Shutdown Mode Research Articles

Effect of technological shutdown mode on life of hightemperature equipment made of HP40NbTi alloy

The effect of heating —cooling cycles with different cooling rate on the structure, short-term and long-term mechanical properties of a high-temperature Fe —Cr—Ni-based HP40NbTi alloy is experimentally studied. The long-term strength of the HP40NbTi alloy is determined at a temperature of 1150 °C after preliminary exposure at 1150 °C for a duration of 2...100 hours, followed by cooling with a furnace and in water. It is established that accelerated cooling from operating to room temperature in the initial period of operation contributes to an increase in the long-term strength of Fe —Cr—Ni-based alloys compared to the cast state and largely prevents a decrease in the performance characteristics of heat-resistant alloys based on the Fe—Cr—Ni system during operation.

НАБЛЮДАТЕЛЬ УПРУГОГО МОМЕНТА ДВУХМАССОВОЙ ЭЛЕКТРОМЕХАНИЧЕСКОЙ СИСТЕМЫ

To reduce the accident rate and increase the service life of electromechanical systems with shock load changes, the monitoring of elastic moments in mechanical gears is necessary. This task is relevant for the main lines of stands of hot rolling mills. The implementation of monitoring systems based on physical measuring devices is inefficient due to their complexity and low operational reliability. As an alternative, a relatively simple elastic moment observer is proposed, which is a fragment of an industrial controller software. The structure of the observer is presented and its advantages in comparison with known analogues are shown. The adequacy of the measured and reconstructed elastic moment signals is proved using the example of electromechanical systems of the stand of the thick-sheet mill 5000. A quasi-experimental analysis of emergency modes is substantiated, which allows the processing of signals stored in the form of data arrays. Based on this approach, an assessment of the dynamic moments in the emergency shutdown mode of the crate with metal in the rolls is given. The expediency of creating an online monitoring system for overloads of spindles and methods for calculating their resource is emphasized.

Modeling of the Radiological Behavior During LOCA in Open Pool Type Reactor

This study aims to model the radiological consequences that result from loss of coolant accident in open pool research reactor of 22 MW power. The loss of coolant accident results from rupture in the cooling systems of the reactor and consequently results in decreasing the water level in the reactor pool. Decreasing the water level, that represents the shielding material above the reactor core, results in increasing the dose rate in the top region in the reactor pool as well as the reactor building. LOCA normally results in shutting down the reactor due to the radioprotection system provided in the upper region of the reactor pool. A failure in shutdown systems of the reactor during LOCA is rare but expected and it represents the worst case. So, evaluating LOCA from the radiological point of view must be investigated for the safe shutdown mode as well as the failure of shutdown case. The study also includes occurring LOCA for shutdown reactor taking the decay time into consideration. ORIGEN-S module from scale system was used to estimate the delayed neutrons and gamma rays from the core for the shutdown mode. KENO-VI module from Scale system was used to estimate the prompt neutrons and gamma rays generated from the core for the failure case. Then, MAVRIC/Scale module was used to estimate the dose rate at the top point of the reactor pool for the two cases during LOCA. Studying the dose rate during LOCA aims to determine the water level that verifies the radiological safety limit at the top point of the reactor pool for the two cases. The calculations introduced a relationship between the water level that verifies the permissible radiological limit (WL) and the decay time (DT) in the range between 0 to 30 d.

Simulation of oil pipeline shutdown and restart modes

The paper is devoted to the simulating of non-stationary processes of shutdown and restart on the example of a section of the Zhetybai-Uzen “hot” oil pipeline. A mathematical model of thermal-hydraulic calculation is given taking into account the rheological properties of the pumping oil. The special module of the SmartTran software developed by the work’s authors carried out the calculations. In the calculations, the decrease in time of oil temperature in the pipeline during cooling and the increase in oil pressure, temperature, velocity after the restart are determined. In addition, the calculations determine the power of pumping units, heating furnaces and the power consumption, which are necessary for restart of the pipeline after the shutdown. Simulation the processes of the pipeline cooling and restart after a shutdown makes it possible choosing the optimum parameters of pumping units at pumping stations and the time of safe shutdown of the oil pipeline.

Thermal performances and characteristics of thermosyphon heat pipe using alumina nanofluids

The thermal performance of a double tube two-phase closed thermosyphon (DTTPCT) using alumina nanofluid as working fluid in startup, steady state and shut down modes has been experimentally and theoretically evaluated. Gamma-Alumina (γ-Al2O3) nanoparticles with size of 40 nm were well dispersed, prepared and stabilized in distilled water base fluid at different particle concentrations.The axial wall temperature distribution, the nanofluid temperature along the thermosyphon, the thermal conductivity and overall heat transfer coefficient were investigated to propose the best combination of parameters by varying parameters such as concentration of nanoparticles, heat load on heat pipe. The effect of nanofluid volume fraction of 0.5%, 1.0%, 1.5%, and 2.0% with heat load of 500 W, 750 W, 1000 W and 1250 W on the overall thermal conductivity of the heat pipe were studied to evaluate the optimal thermal performance. The results indicate that the DTTPCT filled with alumina nanofluid in 2% volume fraction yields higher thermal performance when it is operated at 1000 W heat load. The experimental results show that the optimal thermal performance of TPCT filled with Al2O3/water nanofluid at a heat load of 1000 W is 3 times better than that of pipes using distilled water as the working fluid. Theoretical model describing both thermal performance and phase flow of the DTTPCT has been compared with the experimental results at start-up, steady-state and shut-down modes.

Research on Metal Supervision and Inspection Standards for Gas-steam Combined Cycle Units

Domestic gas-steam combined cycle units start and stop frequently, and the load changes greatly, which accelerate the expansion of defects, such as fatigue, cracks, and organizational deterioration of metal components. In view of the problems caused by the material selection characteristics of gas-steam combined cycle units and the daily shutdown mode, several common typical cases of gas-steam combined cycle units are analyzed, such as compressor blade fatigue fracture, main steam combined valve body fatigue cracks, pipeline and pressure vessel weld fatigue cracks. As well, the gas-steam combined cycle unit metal supervision content and inspection emphasis are studied and supplemented.

Problems of conversion of diesel locomotives to gas-diesel cycle

The article focuses on the problem of ensuring the required parameters for gas-air mixture in light load and idle modes. A mathematical modeling of the process in the gas-air duct of the diesel generator 1-PDG-4 was conducted during air blow-off in compressor and throttling at the diesel inlet. It was found that conversion of locomotive engines to gaseous fuel at idle speed can meet the required stoichiometric ratio of gas-air mixture only if air throttling processes at the engine inlet are combined with the engine in the shut-down mode of a cylinder bank.

Transient analysis and control of a heat to power conversion unit based on a simple regenerative supercritical CO2 Joule-Brayton cycle

Supercritical carbon dioxide (sCO2) heat to power systems are a promising technology thanks to their potential for high efficiency and operational flexibility. However, their dynamic behaviour during part-load and transient operation is still not well understood and further research is needed. Additionally, there is not enough literature addressing suitable control approaches when the objective is to follow the dynamics of heat load supplied by the topping process to maximise the power recovery. The current research aims to fill these gaps by proposing a one-dimensional transient modelling formulation calibrated against the major components of a 50 kWe sCO2 test facility available at Brunel University London. The dynamic analysis showed that the system quickly adapts to a 2800s transient heat load profile, proving the flexible nature of the sCO2 system investigated. The turbine by-pass, during startup and shutdown modes of operation, enabled gradual and safe build-up/decline of the pressures and temperatures throughout the loop. The regulation of the inventory in the range 20–60 kg allowed a 30% variation of the turbine inlet temperature with lower penalties on system performance than the turbomachinery speed control. The designed proportional-integral inventory controller showed a rapid response in the control of the turbine inlet temperature around the set point of 773 K during large variations of the heat load.

РЕКОМЕНДАЦИИ ПО ПРОЕКТИРОВАНИЮ ГИДРОСТАТОДИНАМИЧЕСКИХ ПОДШИПНИКОВ СКОЛЬЖЕНИЯ СДВОЕННОГО ТИПА

The task is to develop recommendations for the design of dual-type hydrostatodynamic plain bearings based on the existing experience in designing this type of plain bearings, as well as based on many theoretical and experimental studies performed by the author of this work. The number of the most necessary parameters for the design of dual-type hydrostatodynamic bearings is determined. Particular attention was paid to the development of recommendations for additional parameters specific to the design of double type plain bearings. Attention is paid to the selection of double-type bearing materials and it is shown that the problem of selecting materials for hydrostatic dynamic bearings is not so relevant, however, sometimes in start-up and shutdown modes, as well as in emergencies, to ensure high reliability of the designed machine, it is necessary to pay attention to the choice of bearing materials. The influence of various forms of chambers on the static and dynamic characteristics of hydrostatodynamic bearings is analyzed and it is shown that the greatest distribution in practice, they got rectangular cameras. It is shown that the flow regime of the working fluid also significantly affects both the static and dynamic characteristics of the bearing. It is noted that even with a non-rotating rotor in a hydrostatodynamic bearing, the most turbulent mode of flow of the working fluid is most often observed. The influence of the thickness of the working fluid layer on increasing the rigidity of the supports and expanding the range of stable operation is considered. It is shown that with a decrease in the clearance in the bearing, its bearing capacity increases and the range of stable operation expands, however, this increases the friction power loss, increases the likelihood of clogging of the slit bearing path, and also increases the requirements for the quality of manufacture of the bearing working surfaces. It is recommended that in the double hydrostatodynamic bearing in the outer and inner parts to assign the same clearances. It is shown that in a dual hydrostatodinamic bearing, the existing recommendation on the number of chambers can lead in some cases to large working fluid flow.

ОБОСНОВАНИЕ ТЕХНИЧЕСКИХ РЕШЕНИЙ РЕАКТОРНОГО КОНТУРА УСТАНОВОК БРС-ГПГ МАЛОЙ И СРЕДНЕЙ МОЩНОСТИ С ТЯЖЕЛЫМ ЖИДКОМЕТАЛЛИЧЕСКИМ ТЕПЛОНОСИТЕЛЕМ

The analysis and new scientific and technical solutions corresponding to the evolutionary development of low and medium power reactor plants with heavy liquid metal coolants are presented. The analysis was carried out on the basis of experience in the creation and operation of reactor installation with lead-bismuth coolant and research, primarily experimental, performed at the Nizhny Novgorod State Technical University (NSTU) in rationale of the small and medium-sized power plants developed at NNSTU reactor installation with horizontal steam generators (BRS-GPG). The paper substantiates the choice of coolant. With the proposed arrangement of the reactor loop, the maximum possible natural circulation is achieved, which significantly increases the safety of reactor installation. The results of studies (simulations) of one of the most potentially dangerous accidents in reactor installation with HLMC - ″large steam generator leak″ can qualitatively reduce the consequences of the accident when using the design of a horizontal steam generator in which the pipe system is placed with minimal burial of pipes under the level of HLMC, which eliminates the flow of water into the reactor core, re-pressurization of the reactor circuit, etc. It is probably advisable to consider the characteristics of the core, analog ary accepted for SVBR or BREST-OD-300. A system is proposed for cooling the reactor and providing the reactor installation shutdown modes, its characteristics are studied and tested at the NSTU stands.

Toward developing accelerated stress tests for proton exchange membrane electrolyzers

Abstract Proton exchange membrane water electrolysis is technically the most suitable technology for the production of green hydrogen on a large scale. Although it is still more expensive than hydrogen produced from fossil sources, it has already been commercialized. Novel components with cost-effective materials and efficient manufacturing processes are being rapidly developed. However, these components must endure durability tests that can guarantee a lifetime of at least 50,000 operation hours. Consequently, there is an urgent need to develop accelerated stress test protocols based on a deep understanding of degradation mechanisms of stack components. Recent reports show that the main degradation mechanisms are associated to anode catalyst dissolution, membrane chemical decomposition, and formation of semiconducting oxides on the metal components. These mechanisms can be accelerated by stressors such as high current density, dynamic operation, and shutdown modes. On the basis of these reports and knowledge of the operational requirements for large-scale proton exchange membrane water electrolysis, we propose an accelerated stress test protocol for the fast evaluation of newly developed cost efficient and durable components.

Viscoelasticity of Rubber Springs Affects Vibration Characteristics of a Flip-Flow Screen With the High G Value

With the high G value of vibration, outstanding sieving behaviors of a flip-flow screen are more likely to appear, but structural damages are aggravated under the high amplitude vibration. Considering rubber springs role on the vibration energy dissipation, viscoelasticity of rubber springs (i.e., shear springs and vibration isolation springs), is noticed to deal with the above contradiction. However, when rubber springs experience large amplitude vibration, viscoelastic responses influence more on the amount of damping than in the linear (i.e., small amplitude) vibration regime, as the frequency dependence of rubber springs is noteworthy. For this purpose, the Generalized Maxwell model is used to depict the frequency dependence of rubber springs and the practical damping is converted to a series damping parameters of the system, numerical models of the flip-flow screen under startup and shutdown modes and steady working conditions are proposed and verified firstly. Secondly, in order to explore kinetics responses of the elastic screen panel under different rubber springs damping coefficients, nonlinear finite element model of which is established. Finally, effects of rubber springs nonlinear damping on screen frames vibrations and screen panels nonlinear responses are studied. Results indicate that hysteretic damping of rubber springs can effectively solve the conflict between vibration strength and structural reliability of the flip-flow screen, since the low sensitivities of maximum stresses and the high sensitivities of accelerations to rubber springs damping are found.

Advanced control strategy for bidirectional three phase AC/DC converter

This paper describes an advanced control strategy of a bidirectional three-phase PWM AC/DC converter embedded between a micro-grid and utility. This converter proves an ability to control a bidirectional power flow. Firstly, the improved control strategy is based on direct power control using a new switching lookup table obtained from the derivative analysis of the active and reactive power. Furthermore, the improved control strategy is verified by simulation. In addition, many operating modes are established due to verify the capability of a bidirectional power flow of the converter. Particularly, authors focus on three operating scenarios which are cited as follow: Inversion Mode (IM), Shut-Down Mode (S-DM) and Rectification Mode (RM). Moreover, the authors show the capability of the DPC with respect to the LVRT for Tunisian grid. Finally, the performances of this converter are validated experimentally using a Dspace 1104 board, a bidirectional AC/DC converter and the wind turbine using a SM connected with the rectifier. The simulation results compared to the experimental ones demonstrated the good performances of the proposed control strategy.

A Model and Multi-Mode Control of a Centrifugal Chiller System: A Computer Simulation Study

In this paper, a model of a water-cooled centrifugal chiller system is developed and its control performance is studied. The overall system consists of three control loops: (i) a compressor speed control; (ii) an inlet guide vane control and (iii) a condenser liquid-level control. The model is validated by comparing the simulation results with the experimental data under steady state conditions. The results match to within 10% accuracy. A multi-mode control strategy was designed to simulate the operation of the centrifugal chiller as it transitions between start-up, speed control mode, IGV control mode and shutdown mode during a typical day operation. COP of the chiller was studied by conducting simulation runs under a wide range of operating conditions. The results showing the coefficient of performance of the system at different cooling loads as a function of cooling water temperature under IGV control mode and compressor speed control mode are presented.

A simple and versatile overcurrent protection circuit for power MOSFETs

ABSTRACTThis paper proposes an overcurrent protection (OCP) circuit for power MOSFETs employed in low voltage power converters. The proposed configuration requires only discrete components with a gate driver IC and uses the voltage drop across the device for overcurrent detection. It can operate independently in cycle-by-cycle shutdown and multiple cycle shutdown modes. In coordination with a micro-controller based driver IC input signal generator and controller, the proposed OCP circuit can also operate in a single cycle latch-up and hiccup OCP modes. The performance of the proposed scheme is evaluated experimentally at both, hard and soft fault conditions. By experimentation, it is shown that the proposed circuit can operate in various protection modes and capable of protecting a MOSFET in both, hard and soft fault conditions.

A 290-mV, 7-nm Ultra-Low-Voltage One-Port SRAM Compiler Design Using a 12T Write Contention and Read Upset Free Bit-Cell

In this paper, we present an ultra-low voltage one-port static random access memory (SRAM) compiler targeting small to medium array sizes to provide a smaller area solution compared to conventional 6T-based SRAMs. A 12T write contention and read upset free bit-cell are used in the design. Array architecture employs a read–modify–write scheme to support bit-write (BW) masking and column multiplexing. Built-in-self-test (BIST) and synchronous write-through (SWT) options are also supported to provide testability features, while power management (PM) option is included to provide low-leakage sleep and shut-down modes. The proposed design is fabricated in 7-nm FinFET technology and achieves the lowest reported $V_{\mathrm {min}}$ of 290 mV in this technology.

Design and energy-efficient architectures for nonvolatile static random access memory using magnetic tunnel junctions

Design methodology for nonvolatile SRAM (NV-SRAM) using magnetic tunnel junctions (MTJs) and architectures for improving its energy efficiency are investigated. The cell is comprised of an ordinary 6T-SRAM cell and MTJs connected to its storage nodes through additional pass transistors that enable it to electrically separate the MTJs from the 6T cell part during the normal SRAM operation mode. From the viewpoints of the stabilities (noise margins) of all the operation modes and the store currents to the MTJs with careful consideration for device process variability, the design methodology is developed. The energy efficiency is dramatically enhanced by reducing leakage currents during the normal SRAM operation and shutdown modes and by optimizing store energy to the MTJs. A newly introduced hierarchical store-free (HSF) architecture is also highly effective at improving the energy efficiency. The energy performance is computationally analyzed and experimentally verified using circuit parameters extracted from fabricated test-element-group circuits of the NV-SRAM.

Planning and analysis of the demonstration project of the MVDC distribution network in Zhuhai

The DC distribution system is an important development direction of the distribution system, which can improve the reliability and the quality of the power supply, and support the new energy, the energy storage, the electric vehicles, and the flexible access of AC and DC loads to grid. To realize the demonstration application of the DC distribution technology, China’s first demonstration project of the medium voltage DC distribution network will be built in Zhuhai, Guangdong Province to support the construction of the city energy internet. First, this paper analyzes the demand of the DC distribution network project, and puts forward the construction content and construction target. Then, it designs and analyzes the electrical connection mode, system operation mode, and startup and shutdown mode of the DC distribution network, and proposes the overall project construction plan. Finally, it conducts the specific project design and analysis, which mainly include the selection of equipment such as inverters, DC transformers and DC circuit breakers, the design and analysis of the DC control and protection system, the design and analysis of the over-voltage protection and the configuration scheme of the lightning arrester, and analysis of the system transient characteristics. The design and analysis of the engineering program is a combination of China’s distribution network engineering practice and technical characteristics, which lays a solid foundation for the advancement of the DC power distribution technology in China, and has reference value and demonstration effect for the design and construction of other projects.

Model-based fault detection, fault isolation and fault-tolerant control of a blade pitch system in floating wind turbines

Abstract This paper presents model-based fault detection, fault isolation, and fault-tolerant control schemes focused on blade pitch systems in floating wind turbines. Fault detection, isolation, and accommodation techniques are required to achieve high power capture efficiency and structural reliability in floating wind turbines. Faults in blade pitch systems should be detected at an early stage to prevent catastrophic failures. To detect faults of the blade pitch systems, a Kalman filter is designed to estimate the blade pitch angle of the system. The fault isolation algorithm is based on inference methods and capable of determining the fault type, location, magnitude and time. The fault-tolerant controller based on a reconfiguration block with a virtual sensor and shutdown mode controls the floating wind turbine to avoid unexpected external loads. The proposed methods are demonstrated in case studies with stochastic wind and wave conditions that considering different types of faults, such as biases and fixed outputs in pitch sensors and stuck pitch actuators. The simulation results show that the proposed methods can detect and isolate multiple faults effectively at an early stage. Additionally, the effectiveness of the fault-tolerant control systems for different load cases for single and multiple fault conditions is verified by numerical simulations.

Primary coolant drainage level response analysis and optimization of CPR1000 units

During primary coolant drainage operation of CPR1000 units in maintenance shutdown mode (MCS), the high deviation of level gauge often directly influences the actual indication of primary coolant inventory, and greatly threatens the monitoring of nuclear fuel uncovering and core safety. According to the inventory arrangement characteristics and drainage level response tendency of the primary circuit, the drainage process is divided into 4 stages, i.e., single cavity drainage zone, dynamic deviation zone, bundle drainage zone and stable consistence zone. With the typical examples of primary coolant drainage of CPR1000 units, the usual drainage operations during primary coolant drainage and the level gauge response tendency for different level measuring zones are described, and analysis of the cause of level deviation in different stages is given on the basis of fluid mechanics principle and level gauge measuring characteristics. Additionally, the optimization solution for the primary coolant drainage process is proposed in the aspects of deviation criteria setting, drainage process optimization, system design improvement and volume assisted judgement.