Comparison of Two Electro-Quasistatic Field Formulations for the Computation of Electric Field and Space Charges in HVDC Cable Systems

2019 ◽  
Author(s):  
Christoph Jorgens ◽  
Markus Clemens
Keyword(s):  
Electric Field ◽  
Space Charges ◽  
Cable Systems ◽  
Quasistatic Field

Modeling the electric field at interfaces and surfaces in high-voltage cable systems

2020 ◽  
Vol 39 (5) ◽  
pp. 1099-1111 ◽  
Author(s):  
Christoph Jörgens ◽  
Markus Clemens
Keyword(s):  
Electric Field ◽  
Electric Conductivity ◽  
High Voltage ◽  
Analytic Description ◽  
Time Varying ◽  
Content Type ◽  
Field Stress ◽  
Space Charges ◽  
Stationary Electric Field ◽  
Cable Systems

Purpose In high-voltage direct current (HVDC) cable systems, space charges accumulate because of the constant applied voltage and the nonlinear electric conductivity of the insulating material. The change in the charge distribution results in a slowly time-varying electric field. Space charges accumulate within the insulation bulk and at interfaces. With an operation time of several years of HVDC systems, typically the stationary electric field is of interest. The purpose of this study is to investigate the influence of interfaces on the stationary electric field stress and space charge density. Design/methodology/approach An analytic description of the stationary electric field inside cable insulation is developed and numerical simulations of a cable joint geometry are applied, considering spatial variations of the conductivity in the vicinity of the electrodes and interfaces. Findings With increasing conductivity values toward the electrodes, the resulting field stress decreases, whereas a decreasing conductivity results in an increasing electric field. The increased electric field may cause partial discharge, resulting in accelerated aging of the insulation material. Thus, interfaces and surfaces are characterized as critical areas for the reliability of HVDC cable systems. Research limitations/implications This study is restricted to stationary electric field and temperature distributions. The electric field variations during a polarity reversal or a time-varying temperature may result in an increased electric conductivity and electric field at interfaces and surfaces. Originality/value An analytical description of the electric field, considering surface effects, is developed. The used conductivity model is applicable for cable and cable-joint insulations, where homo- and hetero-charge effects are simulated. These simulations compare well against measurements.

Effects of Space Charge on ESEM Gas Amplification

1997 ◽  
Vol 3 (S2) ◽  
pp. 609-610 ◽  
Author(s):  
B.L. Thiel ◽  
M.R. Hussein-Ismail ◽  
A.M. Donald
Keyword(s):  
Electric Field ◽  
Electrostatic Field ◽  
Secondary Electron ◽  
Sample Surface ◽  
Cascade Process ◽  
Secondary Electrons ◽  
Positive Ions ◽  
Space Charges ◽  
Cascade Amplification ◽  
Environmental Sem

We have performed a theoretical investigation of the effects of space charges in the Environmental SEM (ESEM). The ElectroScan ESEM uses an electrostatic field to cause gas cascade amplification of secondary electron signals. Previous theoretical descriptions of the gas cascade process in the ESEM have assumed that distortion of the electric field due to space charges can be neglected. This assumption has now been tested and shown to be valid.In the ElectroScan ESEM, a positively biased detector is located above the sample, creating an electric field on the order of 105 V/m between the detector and sample surface. Secondary electrons leaving the sample are cascaded though the gas, amplifying the signal and creating positive ions. Because the electrons move very quickly through the gas, they do not accumulate in the specimen-to-detector gap. However, the velocity of the positive ions is limited by diffusion.

Surface discharge imaging in presence of deposited space charges in non‐uniform DC electric field

High Voltage ◽  
2021 ◽  
Author(s):  
Marek Florkowski ◽  
Dariusz Krześniak ◽  
Maciej Kuniewski ◽  
Paweł Zydroń
Keyword(s):  
Electric Field ◽  
Surface Discharge ◽  
Space Charges ◽  
Dc Electric Field

Thermal breakdown in high voltage direct current cable insulations due to space charges

2018 ◽  
Vol 37 (5) ◽  
pp. 1689-1697 ◽  
Author(s):  
Christoph Jörgens ◽  
Markus Clemens
Keyword(s):  
Electric Field ◽  
Breakdown Voltage ◽  
High Voltage ◽  
Direct Current ◽  
Aging Effect ◽  
Radial Symmetry ◽  
Thermal Breakdown ◽  
Content Type ◽  
High Voltage Direct Current ◽  
Space Charges

Purpose In high voltage direct current (HVDC), power cables heat is generated inside the conductor and the insulation during operation. A higher amount of the generated heat in comparison to the dissipated one, results in a possible thermal breakdown. The accumulation of space charges inside the insulation results in an electric field that contributes to the geometric electric field, which comes from the applied voltage. The total electric field decreases in the vicinity of the conductor, while it increases near the sheath, causing a possible change of the breakdown voltage. Design/methodology/approach Here, the thermal breakdown is studied, also incorporating the presence of space charges. For a developed electro-thermal HVDC cable model, at different temperatures, the breakdown voltage is computed through numerical simulations. Findings The simulation results show a dependence of the breakdown voltage on the temperature at the location of the sheath. The results also show only limited influence of the space charges on the breakdown voltage. Research limitations/implications The study is restricted to one-dimensional problems, using radial symmetry of the cable, and does not include any aging or long-term effect of space charges. Such aging effect can locally increase the electric field, resulting in a reduced breakdown voltage. Originality/value A comparison of the breakdown voltage with and without space charges is novel. The chosen approach allows for the first time to assess the influence of space charges and field inversion on the thermal breakdown.

scholarly journals Study of electric field distorted by space charges under positive lightning impulse voltage

2018 ◽  
Vol 8 ◽  
pp. 955-962 ◽  
Author(s):  
Zezhong Wang ◽  
Yinan Geng
Keyword(s):  
Electric Field ◽  
Space Charges ◽  
Impulse Voltage ◽  
Lightning Impulse

scholarly journals Statistical Study on Space Charge effects and Stage Characteristics of Needle-Plate Corona Discharge under DC Voltage

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2732 ◽  
Author(s):  
Disheng Wang ◽  
Lin Du ◽  
Chenguo Yao
Keyword(s):  
Electric Field ◽  
Space Charge ◽  
Corona Discharge ◽  
Discharge Process ◽  
Space Charge Effects ◽  
Discharge Characteristics ◽  
Charge Effects ◽  
Dc Voltage ◽  
Field Distributions ◽  
Space Charges

The air’s partial discharges (PD) under DC voltage are obviously affected by space charges. Discharge pulse parameters have statistical regularity, which can be applied to analyze the space charge effects and discharge characteristics during the discharge process. Paper studies air corona discharge under DC voltage with needle-plate model. Statistical rules of repetition rate (n), amplitude (V) and interval time (∆t) are extracted, and corresponding space charge effects and electric field distributions in PD process are analyzed. The discharge stages of corona discharge under DC voltage are divided. Furthermore, reflected space charge effects, electric field distributions and discharge characteristics of each stages are summarized to better explain the stage discharge mechanism. This research verifies that microcosmic process of PD under DC voltage can be described based on statistical method. It contributes to the microcosmic illustration of gas PD with space charges.

Calculation of Capacitance Variation in Corona Cage

2015 ◽  
Vol 740 ◽  
pp. 405-410
Author(s):  
Xiao Ming Li ◽  
Yong Zhong Pan ◽  
Hong Jun Li ◽  
Jie Shuai Ren ◽  
Po Hu ◽  
...  
Keyword(s):  
Electric Field ◽  
Transmission Lines ◽  
Simulation Method ◽  
Calculation Model ◽  
Meteorological Conditions ◽  
Charge Simulation Method ◽  
Tight Coupling ◽  
Space Charges ◽  
Supplementary Method ◽  
Capacitance Variation

Corona cage is an important supplementary method for studying corona phenomenon, which is an indispensable for designing transmission lines. In this paper, the bundle conductors are chosen as research objects and the charge simulation method (CSM) is applied to build calculation model, using line electric charges to simulate bundle conductors, walls of corona cage and space charges. The method of tight coupling of electric field and potential is first introduced in corona processing, in which the Kaptzov hypothesis is directly applied to establish equations of charge - electric field and charge - electric potential. In addition, in order to analyze the capacitance value variation of corona cage when corona onset occurs, the emission, migration and composite process of space charges is simulated. Finally, 4, 8, 12 conductors in corona cage under different meteorological conditions are modeled, and the research results are analyzed. This research can also be applied to model corona cage and high voltage transmission lines at different voltage levels and different bundles under different meteorological conditions.

scholarly journals Empirical Conductivity Equation for the Simulation of the Stationary Space Charge Distribution in Polymeric HVDC Cable Insulations

Energies ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 3018 ◽  
Author(s):  
Christoph Jörgens ◽  
Markus Clemens
Keyword(s):  
Electric Field ◽  
Space Charge ◽  
Charge Distribution ◽  
Euler Method ◽  
Accurate Description ◽  
Conductivity Equation ◽  
Transient Model ◽  
Space Charges ◽  
Sigmoid Functions ◽  
Conductivity Gradient

Many processes are involved in the accumulation of space charges within the insulation materials of high voltage direct current (HVDC) cables, e.g., the local electric field, a conductivity gradient inside the insulation, and the injection of charges at both electrodes. An accurate description of the time dependent charge distribution needs to include these effects. Furthermore, using an explicit Euler method for the time integration of a suitably formulated transient model, low time steps are used to resolve fast charge dynamics and to satisfy the Courant–Friedrichs–Lewy (CFL) stability condition. The long lifetime of power cables makes the use of a final stationary charge distribution necessary to assess the reliability of the cable insulations. For an accurate description of the stationary space charge and electric field distribution, an empirical conductivity equation is developed. The bulk conductivity, found in literature, is extended with two sigmoid functions to represent a conductivity gradient near the electrodes. With this extended conductivity equation, accumulated bulk space charges and hetero charges are simulated. New introduced constants to specify the sigmoid functions are determined by space charge measurements, taken from the literature. The measurements indicate accumulated hetero charges in about one quarter of the insulation thickness in the vicinity of both electrodes. The simulation results conform well to published measurements and show an improvement to previously published models, i.e., the developed model shows a good approximation to simulate the stationary bulk and hetero charge distribution.

Corona point discharges from grounded rods under high background electric field

2021 ◽  
Author(s):  
Marcelo Arcanjo ◽  
Joan Montanyà ◽  
Victor Lorenzo ◽  
Nicolau Pineda
Keyword(s):  
Electric Field ◽  
Ground Level ◽  
Pulse Frequency ◽  
High Background ◽  
Lightning Strikes ◽  
Space Charges ◽  
Average Current ◽  
Microphysical Processes ◽  
A Site ◽  
Fast Rise

<p>During the formation of thunderclouds, simultaneous macrophysical and microphysical processes cause the separation of charges inside the cloud, forming the electrical structure of storm clouds. As a result of that, the electric field at the ground level can change significantly. Irregularities on the surfaces of grounded structures can provide conditions for corona discharges that generate ions and form a space charge layer at ground level.</p><p>In this work, we investigate the features of corona point discharges from grounded conductive rods installed in three different sites. In all of them, we measured current along the grounded rod under high background electric field conditions or during its fast changes caused by lightning strikes. The current signals reveal pulses with a fast rise time (tens of nanoseconds) and slow decay (hundreds of nanoseconds), with polarity compatible with the background electric field. Comparing laboratory experiments with the results in the field, we observed that positive discharges required a lower electric field threshold than negative discharges. Their pulse frequency is also equivalent to one-tenth of the pulse frequency of negative discharges, for a similar electric field level.</p><p>In one of the sites, one current sensor coupled to a grounded rod, 1.5 m above a roof, was installed in a site located at an altitude of 2525 m, near a ski-station. We observed a large number of events, and we were able to correlate the frequency of the pulses with the electric field, as well as evaluate the effect of the wind on the discharges. In the other two sites, the rods were placed near the ground and on the roof of a conventional building. Pulses were registered on some occasions when there was lightning activity nearby, either before or after lightning events. Previous works on this topic correlate the electric field with the average current flow, and on this work, we evaluate the pulse frequency and electric field. This investigation is relevant for understanding the production of corona and space charges from high structures.</p>

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