Abnormal Operating Modes Research Articles

Transient processes of electrical parameters in different modes of operation of air supply systems in the design and testing of aviation equipment

The article is devoted to the research and quality assurance of electrical parameters of modern air-conditioning systems in the conditions of transitional processes in normal, abnormal and emergency modes of operation. The analysis of the composition of the consumers on a modern aircraft, the requirements of international normative and technical documents concerning the parameters of the quality of electrical equipment of the aircraft, the choice of the drive and the generator, taking into account the specific conditions of normal, abnormal and emergency work of the air supply system, as well as in the conditions of the transitional processes, has been carried out. The purpose of the study is realized on the example of the estimation of the quality of electric energy in the channels of the synchronous generator of the aircraft, which shows transient processes at a load value of 50% of rated power, and with a jump-like load change from 50% to 150% of nominal power.

Study on the influence of backlash phenomenon on wind turbine power using bond graph approach

This work presents a multi-body model for studying the influence of backlash phenomenon on wind energy using a bond graph approach. This analysis is carried out in two steps; first, the residual technique is used to discriminate between the healthy and the abnormal operating mode. The second one consists in using energy levels calculated from the spectral energy of the residual signals using a moving Hanning window to estimate the faults amplitude. Simulations tests verify the effect of the backlash magnitude on the good functioning of the wind turbine and indicate that the backlash within a certain range has little effect on the wind energy but with the enlargement of backlash, the dynamic response of the system is significantly changed.

Markov chain model of fault-tolerant wireless networked control systems

Wireless networked control systems (WNCS) are composed of spatially distributed sensors, actuators, and controllers communicating through wireless networks instead of conventional point-to-point wired connections. While WNCSs have a tremendous potential to improve the efficiency of many critical control systems, for instance, in building automation and process control, the systems are fundamentally constrained by the packet losses and the functional faults of the underlying wireless sensor and actuator networks. Understanding the interaction between wireless networks and control systems is essential to characterize the performance limitations of the critical control systems and optimize its wireless network resources. This paper presents an analytical framework for modeling the behavior of the control loop over lossy and faulty network. The control loop over wireless networks is modeled through a Markov chain taking into account sensing links, actuating links, and recovery mechanism to compensate the faulty nodes. By using this model, the novel performance metrics are mathematically derived and are evaluated through both theoretical analysis and simulation results. The performance evaluation shows the critical tradeoff between the average performance when the control loop is in the normal operation mode and the recovery performance when it is in the abnormal operating mode due to the faulty nodes.

Bifurcation and Large-Signal Stability Analysis of Three-Phase Voltage Source Converter Under Grid Voltage Dips

Three-phase voltage source converters (VSCs) are commonly used as power flow interface in ac/dc hybrid power systems. The ac power grid suffers from unpredictable short-circuit faults and power flow fluctuations, causing undesirable grid voltage dips. The voltage dips may last for a short time or a long duration, and vary the working conditions of VSCs. Due to their nonlinear characteristics, VSCs may enter abnormal operating mode in response to voltage dips. In this paper, the transient response of three-phase VSCs under practical grid voltage dips is studied and a catastrophic bifurcation phenomenon is identified in the system. The converter will exhibit an irreversible instability after the dips. The expanded magnitude of ac reactive current may cause catastrophic consequence for the system. A full-order eigenvalue analysis and a reduced-order mixed-potential-theory-based analysis are adopted to reveal the physical origin of the large-signal instability phenomenon. The key parameters of the system are identified and the boundaries of instability are located. The bifurcation phenomenon and a set of design-oriented stability boundaries in some chosen parameter space are verified by cycle-by-cycle simulations and experimental measurement on a practical grid-connected VSC prototype.

TO THE FEATURE OF BEHAVIOR OF HYDROGEN IN THE METALS AND ALLOYS, GOT ELECTROLYSIS, AND POSSIBILITY OF THEIR APPLICATION IN ALTERNATIVE ENERGY SOURCES

The question of the role of hydrogen energy in the development of the welfare society can be seen in only one aspect, namely the decent life of a community can only be achieved with full use of hydrogen technologies. The potential of hydrogen is far from being exhausted in the traditional energy sector. As the successful solution of the problems of hydrogen storage and the creation of highly efficient fuel cells will be implemented absolutely reliable backup system own needs when abnormal modes of operation of the power plant. One of the limiting factors in the development of hydrogen energy are existing storage technologies (cryogenic and bottled) and energy consuming unsafe.

A method of diagnostics of induction-motor rotor eccentricity

Electroenergetics and industry mainly use induction motors (IMs) as drives of mechanisms. One method to improve their operational reliability and service life is effective and timely diagnosis of abnormal operating modes, in particular, rotor eccentricity. However, for a number of reasons, it has not before been possible to develop a diagnostic system that would allow one to effectively identify the rotor static eccentricity during an operational process. To solve this problem, a method of diagnostics of rotor eccentricity in IM has been proposed that uses a stator current, and the amount of eccentricity is determined by the operative value of additional current. It is proposed to carry out IM diagnostics in an idling regime in two stages. At the first stage, the reference values of a harmonics of stator current’s components of additional current, its operative value, and dependence from the rotor eccentricity are determined and saved for a fully functioning machine. At the second stage, the values of a harmonics of stator current’s and components of additional current are determined. The operative value of additional current is calculated taking into account the relation of the received harmonics to their reference value, and the shift of a rotor is determined by reference dependence.

Torsional vibrations in steam turbine shafting in turbogenerator abnormal modes of operation

The paper presents some findings of numerical investigations of torsional vibrations in steam turbine shafting in the turbogenerator abnormal operation modes (short circuit, random paralleling start, etc.). The shafting vibrations are shown to be essentially dependant on the reaction torque surge parameters (magnitude, duration, and form). For three types of the reaction torque surge a comparative hazard analysis is performed from the standpoint of initiation of cyclic damage in the rotor material and the risk of shafting failure.

Assessment of fatigue damage in steam turbine shafting due to torsional vibrations

We present a technique and results of fatigue damage evaluation of steam turbine shafting material under conditions of torque vibrations occurring at turbogenerator abnormal modes of operation (short circuit, random paralleling start, etc.). Combinations of loading parameters, which provide the shafting limiting conditions, are identified.

Abnormal operating modes and reliability of modern hydraulic generating sets

Abnormal operating modes and reliability of modern hydraulic generating sets

Simulation of PWM DC-DC 4-Q converter driven S.E. DC motor

In this work, the authors propose a comprehensive mathematical model for PWM DC-DC converters with unipolar switching scheme (including all classes: A, B, C, D and four-quadrant E) and closed-loop PWM DC-DC converter driven DC S.E. motor for transportation drives. The model is useful for electric drives designers for the investigation of both normal and abnormal modes of operation of the drive.

Analysis of the ITER cryoplant operational modes

In the framework of an EFDA task, CEA is carrying out an analysis of the various ITER cryoplant operational modes. According to the project integration document, ITER is designed to be operated 365 days per year in order to optimize the available time of the Tokamak. It is anticipated that operation will be performed in long periods separated by maintenance periods (e.g. 10 days continuous operation and 1 week break) with annual or bi-annual major shutdown periods of a few months for maintenance, further installation and commissioning. For this operation schedule, auxiliary subsystems like the cryoplant and the cryodistribution have to cope with different heat loads which depend on the different ITER operating states. The cryoplant consists of four identical 4.5 K refrigerators and two 80 K helium loops coupled with two LN2 modules. All of these cryogenic subsystems have to operate in parallel to remove the heat loads from the magnet, 80 K shields, cryopumps and other small users. After a brief recall of the main particularities of a cryogenic system operating in a Tokamak environment, the first part of this study is dedicated to the assessment of the main ITER operation states. A new design of refrigeration loop for the HTS current leads, the updated layout of the cryodistribution system and revised strategy for operations of the cryopumps have been taken into consideration. The relevant normal operating scenarios of the cryoplant are checked for the typical ITER operating states like plasma operation state, short term stand by, short term maintenance, or test and conditioning state. The second part of the paper is dedicated to the abnormal operating modes coming from the magnets and from those generated by the cryoplant itself. The occurrence of a fast discharge or a quench of the magnets generates large heat loads disturbances and produces exceptional high mass flow rates which have to be managed by the cryoplant, while a failure of a cryogenic component induces a major disturbance for the magnet system. Thanks to this analysis, modifications of the architecture of the present PFD are proposed to make match the technical specifications of the cryogenic system with the ITER operation requirements.

Mathematical Model of 4-Quadrant DC Electric Drive with 6-Pulse Dual Converter

Mathematical model simulating the operation of DC electric drive hoisting mechanism has been developed. The study illustrates the capabilities of the developed model for investigation both normal and abnormal modes of operation of the converter and the supplying voltage. Large attention was given to the thyristor converter and its firing system so that fast-proceed micro-processes occurring in the converter can be simulated with a high degree of accuracy.

On the Abnormal Operating Modes Management in a Transportation System

Transportation systems have a major influence on the performance of manufacturing systems, and their complexity sets the problem of their availability. The management of abnormal operating modes requires efficient decision support, first in order to forecast the possible performance provided by the different solutions, then in order to compare this performance with the transportation system objectives. This paper suggests an approach based on fuzzy logic in that purpose.

Modelling Rectifier Loads for a Multi-Machine Transient-Stability Programme

An improved rectifier load model for use in transient-stability studies is developed. The model, which simulates abnormal modes of operation and the dynamics of the d.c. load, is used to investigate the stability of a power-system where the rectifier can represent a large percentage of load.

Precision table for surface scattering in foils

In the framework of an EFDA task, CEA is carrying out an analysis of the various ITER cryoplant operational modes. According to the project integration document, ITER is designed to be operated 365 days per year in order to optimize the available time of the Tokamak. It is anticipated that operation will be performed in long periods separated by maintenance periods (e.g. 10 days continuous operation and 1 week break) with annual or bi-annual major shutdown periods of a few months for maintenance, further installation and commissioning. For this operation schedule, auxiliary subsystems like the cryoplant and the cryodistribution have to cope with different heat loads which depend on the different ITER operating states. The cryoplant consists of four identical 4.5 K refrigerators and two 80 K helium loops coupled with two LN2 modules. All of these cryogenic subsystems have to operate in parallel to remove the heat loads from the magnet, 80 K shields, cryopumps and other small users.After a brief recall of the main particularities of a cryogenic system operating in a Tokamak environment, the first part of this study is dedicated to the assessment of the main ITER operation states. A new design of refrigeration loop for the HTS current leads, the updated layout of the cryodistribution system and revised strategy for operations of the cryopumps have been taken into consideration. The relevant normal operating scenarios of the cryoplant are checked for the typical ITER operating states like plasma operation state, short term stand by, short term maintenance, or test and conditioning state.The second part of the paper is dedicated to the abnormal operating modes coming from the magnets and from those generated by the cryoplant itself. The occurrence of a fast discharge or a quench of the magnets generates large heat loads disturbances and produces exceptional high mass flow rates which have to be managed by the cryoplant, while a failure of a cryogenic component induces a major disturbance for the magnet system.Thanks to this analysis, modifications of the architecture of the present PFD are proposed to make match the technical specifications of the cryogenic system with the ITER operation requirements.