from the electron attachment rate coefficients. The cross sections derived independently by the two methods are in very good agreement. We additionally discuss the dissociative electron attachment fragmentation patterns and their role in the radical production in industrial HFPO plasmas. [ABSTRACT FROM AUTHOR]

This paper presents important results of the European HVDC Study Group founded on an initiative by the German Commission for Electrical, Electronic and Information Technologies in September 2010. The main task of the Study Group has been defining “Technical Guidelines for first HVDC Grids”: 1) to gain a common understanding of basic operating and design principles of HVDC grid systems, and 2) to prepare the ground for more detailed standardization work. The HVDC systems are moving from the stage of point-to-point (PTP) connectors to the stage of the transmission systems interconnecting more than two stations and utilizing multiterminal (MT), multivendor (MTMV) HVDC voltage-source converter (VSC) systems. The development will be modular, for example, in steps, starting with interconnecting PTP connectors and establishing three-pod, radial systems. Then, such simple systems may gradually be interconnected into radial and meshed HVDC–VSC systems comprising more HVDC lines and dc converter stations. This paper describes understanding, specification, and standardization of design and operation principles of the HVDC grids seen as the first needed steps toward such MTMV systems. [ABSTRACT FROM PUBLISHER]