Emergency Operating Conditions Research Articles

Research of creep parameters of VVER reactor steel 15Kh2NMFA-A AT temperatures of 500 – 1200°C

The paper is devoted to the study of the creep characteristics of 15Kh2NMFA-A vessel steel in the temperature range of 500 – 1200 °C, which can be achieved during emergency operating conditions of VVER-type nuclear reactors. An analysis of the creep curves of the 15Kh2NMFA-A steel in the studied temperature range obtained during specimens tensile tests was carried out with the construction of the parametric Larson – Miller relationship. It is shown that in the temperature range of 600 – 850 °C the generalized Larson – Miller temperature dependence has a changed slope, resulting in a high error in estimating the time to fracture of 15Kh2NMFA-A steel under creep conditions in this temperature range. To reveal the reasons for the change in creep resistance in the specified temperature range, the studies of the metal microstructure using optical and scanning electron microscopy on specimens in the initial state and after creep testing were carried out. Studies of the microstructure of steel have shown that in the temperature range of 600 – 700 °C, coagulation of V(CN) type carbonitrides occurs, leading to a change in the slope of the Larson – Miller parametric relationship. It is shown that in the temperature range of Ac1 – Ac3 there is an abrupt change in creep characteristics associated with phase transformations. The feasibility of dividing the Larson – Miller parametric relationship into several sections depending on temperature, taking into account structural changes in the steel, is substantiated, which makes it possible to increase the accuracy of estimating the destruction time of 15Kh2NMFA-A steel by at least an order of magnitude. Based on the results of the study, a calculated dependence of the long-term strength of steel on temperature was obtained on a basis of 6,24 and 120 hours.

Testing Algorithms for Controlling the Distributed Power Supply System of a Railway Signal Box

Trends in the use of renewable energy sources to power buildings do not bypass objects for which maintaining a power supply is critical. This also applies to railway signal boxes. The aim of the research work was to test the multisource power supply system for a railway signal box with power electronic converter systems and a DC bus, built as part of the research project. The assumption for powering the railway signal box building was to use renewable sources, energy storage devices, and a 3 kV DC traction network as the second required power supply grid. Both power grids were connected by power electronic converters, and the power values of the converters were set based on the calculated power balance values using the values measured at the system nodes and the set constraints. The tests primarily tested the response of the power supply system to changes in load power and power generated by the photovoltaic source, as well as the charge level of the energy storage devices. The correctness of the control algorithm’s operation was assessed based on the recorded power values in the power supply system nodes. The tests were carried out for 60 scenarios that covered all normal and emergency operating conditions. During the tests, delays in response to changes in the power supplied to the converters and the values of circular power flow between the power grid connections were recorded. The recorded delays ranged from 2 to about 50 s and the circular power flows did not exceed 1500 W. Based on the results of the tests, it was found necessary to improve the power measurement system in the power supply system nodes and to improve the quality of communication and the transmission time of measurement data transmission time.

НАУЧНЫЕ ОСНОВЫ ПРЕДУПРЕЖДЕНИЯ ВОЗГОРАНИЯ АВТОМОБИЛЬНЫХ НЕЙТРАЛИЗАТОРОВ В ЭКСПЛУАТАЦИИ

The issue of physical and mathematical representation of the thermal dynamics (kinetics) of the process of conversion of exhaust gases in a catalytic converter in dangerous, from the point of view of fire, uncontrolled emergency operating modes of its operation
 is considered. Modern automobile engines are required to ensure fire safety. On engines with converters, this conflicts with stringent international environmental standards, the satisfaction of which requires the dangerously heated converter to be placed in the engine compartment next to flammable combustible materials. It is proposed to solve the problematic issue by monitoring and diagnosing fire and emergency operating conditions of neutralizers in an in-place method, scientifically substantiated on an interdisciplinary basis – by analyzing the composition of the exhaust gases. The method has been positively tested under real operating conditions.

Защита электрогенераторов объектов распределенной генерации от аварийных режимов

Distributed generation is a good solution for areas remote from centralized power supply sources as it helps increase the reliability of consumer operation. Distributed generation power supply systems use renewable sources of electricity, diesel generators and gasoline generators in the form of mobile power stations, which in most cases are not equipped with modern means of protection. This study presents an analysis of existing means of protecting electric generators from abnormal and emergency operating conditions, including voltage asymmetry, which is one of the factors reducing the service life of generators and is typical for rural electrical networks. During the analysis, the authors determined the main types of generator protection against emergency operation modes: protection of stator windings, protection against underfrequency and overfrequency, protection against undervoltage and overvoltage, protection against voltage (current) asymmetry. It is noted that the main cause of voltage asymmetry leading to mechanical vibration and rapid overheating of the rotor is single-phase loads in the system, which are unevenly distributed over three phases. The problem of voltage asymmetry is mainly solved by redistributing loads in transmission lines and/or installing compensating devices. However, in rural power supply systems, unbalanced load distribution is rarely corrected. The voltage asymmetry can be compensated through the use of hybrid active power filters of series compensation and improved control methods of these filters. Voltage converters that are effective in equalizing voltage asymmetry in PV systems can effectively protect small capacity diesel power generators provided that the use of additional equipment is economically viable.

Looking beyond individual failures: A system-wide assessment of water infrastructure resilience to extreme events

Water infrastructure systems throughout the United States face compounding challenges due to aging infrastructure and increasingly extreme and more frequent weather events. Identifying vulnerabilities and assessing systems’ ability to withstand and recover from such events is a critical component of water infrastructure planning and management. Pipe failures and system structure can substantially impact water infrastructure resilience, but these two factors are often assessed separately. Here, we present a holistic assessment of system performance that considers pipe failures, active water storage, and system structure utilizing data collected during normal and emergency operating conditions. The four-step framework evaluates pipe failures spatially and temporally to assess overall system performance, as measured by active storage, and identifies targeted areas for improvements. Employing control charts, resilience curves, and spatial clustering analysis, our results simultaneously reveal an agreement between trends in pipe failures during normal and emergency operating conditions as well as unexpected discrepancies between pipe failures and system performance due to the water system structure. Our results offer insights to utilities seeking to assess system vulnerabilities to increase water infrastructure resilience to extreme events.

Development of a system for testing electronic control units of agricultural machinery

Modern agricultural vehicles contain a large number of components, which include microcontrollers that implement various algorithms, so deviations and inaccuracies in their work naturally lead to failures and errors in the system as a whole. At the moment, manufacturers of agricultural machinery have in their arsenal relatively simple systems and testing methods that do not allow for a deep check of algorithms and their electronic components, so the development of a comprehensive system for testing electronic components is an urgent task. The article describes the development and operation of a testing system for setting up, testing and debugging the logic of the operation of existing and future (under development) electronic units, including control units from the on-board control system of agricultural machinery. In the process of work, methods of computer modeling, programming and software packages FreeCAD, CAD KOMPAS-3D v21 and SW4STM32 were used. The programming languages Python 3 and C/C++ were used to write the code. The result of the study is the development of a methodology and the manufacture of a prototype testing system (software and hardware complex), the practical use of which has shown its versatility and versatility. The developed system makes it possible to implement an analysis of the response of the control system to pre-designed test effects, to diagnose defects, breakdowns and malfunctions of the device, both in normal and emergency operating conditions. The system also allows you to simulate the emergency conditions of agricultural machinery and check the stability of the control device in limiting and emergency modes.

Integration of measured data for the seismic fragility assessment of deteriorated bridges

AbstractThe reliable assessment of bridge capacity is necessary in order to ensure the functionality of the roadway network under normal, or emergency operating conditions. Damage due to the interaction with the environment (e.g., corrosion of coastal reinforcement) has been observed in many cases, even in newly built interurban road networks. Therefore, the need for obtaining and including measured data in fragility assessment analysis has emerged. In line with the above, the proposed research introduces a framework for the assessment of bridges considering integrating data obtained with NDTs. The scope of NDTs is to track down the evolution damage on bridges and determine its risk of failure. The work presents a structural damage identification approach that successfully updates a digital twin of the structure. Subsequently the digital twin is used in order to determine the bridge fragility. Fiber modeling is used for creating the digital twin of the structure. Modified uniaxial material laws are applied for the fragility assessment of a deteriorated case study bridge also providing comparative assessment results for the pristine bridge, i.e. without damage.

Keeping a Constant Level of Losses in the Low-Voltage Cells of a High-Voltage Multilevel Frequency Converter in Emergency Modes of Its Operation

High-voltage adjustable-frequency drives require special inverters for their operation. A cascaded multilevel frequency converter constructed on the basis of a multi-winding transformer and a set of low-voltage cells has received a widespread use. The main advantage of this converter topology are a low harmonic distortion level of the output voltage and current waveforms, as well as high reliability owing to the possibility to exclude a failed cell from operation without the need to shut down the drive. For equalizing the losses among the converter’s power cells, a pulse-width modulation (PWM) algorithm with a “walking” cell has been developed. Owing to a series connection of the cells, the effective PWM frequency is increased in proportion to the number of cells. However, if one cell fails, the switching frequency of the cells remained in operation increases in comparison with the switching frequency of phase cells when all of them are in the healthy state. This results in a growth of switching losses in the phase with one of its cells taken out from operation. The article discusses a control algorithm with which the nominal level of losses is kept in the cells of all phases under emergency operation conditions. The proposed algorithm has been verified on a model, in which a uniform distribution of losses and high quality of the output voltage have been obtained.

Development of an algorithm for identifying single-phase ground fault conditions in cable and overhead lines in the networks with isolated neutral

The paper addresses the issue of identification of the type of single-phase ground fault in medium voltage networks operating mainly with an isolated neutral. By analyzing the published research, the most promising methods for detection of a single-phase ground fault were selected. Further, using the selected parameters, algorithms were designed to determine the parameters, process them, and use them to identify the type of a single-phase ground fault. The algorithm developed by the authors was formalized for the application on the basis of microprocessor-based protection systems using digital signal processors. The operation process was modeled using real oscillograms of single-phase ground fault. The use of high-frequency zero-sequence current and voltage components, as well as the root-mean-square value of the zero-sequence voltage, made it possible to design an algorithm that identifies any of the possible single-phase ground fault types (bolted, arc, or contact resistance ones). The first part of the article gives an overview of the state-of-the-art of research in the field of detection and identification of single-phase-to-earth faults. In the second part, the parameters of emergency operating conditions are analyzed and the key parameters are determined based on them. The third part contains a description of the single-phase fault identification algorithm developed by the authors and the output oscillograms. The fourth part makes conclusions on the applicability of the algorithm.

Effect of compression molding temperature on the characterization of asbestos-free composite friction materials for railway applications

<abstract> <p>Brake pads significantly affect the braking performance of railways under both normal and emergency operating conditions. In previous studies, brake pads were made using the hand lay-up method and produced the best properties on specimens with epoxy, rice husk, Al<sub>2</sub>O<sub>3</sub> and Fe<sub>2</sub>O<sub>3</sub> compositions of 50%, 20%, 15% and 15%. However, the resulting density does not meet the density standard set by PT Industri Kereta Api Indonesia (PT INKA), which is 1.7–2.4 g/cm<sup>3</sup>. To date, there has been limited research into the utilization of the compression hot molding method for the production of asbestos-free composite friction materials composed of epoxy, rice husk, Al<sub>2</sub>O<sub>3</sub> and Fe<sub>2</sub>O<sub>3</sub> for railway applications. In this study, we aimed to determine the effect of compression molding temperature on the characterization of composite brake pads for railway applications. The brake pad specimens were made of epoxy resin, rice husk, Al<sub>2</sub>O<sub>3</sub> and Fe<sub>2</sub>O<sub>3</sub> with a composition of 50%, 20%, 15% and 15%, respectively. The manufacture of composites in this study used the compression molding method with a pressure of 20 MPa for 15 min holding time. The mold temperature used were 80, 100, 120 ℃. Density, hardness, tensile, wear, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) tests were performed to evaluate the properties of the specimens obtained. The results demonstrated that an increase in molding temperature improved the characterization of the brake pads, with the best results achieved at a molding temperature of 120 ℃ (SP-3 specimen). SP-3 specimens had the best density, hardness, tensile properties and thermal properties compared to other specimens.</p> </abstract>

Simulation of Power Router-Based DC Distribution Systems with Distributed Generation and Energy Storage Units

The development of the electric power industry needs to be understood against the current backdrop of the transition to technological platforms facilitating the adoption of smart grids. Smart grids can be made up of separate clusters (microgrids) consisting of power consumers, power grids, and distributed generation (DG) units. To improve energy efficiency, DC microgrids can be integrated into smart grids to deliver power to consumers within a building (or several buildings) and at the sites of C&I facilities. It is advisable to carry out integrations of DC and AC microgrids with DG and energy storage units on the basis of power routers used to couple grids of different voltage classes. This study outlines a computer model of power router-based integration of DC and AC microgrids with distributed generation and energy storage units. The model was developed in the MATLAB environment. The paper also features the results of a study of the proposed methods as applied to voltage control under normal and emergency operating conditions of a DC and AC distribution grid.

A three-stage hybrid stochastic/IGDT framework for resilience-oriented distribution network planning

This article tackles the resilience-oriented distribution network planning (RODNP) problem utilizing a novel three-stage hybrid framework. The decision-making on the line hardening and DG placement is carried out in the first stage. In the second stage, emergency and normal operation optimization are conducted. The worst-case scenario is considered for evaluating the effect of a potential hurricane in post-event emergency operation conditions. In addition, a scenario-based stochastic approach is used to assess normal operation conditions. Finally, a risk-averse hardening re-plan is implemented in the third stage using the information gap decision theory (IGDT) notion as an effective non-deterministic optimization strategy under severe uncertainty. At this stage, distribution system planner (DSP) tries to develop a more resilient distribution network scheme against the most powerful hurricane possible while taking into account a predetermined parameter known as the resilience budget. The efficacy of the proposed approach is validated by conducting several case studies on the IEEE-33 bus test system. The results reveal that the proposed strategy may dramatically reduce the cost of both normal and emergency operations simultaneously.

Cost–Benefit Analysis of Introducing Custom-Made Small Thermal-Frictional Sterilization System to the Existing Hospital Waste Disposal System: A Case Study of Chinese Hospital

This manuscript proposes an integrated system for treating hospital solid waste (H.S.W.) consisting of an incineration and frictional sterilization system capable of operating during normal and emergency situations. We analyzed the benefits of integrating different hospital solid waste (H.S.W.) treatment systems with the existing stand-alone incineration system, with a particular emphasis on the thermal friction sterilization integration system. The objective was to define the economic advantages and benefits in terms of resources recovery of using the thermal frictional sterilization–incineration integrated system during the hospital’s normal and emergency/pandemic operating conditions. We modeled three modeling scenarios based on normal and emergency operating conditions. The results show that the H.S.W. was composed of 74% general H.S.W. Existing incineration systems would be the most expensive process because the sanitary transportation cost represented approximately 96% of the H.S.W. costs. The hospital would realize 40–61% savings relative to the existing method if the integrated incineration–frictional systems were implemented to treat 50–70% of H.S.W.; the savings were better than in other scenarios. Proposed scenario 3 had a much better resources recovery factor than scenarios 1 and 2. This modeling study showed that a thermal frictional sterilization–incineration system could work well even under emergency conditions if the H.S.W. in-house sorting/transportation/storage process is modified to cater to other H.S.W. treatment/sterilization systems.

Demand Response Program Integrated With Electrical Energy Storage Systems for Residential Consumers

This article presents a distributed resilient demand response program integrated with electrical energy storage systems for residential consumers to maximize their comfort level. A dynamic real-time pricing method is proposed to determine the hourly electricity prices and schedule the electricity consumption of smart home appliances and energy storage systems commitment. The algorithm is employed in normal and emergency operating conditions, taking into account the comfort level of consumers. In emergency conditions, the power outage of consumers is modeled for different hours and outage patterns. To evaluate the applicability of the proposed model, real samples of Southern California households are considered to model the smart homes and their appliances. Further, a sensitivity analysis is performed to assess the impacts of the number of households and number of persons per household on the output results. The results showed that the proposed model reduced the costs of utility in normal and emergency conditions by about 33.77% and 30.92%, respectively. The values of total payments of consumers in normal and emergency conditions were decreased by about 34.26% and 31.31%, respectively. Further, the consumers comfort level for normal and emergency conditions increased by about 146.78% and 110.2%, respectively. Finally, the social welfare for normal and emergency conditions increased by about 46% and 49.06%, respectively.

A hierarchical scheduling framework for resilience enhancement of decentralized renewable-based microgrids considering proactive actions and mobile units

Nowadays, decentralized microgrids (DC-MGs) have become a popular topic due to the effectiveness and the less complexity. In fact, DC-MGs resist to share their internal information with the distribution system operator (DSO) to protect their privacy and compete in the electricity market. Further, lack of information sharing among MGs in normal operation conditions leads to form a competitive market. However, in emergency operation conditions, it results numerous challenges in managing network outages. Therefore, this paper presents a hierarchical model consisting of three stages to enhance the resilience of DC-MGs. In all stages, the network outage management is performed considering the reported data of MGs. In the first stage, proactive actions are performed with the aim of increasing the network readiness against the upcoming windstorm. In the second stage, generation scheduling, allocation of mobile units and distribution feeder reconfiguration (DFR) are operated by DSO to minimize operating costs. In the final stage, the repair crew is allocated to minimize the energy not served (ENS). Uncertainties of load demand, wind speed and solar radiation are considered, and the effectiveness of the proposed model is investigated by integrating to the 118-bus distribution network. Finally, the results of the simulation indicate that DFR and proactive actions decrease the ENS by 19,124 kWh and 4101 kWh, respectively. Further, the sharing of information among MGs leads to a 48.16% growth in the supply service level to critical loads, and consequently a 3.47% increase in the resilience index.

Automation of the Control of Electric Drive of Manned Submersibles

Currently, there is an intensive development of manned and unmanned submersibles due to development of offshore oil and gas fields, development of underwater archaeology and exploration activities in transit zones regarding seabed mineral extraction. The depth of immersion and the nature of the underwater technical works performed determine not only the design of the underwater vehicle, its power-to-weight ratio and technical equipment, but also impose high requirements on reliability, survivability, and habitability, if the underwater vehicle implies that the operator is on board inside a pressure hull. The main objectives of the study carried out by the authors were to achieve high reliability and survivability of the main elements of the propulsion-steering complex, which ensure movement of a human-occupied vehicle in the water column, its positioning and retention at a given point in the water area.For this purpose, it was proceeded to development of an automated control system for the electric drive of the propulsive device of manned immersible. The proposed developments include a flowchart of the movement control system, circuitry engineering solutions using power semiconductor devices to maintain operability of the electric drive in extreme and emergency operating conditions, and movement control algorithms. Electromagnetic calculations of the active part of the electric machine were performed by the finite element method, considering the geometric features of the dental zone of the rotor and stator. The proposed mathematical apparatus served to calculate optimal control actions of the electric drive and to quantitatively assess the reduction in electrical losses once optimal control was applied. The calculation of the optimal control parameters was carried out using the maximum principle. The initial conditions for auxiliary functions are determined by the Newton‒ Raphson method. A comparison of various modes of operation of the electric drive was made regarding their influence on duration of the campaign, and other parameters.The calculations did not consider the parameters and geometry of the propulsive device (the propeller) since the developers of electric propulsion systems for manned and unmanned underwater vehicles of various classes often deliberately reduce the efficiency of the propeller to increase speed of the electric motor shaft, resulting in a decrease in the dimensions and weight of the latter.

A non-linear resilient-oriented planning of the energy hub with integration of energy storage systems and flexible loads

This paper develops a two-stage model for planning of the hub, taking into account various uncertainties, in which the sizing of hub converters is performed with the aim of improving hub resilience. In the first stage, the capacity of hub converters is selected and in the second stage, the operation problem is solved under N-1 contingency conditions. In the proposed model, Price-based demand response (DR) and direct load control (DLC) programs are considered to implement in normal and emergency situations, respectively. The robust optimization method is utilized to deal with the uncertainties the problem is formulated as a mixed-integer non-linear programming (MINLP) problem. Finally, DICOPT solver in GAMS environment is used to solve the model and the results demonstrate that considering the N-1 contingency conditions in the design problem leads to the installation of more converters as well as larger capacities. The results also indicate that the operating cost of the hub during the outage condition of combined heat and power (CHP) is reduced by 63.48% through the implementation of the DLC program considering energy storage system. Overall, the results illustrate that considering the emergency operating conditions in the hub design problem, leads to a significant enhancement in its resilience.

Turbulence model assessment and heat transfer phenomena inside a rectangular channel under forced and mixed convection

A very high-temperature gas-cooled reactor (VHTR) is an attractive option for hydrogen production due to its high operating temperature. The reactor cavity cooling system (RCCS), a passive safety system of the VHTR, surrounds the reactor vessel with rectangular riser channels and removes decay heat from it. Under emergency operation conditions such as a decrease in the flow rate of the RCCS, the flow condition inside the RCCS riser can become a mixed convection condition accompanying heat transfer deterioration. To design and operate the VHTR with reliable safety, accurate predictions for various convective heat transfer conditions in RCCS riser channels are required. In this study, by comparing the results of an air flow visualization experiment, the predictability of the turbulence models was assessed for the convective heat transfer and complex flow characteristics near the corner region of the rectangular duct confirmed from the experimental study. In this paper, the heat removal rate through the test section of the visualization experiment was quantified under various convective heat transfer conditions, and local temperature measurement data from the experiment were presented to describe the heat transfer deterioration phenomena inside a rectangular riser in turbulent mixed convection. Linear and nonlinear eddy viscosity models were evaluated by comparing the heat transfer coefficient, local temperature, local flow structure including secondary flow, and turbulence quantities obtained from the experiment. Furthermore, improvements to turbulence models for enhancing the prediction of mixed convection heat transfer in rectangular riser ducts were proposed.

The gravitational search algorithm for incorporating TCSC devices into the system for optimum power flow

<span lang="EN-US">This paper proposes a gravitational search algorithm (GSA) to allocate the thyristor-controlled series compensator (TCSC) incorporation with the issue of reactive power management. The aim of using TCSC units in this study is to minimize active and reactive power losses. Reserve beyond the thermal border, enhance the voltage profile and increase transmission-lines flow while continuing the whole generation cost of the system a little increase compared with its single goal base case. The optimal power flow (OPF) described is a consideration for finding the best size and location of the TCSCs devices seeing techno-economic subjects for minimizing fuel cost of generation units and the costs of installing TCSCs devices. The GSA algorithm's high ability in solving the proposed multi-objective problem is tested on two 9 and 30 bus test systems. For each test system, four case studies are considered to represent both normal and emergency operating conditions. The proposed GSA method's simulation results show that GSA offers a practical and robust high-quality solution for the problem and improves system performance.</span>

Development of a new control rod drive mechanism design for the ISU AGN-201M reactor

The Aerojet General Nucleonics (AGN) model 201-Modified, known as the AGN-201M reactor, plays an essential role in the educational and research activities at Idaho State University (ISU). The ISU AGN-201M's original Control Rod Drive Mechanism (CRDM) has been in operation for more than fifty years with no large-scale redesigns. The CRDM is required to eject the fuel rods within one second during a SCRAM event (also known as a 'reactor trip') and adjust the control rods' insertion speed, and keeps the rod insertion sequence correct. The existing control rod drive mechanisms meet these criteria but experience a few concerns due to aging. Concerns include complex maintenance and costly repairs for old electromechanical components, rod position feedback errors, and the impediment of the plate during a SCRAM due to binding of the lead screws of the existing mechanism. During a binding event, the drive mechanism becomes locked, preventing the control rod's magnetic plate from moving in or out under the reactor's normal and emergency operating conditions. Although, the binding has no effect on the ability of the rod to exit the core during the SCRAM. To counteract the concerns and issues with the current CRDM, a new design has been proposed using newer components and a simplified design.The new design utilizes more advanced electric and mechanical components that are commercially available. The new CRDM system is divided into four main aspects: (1) control rod movement design (motor, lead screw, guide rods), (2) control rod ejection (springs, electromagnet), (3) control rod position and feedback (position transducer, microswitches), and (4) material selection and structural analysis. The new design aims to reduce the overall complexity and probability of failure to improve the reactor's overall reliability. With proper material selection and improved structural design, the new drives are lighter with little to no change in structural integrity. The new control rod drive mechanism eliminates binding scenarios by using a single lead screw and implementing additional guide rods. An advanced linear position sensor and microswitches replace the existing and aging synchro system for accurate rod position feedback resulting in better reactivity control. The new design meets the reactor's operational limits by having an average reactivity insertion of 0.065% Δk/k per second, which corresponds to a total control rod insertion time of 19.23 s, while the control rod's ejection time remains less than one second during a SCRAM event. The new design ensures the reactor's long-term viability for educational and research activities by increasing the reliability and safety of operation for years to come.