Transient Analysis Method Research Articles

Simulation of Temperature Distribution in a Brake Pad Ceramic Composite Material

The temperature distribution is an important aspect of any brake pad composite material. The braking temperature affects the performance and efficiency of any brake pad composite material. It is difficult to measure the interface temperature between the brake pad and disc by thermocouples or infrared thermal sensors during braking. This work investigates the temperature distribution of a ceramic composite brake pad material by the transient thermal analysis method. The transient thermal approach method helps to visualize the interface temperature through simulation. Also, it provides pin temperature at a distance of 4 mm and 6 mm away from the disc surface to observe the temperature distribution of the brake pad. The experimental values of the temperature of the pin at 4 mm and 6 mm away from the disc are collected from the literature and compared with the predicted temperature through simulation. It is found that there is a close agreement between the predicted and experimental temperature values.

A comparative study of propagation delay applied on varieties carbon nanotubes Bundles interconnects using the FDTD and the ABCD matrix method

Due to their hilarious properties, carbon nanotubes (CNTs) with their different varieties have been suggested as potential alternatives for interconnects in many industrial applications related to Artificial Intelligence. This work made an overview of the various models of the resistive effect inside several CNT based interconnects. In addition, it has studied the propagation delay inside the CNT interconnect varieties by comparing two validated transient analysis methods, namely the FDTD and the ABCD matrix. The work has concluded the superiority of the ABCD-matrix method since it has given a better performance.

Non-standard analysis in electrical engineering. Transient analysis in second-order electrical circuits with violation of switching laws

For the first time, the authors proposed the use of the mathematical apparatus of non-standard analysis to solve certain non-trivial problems of theoretical electrical engineering. It was established that the axiomatics of non-standard analysis allows to simplify the analysis of transient processes in high-order electric circuits when the switching laws are violated. It is shown that the application of non-standard analysis methods in theoretical electrical engineering provides an opportunity to use the traditional classical method of transient processes analysis of circuits with violation of switching laws. Only by using methods of non-standard analysis, it is possible to strictly prove the fulfillment of the law of energy conservation in such schemes. Also, examples of solving such tasks are given. It is recommended to expand the scope of application of non-standard methods of analysis in problems of various branches of science and technology, which use differential calculus and boundary transitions, and the solution of which is limited or impossible by standard approaches.

Fast electromigration stress analysis using Low-Rank Balanced Truncation for general interconnect and power grid structures

Electromigration (EM) has become one of the most significant challenges considering longterm reliability in integrated circuit design. The problem is caused by the large current density in circuit interconnections. However, in most cases, we are interested in the EM stress at specific points of the interconnect, such as vias, junctions and boundaries. As a result, Model Order Reduction (MOR) techniques can provide attractive methodologies to reduce the complexity of the original systems. System-theoretic techniques like Balanced Truncation (BT) offer very reliable bounds for the approximation error, compared to moment-matching methods. In this paper, we apply a computationally efficient Low-Rank BT procedure based on the extended Krylov subspace method, that can handle large-scale models and significantly accelerate the EM stress analysis for any general interconnect or power grid structure. For the experimental evaluation, we first consider a general structure interconnect tree to demonstrate the generalizability of the proposed method and then we employ our method on the industrial IBM power grid benchmarks where the its scalability is shown. For the latter, we demonstrate that our method can achieve a speedup up to 238× over a standard transient analysis method and a speedup up to 15× over COMSOL, while exhibiting negligible error.

Hybrid HVDC system fault transient analysis considering traveling wave propagation and converter control response

Accurate fault analysis is essential for protection and control design of hybrid HVDC transmission system. This paper proposes a dc fault transient analysis method, which considers both the traveling wave propagation process and converter control response. Firstly, the multiple reflected and refracted traveling waves at line terminals as well as fault point are calculated by building propagation coefficient matrices. Secondly, the transfer function between the converter equivalent source and the traveling wave transients is built, then the fault current and voltage are calculated by compensating multiple traveling waves with corresponding control response. Compared with existing methods, the proposed method can calculate long-period traveling waves in a simplified way, and implement more accurate analysis for the converter response caused by the basic control strategy and the fault control strategy. An LCC-MMC HVDC system is built based on PSCAD/EMTDC, and the simulation cases are carried out to verify the correctness and superiorities of the proposed method. Finally, the impact of control response on the performance of traveling-wave-based directional protection is evaluated by the proposed fault analysis method.

A novel transient thermal circuit model of buried power cables for emergency and dynamic load

In order to improve the utilization rate of cable while ensuring safety and reliability, accurate and rapid evaluation of transient temperature rise of directly buried power cables is useful to improve the management level of dynamic capacity increase and emergency load conditions. Since the existing thermal circuit model is relatively complex or not very accurate, an equivalent three-branch transient thermal circuit model is presented for the complex cable structure and heat dissipation environment based on the uniqueness of the temperature field. Considering the electric circuit similarity, the transient analysis method of the centralized parameter network in the circuit is used to establish the transient adjoint model of the thermal capacity branch, provide the node conduction matrix of the transient thermal circuit model, and write the node temperature rise equation as a function of the node heat flow. By comparing the solution of the thermal circuit model with the finite element results, and the genetic algorithm is used to optimize and obtain the equivalent thermal resistance and thermal capacity parameters of the transient thermal circuit model. The comparison of finite element calculation results proves that the proposed three-branch transient thermal circuit model is more accurate than the two-branch thermal circuit model. Compared to the traditional all-part thermal circuit model, the three-branch model can be rapidly solved and easily applied in engineering.

Hybrid Method for Predictive Transient Nonlinear Analysis of a Radiative-Convective Moving Porous Fin with Temperature-variant Internal Heat Generation

In this work, Laplace transform-Legendre-wavelet collocation method is adopted for a semi-numerical analysis of predicting transient nonlinear behaviour of a radiative-convective fin with temperature-variant internal heat generation. The verification of the results of the hybrid method shown good agreements with the direct numerical and approximate analytical method s in previous works. Parametric analysis depicts the significance of the model parameters in a way that it is found that as the convective-conductive and radiative-conductive parameters increase, temperature distribution decreases in the extended surface. The thermal distribution is augmented in the passive device as thermal conductivity is amplified. At the different positions in the fin, the temperature is enhanced as time progress. The semi-numerical solution provides a very good platform for the predictive analyses of the extended surfaces.

A dynamic fracture model combining with Laplace transform and synchronous iteration method for transient behavior analysis of a four-zone system

A robust and generic semi-analytical model with the capture of dynamic fracture behaviors under long-term pumping rate condition is developed for transient flow analysis in this four-zone system. To characterize the variations of fracture length, the improved pressure-dependent dynamic fracture factor is introduced and incorporated into this model. The Laplace domain with predetermined time discretization and synchronous iteration technique are deployed to obtain the solutions of pressure and pumping rate with the least computational burden. Meanwhile, the stability and convergence of this semi-analytical model can be met within the discrete time. Furthermore, the pressure and pumping rate solutions of this model under the static fracture condition are in good agreement with those of the constant length fracture, which verifies the reliability of this model.The dynamic fracture model with the four -zone system develops five flow stages on the dimensionless pressure and its derivative curves: fracture bilinear flow, dynamic fracture flow, inner area linear flow, transitional flow and boundary-dominated flow. The dynamic fracture behavior is mainly reflected in the obviously positive upwards and pressure derivative curve presents a higher than unit slope. Moreover, the significant decrease of flow rate indicates that fracture closure could result in a rapid decline in pumping rate, which might be the reason why the pumping rate decrease quickly during the long-term pumping period. As the shrinkage coefficient increases, fractures are closed from abruptly to gradually, and typical signatures of fracture closure may be hidden if the shrinkage factor is too small, which may be caused by the instantaneous pressure depletion in the fractures. With the decrease of retained fracture coefficient, there is greater in the positive upward of transient pressure behavior and a lower in pumping rate. As a result, the flow rate will be seriously overestimated if the fracture closure is not considered especially for the tight formation.

Transient Fault Analysis Method for VSC-Based DC Distribution Networks With Multi-DGs

Flexible direct current (dc) distribution networks are the development trend for the future distribution system. However, the protection and control of these networks are vulnerable to complicated dc faults, accurate fault analysis is required. In this article, we propose a three-stage transient fault analysis method to improve the accuracy of fault characteristic calculation for the voltage source converter based dc distribution network with multi distributed generators, which can unify and simplify the calculation process of different transient fault stages. An impedance parameter decoupling approach is proposed based on the dc line parameters, which can avoid the influence of the coupling impedance on fault response. The decoupled equivalent fault circuits are established for accurate fault analysis with flexibility and independence. In addition, a three-stage fault analysis is proposed, which is able to unify the calculation process. Finally, numerical simulations based on PSCAD/EMTDC have been carried out, which well demonstrates the effectiveness of the proposed impedance decoupling approach and the accuracy of the proposed method for fault analysis. Compared with the traditional fault analysis without decoupling, the proposed method stands out the conciseness and correctness.

Structure-Informed Graph Learning of Networked Dependencies for Online Prediction of Power System Transient Dynamics

Online transient analysis plays an increasingly important role in dynamic power grids as the renewable generation continues growing. Traditional numerical methods for transient analysis not only are computationally intensive but also require precise contingency information as input, and therefore, are not suitable for online applications. Existing online transient assessment studies focus on the determination of post-contingency system stability or stability margin. This paper develops a novel graph-learning framework, Deep-learning Neural Representation or DNR, for online prediction, of the time-series trajectories of the system states using initial system responses that can be measured by phasor measurement units (PMUs). The proposed DNR framework consists of two sequential modules: a Network Constructor that captures network dependencies among generators, and a Dynamics Predictor that predicts the system trajectories. The key to improved prediction performance is the introduction of the spatio-temporal message-passing operations into graph neural networks with structural knowledge. Its effectiveness and scalability are validated through comparative studies, demonstrating the prediction performance under different contingency scenarios for systems of different sizes. This framework provides a solution to online predicting post-fault system dynamics based on real-time PMU measurements. Additionally, it can also be applied to facilitate the offline transient simulation without simulating the entire trajectories.

Effect of vulcanization on deformation behavior of rubber seals: Thermal–mechanical–chemical coupling model, numerical studies, and experimental validation

Vulcanization molding has a significant impact on dimensional changes of rubber seals. Numerical analysis of this process can improve dimensional accuracy of molded sealing products. In this study, a stress–strain relationship model that considers thermal expansion, cold contraction, and shrinkage caused by a crosslinking reaction under the constraint of a mold boundary was established, a transient analysis method for thermal–mechanical–chemical coupling of the process from rubber seal vulcanization to mold opening was developed, and dimensional changes of the rubber seal in the mold and after cooling were predicted. Results calculated by the model were verified by the production of typical seals. The influences of vulcanization process parameters on changes in molded seal size were numerically analyzed. The numerical results showed that the dimensional shrinkage ratio increased nonlinearly from 3.2 % to 3.8 % when the vulcanization temperature increased from 165 to 185 °C, i.e., an increase of 0.206 % for every 1 % increase in shrinkage caused by the vulcanization reaction. These research results can be utilized in the design of vulcanization molds for high-precision rubber seals.

A Promising Crystalline KCl: Electrolyte Material for Studying the Electrochemical Properties of Cerium on Liquid Indium Electrodes

Potassium chloride crystals are good conductors in the UV to mid-infrared broadband and can be widely used as materials for high-power CO2 lasers. However, the most important use of potassium chloride crystals has been overlooked; their stable chemistry and wide electrochemical window allow them to form molten eutectic salts with other chlorides for the dry reprocessing of spent fuel. The aim of this work is to investigate the electrochemical properties of the actinide substitute cerium metal on liquid indium media in order to provide basic data for further realization of lanthanides (Ln)/actinides (An) separation. In this paper, we investigated the electrochemical behavior of 3LiCl-2KCl-CeCl3 melt at liquid metal media indium (In) electrode using various transient electrochemical analysis methods, such as cyclic voltammetry, square wave voltammetry and open circuit potential technique. The quasi-equilibrium potentials of Ce3+ at different temperatures on the liquid metal In electrode were determined. On the redox process, the reaction kinetics of the oxidation–reduction process in the 3LiCl-2KCl-CeCl3 system is studied. It was determined that the reduction of Ce3+ at the liquid metal In electrode is an irreversible single-step process with three electron transfers. The relationship between the diffusion coefficient and the reduction process of Ce3+ ions on liquid metal indium electrodes at different temperatures was determined. The expression for the diffusion coefficient and temperature of Ce3+ at the liquid metal indium electrode is: lnD = 1.43 − 7974.69/T.

Hybrid domain-based fast transient thermal evaluation method for power semiconductor modules in EV motor drive

Performance screening and reliability evaluation of electric vehicle (EV) motor drives require fast and precise thermal evaluation of power devices in both steady-state and transient-state analysis. In this paper, a hybrid-domain calculation method is proposed to fulfil the requirement. Firstly, the matrix form model is selected by characterizing the thermal response of an EV module. To quantitatively investigate the speed of different calculation methods, a generalized calculation burden evaluation is conducted based on counting the number of algebraic operations. Both the steady-state and transient-state scenarios for EV motor drives are considered. Accordingly, a hybrid calculation method for transient analysis is proposed by combining the advantages of time-domain and frequency-domain methods. Its advantage is validated by evaluating the elapsed time for a real case. Since numerous evaluation points are required for the performance screening of converters at the early design stage, the proposed method accelerates the thermal evaluation process without reducing the accuracy.

Effect of Temperature on the Fatigue Life Assessment of Suspension Bridge Steel Deck Welds under Dynamic Vehicle Loading

The present study proposes a novel fatigue life prediction considering the temperature load, which may be neglected in the traditional assessment of suspension bridge steel deck welds under dynamic vehicle load. Vehicle fatigue, pavement temperature, and temperature gradient models are developed based on the test data from the weight-in-motion system, U-rib welds, pavement temperature, and environment temperature. The U-rib-to-deck and U-rib-to-U-rib welds fatigue stresses are obtained considering both vehicle and temperature loads with transient analysis method in ANSYS package. Then, the temperature gradient fatigue stress spectra are calculated. After that, the fatigue life of two weld types is predicted considering the coupled vehicle-temperature loads. The results indicate that the fatigue stress varies linearly with the temperature of the asphalt concrete. The effect of the temperature on the weld’s fatigue life decreases as the distance increases between the welds and the pavement. The dynamic vehicle load results in a higher fatigue stress than the temperature gradient, indicating that the vehicle load contributes mainly to the bridge’s fatigue damage. Finally, it is calculated that the fatigue damage of two weld types is magnified 5.06 and 1.50 times when the temperature effect is considered after 100-year service of Nanxi Yangtze River Bridge.

Variable speed induction motors’ fault detection based on transient motor current signatures analysis: A review

Induction motor is a major component in the industrial sector. It is experiencing great development concerning size, market share, and technological design. Any sudden failure in this element may lead to great damage. Condition monitoring is a fast emerging technology for the online detection of induction motor incipient faults. It avoids unexpected failure of a critical system, by increasing the life expectancy of the concerning elements while reducing operation and maintenance costs. This paper presents the condition monitoring techniques used with these machines, focusing on the Transient Motor Current Signatures Analysis method that has proven its effectiveness in diagnosing faults of electrical rotating machines, gathering a review on the most important applications that can be used with this technology, and how to process these signals to find out the type and cause of the fault. What distinguishes this paper is that it focuses on applications with variable speeds, so two promising techniques that will be effective in non-stationary signals frequency estimation are presented, which are the Adaptive Notch Filtering method and the Adaptive-Observer approach. Challenges and future goals are also discussed to guide researchers wishing to delve into this field.

The influence of different orientations and ventilation cases on temperature distribution of the car cabin in the hot soak

Thermal discomfort, fuel wastage, health risks, and the death threat of passengers/infants due to the hot soak of car cabin is a hot spot topic all the time. Therefore, the transient analysis method is used to study the distribution of the heat soak temperature in the passenger compartment under different orientation. Besides the research analyzed the effects of four ventilation cases on the driver and rear infant. The results show that both of the driver and infant are subjected to the lowest heat load while the vehicle parked outdoors is facing east at 14:00 and the air temperature around the driver is about 52 °C. The roof ventilation is a effective energy conservation ventilation way for both of driver and infant, as there is the most heat removal efficiency(0.471) and the best cooling effect. The head temperature of driver and infant in roof ventilation is at least 7 °C and 3 °C lower than the other three cases. In addition, the seats ventilation is a better heating way for driver than other ventilation cases, because the air temperature is more even and can be heated to 26.5–29.2 °C for the driver.

МОДЕЛЬ АВТОКОЛЕБАТЕЛЬНОЙ ЦЕПИ ДЛЯ ТЕСТИРОВАНИЯ МЕТОДОВ ЧИСЛЕННОГО АНАЛИЗА ПЕРЕХОДНЫХ ПРОЦЕССОВ В SPICE-СИМУЛЯТОРАХ

At present time the problem of developing methods for numerical analysis of RF circuits in thetime domain remains actual because the known Gear and trapezoidal methods used in SPICE simulatorshave a number of significant disadvantages. To evaluate the effectiveness of new numerical methods,special test problems are needed to determine the accuracy of methods in various operating modes.Numerical analysis of self-oscillating circuits in the time domain offers the most difficulties for circuitsimulation programs (SPICE-simulators) since models of self-oscillating circuits can be both oscillatoryand stiff simultaneously. The aim of this work is to create the model of a self-oscillating circuit that allowsto quantify the accuracy of numerical methods. In accordance with the aim, the following problemsare solved: the features of the numerical analysis of classical self-oscillators in SPICE-simulators areinvestigated; the generalized mathematical model of self-oscillating circuits is described; the universalcircuit model of self-oscillating circuits for SPICE-simulators is presented; the quantitative accuracyassessment of numerical methods of transient analysis in SPICE-simulators was carried out. The modelproposed in this paper makes it possible to determine the relative errors of numerical methods in theharmonic oscillations mode, in the relaxation oscillations mode, as well as in the «mixed» mode, whenthe circuit response contains both exponential components with different rates of change and quasiharmoniccomponents. The obtained results confirm the high accuracy of the trapezoidal method in themode of harmonic oscillations, and the Gear method in the mode of relaxation oscillations. The relativeerrors in determining the amplitude of oscillation using these methods for the corresponding operatingmodes do not exceed 3%. At the same time, in the «mixed» mode, the relative errors in determining theamplitude of oscillation for both methods can reach 100%, that confirms the need to use additionaloptions or special methods of numerical analysis in SPICE-simulators.

DC fault current approximation and fault clearing methods for hybrid LCC-VSC HVDC networks

The DC-side fault analysis of Line commutated converter based high voltage direct current (LCC-HVDC) and Voltage source converter based high voltage direct current (VSC-HVDC) networks has been studied by most researchers and achieved fruitful results. However, the traditional fault analysis method does not consider in detail the change process of the trigger angle of the LCC converter station and the AC current feeding of the VSC converter station caused by the control strategy. Therefore, this paper proposes a new DC side fault transient analysis method suitable for hybrid multi-terminal HVDC transmission networks. In addition, considering the deficiency that the active fault current suppression method only relying on the control strategy cannot fundamentally clear the DC fault, this paper proposes a new Z-source current-limiting circuit (ZCLC) with reference to the topology of the Z-source dc circuit breaker (DCCB). Then, ZCLC will cooperate with DCCB to improve the fault clearing capacity of the whole system. Firstly, this paper establishes the equivalent Laplace transform model of the three-terminal LCC-VSC-VSC, and analyzes the short-circuit current expression on both sides. Then, the change process of trigger angle is approximately linearized by the least square method, which obtains a new expression of fault transient current on the LCC side. Similarly, the composition of AC current fed to DC side is deduced by using the commonly used inner-loop PI controller model, which also obtains a new expression of fault transient current on the VSC side. Secondly, referring to the traditional crossed-type Z-source DCCB, series-type Z-source DCCB, and parallel-type Z-source DCCB, this paper also proposes a new ZCLC and analyzes its working principle and parameter design. Then, the newly proposed ZCLC is combined with DCCB to be applied to the hybrid multi-terminal HVDC network. Finally, the simulation results based on Matlab/Simulink verify the effectiveness of the fault analysis and passive fault clearing methods, and the semi-physical experimental platform based on PLECS/RTbox verifies the superiority of the new ZCLC.

Study on Dynamic Characteristics of Single-Phase Grounding Fault of 1000 MW Hydro Generator under Different Grounding Modes

The continuous operation of 1000 MW large hydro generators in China is of great value to the implementation of “double carbon strategy” and power grid safety. However, with the continuous increase of single unit capacity of the hydro generator, the problems of unit fault grounding current and neutral point voltage drift become more and more prominent, and the traditional analysis methods cannot accurately obtain the fault dynamic data. Therefore, starting from the neutral point grounding mode of the large hydro generator, taking a 1000 MW hydro generator as the research object, this paper establishes the single-phase grounding fault model under the condition of three-phase parameter asymmetry of stator winding and analyzes the dynamic characteristics of fault current, transient overvoltage, and neutral point voltage drift under different grounding modes by using transient analysis method; the influence of frequency offset on neutral voltage drift and the dynamic characteristics of single-phase grounding fault of the large hydro generator under different grounding modes are also obtained. Finally, according to the analysis results, the selection and optimization method of neutral grounding parameters are proposed, which provides a reference for the selection of neutral grounding mode and the research of protection strategy of the large hydro generator.

Three Technical Challenges Faced by Power Systems in Transition

In the 21st century, the worldwide concern about global warming has forced energy to transform in the direction of low-carbon and non-carbon. The utilization of renewable energy is developing rapidly, which makes the non-synchronous generator sources become the main part of the newly added power sources. Based on the fundamentals of AC power grid operation, this paper describes three technical challenges faced by the power system in transition: the inadequacy of the classic synchronization stability concept in representing the new synchronization connotation of AC power systems with large proportion of non-synchronous generator sources; the inapplicability of the electromechanical transient analysis method in analyzing the generalized synchronization stability; and the wideband resonance instability caused by negative resistance of power electronic equipment. The decisive factors for maintaining the generalized synchronization stability, the countermeasure to solve the inapplicability of the electromechanical transient analysis method and a systematic approach to tackle the broadband resonance instability are proposed in the paper.