Partial Breakdowns Research Articles

A review of non-destructive methods for the detection tiny defects within organic insulating materials

In recent years, solid organic materials such as silicone rubber and epoxy resin have been widely used in electrical equipment due to their excellent insulation properties. However, as a result of manufacturing and design flaws as well as aging issues during operation, the insulating materials in the linked state no longer fit tightly and tiny structural defects (defect size less than 10 mm) develop, such as debonding at the composite interface, pores or cracks within the insulating material, etc. Tiny defects are prone to partial discharges and breakdowns, compromising the safety of high-voltage power equipment, particularly when subjected to strong electric fields. Therefore, it is necessary to carry out non-destructive testing (NDT) for such tiny defects. Such defects are small in size, easily buried in the material, and even some are wrapped in metal, which in turn requires very high detection accuracy, but traditional methods are difficult to achieve, so NDT technologies for tiny defects within insulating materials have become a research hotspot in the field of electric power in recent years. This paper firstly introduces the sources of tiny defects in solid organic insulating materials for electrical equipment. Secondly, the harm caused by structural defects is elaborated. Finally, emerging NDT methods and their advantages and limitations in defect detection are described in detail. The review aims to provide the reader with a comprehensive overview of most of the NDT techniques used in the detection of tiny defects within solid organic insulating materials for electrical equipment and their most salient features.

MACHINE LEARNING BASED FAULT DIAGNOSIS SCHEME FOR GRID-CONNECTED PV SYSTEM

Photovoltaic (PV) systems have recieved a lot of attention in recent decades due to their accessibility and advancements in PV technology. The protection of PV systems from faults such as String to String (SS), String to Ground (SG), Open circuit (OC), and partial shading are the key challenges to the realization of cost-effective and environmentally friendly PV systems. Such unusual circumstances reduce the maximum available PV power. Partial shading and breakdowns in a PV array must therefore be noticed quickly for enhanced system efficiency and reliability. The significant fault current in PV systems can be detected using the existing safety devices in PV systems, such as fuses and residual current detectors. The flowing fault current being of low order is not significant enough for current protection devices to detect if the solar and/or fault mismatch is modest and the fault resistance is high. As a result, under cloudy and low irradiance conditions, the traditional protection devices fail to identify problems, resulting in reliability concerns and photovoltaic fire threats. In this context, a fault diagnosis scheme for PV systems is presented in this paper, which includes feature extraction using the Discrete wavelet transform, and classification of various defects on the PV system using Decision tree.

Equilibrium threshold strategies and social benefits in the fully observable Markovian queues with partial breakdowns and interruptible setup/closedown policy

ABSTRACT This paper studies the equilibrium balking strategies in the single-server Markovian queues with partial breakdowns and interruptible/setup closedown policy. That means the server may fail at any point in time, no matter the server is idle or busy and the service continues at a slower rate instead of stopping service totally. When the system becomes empty, the server ceases to operate by a closedown time. If a customer arrives during the closedown period, the system starts the service immediately without a setup time. After the closedown period, the server needs a setup time before providing the service upon arrival. We presume that the customers decide whether to join or balk immediately after their arrival based on the reward-cost structure of the system. The fully observable case is discussed and the equilibrium threshold strategies and the equilibrium social benefits for all customers are derived. A numerical example and a case study for a bank system are investigated in this regard. Eventually, the effects of several parameters on the equilibrium thresholds, social benefits, balking probability, probability of empty system and stationary distribution are expressed.

Bargaining delay under partial breakdowns and externalities

We consider a noncooperative coalitional bargaining game where partial breakdowns, such as the rejecter of a proposal exiting from the game, take place with a positive probability, and externalities accompany the formation of coalitions. We present an example in which there exists a stationary subgame perfect equilibrium (SSPE) such that a bargaining delay occurs. We also show that under no partial breakdowns or no externalities, delay does not occur in any SSPE.

Simulation of partial discharges under influence of impulse voltage

The object of research is an equivalent circuit for a dielectric with a weakened insulation (for example, with a gas cavity) with a partial discharge. The test with partial discharge measurement by application of alternating voltage is one of the main methods of diagnostics and non-destructive tests. According to GOST 1516.2, the application of impulse test voltage does not necessarily end with a breakdown of the electrical equipment insulation or the absence of breakdown. There may be a partial breakdown of insulation, in which not all insulation of electrical equipment will be damaged, but only some of its part. It is quite difficult to detect such damage in accordance with GOST 1516.2, but registration of partial discharges will allow this to be detected by increasing their intensity. The use of existing technical means for measuring the characteristics of partial discharges at alternating voltage is not acceptable for the task in question. Therefore, it is preliminary necessary to carry out computer simulation of partial discharges when the impulse voltage is applied. A circuit simulation model of a dielectric with a gas cavity with partial discharge has been created. It is shown how, by means of a combination of various elements, to simulate the breakdown of a gas cavity. The operability of the model under the influence of alternating voltage is checked. It is confirmed that voltage harmonic distortions lead to an increase in the number of partial discharges. A study of the model is carried out when it is subjected to a full lightning voltage impulse. As a result, it has been established that partial discharges occur in the gas cavity both at the impulse front and at its tail. Diagnosis of the insulation condition using the measurement of the partial discharge characteristics under the influence of impulse voltage will be more informative. In particular, it will allow to detect partial breakdowns of insulation that occur during impulse tests and are absent in standard tests with application of alternating voltage. To carry out such measurements it is necessary to develop new techniques, equipment and diagnostic procedures.

Strategic behavior in the partially observable Markovian queues with partial breakdowns

This paper studies the equilibrium strategies in the almost observable and almost unobservable M∕M∕1 queues with partial breakdowns. This work compensates the game theoretic analysis in Li et al. (2013) by studying the corresponding partially observable cases.

CME Accreditation Page

This paper studies the equilibrium strategies in the almost observable and almost unobservable M∕M∕1 queues with partial breakdowns. This work compensates the game theoretic analysis in Li et al. (2013) by studying the corresponding partially observable cases.

Исследование неполного пробоя диэлектриков и стекла

Works aimed at studying electrical breakdown of solid dielectrics placed in sharply nonuniform fields have revealed a number of interesting phenomena for partial and sequential breakdown cases. The article analyzes the properties pertinent to partial breakdown of dielectrics. Partial breakdown depends on the applied voltage level, time, thickness, and crack length growth rate. When a dielectric is placed in electric field, charges appear on the surface of its air inclusions. Once the field strength caused by these surface charges reaches the breakdown voltage of air inclusions, air ionization processes are initiated. The ionization will take place until air ions have neutralized the surface charges. After that, the cycle is repeated. The ratio between the electromagnetic field attraction and repulsion forces that arise when the atoms approach each other determines the stable existence of a solid body and its mechanical properties, adhesion, and surface tension. Formulas for calculating the adhesion energy are obtained, and the calculation results are presented. The theoretical values of these quantities can be used in performing a comparative analysis of adhesion energy variations for different solid materials. The electrical breakdown of glass coated with an electrically conducting film was investigated. A 2...3 mm wide part of the film was removed by means of a laser to form insulating cut-offs. Such cut-offs on the surface of glass coated with a conducting film and placed in electric field give rise to nonuniformities in electric field distribution. These nonuniformities concentrate over the perimeter of insulation cut-offs and at the corners. To investigate the electrical breakdown of glass, its samples were prepared with various types of cutoff shapes: linear cut-offs and cut-offs with the perimeter of a square or rectangle. The glass plate was laid with its non-coated side facing the breakdown installation’s lower electrode, whereas the upper electrode was placed on the film surrounded by cut-offs or insulated strips without film. The electrical breakdown phenomena were investigated by applying AC voltage. The breakdown occurred over the film periphery at the boundary with cut-offs. It has been found from the experiment that numerous discharges are observed over the boundary between the film and insulating strip during the breakdown. It has also been found that glass melting occurs on the glass surface at the air ionization spots. Experimental data on partial breakdown of glass having different configurations, with and without cut-offs, for glass samples with film coated on one side are presented. It is shown that partial breakdowns in glass occur at field strengths less than those causing the real breakdown, which is characteristic of the gas medium in which the breakdown occurs.

Equilibrium customer strategies in Markovian queues with partial breakdowns

We consider equilibrium analysis of a single-server Markovian queueing system with working breakdowns. The system may become defective at any point of time when it is in operation. However, when the system is defective, instead of stopping service completely, the service continues at a slower rate. We assume that the arriving customers decide whether to join the system or balk based on a natural reward-cost structure. With considering waiting cost and reward, the balking behavior of customers is investigated and the corresponding Nash equilibrium strategies are derived. The effects of the information level on the equilibrium behavior are illustrated further via numerical experiments.

Advancement flap in the management of chronic anal fissure: a prospective study

Lateral internal sphincterotomy is the surgical treatment of choice of chronic anal fissure after failure of conservative measures. Several randomized trials identified an overall risk of incontinence of 10 % mostly for flatus. Fissurectomy is the most commonly used procedure to preserve the integrity of the anal sphincters. However, a possible complication is keyhole defect that may lead to faecal soiling. In this study, chronic anal fissure (CAF) was treated by fissurectomy and anal advancement flap to preserve the anatomo-functional integrity of sphincters and to reduce healing time and the risk of anal stenosis. In patients with hypertonia, surgical treatment was combined with chemical sphincterotomy by injection of botulinum toxin to enhance tissue perfusion. Forty eight patients with CAF underwent fissurectomy and anal advancement flap. In 22 subjects with hypertonia of the internal anal sphincter, intrasphincter injection of 30 UI of botulinum toxin at the completion of the surgical operation was used. All patients were followed up to 24 months. Since the first defecation, the intensity and duration of pain were significantly reduced. Two patients had urinary retention, five had infections and three had partial breakdowns. No anal stenosis, keyhole deformity or necrosis flap was recorded. At the 24 months follow-up visit, anal incontinence was similar to those detected preoperatively. Only four recurrences were detected at 18 and 20 months. After medical treatment failure, fissurectomy with advancement flap is a valid sphincter-conserving procedure for treatment of anterior or posterior CAF, regardless of hypertonia of the internal anal sphincter.

A strong analogy between the dielectric breakdown of high-K gate stacks and the progressive breakdown of ultrathin oxides

The breakdown of high-K (HK) stack gate dielectrics is shown to be analogous to the failure of ultrathin SiO2-based oxides showing progressive breakdown. The breakdown of a HK stack is shown to occur in two phases. First, one or several percolation paths are formed in the SiO2-based interfacial layer. Then, these partial breakdowns propagate into the HK through defect generation in this layer. This propagation phase is equivalent to the progressive breakdown local degradation phenomenon. As a consequence of this analogy, the reliability assessment tools developed for ultrathin single-layer oxides can also be used without significant changes to assess the reliability of HK stacks. This analogy is so strong that the experimental distinction between HK propagation and conventional progressive breakdown appears to be rather difficult. However, the residual time distribution from first breakdown to final oxide failure is shown to be significantly different for both processes at low failure percentiles. This has allowed us to obtain experimental evidence of HK propagation (as opposed to conventional progressive breakdown effects) in relatively thick Hf-based gate stacks where the detection of first BD appears to be feasible.

Professional Citation Practices in Child Maltreatment Forensic Letters

Using rhetorical genre theory and research on reported speech, this study investigates the citation practices in 81 forensic letters written by paediatricians and nurse practitioners that provide their opinion for the courts as to whether a child has experienced maltreatment. These letters exist in a complex social situation where a lack of clarity exists as to which professional group (healthcare providers, police, social workers) is primarily responsible for gathering accounts of children’s injuries. Yet physicians need these accounts into order to compare them to actual injuries. The study documents the direct and indirect citations that occur in the letters, observes documentation strategies, notes the instances in which partial breakdowns in citation occur, and points to the linguistic factors contributing to these breakdowns.

‘Memory’ and sustention of microdischarges in a steady-state DBD: volume plasma or surface charge?**Hot topic report presented at the 20th ESCAMPIG, 13–17 July 2010, Novi Sad, Serbia.

The results of a numerical study on the spatio-temporal behavior of transient microdischarges (MDs) in a steady-state dielectric barrier discharge (DBD) excited by a sinusoidal voltage are presented. MDs have a spatial ‘memory’—every subsequent MD appears at exactly the same location occupied by the MD at the preceding half-period (HP). In the majority of cases each MD appears at its location only once during every HP. For such a case, the memory effect is not attributed to the residual surface charge deposited by the preceding MD but determined by the residual MD plasma column shunting the gap right up to the beginning of the next HP. In contrast to good memory in space, each individual MD has a large scatter with time in its appearance within every HP, i.e. there is no ‘memory’ concerning the phase of an applied voltage. This MD jittering within the period is attributed to the stochastic nature of partial surface breakdowns around the bases of the MD plasma column. Numerical calculations show that surface breakdown provides an MD current splash at every HP. Hence, in the steady-state DBD, the volume plasma is responsible for the existence of MD spatial ‘memory’ (i.e. where the MD appears), and the deposited surface charge is responsible for MD jittering in time (i.e. when the MD appears).

Early Results of Fissurectomy and Advancement Flap for Resistant Chronic Anal Fissure without Hypertonia of the Internal Anal Sphincter

The aim of this study was to assess the efficacy of fissurectomy with skin advancement flap in healing chronic anal fissures without hypertonia of the internal anal sphincter. Twenty-six consecutive patients who failed healing after well-practiced topical medical therapy were enrolled. Anorectal manometry was performed preoperative and 6 months postoperatively. All patients were treated with fissurectomy and advancement flap through healthy skin tissue. All patients healed completely within 30 days from operation. The intensity and the duration of pain post-defecation was reduced significantly with respect to the preoperative values starting from the first defecation. One patient suffered urinary retention, two patients suffered infections, and two partial breakdowns were recorded. At 6 months the maximum resting pressure values were similar to those were detected preoperatively. One month after surgery, anal incontinence was reported in seven patients, four of whom complained about it preoperatively. At 12 months, only three subjects reported incontinence. No patients needed reoperation and no recurrences were detected. The fissurectomy, in combination with advancement flap, is a safe sphincter-saving procedure for the treatment of chronic anal fissures without hypertonia of internal anal sphincter that fails medical conservative treatment.

High-voltage elements of a tandem accelerator with vacuum insulation

The design of a tandem accelerator with vacuum insulation intended for obtaining a proton beam with an energy of 2.0 MeV and a direct current of several tens of milliamperes is described. Calculated and experimental data obtained in tests of both a glass-ceramic feedthrough insulator for a voltage of 1.0 MV and high-voltage vacuum accelerating gaps with electrodes of area of tens of square meters are presented. Issues of optimizing high-voltage aging of the tandem in the cases of its complete and partial breakdowns are considered. The first experimental results of tests of the breakdown strength of individual high-voltage elements and the tandem as a whole are presented.

A robust system for human-machine dialogue in telephony-based applications

This paper presents a real-time system for human-machine spoken dialogue on the telephone in task-oriented domains. The system has been tested in a large trial with inexperienced users and it has proved robust enough to allow spontaneous interactions even for people with poor recognition performance. The robust behaviour of the system has been achieved by combining the use of specific language models during the recognition phase of analysis, the tolerance toward spontaneous speech phenomena, the activity of a robust parser, and the use of pragmatic-based dialogue knowledge. This integration of the different modules allows the system to deal with partial or total breakdowns at other levels of analysis. We report the field trial data of the system with respect to speech recognition metrics of word accuracy and sentence understanding rate, time-to-completion, time-to-acquisition of crucial parameters, and degree of success of the interactions in providing the speakers with the information they required. The evaluation data show that most of the subjects were able to interact fruitfully with the system. These results suggest that the design choices made to achieve robust behaviour are a promising way to create usable spoken language telephone systems.

Phase diagram of the S=1/2 quantum spin chain with bond alternation.

We study the ground state properties of the bond alternating $S=1/2$ quantum spin chain whose Hamiltonian is H=\sum_j (S_{2j}^x S_{2j+1}^x +S_{2j}^y S_{2j+1}^y +\lambda S_{2j}^z S_{2j+1}^z ) +\beta \sum_j {\bf S}_{2j-1} \cdot {\bf S}_{2j} . When $\beta=0$, the ground state is a collection of local singlets with a finite excitation gap. In the limit of strong ferromagnetic coupling $\beta \to - \infty$, this is equivalent to the $S=1 \ XXZ$ Hamiltonian. It has several ground state phases in the $\lambda$-$\beta$ plane including the gapful Haldane phase. They are characterized by a full breakdown, partial breakdowns and a non-breakdown of the hidden discrete $Z_2 \times Z_2$ symmetry. The ground state phase diagram is obtained by series expansions.

High dose hyperfractionated radiotherapy in the treatment of extremity soft tissue sarcomas

A hyperfractionated radiotherapy schedule has been evaluated in the treatment of 29 adults with limb or limb girdle soft tissue sarcomas. The objective was to increase the total administered dose and possibly improve local control, without increasing late normal tissue damage. Twice daily 1.25 Gy fractions (with a minimum interval of 6 h) have been given over 5 to 6 weeks to 12 patients pre-operatively, 10 post-operatively and 7 palliatively. Five patients received 62.5 Gy in 5 weeks pre-operatively and 3 palliatively. Nineteen of the remaining 21 patients received 75 Gy in 6 weeks with a field size reduction after 5 weeks. Sixteen of 29 tumours were situated in the thigh and only 2 were in the upper limb. Twenty were of high grade. The mean tumour size of those treated radically was 13.1 cm (range 5 to 40 cm). Sixteen patients (76%) given 75 Gy developed moderate or severe skin erythema maximal at 5 weeks. Despite the large field sizes used (mean phase one of 34.5 cm, and phase two of 22.8 cm) only 2 patients failed to complete the planned treatment because of the severity of these reactions. Two other patients developed partial wound breakdowns after the end of treatment — both healing spontaneously. Fourteen patients developed an area of moist desquamation — 11 mild, 2 moderate and one severe. There have been four late wound breakdowns requiring surgical intervention; all have since healed well. The median follow up is short at 556 days. Ten of 19 evaluable patients have developed moderate/severe induration, 5/19 mild and 4/19 none. There has been one local failure associated with regional node involvement and lung metastases. Although it was feasible to deliver the planned very high doses to these patients by the use of hyperfractionation, early results suggest that the late damage caused by this regime is greater than that from standard once daily 2 Gy fractionation to a total dose of 60 Gy in 6 weeks. A lower dose per fraction is now being evaluated.

Development of a Quantitative Model for Enzyme-Catalyzed, Time-Dependent Changes in Protein Composition of Cheddar Cheese During Storage

To determine changes in protein composition in long-term storage of cheese, two types of cheese, traditional Cheddar and stirred curd Cheddar, were studied. The degradation of caseins in both cheeses during the process of ripening was evaluated by SDS-PAGE and densitometry. Relationships between the method of cheese manufacture and the effects of freezing and thawing of cheese at selected ages were studied. During the storage of cheese in the coolers, the ripening process continued, and as the age of the cheese increased, there were partial breakdowns of caseins into fragmentary products and peptides. Nonlinear regression analysis was used to model the time-dependent changes in casein components. From these analyses, “half-lives” for casein changes could be calculated. Notably, αs1-casein disappears with a half-life of 2 wk; half-life of β-casein is 37 wk. Neither young nor aged Cheddar cheese was affected by differences in freezing temperatures, nor were there differences between samples collected before and after freezing, nor were there significant differences between the stirred curd and traditional Cheddars.