Breakdown Stress Research Articles

A thermal pressurization model for the spontaneous dynamic rupture propagation on a three‐dimensional fault: 1. Methodological approach

We investigate the role of frictional heating and thermal pressurization on earthquake ruptures by modeling the spontaneous propagation of a three‐dimensional (3‐D) crack on a planar fault governed by assigned constitutive laws and allowing the evolution of effective normal stress. We use both slip‐weakening and rate‐ and state‐dependent constitutive laws; in this latter case we employ the Linker and Dieterich evolution law for the state variable, and we couple the temporal variations of friction coefficient with those of effective normal stress. In the companion paper we investigate the effects of thermal pressurization on the dynamic traction evolution. We solve the 1‐D heat conduction equation coupled with Darcy's law for fluid flow in porous media. We obtain a relation that couples pore fluid pressure to the temperature evolution on the fault plane. We analytically solve the thermal pressurization problem by considering an appropriate heat source for a fault of finite thickness. Our modeling results show that thermal pressurization reduces the temperature increase caused by frictional heating. However, the effect of the slipping zone thickness on temperature changes is stronger than that of thermal pressurization, at least for a constant porosity model. Pore pressure and effective normal stress evolution affect the dynamic propagation of the earthquake rupture producing a shorter breakdown time and larger breakdown stress drop and rupture velocity. The evolution of the state variable in the framework of rate‐ and state‐dependent friction laws is very different when thermal pressurization is active. In this case the evolution of the friction coefficient differs substantially from that inferred from a slip‐weakening law. This implies that the traction evolution and the dynamic parameters are strongly affected by thermal pressurization.

A thermal pressurization model for the spontaneous dynamic rupture propagation on a three‐dimensional fault: 2. Traction evolution and dynamic parameters

We investigate the dynamic traction evolution during the spontaneous propagation of a 3‐D earthquake rupture governed by slip‐weakening or rate‐ and state‐dependent constitutive laws and accounting for thermal pressurization effects. The analytical solutions as well as temperature and pore pressure evolutions are discussed in the companion paper by Bizzarri and Cocco. Our numerical experiments reveal that frictional heating and thermal pressurization modify traction evolution. The breakdown stress drop, the characteristic slip‐weakening distance, and the fracture energy depend on the slipping zone thickness (2w) and hydraulic diffusivity (ω). Thermally activated pore pressure changes caused by frictional heating yield temporal variations of the effective normal stress acting on the fault plane. In the framework of rate‐ and state‐dependent friction, these thermal perturbations modify both the effective normal stress and the friction coefficient. Breakdown stress drop, slip‐weakening distance, and specific fracture energy (J/m2) increase for decreasing values of hydraulic diffusivity and slipping zone thickness. We propose scaling relations to evaluate the effect of w and ω on these physical parameters. We have also investigated the effects of choosing different evolution laws for the state variable. We have performed simulations accounting for the porosity evolution during the breakdown time. Our results point out that thermal pressurization modifies the shape of the slip‐weakening curves. For particular configurations, the traction versus slip curves display a gradual and continuous weakening for increasing slip: in these cases, the definitions of a minimum residual stress and the slip‐weakening distance become meaningless.

Influence of Low Speed Rolling Movement on High Electrical Breakdown for Water Dielectric with Microsecond Charging

By means of a coaxial apparatus, high electrical breakdown experiments are carried out in the rest state and the low speed rolling state with microsecond charging and the experimental results are analyzed. The conclusions are: (1) the breakdown stress of water dielectric in the rolling state is in good agreement with that in Martin formula, and so is that in the rest state; (2) the breakdown stress of water dielectric in the rolling state is about 5% higher than that in the rest state; (3) the results simulated with ANSYS demonstrate that the breakdown stress of water dielectric decreases when the bubbles appear near the surface of electrodes; (4) the primary mechanism to increase the breakdown stress of water dielectric in the rolling state is that the bubbles are driven away and the number of bubbles near the surface of electrodes is decreased by rolling movement.

低温絶縁超電導ケーブルの絶縁設計とその実証

A High Temperature Superconducting (HTS) cable has a bulk power transmission capacity as a candidate for the replacement of the aged cable and/or for the increase of the power transmission capacity, and its diameter is prefer to be smaller than inner diameter of the duct for the existing cables. To reduce the diameter of HTS cable, the cold dielectric (CD) type electrical insulation in which a cable core is immersed into liquid nitrogen (LN2) should be adopted, and the thickness of its electrical insulation layer has to be optimized. Since a partial discharge (PD) in the electrical insulation layer of the CD type HTS cable is considered as a major causes for the aging of the insulation layer, PD-free design must be adopted for the CD type HTS cable.This paper describes a design method for the electrical insulation layer of the CD type HTS cable adopting the PD-free design under ac stress, based on the experimental results such as a PD inception stress (PDIE), an impulse breakdown stress, and PD extinction characteristics under ac stress superimposed with an impulse stress. Moreover, the proposed design method was applied to a 500-m HTS cable and was verified by a field test.

Experimental Study on High Electrical Breakdown of Water Dielectric

By means of a coaxial apparatus, pressurized water breakdown experiments with microsecond charging have been carried out with different surface roughness of electrodes and different ethylene glycol concentrations of ethylene glycol/water mixture. The experimental results about the breakdown stress and the effective time are presented. The breakdown stress is normalized to the situation that the effective time is transformed to 1 μs and analyzed. The conclusions are as follows: (1) the breakdown stress formula is modified to E = 0.561M A-1/10teff-1/N P1/8; (2) the coefficient M is significantly increased by surface polishing and ethylene glycol additive; (3) it is accumulative for the capacity of improving electrical breakdown strength for surface polishing, ethylene glycol additive, and pressurization, of which pressurization is the most effective method; (4) the highest stress of 235.5 kV/cm is observed in ethylene glycol/water mixture with an ethylene glycol concentration of 80% at a hydrostatic pressure of 1215.9 kPa and is about one time greater than that in pure water at constant pressure; (5) for pressurization and surface polishing, the primary mechanism to improve the breakdown strength of water dielectric is the increase in the breakdown time delay. Research results indicate great potential in the application of the high power pulse conditioning system of water dielectric.

Bonding configuration and electrical properties of nitrogen and fluorine incorporated SiOC:H thin film prepared by plasma enhanced chemical vapor deposition

In this study, the organosilicate glass (OSG) incorporated with nitrogen and fluorine (N-F:OSG) was investigated by examining the bonding configuration, refraction index, modulus, permittivity and breakdown field strength. The results of Fourier transform infrared spectroscopy show that Si–O, Si–C, Si–N, and Si–F are the major bonding in the N-F:OSG films. The XPS analysis shows that the Si 2p, F 1s, and N 1s core levels of the N-F:OSG film shifts to higher binding energy due to the neighborhood bonding of higher electronegative elements. For electrical properties, the permittivity and breakdown stress of the N-F:OSG are comparable with the OSG film accompanied with superior mechanical hardness to the OSG film.

Research on Insulation Design of 22.9-kV High-<tex>$rm T_rm c$</tex>Superconducting Cable in Korea

The electrical insulation design is important for high-Tc superconducting (HTS) cable because the cable is operated in a medium voltage environment. For the insulation design of HTS cable, it is necessary to investigate the ac, impulse breakdown, and partial discharge inception stress of a liquid nitrogen/polypropylene laminated paper composite insulation system. These results were used to design the electrical insulation of 22.9-kV-class HTS cable in Korea and cable was manufactured. A manufactured mini-model HTS cable was evaluated for ac withstand voltage, impulse withstand voltage, breakdown and dielectric tangent loss (tan/spl delta/). From these tests, the cable has satisfied the standard technical specification of KEPCO in Korea. The breakdown voltage was 110 kV.

The Effect of Temperature on the Breakdown Stress in Saturated Hydrocarbon Liquids

The Effect of Temperature on the Breakdown Stress in Saturated Hydrocarbon Liquids

Electrical characteristics of high- Tc superconducting mini-model cable under mechanical stresses in liquid nitrogen

To develop 22.9 kV class high- T c superconducting (HTS) cable in Korea, we have been studying electrical insulation properties of dielectric paper, such as breakdown voltage, partial discharge, which is one of the HTS cable structure elements. However, the research on the mechanical stress of dielectric paper compared to breakdown properties of dielectric paper is insufficient. A cracking and variation of the electrical insulation due to mechanical stresses during cooling and bending of HTS cables in cryogenic temperature is a serious problem. Thus, we investigated tensile stress and breakdown stress of dielectric paper under mechanical stress. Moreover, we manufactured mini-model cables investigated breakdown stress under bending stress to design a cable drum for conveyance. In the AC, impulse and partial discharge properties, all test results showed a similar tendency, and the suitable bending radius ratio R/ r was decided to be more than 25.

Temperature-dependent breakdown and hot carrier stress of PHEMTs

The main issues this work addresses, with reference to commercial GaAs PHEMTs, are the temperature dependence of the off-state breakdown voltage (BV DG ), the physical mechanisms that determine it, and the relationship between BV DG and device degradation and failure, as determined by accelerated step-stress performed at temperatures ranging from 25 to 100°C. BV DG is seen to decrease with temperature between room temperature and 160°C. Temperature-dependent analysis of the gate leakage current indicates that thermionic-field emission and thermionic emission over a field-dependent barrier are the limiting mechanisms for off-state breakdown. Roomtemperature, hot carrier step-stress tests with 24 h step duration show reduced loss after the stress and a tight correlation between the BV DG measured at I G = - 1 mA/mm and the stress bias producing substantial device degradation or catastrophic failure. Shorter (2 h) step stress experiments carried out between 25 and 100°C again show a tight correlation between the BV DG measured at I G = - 1 mA/mm and the stress bias producing dramatic degradation or failure. This correlation, coupled with the negligible temperature dependence of the breakdown voltage in this temperature range, results in temperature-independent device degradation.

The Dependence of Constitutive Properties on Temperature and Effective Normal Stress in Seismogenic Environments

We have evaluated how the parameters prescribing the slip-dependent constitutive law are affected by temperature and effective normal stress, by conducting the triaxial fracture experiments on Tsukuba-granite samples in seismogenic environments, which correspond to a depth range to 15 km. The normalized critical slip displacement D c almost remains constant below 300°C (insensitive to both temperature and effective normal stress σ n eff ); D c increases with increasing temperature above 300 °C, and the rate of D c increase with temperature tends to be largest at higher σ n eff . The breakdown stress drop Δτ b for the granite at constant σ n eff is roughly 80 MPa below 300 °C, and does not depend on σ n eff . Above 300 °C, Δτ b of reduction with temperature increases at higher σ n eff . The peak shear strength τ p increases nearly linearly with σ n eff increasing below 300 °C. However, τ p becomes lower above 300 °C, deviating from the linear relation extrapolated from below 300 °C. This is consistent with the onset of crystal plastic deformation mechanisms of Tsukuba granite.

Reliability challenges of high performance PD SOI CMOS with ultra-thin gate dielectrics

With the introduction of ultra-thin (<15Å) gate dielectrics, which have significantly higher nitrogen concentration, and thus a higher dielectric constant, many new reliability challenges need to be addressed. At the same time, high-performance transistors are now migrating from bulk to silicon-on-insulator (SOI) to boost the performance. This paper will discuss major reliability issues such as negative bias temperature instability (NBTI), hot carrier injection (HCI), time dependent dielectric breakdown (TDDB) and electro-static discharge stress (ESD), etc., facing the state of art technology for SOI.

The dependence of traction evolution on the earthquake source time function adopted in kinematic rupture models

We compute the temporal evolution of traction by solving the elasto‐dynamic equation and by using the slip velocity history as a boundary condition on the fault plane. We use different source time functions to derive a suite of kinematic source models to image the spatial distribution of dynamic and breakdown stress drop, strength excess and critical slip weakening distance (Dc). Our results show that the source time functions, adopted in kinematic source models, affect the inferred dynamic parameters. The critical slip weakening distance, characterizing the constitutive relation, ranges between 30% and 80% of the total slip. The ratio between Dc and total slip depends on the adopted source time functions and, in these applications, is nearly constant over the fault. We propose that source time functions compatible with earthquake dynamics should be used to infer the traction time history.

The Breakdown Characteristics of the Silicone Oil for Electric Power Apparatus

The basic breakdown characteristics of the silicone oil as an insulating medium was studied with aim of realization of electric power apparatus which may be considered to be SF6 free and flame-retarding. As the first step, the impulse breakdown characteristics was measured with three kinds of electrodes whose electric field distributions differed. The breakdown characteristics in silicone oil was explained in relation to stressed oil volume (SOV) and the breakdown stress. At the second step the surface breakdown characteristic for impulse voltage was measured with two kinds of insulators which was set to between plane electrodes. The surface breakdown characteristic for impulse voltage was explained in relation to the ratio of the relative permittivity of oil and insulator. And on the third step, the breakdown characteristics of oil gap after interrupting small capacitive current was studied. In this experiment, the disconnecting switch to interrupt capacitive current was simulated by oil gap after interrupting impulse current, and to measure breakdown characteristics the high impulse voltage was subsequently applied. The breakdown stress in silicone oil after application of impulse current was discussed for insulation recovery characteristics.

Constitutive properties for the shear failure of intact granite in seismogenic environments

To investigate how the parameters prescribing the slip‐dependent constitutive law are affected by seismogenic environments, we conducted a series of triaxial fracture experiments using intact Tsukuba‐granite samples, which were deformed at wet, temperature‐pressure conditions that correspond to a crustal depth range down to 15 km at a strain rate of 10−5/s. It is conclusively demonstrated that the critical slip displacement Dc is virtually constant at the conditions of depths shallower than 10 km, and that Dc increases with increasing depth at depths greater than 10 km, because of the effect of temperature in the brittle‐plastic transition regime. The breakdown stress drop for intact rock is found to be roughly constant (100 MPa) in a depth range down to 15 km. The apparent fracture energy increases with increasing depth at depths greater than 10 km. These results consistently lead to the conclusion that the stability of the breakdown process is enhanced at depths greater than 10 km.

Electrical insulation characteristics of cold dielectric high temperature superconducting cable

For the optimization of electrical insulation design for high temperature superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN/sub 2/ impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN/sub 2/ plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN/sub 2/ impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN/sub 2/ and cable model with short length with polypropylene laminated paper (PPLP/sup /spl reg//), Nomex/sup /spl reg// paper and cellulose paper. PD current pulse was found to have a steep rise time of /spl sim/ ns and amplitude of /spl sim/ tens /spl mu/A at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be /spl sim/ 5 mm under PD-free condition from viewpoint of long-term reliability.

Fault low velocity zones deduced by trapped waves and their relation to earthquake rupture processes

Detailed structures of fault low velocity zones (LVZ) have been studied by analyzing fault-zone trapped waves at various active faults. These studies demonstrate that widths of the fault LVZ are ranging from an order of 10 m to a few hundred meters. In order to evaluate the effect of fault LVZ on the earthquake rupture process, a model of the LVZ related to the plastic deformation around an edge of propagating earthquake rupture is proposed. In this study, earthquake rupture processes are regarded as Mode III crack propagation. The LVZ is identical to the fault damaged zone which is related to plastic deformation in the vicinity of the crack tip. The Mode III crack analysis gives a simple relationship between the width of the low velocity zone, the breakdown stress drop at the crack tip, and characteristic slip distance d0 in friction laws. The parameters applicable to the Nojima fault producing the 1995 Hyogo-ken Nanbu earthquake show that the breakdown stress drop is 10 times larger than the static stress drop and d0 is about 10 cm. These values are consistent with the value obtained by the other study for the Nojima fault so the present model is applicable for considering earthquake rupture within the damaged zone.

Effect of water on aging of XLPE cable insulation

Abstract Cables as elements of power distribution system have great influence on its reliable service and overall planning requirements. During last years, crosslinked polyethylene (XLPE) cables have been more and more used in power systems. This paper presents the results of an investigation of changing of (XLPE) cables insulation breakdown stress (AC BDS) due to water absorption. The paper deals with AC BDS of the following kinds of XLPE cable insulations: steam and dry cured with water tree retardant crosslinked polyethylene (TR-XLPE) and non-tree retardant crosslinked polyethylene (XLPE). During tests, the tap water was injected into, (1) conductor with cable ends closed; (2) into cable conductor with ends opened; and (3) into metallic screen with cable ends opened. The presence of water in XLPE cables was subjected to electrical stress and heating. AC BDS tests were performed as a function of aging time and water content in the cable insulation at different aging temperatures. Also, in this investigation, tests with the changing of AC BDS in the radial direction of unaged and aged XLPE cable insulations were carried out.

Thickness and Stress Polarity Effects on the Reliability of the Low Thermal Budget Polyoixdes

In this paper, the thickness and the stress polarity effects on the reliability of the low thermal budget polyoxides are investigated. The polyoxides are prepared by two methods: the low-temperature tetraethylorthosilicate (TEOS) polyoxide deposition and in the rapid thermal chamber in N2O ambient (RTN2O). It is observed that the thinner TEOS polyoxides exhibit higher charge to breakdown (Qbd) and larger stress polarity effect than those of the thicker TEOS polyoxides. However, for the RTN2O grown polyoxides from 8.5 nm to 12.9 nm, they have the similar values of the Qbd and the stress polarity effects. The nitrogen atoms incorporated in the RTN2O grown polyoxides may be the reason to this less thickness dependence of the Qbd. Higher barrier height is also observed for the RTN2O grown polyoxides than that of the deposited TEOS polyoxide to obtain a lower tunneling current under a fixed electric field.

Characteristics of Large-Area Plasma Enhanced Chemical Vapor Deposited TEOS Oxide with Various Short-Time Plasma Treatments

AbstractIn this work, high quality silicon dioxide (SiO2) films were prepared by large-area plasmaenhanced chemical vapor deposition (LA-PECVD) using tetraethylorthosilicate(TEOS)-oxygen based chemistry. The effects of various short-time plasma treatments on these as-deposited TEOS oxide were also investigated. Different plasma treatments such as O2, N2O, and NH3 were used in our experiments. Electrical characteristics were exploited to examine the effects of plasma treatments. It was shown that after N2O, and NH3 plasma treatments, the electrical strength of oxide was enhanced. Besides, NH3 plasma treatment exhibited the highest enhancement efficiency. O2- plasma treatment, however, showed some harmful effects on the electrical properties of the TEOS oxide. The reliability tests including charge to breakdown (Qbd) and bias temperature stress (BTS) were also analyzed in these samples. Although better pre-stress characteristics were observed in those samples treated by NH3-plasma, samples with N2O plasma treatment showed superior stress endurance. Consequently, N2O plasma treatment seems to be the best candidate for future TFTs under the consideration of long-term reliability.