Methods of increasing the dielectric strength of the accelerating gap in an electron source with a plasma cathode

This work represents the investigations for decreasing acceleration gap breakdown probability of plasma source of electrons SOLO, with grid stabilization of the boundaries of the arc cathode plasma. We increased the distance to the treated target, bent the transportation channel of the electron beam, created additional plasma in the anode space, and increased the beam front. The effect of the above measures on the breakdown probability when the target is exposed of a low-energy electron beam with a power density of up to 0.5 MW/cm2 with a diameter of 2.5 cm was investigated separately. Beam deflection is most effective at relatively long pulse durations of 150 μs and accelerating voltage of 20 kV, rather than a lower one. It was possible to double the maximum power for the same beam transport length applied to a low-melting target. Preionization in the anode proved to be effective for relatively short beams of 15 μs duration.

A Risk-Based Approach to the Sustainable Management of Spill Response Equipment

ABSTRACT> Spill response equipment is often kept for prolonged periods until required; such equipment would be operated continuously when deployed, often under harsh conditions detrimental to any equipment. Uncertainty in the reliability of response equipment bears significant risks to operational safety and incident management, especially in critical operations that have a widespread impact during an incident. A qualitative risk assessment was conducted on OSRL's equipment stockpile, considering their known history of breakdown (probability) and foreseeable impact (severity) during an incident. The resultant matrix categorises them into five different risk levels from low to very high. Response equipment is categorised in accordance with OSRL's prescribed service life, a set of guidance documents based on the organisation's operational experience and consultation with various manufacturers and other users, forming baseline data of the stockpile. Coupled with the results from the risk assessment conducted, it provides a wider understanding of response equipment from a risk-based perspective. The existing equipment risk profile is mapped out using the above method to provide a high-level overview to decision-makers. Upon discussion with stakeholders, the desired position on the risk profile can be achieved by replacing identified critical equipment or extending the service life of non-critical equipment. A risk-based approach allows a logical prioritisation of actions to be undertaken, in line with the organisation's strategy and enables decision-makers to make plans for a sustainable equipment reinvigoration program over a projected budget and period. With continual monitoring and assessment in place during planned maintenance, timely feedback can be provided to decision-makers on any changes to risk profile in the equipment stockpile; this not only helps in accurately updating the equipment condition, but also enables the early detection of equipment failure and prompts timely actions for resolution. Response equipment constitutes a valuable resource in response readiness; an evolved approach to the management of response equipment is discussed here and can be applied for Tier 1 and 2 response equipment to assure equipment reliability.

ИССЛЕДОВАНИЕ ЭЛЕКТРИЧЕСКОГО ПРОБОЯ ГАЗОВОЙ ИЗОЛЯЦИИ ЭЛЕКТРОСТАТИЧЕСКОГО УСКОРИТЕЛЯ

Для расчета пробивного напряжения высоковольтных структур наиболее универсальным является статистический метод, основанный на численном моделировании вероятности пробоя системы газоизолированных электродов (законе роста). Метод был адаптирован автором для высоковольтных ускорителей прямого действия и совершенствовался на протяжении более чем двадцати лет. В статье рассмотрено применение метода расчёта рабочего напряжения высоковольтной газоизолированной структуры на основе закона роста (преобразования масштаба). Путем анализа расчетных и экспериментальных данных для электростатического ускорителя на напряжение 2 мегавольта проведена верификация метода для случая газовой изоляции на основе бинарной смеси азота N2 и гексафторида серы (элегаза) SF6 . Для ускорителя «СОКОЛ» Института прикладной физики Национальной Академии наук Украины рассчитан оптимальный состав смеси. Погрешность расчёта составляет величину порядка точности измерения напряжения на высоковольтном электроде ускорителя. Предлагаемый метод расчёта электрической прочности в дальнейшем предполагается использовать для оптимизации высоковольтной структуры электростатических ускорителей с целью повышения надёжности работы установки. Ключевые слова: электрический пробой, высоковольтная структура, электростатический ускоритель, азот, гексафторид серы. Breakdown voltage of high-voltage structures is generally calculated with a statistic method based on numerical modeling of a breakdown probability in a gas-insulated electrode system. The method was adjusted by the author to the direct voltage accelerators and has been improved for more than twenty years. The article considers a method for calculating the operating voltage of high-voltage gas isolation for a 2 MeV proton accelerator. The method was verified for gas isolation with a binary nitrogen (N2) and sulfur hexafluoride (SF6) mixture, through analysis of calculated and experimental data for the 2 MeV electrostatic accelerator. The best composition of the mixture for the "SOKOL" accelerator at Institute of Applied Physics of National Academy of Sciences of Ukraine has been calculated. Calculation accuracy is the order of accuracy of voltage measurement at the high-voltage electrode of the accelerator. The suggested method for calculating the insulation strength is expected to be further used in enhancing high-voltage structure of electrostatic accelerators in an effort to improve their operational reliability. Keywords: breakdown voltage, electrostatic generator, accelerator, nitrogen, sulfur hexafluoride.

Development of Breakdown Probability Models and Heavy Vehicle Passenger Car Equivalents for Rural Freeway Work Zones

With nearly nine million lane-miles of public roadway and an economy driven by the automobile, interruptions to normal traffic operations for construction and maintenance are inevitable in the U.S.A., but the substantial safety and mobility impacts associated with queueing at freeway lane closures are mitigable. The current freeway work zone capacity methodology in the 6th edition of the Highway Capacity Manual is a vast improvement over historical guidance but still approaches the issue differently than research suggests agencies and practitioners should. Namely, a capacity defined by the mean queue discharge rate is deterministic and fails to account for the stochastic nature of traffic flow and breakdown. These core issues were addressed in this research by developing a methodology for obtaining probabilistic estimates of rural freeway work zone capacity from simulated data in PTV Vissim. Results for a two-to-one lane closure were presented as a series of breakdown probability distributions to demonstrate the viability of this methodology. The data indicated that the impact of trucks on freeway capacity is exacerbated in the presence of lane closures and led to the development of work zone capacity-based passenger car equivalents. Such a procedure may be extended to freeway facilities exhibiting different geometric, traffic, and environmental characteristics and utilized by agencies to make data-driven, risk tolerance-based planning, design, and operations decisions at freeway work zones.

Breakdown at Multiple Protrusions in SF6 and CO2

The electric breakdown at single and multiple protrusions in SF6 and CO2 is investigated at 0.4 and 0.6 MPa, respectively. Additionally, the breakdown fields at rough surfaces of two different areas were determined. From the measurements, breakdown probability distributions for single protrusions were determined and fitted by Weibull distributions. This allowed the determination of statistical enlargement laws for the 50% breakdown probability fields E50. Such enlargement laws describe, for example, the scaling of breakdown field with electrode area or number of protrusions. The predictions were compared to the experimental data, and both agreement and discrepancies were observed depending on polarity and number of protrusions and gas. Discharge predictions including first electron, streamer inception and crossing, as well as leader propagation, gave further insight to this. It was found that predictions from enlargement laws based on statistical processes may not describe the measured breakdown fields well and that relevant physical breakdown criteria must also be considered.

Influence of Rain on Highway Breakdown Probability

Capacity has been used to describe a deterministic value that represents the maximum volume of traffic supported by a road. Studies have pointed out the importance of not using a single value for capacity, but rather the concept of probability of occurrence of a traffic-flow breakdown. In this paper the probabilities of breakdown for a Brazilian highway under different weather conditions are compared. Data collected from inductive loop detectors and pluviometric data from automatic rain gauges are combined. Two methodologies of breakdown identification are then compared. The most consistent methodology for identifying breakdowns is used to generate breakdown probability distributions using the product limit and maximum-likelihood methods with the Weibull distribution. The results indicate significant differences in probability of breakdown for each studied climatic condition, including a maximum difference greater than 50% between dry and heavy rain conditions under the same traffic flow.

Application of Synthetic Ester for Drying Distribution Transformer Insulation—The Influence of Cellulose Thickness on Drying Efficiency

A high level of insulation moisture in a transformer increases the breakdown probability and forces a reduction of its load. Therefore, there is a need to dry the transformer insulation. For technical reasons, there are some restrictions on the use of common drying methods for cellulose insulation available on the market. The aim of the research was to check the possibility of using synthetic ester for effective drying of cellulose materials of various thickness and an evaluation of the drying dynamics. The replacement of mineral oil with a synthetic ester caused a reduction of moisture in paper and thin pressboard by one percentage point. It was possible in the case of drying these materials for seven days at a temperature of 70 °C. The effects of drying were much smaller in the case of thicker cellulose samples. This paper also shows the complex problem of simultaneously drying materials of different thicknesses. Drying thin paper and thick pressboard at the same time significantly slows down the drying process of the pressboard. Presented results will be used to develop a procedure for drying the transformer insulation system using a synthetic ester.

Prediction and Mitigation of Flow Breakdown Occurrence for Weather Affected Networks: Case Study of Chicago, Illinois

This study investigates the prediction and mitigation of the phenomenon of traffic flow breakdown when affected by varying weather conditions. First, the probability of breakdown occurrence is examined using a survival analysis approach to obtain distributions of pre-breakdown flow rates under different weather conditions. Second, pre-breakdown flow rate distributions were applied in breakdown prediction for the implementation of breakdown mitigation strategies. In the first part, a set of data from the network of Kansas City was used to demonstrate the applicability of the Kaplan–Meier Product Limit method to estimating the breakdown probability under various weather conditions. Then, using simulated data on the network of Chicago, the K-M approach was used again to obtain survival likelihood distributions, which in turn yield breakdown probability, for 13 different weather cases as combinations of weather categories for different levels of visibility, rain, and snow precipitation. In the second part, continuing with the simulated data, dynamic speed limits (DSL) were applied to demonstrate the effectiveness of the prediction method presented. A sensitivity analysis of the threshold probability and upstream distance at which DSL should be implemented was performed for clear and inclement weather conditions. In clear weather the performance of the strategy is better at a lower probability threshold and farther upstream location, whereas in inclement weather the performance is better at a lower probability threshold and closer upstream location. The paper demonstrates the effect of changing weather conditions on the likelihood of breakdown occurrence and the implementation of breakdown mitigation strategies.