Alain Girodet

Bio: Alain Girodet is an academic researcher from Alstom. The author has contributed to research in topics: High voltage & Partial discharge. The author has an hindex of 10, co-authored 62 publications receiving 426 citations. Previous affiliations of Alain Girodet include Schneider Electric & Brown, Boveri & Cie.

Fluoronitriles/CO2 gas mixture as promising substitute to SF6 for insulation in high voltage applications

Abstract: This paper is aimed at the breakdown characteristics of Fluoronitriles – CO2 gas mixtures in different experimental conditions; these mixtures constitute promising substitutes to SF6 gas in high voltage applications especially gas insulating switchgear (GIS). Fluoronitriles chemical gas compound based on 3M NOVEC 4710 have a high dielectric strength, more than 2 times that of SF6 and a low Global Warming Potential (GWP). Mixed with CO2 as gas carrier, the obtained mixtures offer interesting dielectric properties and the possibility to be used for low temperature applications. The experiments are conducted with different electrodes geometries namely plane-to-plane, sphere-to-sphere, sphere-to-plane and rod-to-plane (i.e. in homogeneous, quasi-homogeneous and inhomogeneous electric field distribution) and different field utilization factors, under AC and lightning impulse voltages. The same experiments are reproduced for pure SF6 for the comparison. The comparison of breakdown voltages results of mixtures with different concentrations of Fluoronitriles in CO2 in sphere-to-sphere electrodes arrangement shows that the 3.7 % Fluoronitriles / 96.3% CO2 mixture constitutes a good compromise and an appropriate gas mixture for high voltage apparatus insulation in point of view of pressure and low ambient temperature application (-30°C).

Effective ionization coefficients and limiting field strength of fluoronitriles-CO2 mixtures

Abstract: The density normalized effective ionization coefficients and critical breakdown electric field of the Heptafluoro-iso-butyronitrile (Fluoronitriles), and Fluoronitriles-CO2 mixture are investigated using the steady state Townsend (SST) experimental setup, over a range of the density normalized critical electric field (E/N) from 200–1066 Td (E is the electric field and N the gas density). Breakdown voltage measurements are also performed to plot the Paschen curves for small product values (N×d) (d being the electrode gap), to identify the Paschen minimum, and to validate the density normalized critical electric field (E/N)0 when α=η (α and η are the ionization and attachment coefficients, respectively). The influence of electrode surface roughness is also analyzed.

Partial discharge analysis of gas insulated systems at high voltage AC and DC

Abstract: Partial discharge (PD) measurements are commonly used for monitoring and diagnostics of AC gas insulated systems (GIS). Because of the growing importance of DC GIS, a research project was started focused on the measurement and interpretation of PD signals obtained under DC stress. Results are presented using IEC60270 and unconventional methods through UHF antenna and high frequency current transformer (HFCT) on three different PD generating defects in a GIS chamber. The results of the PD analysis of the defects are compared for AC and DC stress. Phase resolved partial discharge patterns (PRPD) are used for the HVAC analysis, whereas time resolved partial discharge patterns (TRPD) are used for HVDC analysis. Finally, relevant characteristics of PD patterns in HVAC and HVDC are presented and related with the physical phenomena of the discharges.

Partial discharge behavior of protrusion on high voltage conductor in GIS/GIL under high voltage direct current: Comparison of SF 6 and SF 6 alternative gases

Abstract: Recent studies have demonstrated that fluoronitrile (FN) Novec™ 4710 and fluoroketone (FK) Novec™ 5110 show higher dielectric strength than SF 6 . These gases can be mixed with a buffer gas such as CO 2 and technical air to have suitable dielectric properties for high voltage insulation applications. With the rapid growth of HVDC networks, these gases may replace SF 6 in future HVDC apparatus such as GIS/GIL. This paper focuses on the study of the partial discharge (PD) characteristics of SF 6 and SF6 alternative gases with a protrusion defect on the high voltage conductor with DC voltage. The results show that, for calculated equivalent SF 6 dielectric strength under homogeneous electric field, a difference in terms of partial discharge inception voltage was noted for gas mixtures compared to SF 6 . This difference may be due to the influence of gas pressure under highly inhomogeneous electric field. FN-CO 2 and FK-Air mixtures showed the highest PD amplitude under positive polarity while it was higher under negative polarity for SF 6 . Moreover, PD repetition frequency is higher for SF 6 investigated alternative gases. The results can help for the design of SF 6 free HVDC GIS partial discharge monitoring system.

Surface charge measurements on epoxy spacer in HVDC GIS/GIL in SF6

Abstract: The design of reliable high voltage equipment remains a challenge nowadays. The surface charge accumulation at gas/solid interface is a major problem for HVDC GIS/GIL. The electric field can be distorted and the dielectric strength of the system can be thus reduced dramatically due to surface charges. This paper presents the measurement of surface charge (surface potential) on spacer in DC GIS/GIL under pressurized SF6 condition. The surface potential distribution on the spacer is obtained by an electrostatic probe connected to a displacement system. Firstly, the importance of preparation process for DC GIS/GIL spacer for the measurement of surface charge is introduced. The influence of DC voltage, electrode roughness on the surface charge accumulation and the time constant of the system is then investigated. The dominant mechanism for surface charge accumulation is also identified.

Assessment of Eco-friendly Gases for Electrical Insulation to Replace the Most Potent Industrial Greenhouse Gas SF6

Abstract: Gases for electrical insulation are essential for the operation of electric power equipment. This Review gives a brief history of gaseous insulation that involved the emergence of the most potent industrial greenhouse gas known today, namely sulfur hexafluoride. SF6 paved the way to space-saving equipment for the transmission and distribution of electrical energy. Its ever-rising usage in the electrical grid also played a decisive role in the continuous increase of atmospheric SF6 abundance over the last decades. This Review broadly covers the environmental concerns related to SF6 emissions and assesses the latest generation of eco-friendly replacement gases. They offer great potential for reducing greenhouse gas emissions from electrical equipment but at the same time involve technical trade-offs. The rumors of one or the other being superior seem premature, in particular because of the lack of dielectric, environmental, and chemical information for these relatively novel compounds and their dissociation...

Recent Advances in the Quest for a New Insulation Gas with a Low Impact on the Environment to Replace Sulfur Hexafluoride (SF6) Gas in High-Voltage Power Network Applications

Abstract: The growing environmental challenge of electrical energy systems has prompted a substantial increase in renewable energy generation. Such generation systems allow for significant reduction of CO2 emissions compared with a traditional fossil fuel plant. Furthermore, several improvements in power systems network configuration and operation combined with new technologies have enabled reduction of losses and energy demand, thus contributing to reduction of CO2 emissions. Another environmental threat identified in electrical networks is the leaking of insulating sulfur hexafluoride (SF6) gas used in electrical gas insulated substations (GIS) and equipment. Because of its Global Warming Potential (GWP) of nearly 24,000 and its long life in the atmosphere (over 3000 years), SF6 gas was recognized as a greenhouse gas at the 1997 COP3; since then its use and emissions in the atmosphere have been regulated by international treaties. It is expected that as soon as an alternative insulating gas is found, SF6 use in high-voltage (HV) equipment will be banned. This paper presents an overview of the key research advances made in recent years in the quest to find eco-friendly gases to replace SF6. The review reports the main properties of candidate gases that are being investigated; in particular, natural gases (dry air, N2 or CO2) and polyfluorinated gases especially Trifluoroiodomethane (CF3I), Perfluorinated Ketones, Octafluorotetra-hydrofuran, Hydrofluoroolefin (HFOs), and Fluoronitriles are presented and their strengths and weaknesses are discussed with an emphasis on their dielectric properties (especially their dielectric strength), GWP, and boiling point with respect to the minimum operating temperature for HV power network applications.

Understanding surface charge accumulation and surface flashover on spacers in compressed gas insulation

Abstract: Surface charges have the effect of changing the electric field over spacers in compressed gases, which may affect the stable operation of gas insulated equipment and could possibly trigger a catastrophic surface flashover without warning. In this paper, we review the literature on surface charge accumulation and related surface flashover phenomenon on spacers in compressed gases. A summary of experimental research of surface charge accumulation is presented and, the surface charge accumulation mechanism is also summarized, with some newly identified factors in mind that may affect surface charge transport and measurements thereof. Subsequently, the correlation between surface charge accumulation and the surface flashover phenomenon is thoroughly discussed, and the effect of surface charges on surface breakdown under applied voltage pulses of various waveforms is analyzed. Finally, several important research topics in this area are proposed. In addition, some ideas on potential surface charge control methods are presented to aid the design of a better spacer free from surface charges in future studies.