Current Overload Research Articles

Prediction and policy: Do empirical gross calorific value prediction help reduce coal testing overload?

The gross calorific value (GCV) of coal is pivotal in shaping policies across various sectors of the Indian economy. It plays a crucial role in classification and valuation of coal and is a major factor in determining electricity tariffs charged by thermal power plants. With coal production escalating year-on-year to meet India's increasing electricity demand, there is significant rise in coal testing activities along the pit-to-power supply chain at multiple points and by multiple testing agencies often driven by sector-specific policy requirements. While laboratory testing accurately determines GCV, it is costly and time-consuming due to the reliance on expensive equipment and skilled personnel. Global researchers have previously devised a plethora of empirical formulae predicting GCV based on its correlations with easy-to-measure properties like moisture and ash content. However, the applicability and utility of these formulae to the prevalent policy matrix of coal and power sector remain to be explored. The introduction of independent third-party assessment of coal quality by Coal India Limited in 2016 has generated a vast dataset of coal sample-test results, offering an opportunity to reassess existing empirical formulae, test their alignment with existing policies, and explore possibility of a unified, region-neutral formula for rapid GCV prediction with a special focus on alleviating the current overload in coal testing.

Pengaruh Ukuran Kawat dan Jarak Alur Stator Terhadap Nilai Arus Starting Motor Induksi 3 Fasa

<p><strong>The use of electric motors in industry often experiences damage caused by several things, including high <em>starting</em> current surges, overload or full load, loss of one phase in the electric motor, and other causes of damage to the 3-phase motor. The main problem that occurred in this research was damage caused by high <em>starting</em> currents, where in the case study many 3-phase motors were used to drive factory machines. The use of 3-phase motors to drive factory machines is often damaged by unstable currents in the machines. This is because the time and workers for monitoring are very minimal and the materials for repairing machines are inadequate. In this way, the solution for repairing a 3-phase motor is to replace and rewind the damaged motor so that it can be used again. This research aims to find a solution on how to reduce high <em>starting</em> currents in 3-phase motors by utilizing the influence of replacing damaged induction motor components as well as repair methods used in <em>starting</em> when <em>rewinding</em> 3-phase motors. The research results from the groove distance with a wire size of 0.90 mm showed that the groove distance of 9, 9, 8 was 29.3, and at a distance of 10, 10, 10 it had a current of 31 A with no-load testing and recommended groove distances of 10, 10, 10. Next, testing wire sizes of 0.75 mm and 0.90 mm with distances of 10, 10, 10, and 9, 9, 8 without load obtained 26.1 A and 27.4 A while 0.90 mm was 30, 7 A and 28, 1 A. The load was 43.5 A and 43.9 A, while 0.90 mm was 51.3 A and 49.3 A. From the test results, the largest current decrease was at a distance of 10, 10, 10 with a wire size of 0.75 mm. </strong></p><p><strong>Keyword - <em>3 Phase Induction Motor, Groove Spacing, Starting, Wire Size.</em></strong></p>

The effect of overload current on the thermo-oxidative decomposition behavior of polyvinyl chloride insulated wires investigated by TG-FTIR technique

The effect of overload current on the thermo-oxidative decomposition behavior of polyvinyl chloride insulated wires investigated by TG-FTIR technique

Contribution to the determination of the effect of magnetic storms on the electric power transmission system

Abstract When a magnetic storm hits a power transmission system, quasi-stationary geomagnetically induced currents (GIC) are generated in the high-voltage part of the system. These currents cause semi-saturation of the magnetic circuits of power transformers, which induces current overload in their high-voltage windings and subsequently thermal overload, which can lead to system failures. This rather complex phenomenon was described in [11] by a system of nonlinear differential equations and subsequently solved. This very challenging method is replaced in the present work by a simple approach. It allows not only predicting the imminent danger of system collapse, but gives transformer designers valuable information on how they can counteract this danger.

A Stabilization Control Strategy for Wind Energy Storage Microgrid Based on Improved Virtual Synchronous Generator

In high-penetration renewable-energy grid systems, conventional virtual synchronous generator (VSG) control faces a number of challenges, especially the difficulty of maintaining synchronization during grid voltage drops. This difficulty may lead to current overloads and equipment disconnections, and it has an impact on the security and reliability of the system, as well as limiting the dynamic reactive power support capability of the system. To solve this problem, in this study, a wind–solar hybrid power generation system is designed with a battery energy storage device connected on the DC side, and proposes a low voltage ride-through (LVRT) control strategy for the grid-connected inverter based on an improved VSG. The control strategy employs an integrated current limiting technique combining virtual impedance and vector current limiting to ensure that the VSG exhibits good dynamic power support characteristics during symmetrical faults by adjusting the setpoint value of reactive power. At the same time, it maintains the synchronization and power angle stability of the VSG itself to achieve the goal of LVRT. Simulation results show that the proposed control strategy can effectively suppress the renewable power fluctuations (about 30% reduction in fluctuations compared to the conventional strategy) and ensure the safe and reliable operation of the renewable energy sources and VSGs during grid-side faults. In addition, it provides a given reactive power support and stable grid voltage control (voltage dips reduced by about 20%), which significantly enhances the LVRT capability of the hybrid wind–solar-storage generation system.

Analysis of the extent of heavy vehicle overloading on Namibian trunk roads and evaluation of the effectiveness of existing mitigation measures

Overloading of heavy vehicles reduces pavement life and increases pavement life cycle costs. As part of Namibia's strategy to control heavy vehicle overloading on the road network, weighbridge facilities have been constructed at strategic locations on primary routes (trunk roads). The study analysed the extent of heavy vehicle overloading on Namibian trunk roads, as well as the effectiveness of existing overloading mitigation measures. The dataset comprised heavy vehicle loading information from the year 2015 to 2019, from ten static weighbridge facilities. The parameters investigated include overloading magnitude, the effect of overloading on road pavement life, and the effectiveness of current overload mitigation measures. The results showed that 13.3% of the vehicles weighed were overloaded, with a compounded decrease in overloading of approximately 0.5% per annum. Despite the overloading decrease, the study found that the estimated road service life was reduced by as much as nine years over the study period. High levels of weighbridge avoidance and poor stakeholder coordination in mitigating overloading were identified. The study recommends deploying high-speed weigh-in-motion systems, an increase in fines charged for overloading offenses, and developing a demerit point-based system for habitual offenders to strengthen mitigation measures.

Coordinated, Centralized, and Simultaneous Control of Fast Charging Stations and Distributed Energy Resources

The growing penetration of fast charging stations (FCSs) to electric vehicles (EVs) and distributed energy resources (DERs) in the electrical power system brings technical issue changes in the voltage profile throughout grid nodes and feeder current overload. The provision of ancillary services by DERs and FCSs arises as an appealing solution to reduce these adverse effects, enhancing the grid hosting capacity. The control of microgrids is essential for the coordinated implementation of these services. Although microgrid control is widely applied to DERs, few studies address the coordinated control of DERs and FCSs to obtain benefits for the electrical power system. This paper proposes a coordinated and simultaneous control of DERs and FCSs based on the power-based control (PBC) strategy, efficiently exploiting FCSs in a microgrid model previously unaddressed in the literature. The results show that, with the coordinated control of DERs and FCSs, the control of the power flow in a minigrid (MG) is achieved both in moments of high generation and in moments of high load, even with the maximum operation of DERs. This method allows for the maintenance of voltage levels within values considered acceptable by technical standards (above 0.93 pu). The maintenance of voltage levels is derived from reducing the overload on the point of common coupling (PCC) of the minigrid by 28%, performing the peak shaving ancillary service. Furthermore, the method allows for the control of zero power flow in the PCC of the minigrid with the upstream electric grid in periods of high generation, performing the ancillary service of valley filling. The method performs this control without compromising vehicle recharging and power dispatch by DERs.

Model of Static Destruction of a Copper Conductor during Current Overload

Model of Static Destruction of a Copper Conductor during Current Overload

Lactate administration improves laboratory parameters in murine models of iron overload

AbstractCurrent iron overload therapeutics have inherent drawbacks including perpetuated low hepcidin. Here, we unveiled that lactate, a potent hepcidin agonist, effectively reduced serum and hepatic iron levels in mouse models of iron overload with an improved erythropoiesis in β-thalassemic mice.

The Specifics of PTC Thermistor Applications for Limiting Surge Currents

This paper investigates the possibilities of limiting emergency short current pulses by using materials with a positive temperature coefficient. A computational model and method for simulating this process were proposed. Barium titanate was considered a promising material for current-limiting devices due to its low cost, ease of manufacturing and autonomy. The current-limiting properties of a PTC thermistor device were estimated in relation to a significant pulse current overload (10 ms). The value of taking into account the varistor effect when modeling energy dissipation by a PTC thermistor is experimentally demonstrated. The results of the experiment were used in the development of computer models of the current-limiting properties of PTC thermistors. A method for taking into account the varistor effect in the developed models is proposed. It is noted that in order to increase the accuracy of the calculation, it is important to take into account the heat transfer between the PTC thermistor and its contact system. It is also shown that this heat transfer is capable of creating a significant longitudinal temperature gradient inside the PTC thermistor, which creates a high level of thermal stress and leads to mechanical failure. Destruction of this type has been observed during experiments. This research was carried out within the state assignment FSEG-2023-0012.

Analysis of the Magneto-Thermal Bidirectional Coupling Strength of Macro and Micro Integration for Self-Starting Permanent Magnet Hysteresis Synchronous Motors

High-speed permanent magnet synchronous motors (PMSMs) are usually started with the hybrid low-speed open-loop and high-speed closed-loop control mode. However, low-speed open-loop control produces large starting current, or even current overload, resulting in demagnetization and motor damage. Therefore, there is an urgent need to develop a high-speed permanent magnet synchronous motor with self-starting ability at low speed, that is, a permanent magnet hysteresis motor (PMHM). This paper takes the permanent magnet ring hysteresis column rotor structure as the research object. Firstly, the performance of this type of rotor is improved using the micro level of effective layer material AlNiCo, and the mechanical properties of AlNiCo are calculated. Secondly, based on the thick-walled cylinder theory, the analytical model for calculating the strength of the composite rotor considering the temperature effect is deduced, and the tangential and radial stress distribution for each part of the rotor under no-load and load conditions are obtained. Then, the electromagnetic losses and temperature field distribution of the rotor are obtained using the magneto-thermal bidirectional coupling finite element method. Finally, strength of the thermal rotor is analyzed by substituting the temperature rise curve function and AlNiCo parameters at the operating temperature. The comparison of the stress calculation results of the semi-analytical solution and the finite element method showed that the error between both of them is less than 5%, which verified that the semi-analytical solution can accurately analyze the thermal stress distribution of the rotor during high-speed rotation.

Feasibility of using phase-shifting transformers to increase the throughput of interconnected power transmission systems

This paper discusses measures aimed at improving the efficiency of power systems by increasing the capacity of power transmission lines. To that end, a FACTS technology based on a phase-shifting transformer was used. The feasibility of using phase-shifting transformers to increase the throughput capacity of interconnected power transmission systems was investigated by determining the maximum allowable cross-section flows of the United Energy System of the Urals – the United Energy System of Siberia. The studied cross-section included 500 kV transmission lines and the extended 220 kV Nizhnevartovskaya GRES – Tomskaya transit. Calculations were performed for normal and various post-emergency schemes using the RastrWin3 software package. The regulation of phas e-shifting transformer branches and the direction of power flow in the section were taken into account. For the considered cross -section, the use of a phase-shifting transformer was shown to provide for the 220 kV transit operation in a closed mode. This i mproved the reliability of power supply in the region and allowed the maximum allowable overflow to be increased by 35 – 71%. In addition, similar calculations were carried out for the option of strengthening the 220 kV transit through the construction of a parallel 500 kV line. The effect of increasing the capacity of this option was established to reach 20 –35%. The decisive factor limiting the maximum permissible cross-section flows during 220 kV transit short circuit in the normal and reinforced versions was found to be the current overload of the head sections. Recommendations on the preferable use of an open transit mode are formulated. In conclusion, the efficiency of power systems can be improved by increasing the transmission capacity of power lines through the use of phase-shifting transformers. A segment of the Unified National Power Grid of Russia, where such devices are technologically expedient, was identified.

БАЛАНСИРОВКА ФАЗНЫХ НАГРУЗОК В НИЗКОВОЛЬТНЫХ ТРЕХФАЗНЫХ ЧЕТЫРЕХПРОВОДНЫХ СЕТЯХ

The imbalance of phase loads is a natural negative property of a low-voltage three-phase four-wire network due to uneven connection to the phases and the difference in individual consumer demand for electricity. The imbalance of phase loads in the network nodes leads to a decrease in the quality of electricity, overestimated technical losses in the network and to current overloads in one of the phases of power lines. In the paper, balancing of phase loads in the network is performed using a heuristic algorithm based on average hourly readings of loads and voltages readings of consumer smart meters. The effectiveness of the algorithm was evaluated by reducing losses, maximum currents in the phase wires and the neutral wire in a real feeder of the electrical network

Fatigue reliability evaluation of reinforced concrete bridges under stochastic traffic loading based on truck weight limits

To investigate the fatigue reliability of reinforced concrete (RC) bridges under stochastic traffic loading and the effectiveness of limiting the truck load, this study presented an analysis method for evaluating the bridge fatigue reliability under the action of random traffic flows based on truck weight limits. Firstly, a simply RC T-beam bridge was selected as an example to illustrate the presented approach, and the traffic-induced stress spectrum of the tensile rebars in the critical girder of the bridge was obtained. Secondly, based on the collected traffic data from two specific areas, the corresponding random traffic flow was simulated respectively, and then calibrated using the weight limit referring to the current regulation and overload violation rates ( VR) to exclude overweight trucks. Finally, based on the S–N curve from Eurocode 3 and Miner’s cumulative damage model, the effects of violation rate, average daily truck traffic ( ADTT) and truck weight limit ( TWL) on the fatigue reliability index of the bridge were studied. The results show that heavy duty trucks will induce serious cumulative fatigue damage, and degrade the durability of RC bridges, while limiting the truck weight can obviously slow down the reduction of the fatigue reliability index. Both the ADTT and the VR can significantly affect the fatigue reliability of the bridge. More specifically, the bridge fatigue reliability index shows a clear downward trend with the increase in the ADTT and the VR. Furthermore, the performance to satisfy the target fatigue reliability of the bridge was compared between TWL for each type of trucks and unified TWL for all the trucks, and then the unified TWL for all the trucks are determined to ensure the target reliability index of the RC bridge after 100 years’ service life.

A Current-Limiting Scheme for Voltage-Controlled Inverter Using Instantaneous Current to Generate Virtual Impedance

In this paper, a current-limiting scheme is proposed for the voltage-controlled inverter. The method utilizes instantaneous current to quickly activate a resistive fault-current-limiting virtual impedance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FCL</sub> ) to suppress the instantaneous impulse current and steady-state overload current, which can be directly integrated into the existing voltage-type control scheme. When a fault occurs, the inverter can be kept in the voltage control mode without mode switching. After the fault is cleared, it can automatically return to the normal operation mode. The parameter selection method of the current-limiting virtual impedance is analyzed, and the logic criterion for short-circuit fault clearance is presented to realize the automatic startup and exit of the current-limiting virtual impedance. Finally, the RT-LAB hardware in-loop experiment and the single-phase inverter platform experiment prove that the proposed current-limiting scheme can simplify the fault handling process and improve the anti-fault ability of the voltage-controlled inverter.

Auxiliary Circuit Free Maximum Power Efficiency Tracking Scheme for Wireless Motor System With Source-Load Coupling

This paper proposes a real-time maximum power efficiency tracking (MPET) scheme for a series-parallel compensated wireless motor (SP-WM) system, where the system efficiency is maximized based on real-time manipulation of the dc-link voltage. The transient performance of the motor and stability of the dc-link voltage can be improved by series-parallel compensation with higher current overload capacity compared to the series-series one. Compared with the conventional resistive load, the motor drive can be considered as a constant power load (CPL), serving as an adjustable equivalent load resistance. The efficiency curve and resistance adjusting capability of the SP-WM system are investigated under different conditions, which demonstrates the source-load coupling between the motor drive and magnetic coupler. Besides, a dc-link voltage determination (DVBD) method is proposed to ensure the safe operation of the system. The perturbation and observation (P&amp;O) and DVBD are integrated and implemented iteratively in the proposed MPET scheme. The maximum system efficiency can be achieved without an auxiliary circuit under different mutual inductance conditions, which reduces the cost and volume of the system. Finally, the feasibility and effectiveness of the proposed MPET scheme are verified by the experiments. The system efficiency can be increased by up to 4.51&#x0025;.

ANALYSIS OF EMERGENCY MODES OF TRACTION INDUCTION ELECTRIC DRIVE

The operation process of the traction asynchronous electric drive of the rolling stock may be accompanied by the occurrence of emergency modes, which are characterized by current overloads and may lead to damaging power electric circuits or mechanical part of the electric drive. Therefore, studying electromagnetic processes that occur in emergency modes of operation is relevant, in particular, for developing systems aimed at diagnosing and protecting traction equipment. Ukrainian and foreign studies of emergency modes in an asynchronous electric drive were analyzed. The most frequent causes of emergency modes are failures in static converters, therefore it is advisable to conduct an analysis of electromagnetic processes specifically in autonomous inverters. Using Matlab/Simulink software environment a simulation model of the vector control system of the traction asynchronous electric drive with spatial vector pulse width modulation was developed, and the short-circuit modes of the power switch of the autonomous voltage inverter and the disappearance of the supply voltage were simulated. The oscillograms of electromagnetic processes in these modes were shown and compared with the nominal mode of operation. The simulation results show that the analyzed emergency modes, even with a short duration of less than 0.5 s, can lead to significant damage to the electric drive. Both cases lead to significant current overloads: in the case of a short circuit of the power switch, a three-fold excess of the phase current is observed, during recovery after a supply voltage failure, the phase currents increase to the starting level, as well as an almost instantaneous increase in the supply voltage on the input filter capacitor occurs. The Fourier analysis of the phase A current in the above emergency modes shows an increase in the coefficient of nonlinear distortions by 65 %, a decrease in the amplitude of the main harmonic to 60 %, and the appearance of a significant number of subharmonics. In the case of a short circuit, the amplitudes of the subharmonics even exceed the fundamental harmonic. In addition, the process of returning from the emergency mode to normal at the first moment of time was characterized by a reduced moment of resistance (20 % of the nominal), and then by an exit to the nominal parameters.

Entrepreneurs' role overload and empowering leadership: A reciprocal relationship based on conservation of resources.

Role overload is not new, but its increasing prevalence in recent years calls for further research. This study considers empowering leadership as a means of resource investment and proposes that it is exerted by entrepreneurs to reduce their role overload. This study adds clarity by revealing how entrepreneurs' role overload is mitigated via the intermediate mechanism of empowering leadership. Hypotheses are derived from conservation of resources theory. Data were collected from 315 entrepreneurs in China using a three-round questionnaire survey. This study finds that entrepreneurs' previous experience of role overload positively relates to their current empowering leadership behavior and their previous empowering leadership behavior negatively relates to their current role overload, which implies a mediating role of empowering leadership. Specifically, the second stage of the indirect effect of previous role overload on current role overload through empowering leadership is moderated by top management team (TMT) heterogeneity. When TMT heterogeneity is higher, the negative indirect effect is stronger. This study contributes to the idea of positive psychology and extends the scope of conservation of resources theory into the fields of entrepreneurship and leadership.

Normal Zone Propagation and Heating under Current Overload in High-Temperature Superconducting Tapes with Epoxy Coating

Normal Zone Propagation and Heating under Current Overload in High-Temperature Superconducting Tapes with Epoxy Coating

Mental Overload Assessment Method Considering the Effects of Performance Shaping Factors

The assessment of mental overload is essential as mental overload has been proved to be a critical cause of many accidents. Mental overload is affected by various performance shaping factors (PSFs), and harsh PSFs will either increase the task demand or decrease the overload threshold, which is rarely considered in the current mental overload assessment method. This research proposes a VACP-based mental overload assessment model which considers the effects of PSFs. In the VACP model, mental overload can be identified when the sum of the task demand values of every unit task is greater than the given threshold. In human reliability analysis, PSFs are mainly used as weighting factors to modify basic human error probability. In our research, by virtue of the quantitative relationship between human error and mental workload, the weighting factors of PSFs are converted to modify the task demand values and threshold for VACP activities. Furthermore, Bayesian Network (BN) is used to model the influence of PSFs and to calculate the probability of mental overload. The proposed method is applied to an accident involving a helicopter crash that occurred in Maryland, and the results show that, in comparison with the VACP method, the proposed method can more effectively identify the state of mental overload and provide a more rational explanation of the process of the accident.