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.

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 A Review about the Modeling and Simulation of Electro-Quasistatic Fields in HVDC Cable Systems

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5189
Author(s):  
Christoph Jörgens ◽  
Markus Clemens
Keyword(s):  
Electric Field ◽  
Field Distribution ◽  
High Voltage ◽  
Electric Field Distribution ◽  
Computation Time ◽  
Charge Movement ◽  
Time Varying ◽  
Long Distance ◽  
Cable Systems ◽  
Simulation Results

In comparison to high-voltage alternating current (HVAC) cable systems, high-voltage direct current (HVDC) systems have several advantages, e.g., the transmitted power or long-distance transmission. The insulating materials feature a non-linear dependency on the electric field and the temperature. Applying a constant voltage, space charges accumulate in the insulation and yield a slowly time-varying electric field. As a complement to measurements, numerical simulations are used to obtain the electric field distribution inside the insulation. The simulation results can be used to design HVDC cable components such that possible failure can be avoided. This work is a review about the simulation of the time-varying electric field in HVDC cable components, using conductivity-based cable models. The effective mechanisms and descriptions of charge movement result in different conductivity models. The corresponding simulation results of the models are compared against measurements and analytic approximations. Different numerical techniques show variations of the accuracy and the computation time that are compared. Coupled electro-thermal field simulations are applied to consider the environment and its effect on the resulting electric field distribution. A special case of an electro-quasistatic field describes the drying process of soil, resulting from the temperature and electric field. The effect of electro-osmosis at HVDC ground electrodes is considered within this model.

Simulation on motion characteristics of space charge in single oil-paper insulation

2017 ◽  
Vol 36 (6) ◽  
pp. 1663-1675 ◽  
Author(s):  
Zhifei Yang ◽  
Zhiye Du ◽  
Jiangjun Ruan ◽  
Shuo Jin ◽  
Guodong Huang ◽  
...  
Keyword(s):  
Electric Field ◽  
Space Charge ◽  
Electric Field Intensity ◽  
Single Layer ◽  
Simulation Method ◽  
Insulation System ◽  
Content Type ◽  
Space Charges ◽  
Paper Insulation ◽  
Total Electric Field

Purpose The purpose of this paper is numerical calculation of total electric field in oil-paper insulation. Now, there is no effective method to consider the influence of space charges when calculating the total electric field distribution in the main insulation system of the valve-side winding of an ultra-high-voltage direct current converter transformer. Design/methodology/approach To calculate the total electric field in an oil-paper insulation system, a new simulation method in single-layer oil-paper insulation based on the transient upstream finite element method (TUFEM) is proposed, in which the time variable is considered. The TUFEM is used to calculate the total electric field in an oil-paper insulation system by considering the move law of space charges. The simulation method is verified by comparing the simulation results to the test data. The move law of space charges and distribution characteristics of the electric field under difference voltage values in single-layer oil-paper insulation were presented. Findings The results show that the TUFEM has an excellent accuracy compared with the test data. When carrier mobility is a constant, the time to reach the steady state is inversely correlated with the initial electric field intensity, and the distortion rate of the internal total electric field is positively correlated with the initial electric field intensity. Originality/value This paper provides an exploratory research on the simulation of space charge transport phenomenon in oil-paper and has guiding significance to the design of oil-paper insulation.

scholarly journals Short and long term behavior of functionally filled polymeric insulating materials for HVDC insulators in compact gas-insulated systems

2018 ◽  
Author(s):  
Michael Tenzer ◽  
Maximilian Secklehner ◽  
Volker Hinrichsen
Keyword(s):  
Electric Conductivity ◽  
High Voltage ◽  
Dielectric Breakdown ◽  
Dielectric Strength ◽  
Filled Polymers ◽  
Field Stress ◽  
Insulation Materials ◽  
Current Transmission ◽  
Short And Long Term

<p>Conventional insulators optimized for high-voltage alternating current transmission tend to accumulate surface and volume charges in direct voltage applications. This is especially true for gas-insulated systems, where the surrounding gas is extremely dry, thus having very low conductivity. This may result in a strong decrease of the dielectric strength of the insulators and can lead to dielectric breakdown, especially when polarity reversals are applied. Main challenges for the development of HVDC insulators are avoiding surface and volume charge accumulations and featuring both suitable capacitive and resistive field distributions. The use of polymeric insulation materials filled with functional fillers of defined low and possibly non-linear, field dependent electric conductivity avoids these charge accumulations. <br />Several specimens of polymeric insulation materials of different, controlled conductivities for high field stress applications were produced and experimentally investigated for this contribution. Since electric conductivity depends on parameters such as temperature, humidity or long term ageing, the longterm behavior of the specimens was investigated in 1000 h tests under temperature and electrical field stress. Furthermore, tests in a high-voltage gas insulated test setup were performed in order to determine the dielectric strength of the filled polymers under high electric stationary and transient fields as present in gas insulated systems. Results of these investigations are presented and discussed in detail in this contribution.</p>

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