Christian Franck


Last Name

Franck

First Name

Christian

ORCID

0000-0002-2201-7327

Organisational unit

03869 - Franck, Christian / Franck, Christian

Search Results

Publications 1 - 10 of 284
  • Safe and automated control of experiments with a high voltage construction kit
    Item type: Conference Paper
    Truessel, Jonas M.; Weber, Hans-Jürg; Franck, Christian (2015)
    Vydala Fakulta elektrotechnická ~ 19th International Symposium on High Voltage Engineering, ISH 2015
  • Temperature Profiles of All-Aluminum-Alloy Conductors near Wedge Tension Clamps
    Item type: Journal Article
    Bühlmann, Pascal; Franck, Christian (2018)
    CIGRE Science & Engineering
    Conductor temperatures at the wedge tension clamp are significantly lower than in the free-span. In this paper, the reasons for the lower temperatures due to the clamp are investigated. The increased convective and emissive cooling power as well as the decreased power losses at the clamp are causing the lower conductor temperatures. A numerical model is developed and described, which enables to accurately predict axial and radial temperature profiles of the conductor inside and close to the clamp. Experimental measurements of electric resistance, magnetic flux and temperature are used to verify the presented model. This developed numerical tool uses adapted material characteristics that allow to model the conductor as a simplified bulk cylinder. The tool can be adapted to other clamps and applications to analyze and optimize them.
  • Swarm parameter measurement in hydrogen, considering secondary photonic electron emission
    Item type: Working Paper
    Hösl, Andreas; Franck, Christian (2018)
    arXiv
    Discharges in hydrogen at pressures above $1\,$kPa and a reduced electric field of $E/N=100-200\,$Td show a characteristic current oscillation in Pulsed Townsend experiments. This is explained by secondary emission of electrons from the photo-cathode: some hundreds of nano-seconds after the laser-pulse that released the initial $10^4-10^6$ primary electrons, secondary electrons are emitted from the cathode. Mechanisms discussed in literature are UV-emission from neutral molecules, emission by positive ions reaching the cathode, and back-scattering of excited neutrals. For an E/N range up to $500\,$Td and pressures up to $2\,$kPa we model different sources, and agree with previous findings that the observed secondary emission is purely due to ultra-violet light below $200\,$Td: the simulation fits with the complex oscillating waveform. Obtained swarm parameters agree well with the literature. Our findings suggest a very high efficiency of the photo-cathode for UV light of energies above $8\,$eV.
  • High Voltage Insulation Gas Mixtures alternative to SF6
    Item type: Other Conference Item
    Franck, Christian (2013)
  • X-ray triggered PD measurements in small sized spherical voids at the detection limit
    Item type: Conference Paper
    Schmitt, Cédric; Hermann, Lorenz G.; Pancheshnyi, Sergey; et al. (2014)
    2014 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP)
  • Technical Guidelines and Prestandardization Work for First HVDC Grids
    Item type: Journal Article
    Akhmatov, Vladislav; Callavik, Magnus; Franck, Christian; et al. (2014)
    IEEE Transactions on Power Delivery
  • Influence of mixed-frequency medium-voltage and environmental stress on the aging of epoxy
    Item type: Journal Article
    Küchler, Florian; Färber, Raphael; Sefl, Ondrej; et al. (2023)
    Journal of Physics D: Applied Physics
    Recent developments in power electronic technologies lead to new challenges for insulation systems. This contribution aims to clarify the influence of a broad range of mixed-frequency (MF) medium-voltage and environmental stress parameters on the aging of epoxy insulation. For this purpose, test samples are stressed with an AC (50 Hz) or a DC voltage, superimposed with a pulse-width-modulated (PWM) voltage (kHz range). An analysis of the samples' health state is carried out after the aging by the evaluation of potential aging markers (AC breakdown strength, dielectric permittivity, glass transition temperature, Fourier-transform infrared spectroscopy spectra). Although the main focus of this work is on aging below the inception of partial discharges (PDs), it was first confirmed that PD-related aging depends mainly on the peak voltage stress. In contrast, the results obtained by aging below PD inception suggests a dependence on the root-mean-square of the applied voltage stress, and consequently on the energy dissipation. Aging in the PD-free regime was only observed at alternating electric field stress and high relative humidity or elevated temperatures. No influences of space charge and of the slew rate of the PWM voltage were observed. Remarkably, higher PWM frequencies lead to less insulation aging. This might be attributed to the increasing hindrance of polymer side chain movement at higher frequencies, as observed by dielectric spectroscopy. In addition, it is indicated that the aging mechanisms under MF voltage stress result from superimposed single-frequency aging mechanisms and that aging is activated after a latency period. Of the investigated potential aging markers, only the residual breakdown strength revealed aging effects, which correlates with lifetime observations in the PD-free voltage stress regime. It is hypothesized that the aging mechanism is associated with a rearrangement of the free volume in the polymer, followed by a localized breaking of van der Waals bonds.
  • Finite element simulation of ion currents from coronating HVDC overhead lines
    Item type: Conference Paper
    Straumann, Ulrich; Franck, Christian (2011)
    ISH 2011 - 17th International Symposium on High Voltage Engineering August, 22-26, 2011, Hannover, Germany, Book of Abstracts
  • On the drift-diffusion analysis of the Pulsed Townsend experiment: a fitting algorithm and benchmark study
    Item type: Journal Article
    Vemulapalli, Hanut; Akbas, Mücahid; Muccignat, Dale L.; et al. (2025)
    Plasma Sources Science and Technology
    Electron transport properties in gases and gas mixtures can be determined from measurements with a Pulsed-Townsend experiment. Analytical solutions of a drift-diffusion equation are fitted to the measured experimental waveforms to determine electron transport coefficients. However, it is not always unambiguously clear what the published measurement data ultimately represents, under which assumptions published transport data have been derived, and how large the uncertainty is. To address this, we first present an open source code for the analysis of the Pulsed-Townsend experiment waveforms. We then use this code to fit synthetic waveforms generated by Monte-Carlo simulations to estimate the accuracy of transport data obtained by curve fitting. Two benchmark simulation cases are considered: a representative case that closely replicates a typical Pulsed-Townsend experiment and an idealised case that replicates the assumptions that underpin the state of the art analytic solution. For each case simulations are performed for three different gases (Ar, CO₂ and SF₆) and over a wide range of electric field strengths (10-1000 Td), densities (10e²² - 10e²⁴ m⁻³) and electrode spacings (10-30 mm). For the representative model, while the error in the extracted transport coefficients can be as good as 0.1%, it deteriorates with decreasing pressure, decreasing electrode gap distance and increasing electric field strength. While significantly reduced errors were found for the idealised model, errors exceeding 10% were still present in some regimes. We show that these errors are strongly correlated with the third-order transport coefficient, which calls into question the accuracy of analyses that do not account for it, especially for experiments operated at low pressures and small electrode spacings.
  • Continuous Health State Monitoring of High-Voltage Circuit Breakers
    Item type: Journal Article
    Hsu, Chi-Ching; Frusque, Gaëtan; Fink, Olga; et al. (2025)
    IEEE Access
    Circuit breakers (CBs) are renowned for their high reliability and long lifespan. As a result, many CBs installed decades ago are now approaching their predefined end of service life. However, this predefined service life does not always reflect the actual condition, as some may still be far from reaching their true end-of-life, depending on their operating conditions and history. To assess their true lifetime, continuous condition monitoring is essential. While previous studies have effectively demonstrated the ability to distinguish between different CB fault types, the evolution of CB degradation remains unclear when faults are artificially introduced. This paper investigates the health condition of two high-voltage CBs continuously through run-to-failure experiments. A comprehensive dataset was collected for all opening and closing operations with various sensors such as vibration, coil current, and travel curve and has been made publicly available for further analysis. Furthermore, features were derived from the sensor data, revealing distinct degradation trajectories over time that can be used to monitor the condition of the CBs. This paper highlights the degradation patterns of these features, some of which are well-suited for continuous condition monitoring due to their gradual changing trend over time that likely correlates with the true degradation condition, while others are less useful as they show abrupt changes only before or at failure. By leveraging these features, we can progress beyond the focus of previous research using only fault diagnosis towards fault prognosis. This shift opens the possibility for accurate prediction of the CB condition over time, enabling more effective maintenance strategies.
Publications 1 - 10 of 284