Power Systems
M. Moradi; R. Havangi
Abstract
The rail vehicle dynamics are greatly impacted by the different forces present at the contact region of wheel and rail. Since the wheel and rail adhesion force is the key element in maintaining high braking and acceleration performance of rail vehicles, continuous monitoring of this factor ...
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The rail vehicle dynamics are greatly impacted by the different forces present at the contact region of wheel and rail. Since the wheel and rail adhesion force is the key element in maintaining high braking and acceleration performance of rail vehicles, continuous monitoring of this factor is very important. Damage to the infrastructures and lack of transportation convenience are the most obvious consequences of improper levels of adhesion force. Adhesion modeling is a time consuming task. In addition, due to the difficulties exist in directly measuring the adhesion force, the use of alternative methods in which state observers are adopted has attracted much attention. The selection of the primary model of the studied system and the ability of the selected estimator have a significant effect on the success of the proposed approach in estimating the variables. In this paper, the dynamics of the wheelset is simulated in the presence of irregularities that can be encountered in the railroad. Estimation of wheel-rail adhesion force is done indirectly by nonlinear filters as estimators and their accuracies in the estimation are compared to identify the better one. Meanwhile, inertial sensors (accelerometer and gyroscope) outputs are used as measuring matrix and employed to simulate actual situation and evaluate the estimators performances. To check the accuracy and ability of the estimators in estimating states and variables, the proposed approache implemented in Matlab.This study introduces an advantageous approach that uses the longitudinal, lateral and torsional dynamics to estimate wheel-rail adhesion force in variable conditions. Experimental results showed high precision, fast convergence, and low error values in variable estimation. Real time knowledge of the contact condition results in proper traction and braking performances. The results of proposed method can lead to decreasing wheel deterioration and operational costs, minimizing high creep levels, maximizing the use of already-existing adhesion, and mproving the frequency of service. It is worth noting that the proposed method is beneficial for both conventional railway transport and automated driverless trains.
Power Systems
A. Yazdaninejadi; M. Akhavan
Abstract
Background and Objectives: Protection of sub-transmission systems requires maintaining selectivity in the combinatorial scheme of distance and direction overcurrent relays (DOCRs). This presents a complex challenge that renders the need for a robust solution. Thereby, the objective of the present study ...
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Background and Objectives: Protection of sub-transmission systems requires maintaining selectivity in the combinatorial scheme of distance and direction overcurrent relays (DOCRs). This presents a complex challenge that renders the need for a robust solution. Thereby, the objective of the present study is to decrease the number of violations and minimize the tripping time of relays in this particular issue.Methods: This study deals with this challenge by using numerical DOCRs which follow non-standard tripping characteristics without compromising the compatibility of the curves. In this process, the time-current characteristics of relays are described in such a manner that they can maintain selectivity among themselves and with distance relays. Therefore, in addition to the second zone timing of distance relays, time dial settings, and plug settings of overcurrent relays, the other coefficients of the inverse-time characteristics are also optimized. The optimization procedure is formulated as a nonlinear programming model and tackled using the particle swarm optimization (PSO) algorithm.Results: This approach is verified by applying on two test systems and compared against conventional methods. The obtained results show that the proposed approach helps to yield selective protection scheme owing to the provided flexibility.Conclusion: The research effectively enhanced selectivity in sub-transmission systems and minimizing relay tripping times through the innovative use of numerical DOCRs and PSO-based optimization.
Power Systems
H. Sahraei; M. Tolou Askari
Abstract
Background and Objectives: With the ever-increasing growth of electric loads, the need for generating electric power grows correspondingly. By considering the limitations of power generation, utilizing novel technologies has gained persistent momentum, one of which is deploying Phase-Shifting Transformers ...
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Background and Objectives: With the ever-increasing growth of electric loads, the need for generating electric power grows correspondingly. By considering the limitations of power generation, utilizing novel technologies has gained persistent momentum, one of which is deploying Phase-Shifting Transformers (PSTs). Among the more important available relays for the transmission lines are Distance Relays. To this end, Distance Relays measure the voltage and current of the transmission line in its final installation location. On the other hand, the existence of Phase-Shifting Transformers on transmission lines alters the voltage and current signals at the relay location. This issue causes the impedance calculated by the relay to differ from its actual value at the fault location. As a result, the relay detects the fault location falsely, or in some cases does not recognize it at all.Methods: The effect of phase shifting transformer on the relay performance of the distances has been investigated in this study. Furthermore, the digital distance relays are modeled in a software environment and its validity is investigated through analytical relationships. Next, the efficacy of the transformer on distance protection is analytically studied. Finally, a new method has been proposed to improve distance relay performance.Results: Results from analysis and modelling shows that the effect of phase shifting transformers in relay-computed impedance has two faces, the first of which is related to the internal impedance of the transformer, while the other regards the serial voltage of the transformer. The latter face is much more influential than the former one. Conclusion: This fact renders the mere inner Impedance of phase-shifting transformer insufficient for using it to eliminate its effect. To this end, a method has been developed in which the voltages of both ends of the phase shifting transformer are measured by the PMUs and then sent to the facility for protecting power system after synchronization. There, this voltage is reduced from the voltage calculated by the relay, which renders the effect of the phase shifting transformer in the impedance calculated by the relay completely eliminated.
