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>

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.

scholarly journals High electron affinity: a guiding criterion for voltage stabilizer design

2015 ◽  
Vol 3 (14) ◽  
pp. 7273-7286 ◽  
Author(s):  
Markus Jarvid ◽  
Anette Johansson ◽  
Villgot Englund ◽  
Angelica Lundin ◽  
Stanislaw Gubanski ◽  
...  
Keyword(s):  
High Voltage ◽  
Electron Affinity ◽  
Dielectric Strength ◽  
Voltage Stabilizer ◽  
High Electron ◽  
Insulation Materials ◽  
High Electron Affinity ◽  
High Voltage Insulation

A high electron affinity is found to correlate with the ability of voltage-stabilizer additives to improve the dielectric strength of cross-linked polyethylene, which is a highly desirable for high-voltage insulation materials.

Comparison of Degradation and Recovery of SiONx and Hf-Based Dielectric under Electrical-Field Stress

2020 ◽  
Vol 843 ◽  
pp. 47-51
Author(s):  
Jian Ming Chen ◽  
Chi Hao Lo ◽  
Mu Chun Wang ◽  
Tien Szu Shen ◽  
Ching Chuan Chou ◽  
...  
Keyword(s):  
Gate Dielectric ◽  
Electrical Performance ◽  
Recovery Effect ◽  
Electrical Field ◽  
Drive Current ◽  
Field Stress ◽  
High K ◽  
Short And Long Term ◽  
High K Dielectric

Using the electrical-field (E-field) stress at the positive and negative directions to generate the degradation and form the recovery effect is a useful metrology to evaluate the integrity of gate dielectric. This consequence deeply influences the drive current of 2D MOSFET or 3D FinFET species. According to the experimental results with the short and long-term stresses, we found the electrical performance of Hf-based tested devices represented the better recovery than that of SiON-based ones. And the recovery effect is more regular, not only in VT shift, but in gate leakage due to the high-k dielectric probably providing the polar effect and more trap assistants.

Short- and Long-Term Results of Total vs Subtotal Thyroid- ectomies in the Surgical Treatment of Graves' Disease

Swiss Surgery ◽  
2001 ◽  
Vol 7 (1) ◽  
pp. 20-24 ◽  
Author(s):  
Robert ◽  
Mariéthoz ◽  
Pache ◽  
Bertin ◽  
Caulfield ◽  
...  
Keyword(s):  
Recurrent Laryngeal Nerve ◽  
Nerve Palsy ◽  
Recurrent Laryngeal Nerve Palsy ◽  
Laryngeal Nerve ◽  
Long Term Results ◽  
Graves Disease ◽  
Laryngeal Nerve Palsy ◽  
Short And Long Term

Objective: Approximately one out of five patients with Graves' disease (GD) undergoes a thyroidectomy after a mean period of 18 months of medical treatment. This retrospective and non-randomized study from a teaching hospital compares short- and long-term results of total (TT) and subtotal thyroidectomies (ST) for this disease. Methods: From 1987 to 1997, 94 patients were operated for GD. Thirty-three patients underwent a TT (mostly since 1993) and 61 a ST (keeping 4 to 8 grams of thyroid tissue - mean 6 g). All patients had received propylthiouracil and/or neo-mercazole and were in a euthyroid state at the time of surgery; they also took potassium iodide (lugol) for ten days before surgery. Results: There were no deaths. Transient hypocalcemia (< 3 months) occurred in 32 patients (15 TT and 17 ST) and persistent hypocalcemia in 8 having had TT. Two patients developed transient recurrent laryngeal nerve palsy after ST (< 3 months). After a median follow-up period of seven years (1-15) with five patients lost to follow-up, 41 patients having had a ST are in a hypothyroid state (73%), thirteen are euthyroid (23%), and two suffered recurrent hyperthyroidism, requiring completion of thyroidectomy. All 33 patients having had TT - with follow-ups averaging two years (0.5-8) - are receiving thyroxin substitution. Conclusions: There were no instances of persistent recurrent laryngeal nerve palsy in either group, but persistent hypoparathyroidism occurred more frequently after TT. Long after ST, hypothyroidism developed in nearly three of four cases, whereas euthyroidy was maintained in only one-fourth; recurrent hyperthyroidy was rare.

Short- and long-term memory tasks predict working memory performance, and vice versa.

2019 ◽  
Vol 73 (2) ◽  
pp. 79-93 ◽  
Author(s):  
Ian Neath ◽  
Jean Saint-Aubin ◽  
Tamra J. Bireta ◽  
Andrew J. Gabel ◽  
Chelsea G. Hudson ◽  
...  
Keyword(s):  
Working Memory ◽  
Memory Performance ◽  
Long Term Memory ◽  
Term Memory ◽  
Short And Long Term

Short- and Long-Term Consequences of Directed Forgetting

2012 ◽  
Author(s):  
Sara B. Festini ◽  
Patricia A. Reuter-Lorenz
Keyword(s):  
Directed Forgetting ◽  
Short And Long Term ◽  
Long Term Consequences

What You Think You Saw or Heard Depends on Test Delay: Modality Effects on Short- and Long-Term False Memories

2014 ◽  
Author(s):  
Justyna Olszewska ◽  
Patricia Reuter-Lorenz ◽  
Emily Munier ◽  
Sara Bendler
Keyword(s):  
False Memories ◽  
Modality Effects ◽  
Short And Long Term ◽  
Test Delay

Dissociation of short- and long-term memory recency effects: A case study

2001 ◽  
Author(s):  
Randi C. Martin ◽  
Mary R. Newsome ◽  
Monica L. Freedman
Keyword(s):  
Long Term Memory ◽  
Term Memory ◽  
Recency Effects ◽  
Short And Long Term
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