Operator Overloading Research Articles

Identification of transformer overload and new energy planning for enterprises based on load forecasting.

The new energy system constructed by energy storage and photovoltaic power generation system can effectively solve the problem of transformer overload operation in some enterprises. It can not only reduce the cost of electricity, but also realize low-carbon emission reduction. However, due to its low return on investment, the willingness of enterprises to install new energy is not high. In this paper, we first establish a load forecasting model to users whose transformers are overloaded or about to be overloaded, which are potential customers with new energy installation needs. Then, Optimal configuration models of PV and energy storage systems based on nonlinear programming are developed for these potential customers. The optimal installed capacity of the PV energy storage and the optimal charging and discharging strategy for the energy storage system can be obtained. This optimization strategy ensures that the electricity consumption of the enterprise does not exceed the rated capacity, and effectively reduces the enterprise's basic tariff and electricity price to achieve cost reduction and efficiency. Finally, taking a building materials production factory as an example, we obtain the optimal plan for the new energy capacity, as well as the economic benefits of the plan and the specific strategy of energy storage charging and discharging for this factory.

Experimental study on a pump-driven CO2 two-phase thermosyphon loop

In order to better understanding the internal operating principles of liquid pump-driven two-phase thermosyphon loop (LPTPTL) and promote the application of environmentally friendly working fluids, a LPTPTL using CO2 as the working fluid was studied through experiment. Both the operating mechanisms and performance of the CO2 LPTPTL was investigated. It was found that the impact of the pump on the two-phase thermosyphon loop (TPTL) varies significantly across different operation stages. During the oscillatory operation stage, activating the liquid pump eliminated the geyser boiling in the loop and made the TPTL to transition from oscillatory to stable operation. During the normal operation stage, the pump power had little effect on the total thermal resistance of the TPTL. While the system’s EER (Energy Efficiency Ratio) significantly decreased with the increasing pump power. During the overload operation stage, activating the liquid pump helped alleviate overheating or subcooling in the loop. With the pump power increasing from 3.0 W to 18.8 W, the heat transfer limit of the TPTL increased from 1800 W to 3300 W, while the system’s EER decreased from 600 to 176. This study proves the feasibility of CO2 LPTPTL, and provides theoretical guidance for its real application.

Automatic Current Limit Strategy for LLC DC-DC Converter for Overload Operation

Automatic Current Limit Strategy for <i>LLC</i> DC-DC Converter for Overload Operation

Effect of electric field on bubble generation and dissolution characteristics in oil–paper insulation

AbstractThe interturn paper insulation of oil‐immersed power transformer windings, under the combined influence of electric fields, moisture, and conductor heating, will produce bubbles, which pose a significant threat to the insulation system. However, there is limited research on the characteristics of bubble evolution in oil–paper insulation under the influence of electric fields and the subsequent dissolution process. Based on the continuous observation of bubble size using electron microscopes, experimental and theoretical investigations into the formation and dissolution of bubbles under electric field conditions are presented. The effects of different field strengths on bubble evolution and dissolution characteristics were studied. The results showed that the electric field promoted both the generation and dissolution of bubbles, with a more pronounced effect observed at higher field strengths (below partial discharge (PD) inception electric field, hereafter referred to as PDIE). However, when the field strength exceeded PDIE, the bubbles tended to shrink and gradually increase in size. The changes in bubble volume were related to not only gas diffusion but also oxygen consumption and fault gases generation due to PD. A better understanding of the formation and dissolution characteristics of bubbles under varying field strengths is achieved. Furthermore, it also provides a reference for assessing the risk of bubble generation and conducting bubble‐related fault diagnosis during the overload operation of oil‐immersed power equipment.

Optimal operation of pumped storage power plants with fixed- and variable-speed generators in multiple electricity markets considering overload operation

This work studies the optimal operation of pumped storage power plants with fixed- and variable-speed generators in different electricity markets. This paper extends the state of the art by systematically considering the detailed plant behavior for heterogeneous pumped storage power plants and the possible short-term electrical overload operation. The Day-Ahead, ancillary service, and Intraday markets are studied in the first part by developing a mixed integer nonlinear problem (MINLP). The results demonstrate that variable-speed units, especially if equipped with doubly-fed induction machines (DFIMs), yield the highest profit, particularly in the presence of automatic Frequency Restoration Reserve (aFRR). The proposed optimization of the Intraday market shows that the total profit of the Day-Ahead, Ancillary services, and Intraday markets are the highest in the case of variable-speed units with aFRR, where it might be a drawback offering Frequency Containment Reserve. Finally, a robust optimization-based bidding curve generation strategy is developed in the last step. The strategy allows the plant to operate with high profits under price prediction uncertainties and enables optimal reservoir management. The developed optimization tasks and the bidding curve generation strategy also exhibit shorter computation times than the state-of-the-art strategies.

Heat Transfer Characteristics of an Electric Motor with Oil-Dripping Cooling under Overload Conditions

The continuously increasing energy density of electric motors to match the performance of electric vehicles with internal-combustion-engine vehicles demands an advanced cooling strategy. Direct dripping/spray cooling is one of such potential cooling strategies to replace the conventional cooling method for achieving the desired thermal management of next-generation electric motors. In the present work, the heat transfer characteristics of an electric motor with oil-dripping cooling were experimentally investigated considering overload operating conditions. An experimental set-up comprising a 15 kW electric motor and an oil-dripping cooling system was developed. The experimental data were used to evaluate the maximum temperature, heat transfer coefficient and power consumption under the influence of a dripping hole diameter (2 mm, 3 mm, 4 mm), oil flow rate (8 LPM, 12 LPM, 16 LPM) and overload operating power (8.28 kW, 12.05 kW, 14.21 kW). The symmetrical oil distribution over the electric motor and the superior heat transfer from the electric motor to the oil was achieved when the oil-dripping cooling system was designed with the combination of a 4 mm dripping hole diameter and a 12 LPM oil flow rate. The combination of the 4 mm dripping hole diameter and 12 LPM oil flow rate showed the lowest maximum temperatures of 31.9 °C and 46.3 °C for electric motor under overload operating powers of 8.28 kW and 14.21 kW, respectively. In addition, the highest heat transfer coefficient of 7528.61 W/m2-K and lowest power consumption of 18.07 W were achieved for the oil-dripping cooling system with the combination of a 4 mm dripping hole diameter and 12 LPM oil flow rate. The best combination of the operating parameters is proposed for developing the oil-dripping cooling system that enables superior heat transfer characteristics and, thus, an enhanced thermal management of electric motors under overload conditions.

Flow Characteristics Analysis of a 1 GW Hydraulic Turbine at Rated Condition and Overload Operation Condition

Flow stability is extremely important for hydraulic turbines, especially for 1 GW hydraulic turbines, and has a strong impact on mesh stability. However, turbines often operate under non-design conditions, and current research on this aspect is still lacking. So a model of the fluid domains of a high-quality installed 1 GW Francis turbine was established to investigate the flow characteristics of the turbine and fluid domains. CFD simulations of a 1 GW Francis turbine under rated load and overload operation conditions were performed. According to simulation results, when the turbine is under the overload operation condition, the internal flow stability of the 1 GW hydraulic turbine can be obviously different from that of the rated load. In the overload condition, the flow field is more turbulent and a large number of vortices are generated in the draft tube, resulting in significant changes in pressure, flow rate, and output. In order to improve calculation accuracy, a pure clearance model containing only clearances and pressure balance pipes was established. The results of the full flow channel and pure clearance were compared. It was found that under the rated operating condition and the overload condition, compared with the pure clearance model, the axial force of the runner calculated by the full flow channel model is approximately 2–7% biased, the radial force is biased by approximately 7–8%, and the leakage flow is smaller.

AUTONOMOUS MOBILE ROBOT WITH HYBRID PEM FUEL-CELL AND ULTRACAPACITORS ENERGY SYSTEM. DEDALO 2.0

This paper presents a hybrid configuration combining a hydrogen fuel cell and ultracapacitors to create an energy storage system. Hybrid topology is constructed using a SEPIC converter, which connects the fuel cell with the DC bus whereas a bidirectional Buck-Boost converter links the ultracapacitors group with the DC bus. The main aim is to increase the efficiency of the hybrid power system applied about an autonomous mobile robot. An active Fuel Cell voltage control strategy is presented to manage the power flows. In addition, the overall efficiency of the proposed hybrid power system at overload operation is higher than the conventional one. In this paper, an autonomous mobile robot was converted from a conventional lead-acid or lithium-ion battery to a hybrid PEM Fuel-Cell and ultracapacitors as the power source. The integration of UCaps as element of energy storage on the robot was studied with the aim to improve the energetic solution

Comparative Evaluation of Three-Phase Three-Level GaN and Seven-Level Si Flying Capacitor Inverters for Integrated Motor Drives Considering Overload Operation

Comparative Evaluation of Three-Phase Three-Level GaN and Seven-Level Si Flying Capacitor Inverters for Integrated Motor Drives Considering Overload Operation

Investigation of transients in asynchronous generators used in microhydroelectric power plants

In this article, a study of transients in autonomous asynchronous generators used in microgenerators is carried out. This article analyzes the transients occurring in an asynchronous generator by starting an asynchronous motor by exciting an asynchronous generator using capacitor elements of reactive power consumption. To start the asynchronous generator, mechanical energy is supplied to the shaft of the asynchronous motor at a speed 5-10% higher than the nominal number of revolutions, after which the asynchronous motor starts working in generator mode and generates electricity. To launch the CASSY Lab program, the electrical parameters of an asynchronous generator were considered, as well as transients occurring in operating modes by digitally transmitting the parameters of the electrical energy generated by the generator. Starting an asynchronous generator with the help of this program, a real experimental test was also carried out to determine the sinusoidal forms of voltage and current in three phases in the yuksiz, load and overload operating modes. In the course of a real experiment, it was concluded that the improvement of transients occurring in the modes of operation of an asynchronous generator, i.e. transients during the transition from a non-loading mode of operation to a mode of operation with a load, depends on the mechanical energy transmitted to the shaft of an asynchronous generator for grinding.

The role of bionic tubercle leading-edge in a centrifugal pump as turbines(PATs)

The structure of the blade's leading edge significantly affects the centrifugal pump as turbines (PATs) performance. This paper has attempted to investigate the hydraulic performance and pressure pulsations characteristics of PATs with bionic tubercle leading edge impellers by numerical calculation and experiment methods. The results showed that the bionic tubercles structure at the leading edge of the blade does not change the PAT's best efficiency point and helps improve the energy recovery efficiency under all operating conditions, especially with efficiency increased by 6.04 % under the over-load operation condition. Moreover, the bionic tubercles structure at the blade's leading edge can improves the impeller's local flow characteristics and effectively reduces the amplitude of dominant frequency in the main domains of PATs. The maximum reduction amplitude of pressure pulsations in the impeller with the bionic tubercle leading-edge under 0.7Qb, Qb, and 1.3Qb operating conditions is 29.8 %, 23.3 % and 61.1 %, respectively. This research provides a reference for the use of bionic blades to improve the energy recovery efficiency and operation stability of PATs.

Enhancing electrochemical and passive behavior of Ti-based medium entropy alloys in proton exchange membrane water electrolysis anodic environment through Zr and Nb synergy

The synergistic effect of Zr and Nb on the passive behavior of non-equiatomic Zr-Ti-Nb as bipolar plates in proton exchange membrane water electrolysis (PEMWE) was investigated. The experiment revealed that the complementary change of Zr and Nb content resulted in the corrosion resistance sequence of Z40 > Z20 > Z26 > Z34. The primary constituents of the passive films predominantly comprised ZrO2, TiO2, and Nb2O5. The relative content of ZrO2 and Nb2O5 exceeded the atomic proportions of Zr and Nb in the substrate. Additionally, higher potentials had a significant impact on reducing the number of point defects in the passive films while increasing their thickness. The addition of Zr and Nb inhibited the formation of defects in the passive film. The study also investigated operation-induced passive behaviors. Accelerated stress tests were conducted using two square ripple potentials to simulate overload operating conditions. The findings indicated that the lower upper limit potential was insufficient to establish stable passivation.

Unitary canonical forms over Clifford algebras, and an observed unification of some real-matrix decompositions

We show that the spectral theorem – which we understand to be a statement that every self-adjoint matrix admits a certain type of canonical form under unitary similarity – admits analogues over other ∗ -algebras distinct from the complex numbers. If these ∗ -algebras contain nilpotents, then it is shown that there is a consistent way in which many classic matrix decompositions – such as the Singular Value Decomposition, the Takagi decomposition, the skew-Takagi decomposition, and the Jordan decomposition, among others – are immediate consequences of these. If producing the relevant canonical form of a self-adjoint matrix were a subroutine in some programming language, then the corresponding classic matrix decomposition would be a 1-line invocation with no additional steps. We also suggest that by employing operator overloading in a programming language, a numerical algorithm for computing a unitary diagonalization of a complex self-adjoint matrix would generalize immediately to solving problems like SVD or Takagi. While algebras without nilpotents (like the quaternions) allow for similar unifying behaviour, the classic matrix decompositions which they unify are never obtained as easily. In the process of doing this, we develop some spectral theory over Clifford algebras of the form C l p , q , 0 ( R ) and C l p , q , 1 ( R ) where the former is admittedly quite easy. We propose a broad conjecture about spectral theorems.

BENCH TESTS ON THE STRENGTH OF THE Mi-8 TYPE HELICOPTERS MISSILE-BOMBARDMENT INSTALLATIONS SUSPENSION

The article is devoted to the problem of testing the strength of the developed suspensions of Mi-8 type helicopters. The issue of design and calculation of a special test stand for testing the strength of the suspension is considered in detail. The calculation and simulated mathematical modeling of the strength characteristics of the stand structure at maximum operational overloads were performed, which proved that the strength of the structure is sufficient.&#x0D; A method of testing the strength of the external suspension of Mi-8 type helicopters has been developed, which is performed for each suspension during its manufacture.

Analysis and design of air-heat pipe composite cooling of high power density motor

High power density and short-term high overload performance motor is an important part of the aircraft's electric propulsion system. The efficient heat dissipation system can effectively control the temperature rise of the motor, which provides the possibility to improve the power density of the electric propulsion system.An air-heat pipe composite cooling system was designed by using heat pipe technology and the application environment of aviation motors. Firstly, a new composite cooling system was designed based on the structure and loss distribution characteristics of a 34 kW external rotor aero-motor; then four different U-shaped heat pipes were designed and fabricated. In order to select the optimal heat pipes to ensure the efficient performance of the composite cooling system, a test platform was built to carry out experimental research on the thermal conductivity of the heat pipes and the variation laws of thermal conductivity. Then the performance of the composite cooling system is evaluated and verified based on a combination of simulation and experiment. The results show that the cooling effect is better by arranging the heat pipes at the bottom of the stator slot of the motor, which can reduce the stable temperature rise of the motor winding by 19 K and prolong the overload operation time of the motor by 12.7 %. The high efficiency of the composite cooling system can effectively improve the power density of the motor.

Effects of unstable flow structures on energy transfer mechanism in a centrifugal pump

To reveal the energy loss mechanism of the centrifugal pump, numerical simulation and experimental investigation are conducted to obtain the complex flow field of a single-stage centrifugal pump under various flow conditions. Particular emphasis is focused on the qualitative and quantitative analysis of the distribution and variation characteristics of irreversible loss in the pump model. The results show that the energy loss in the centrifugal pump mainly originates from the entropy generation caused by the turbulent dissipation and wall friction, which are typically generated in the volute and impeller domains. It is worth noticing that the energy loss in the volute is closely associated with non-uniform velocity distribution and the evolution of the shedding vortices from the impeller exit whilst the energy loss in the impeller are greatly affected by unstable flow phenomena such as flow separation, backflow, and jet-wake pattern. At the overload operating conditions, the wall entropy generation possesses a substantial influence on energy loss, which is mainly related to the wall shear stress. Meanwhile, the influence of the rotor-stator interaction and inflow impacting on the energy loss is enhanced with increasing flows. Finally, the omega method captured the vorticity structures near the tongue at partial flow conditions, thereby, revealing the relationship between the high magnitude of flow loss and the evolution of different scales of strong vorticity sheets.

Düşey Milli Eksenel Bir Pompada Zamana Bağlı Akışın Deneysel Olarak İncelenmesi

Due to the changes in the system characteristics, pumps may have to be operated far away from the design point, such as in part-load or over-load operating points. Operating the pumps far away from the design point may cause fluctuations in the flow. As a result of the fluctuations mechanical problems in the pump structure may occur. In order to overcome the problem, the operating characteristics of the pump must be determined at part load operating conditions as well as design point operating condition. In this study, flow inside a vertical shaft axial flow pump is investigated experimentally. The experimental setup is designed and constructed for the laboratory tests. The pump which is designed and manufactured is tested in the test setup. The performance of the pump is determined by measuring the flow rate, inlet and outlet pressures, rotational speed and power input of the pump. The part load and over load operating regions are determined. Pressure variations are measured at various performance points with the piezoelectric pressure transducer placed in between impeller and diffuser blade passage. Simultaneously, comparisons are made with the vibration spectrums obtained in the pump.

Operation related maintenance and reinvestment costs for hydropower scheduling

AbstractThis paper addresses the questions: How to calculate the cost of a start/stop cycle? How to calculate the cost of running one hour outside normal operating range, e.g., on part load? The paper presents a model for calculation of start/stop cost for individual hydropower units comprising both direct costs incurring at each start/stop cycle, and indirect cost because of reduced rehabilitation intervals for the main components. The fundamental assumption is that frequent start-ups lead to increased stress, degradation and wear reducing residual service life equivalent to a certain number of normal operating hours, thus accelerating the need for rehabilitation. The proposed model is used for calculation of both average cost and marginal cost for one start/stop cycle. When calculating the marginal cost, the technical condition of the turbine and generator as well as the length of the stand-still period can be considered. Applying a similar approach, the model is extended to calculate the cost of ramping, part load and overload operation, i.e., costs incurring when using the unit outside the normal operating range. This extension for operation related costs is important to include when deciding hydropower scheduling in systems with large shares of variable generation from wind and solar. Such operation related costs are very important to consider when calculating of the optimal operating strategy for the hydropower units in power systems where hydropower delivers flexibility in terms of load following and different types of reserves.

A Novel Active Vibration Control Method for Helicopter Fuselages Based on Diffusion Cooperation

Against the background of low-frequency vibration control for a helicopter fuselage in flight, active control of structural response (ACSR) has been employed for vibration control design. With the increase in control positions in the fuselage, more actuators and error sensors are needed to meet the vibration reduction requirements, forming a large-scale multichannel system. This leads to a rapid increase in the computation amount, causing the control performance of the conventional centralized algorithm main processor to become poor under overload operation. To this end, a novel distributed active vibration control algorithm based on the diffusion cooperative strategy was proposed and explored in this research. The diffusion cooperative strategy is widely used in complex wireless sensor network (WSN) systems to efficiently reduce the computation amount during data aggregation. This distributed algorithm utilizes the advantages of the diffusion-cooperative strategy to reduce the computation amount and coupling relationship of the secondary path in a large-scale multichannel system. First, a novel control law was established by introducing the network topology of the diffusion cooperation strategy into the classical filtered-x least mean square (FxLMS) algorithm, forming the diffusion FxLMS (DFxLMS) algorithm. Then, a secondary path trade-off quantization standard based on the complex undirected network connectivity condition was developed. It determined whether a secondary path was discarded or not and formed the topology of a large-scale multichannel system control network. To examine the effectiveness and superiority of the proposed DFxLMS algorithm, a comparative simulation with a scale of 1 × 10 × 10 was carried out for a simplified helicopter fuselage. Numerical results in realistic scenarios showed the ability of the DFxLMS algorithms to achieve good control performance when proper values of these parameters are chosen.

Pyerrors: A python framework for error analysis of Monte Carlo data

We present the pyerrors python package for statistical error analysis of Monte Carlo data. Linear error propagation using automatic differentiation in an object oriented framework is combined with the Γ-method for a reliable estimation of autocorrelation times. Data from different sources can easily be combined, keeping the information on the origin of error components intact throughout the analysis. pyerrors can be smoothly integrated into the existing scientific python ecosystem which allows for efficient and compact analyses. Program summaryProgram Title: pyerrorsCPC Library link to program files:https://doi.org/10.17632/7ncw242ymh.1Developer's repository link:https://github.com/fjosw/pyerrorsLicensing provisions: MITProgramming language: pythonNature of problem: Data obtained from Markov chain Monte Carlo simulations exhibits autocorrelations. These become particularly severe when approaching the continuum limit of lattice discretized quantum field theories which becomes more and more relevant in modern day large scale simulations. In order to obtain reliable error estimates these autocorrelations have to be taken into account in complex data analysis workflows.Solution method: Linear error propagation in combination with automatic differentiation is implemented in a new python data type which keeps track of statistical errors across multiple sources of uncertainty. Operator overloading allows for a seamless integration into the scientific python ecosystem and into existing workflows. The Γ-method facilitates a controlled estimate of integrated autocorrelation times at any stage of the analysis and provides reliable error estimates without numerical overhead.