Unbalance Factor Research Articles

Simulation on Voltage Unbalance Reduction in Railway Electrification System by Different Special Transformers

In recent years, electric railway system becomes an efficient mass transportation in large urban areas. A railway electrification system supplies electric power to railway trains through the transformers. Therefore, the transformer is a key component to help reduce problems of the unbalance of voltage and current in the power grid. As electric trains have their power delivered on a single-phase system, the single-phase transformer causes the unbalance of voltage and current in the power system network, with which the railway electrification system is connected. In order to alleviate these problems, special transformers, i.e. Scott transformer and Le-Blanc transformer, have been proposed to be used in the railway electrification system. This paper focuses on developing the special transformer models for using in DIgSILENT PowerFactory software. The developed models have been verified with a simple train system in order to study the effectiveness of reduction of voltage unbalance factors from the three types of transformers. In addition, the developed special transformer models can be applied in a large-scale power system network for power quality problem analysis.

Growth and Productivity; The Role of Budget Deficit in the MENA Selected Countries

Abstract Today, efficiency is considered as one of the most effective ways of increasing economic growth by many planners and economic policy makers in different countries; further, huge investments made in this regard. On the other hand, the issue of budget deficit was introduced in economic literature since 1980s. Within this decade, current budget deficit significantly increased in the USA. Emerging of this phenomenon prompted many economists to establish public sector as the macroeconomic unbalancing factor, on the contrary to Keynesy who regarded public sector as the balance factor, particularly in developing countries since developing countries deal with specific problems such as foreign debt, high inflation, difficulties of payment balances, exchange parallel markets as well as various external shocks. Therefore, this research tried to study the effect of growth, efficiency and government budget deficit in MENA selected countries within 2000-2013 by using the recommended static panel models. Results of the estimated relations for the first model in which government budget deficit is the dependent variable indicate positive effect of economic growth and inflation rate variables as well as the negative effect of labor productivity and government budget deficit. Moreover, the second model in which economic growth is the dependent variable demonstrates the positive effect of labor productivity index and economic growth. In addition, negative correlation of government budget deficit with economic growth is also maintained.

고조파발생에 따른 영향과 대책 연구

Skyscrapers, large business buildings, and IT consumers use many appliances, and the electrical power stems can cause fires by overheating. This can result in damaged capacitors, lost data, rising ground potential, and communication obstacles from linear or nonlinear high frequency. To make sure of that we investigated 7 spots of a building, among which 6-spots were fair but the other one needed high frequency control. Spots 3, 6, and 7 needed diagnostic workup, and spots 2, 3, and 5 considered 5 high frequency currents. A phase is all of good but the high frequency current is greater than the standard level except for spot 1. As a result, a zigzag transformer or active filter needs to be installed, and the efficiency needs to be upgraded by investigating load unbalance factors and power factors.

Improved Energy Conversion Process With Coupling Induction Motors And Invastigate Unbalanced Operation With Definition Of The Voltage Unbalance

This paper assesses Voltage unbalance study as one of power quality issues which is especially effected distribution voltages and is noteworthy. however it is possible that voltage in level of producing and transmission be balanced but this voltages in level of distribution can go out of balance and be unbalanced which is because of unbalanced systems, unequal impedances and lack of appropriate and balanced distribution of one phase loads in distribution systems occurs. In this thesis operation of steady state machine conjunction (Induction motor) under unbalanced voltage will be evaluated. Induction motors in small sizes attach as coupled and will be used instead of big sized induction motors, which is proper for improved electromagnetic systems and more efficient energy conversion mechanism in both symmetric and asymmetric states. Two coupled induction motors can have the same or different rates mechanically. This thesis will analyze coupled machinery using symmetric elements and MATLAB software. Definition of unbalance voltage is used by CVUF factor (complex voltage unbalance factor). Induction motors coupling with DC motors (direct current) is analyzed and coupling effect in electromagnetic torque in all system is studied and comparing of unbalanced voltage on standalone and coupled machines is demonstrateed. The purpose of such comparing is finding the best states in balanced and unbalanced working, also this thesis evaluates the effect of induction motors connection as coupling in energy conversion process.

Power Quality Analysis for Photovoltaic System Considering Unbalanced Voltage

Background/Objectives: Voltage unbalance is one of the most important power quality problems in distribution network. In this way, three phase Photo Voltaic (PV) system can increase voltage unbalance. Methods/Statistical Analysis: In this paper a three phase photovoltaic system with Maximum Power Point Tracking (MPPT) has been installed in an unbalance distribution network due to reduce Voltage Unbalance Factor (VUF). Also, a Dynamic Voltage Regulator (DVR) has been used to get better outcomes. Results: Results show that in the case in which load is balance and only network is unbalance, the system comprised of PV, MPPT and DVR can diminish VUF by 10%. Moreover, THD analysis is done and is obtained around 2.27%. This system is modeled in MATLAB/ SIMULINK. Conclusion/Application: Considering the benefits of using PV system for sustainable energy, utilizing MPPT and DVR can lessen voltage unbalance in distribution networks inclusive photovoltaic systems. First, output voltage waveform of three-phase photovoltaic system simulated in this paper with regard to existing controlling structure in PV system is balanced to radiation change (500 –1000W/m2) in a good approximation and acts like a balanced three-phase source. Second, when this photovoltaic system approaches an unbalanced load which is located in an unbalanced network, the voltage imbalance decreases in that bus. Also when PV system gets further from the considered load, the impact of voltage imbalance reduction decreases in that load and also whatever the used photovoltaic system in the network is nearer to a special load, the imbalance compensating effect becomes more sensible. Also according to the performed simulations if there is a load which is sensible to the imposed voltage imbalance from network, PV-DVR system can be used for modify the observed voltage imbalance from network. It is worth noting that the PV-DVR system hasn’t the ability to modify observed imbalance from network due to imbalance load. PV-DVR system in this paper has the ability to compensate voltage imbalance up to 10% and for more, the capabilities of both photovoltaic system and DVR must be added. In addition, or proposed network, FFT analysis is done. Therefore harmonic load flow illustrates the suggested photovoltaic system using PV-DVR is acceptable from harmonic distortion point of view. THD is obtained around 2.27% that is good value for PV-DVR system in comparison with 5% allowable standard value.

Impact assessment of a hybrid energy-generation system on a residential distribution system in Taiwan

In this paper, a Monte Carlo-based three-phase power-flow method is proposed to evaluate the impact of a variety of hybrid energy-generation systems on residential distribution systems. The proposed deterministic power-flow method was based on graph theory, circuit theory and nonlinear numerical solution methods, and was extended to develop the proposed Monte Carlo based power flow method using the commercial software package OPTIMUS. Various technologies for distributed generation were combined in the proposed method. The hybrid energy system at the University of Yuan Ze was used in this research. It consists of a 5kW photovoltaic system, a 3kW wind power system and a 2kW hydrogen-fuel cell system. Then, a comprehensive study of the hybrid-energy micro-grid system was performed to evaluate its impact on the residential distribution power grids. The factors studied included steady-state voltage deviations, power flows, power losses, reverse power flows, short-circuit fault currents, maximum allowable capacity for distributed generation, and voltage unbalance factor. The results of this research should be of value for pre-determining the impacts of hybrid energy systems on the residential distribution systems.

Power Quality, Smart Meters and Additional Information from Different Power Terms

This paper shows how the detailed examination of active and nonactive power components may produce new information for modern smart meters. For this purpose, a prototype of electronic power meter has been implemented and applied to the evaluation of the Conservative Power Theory (CPT). Considering five sorts of loads, under four different operating conditions, the experimental results indicate that the CPT is able to provide a good methodology for load characterization, which could possibly benefits consumers and power utilities in several different ways. The results also show that depending on the situation, the analysis of nonactive power terms may be more important than the observation of traditional power quality indices, such as total harmonic distortion, unbalance factors or the fundamental positive sequence power factor.

Energy Efficiency Evaluation of Power Equipment Based on DEA

As the current situation of imperfect model algorithm of electrical equipment for energy efficiency evaluation, we set up energy efficiency DEA model. In the model, we got average load rate, average power factor and tri-phase unbalance factor as inputs indexes. And we got economic output of per unit of power consumption and energy pollution as outputs indexes. Then we transformed multiple pollutants into a pollutant index through principal component analysis. And we got it as the desired output. The result of 12 industrial enterprises in the energy efficiency of electrical equipment shows that the evaluation model is suitable for energy efficiency evaluation and system analysis. The DEA model is useful to further improvement in the energy efficiency of equipment.

Distributed Energy Storage Systems with an Improved Fuzzy Controller for Mitigating Voltage Unbalance on Low-Voltage Networks

AbstractThe growth of photovoltaic (PV) systems on low-voltage distribution networks can create technical issues such as voltage rise, voltage unbalance, unnecessary neutral current circulation, and reverse power flow. Usually, these happen with little fluctuation. However, they tend to fluctuate seriously because of the low clear sky index in Malaysia and they become more severe when the installation and distribution of single-phase renewable energy sources are rather arbitrary and not monitored by utility companies. To ensure effective operation of distribution networks with PV systems, an improved version of a three-phase fuzzy control algorithm for distributed energy storage (ES) systems is proposed. With this algorithm, distributed energy storage systems can control individual phase voltage to mitigate the voltage unbalance factor effectively, maintaining voltage magnitude without cutting any excess renewable energy. An experimental low-voltage distribution network with two 3.6-kWp PV systems was set...

Point Estimate Method for Voltage Unbalance Evaluation in Residential Distribution Networks with High Penetration of Small Wind Turbines

Voltage unbalance (VU) in residential distribution networks (RDNs) is mainly caused by load unbalance in three phases, resulting from network configuration and load-variations. The increasing penetration of distributed generation devices, such as small wind turbines (SWTs), and their uneven distribution over the three phases have introduced difficulties in evaluating possible VU. This paper aims to provide a three-phase probabilistic power flow method, point estimate method to evaluate the VU. This method, considering the randomness of load switching in customers’ homes and time-variation in wind speed, is shown to be capable of providing a global picture of a network’s VU degree so that it can be used for fast evaluation. Applying the 2m + 1 scheme of the proposed method to a generic UK distribution network shows that a balanced SWT penetration over three phases reduces the VU of a RDN. Greater unbalance in SWT penetration results in higher voltage unbalance factor (VUF), and cause VUF in excess of the UK statutory limit of 1.3%.

Transposition and Voltage Unbalance in High Phase Order Power Transmission Systems

—High phase order systems have been proposed at the early inception of power transmission engineering, but few direct applications have been made. High phase order transmission should be considered as an alternative in the case of high power density applications. In this article, an analysis of transposition of high phase order overhead transmission lines is presented and voltage unbalance in high phase order systems is considered. Definitions are presented for “fully transposed” and “roll transposed” along with advantages and disadvantages of each. A generalized voltage unbalance factor is introduced and utilized to determine the benefits of transposition. The generalized voltage unbalance factor is compared with three other possible unbalance factors to determine if the generalized voltage unbalance factor is an appropriate indication of unbalance. Exemplary results are presented for 6-phase and 12-phase designs. Conclusions show that the generalized voltage unbalance factor is a good indication of transmission line voltage unbalance and certain configurations may not need full rotation transposition to minimize the unbalance factor. The transposition analysis and voltage unbalance are considerations in the assessment of high phase order as a high power transmission alternative.

Study of Stand-Alone Microgrid under Condition of Faults on Distribution Line

Abstract The behavior of stand-alone microgrid is analyzed under the condition of faults on distribution feeders. During fault since battery is not able to maintain dc-link voltage within limit, the resistive dump load control is presented to do so. An inverter control is proposed to maintain balanced voltages at PCC under the unbalanced load condition and to reduce voltage unbalance factor (VUF) at load points. The proposed inverter control also has facility to protect itself from high fault current. Existing maximum power point tracker (MPPT) algorithm is modified to limit the speed of generator during fault. Extensive simulation results using MATLAB/SIMULINK established that the performance of the controllers is quite satisfactory under different fault conditions as well as unbalanced load conditions.

Investigating and Simulating DGs to Improve Voltage Profile and Reducing Power Loss in Unbalanced Distribution Networks

Development of Distributed generations (DGs) has changed the nature of power networks from passive to active. In order to specify a proper model for DG units, function and connection style of DGs to the network (direct or indirect) must be clarified. In this paper, operation of DGs in an unbalanced condition (due to unbalanced loads) will be studied. A three-phase power flow model is used to confirm the certainty of the proposed model. Generally DG modelling, depend on its type and controlling circuit, is like either PV or PQ bus. In this paper a three-phase unbalanced power flow model using Newton-Raphson method over a 4 buses power system is implemented. Based on the type of bus (PV or PQ), Simulation results show that the DGs can improve voltage profile (NEME and IEEE unbalance factor) and reduce network losses.

Neutral current compensation techniques in autonomous wind energy sources

The problem of neutral current compensation has to be addressed in Wind Energy integrated weak micro-grids. This study analyses two types of techniques possible for implementation of neutral current compensation by drawing a comparative research of their application on the same wind energy conversion system. The hybrid micro-grid considered in the study comprises a synchronous diesel generator and an inverter-based wind generator. The results and analysis are conducted by time-domain simulations using MATLAB/Simulink software. The use of electronic power converters that also act as an active neutral current compensator or a zig-zag transformer connected with the load mitigates the problem of neutral current compensation to a large extent. The voltage unbalance factor is also significantly reduced due to neutral current compensation and power quality is enhanced. The results provide the actual operational limits possible under the set of given constraints.

Approximate Algorithm for Fast Calculating Voltage Unbalance Factor of Three-Phase Power System

The method of calculating voltage unbalance factor (VUF) recommended by the IEC61000-4-27 has the disadvantage of requiring square root operation. This paper focuses on the fast and accurate calculation of VUF of three-phase power system. The approximate algorithm for calculating the magnitude of the zero, positive, and negative sequences by simple algebraic equation is presented. In the proposed method, the square root operation is first transformed to simple trigonometric equations based on the geometric figure, and then the trigonometric equations are approximated by the algebraic operations, which thus reduced the computation burden sufficiently. The simulation and practical experiment results show that the proposed method can achieve the same level of precision as the method recommended by the IEC61000-4-27, while much less clock cycles are required, which indicates its wide application in digital signal processor (DSP).

A dual-unit pressure sensor for on-chip self-compensation of zero-point temperature drift

A novel dual-unit piezoresistive pressure sensor, consisting of a sensing unit and a dummy unit, is proposed and developed for on-chip self-compensation for zero-point temperature drift. With an MIS (microholes inter-etch and sealing) process implemented only from the front side of single (1 1 1) silicon wafers, a pressure sensitive unit and another identically structured pressure insensitive dummy unit are compactly integrated on-chip to eliminate unbalance factors induced zero-point temperature-drift by mutual compensation between the two units. Besides, both units are physically suspended from silicon substrate to further suppress packaging-stress induced temperature drift. A simultaneously processes ventilation hole-channel structure is connected with the pressure reference cavity of the dummy unit to make it insensitive to detected pressure. In spite of the additional dummy unit, the sensor chip dimensions are still as small as 1.2 mm × 1.2 mm × 0.4 mm. The proposed dual-unit sensor is fabricated and tested, with the tested sensitivity being 0.104 mV kPa−1 3.3 V−1, nonlinearity of less than 0.08% · FSO and overall accuracy error of ± 0.18% · FSO. Without using any extra compensation method, the sensor features an ultra-low temperature coefficient of offset (TCO) of 0.002% °C−1 · FSO that is much better than the performance of conventional pressure sensors. The highly stable and small-sized sensors are promising for low cost production and applications.

Diagnóstico de fallas estatóricas en motores de inducción de jaula de ardilla por medio de la corriente de secuencia negativa

This paper presents a mathematical model to obtain a failure indicator of stator faults based on the negative sequence component of the electric current. The model can be used in online diagnosis systems to separate the effects of voltage unbalance factor and the constructive asymmetries of the machine. Results of the application of the model were validated trough laboratory tests made into a specially modified motor and results were applied to success diagnosis of two motors of higher electrical power. As a main result of the work, a low computational model was obtained to diagnose a quick evolution failure that can evolve quickly to a thermal collapse of the stator winding with consequent repair costs.

A hybrid method combining JFPSO and probabilistic three-phase load flow for improving unbalanced voltages in distribution systems with photovoltaic generators

This paper presents a new hybrid method that combines jumping frog and particle swarm optimization and probabilistic three-phase load flow to improve unbalanced voltages in distribution systems with photovoltaic generators. This paper applies a new three-phase probabilistic load flow based on the Monte Carlo simulation. The voltage regulation is one of the principal problems to be addressed in photovoltaic distributed generation. The proposed method defines the nodes where photovoltaic grid-connected system is connected and their mean power output minimizing the maximum value of voltage unbalances at the nodes. Numerical applications are presented using the unbalanced distribution system IEEE 13-nodes and including photovoltaic generators at several nodes. The results obtained show the decrease in the unbalance factor due to the presence of distributed generation.

측정된 S-파라메터를 이용한 EMI 필터의 Y-캡 용량 산정에 대한 연구

삽입 손실은 EMI 필터의 노이즈 제거 성능을 나타내는 주된 지표로 쓰인다. 본 논문에서는 기존의 방법보다 좀 더 정확하고 편하게 삽입 손실을 측정할 수 있는 방법에 대하여 연구하였다. 이와 관련하여 EMI 필터의 비이상적인 특성들을 모두 고려하기 위해 4포트 S-파라메터 측정을 통한 임의의 전원/부하 임피던스에 대한 차동 모드와 공통 모드의 삽입 손실을 구하는 방법에 대하여 제시하였다. 이를 활용하여 EMI 필터가 사용될 회로의 전원/부하 임피던스를 알고 있을 때, 시스템에 적용된 EMI 필터의 차동 모드 삽입 손실과 공통 모드 삽입 손실를 구할 수 있다. 또한, 이를 바탕으로 적절한 소자 값을 선택하기 위해 혼합 모드 변환, 체인 혼합 모드 변환 그리고 4포트 모델링을 통하여 임의의 소자 값에 따른 전체 시스템의 삽입 손실을 예측하는 방법에 대하여 제시하였다. Insertion loss is used as the character to express the efficiency of EMI filter. In this paper, we studied the better method that can measure the insertion loss of EMI filter exactly than the original method. For the achievement of this, the method measuring both common mode(CM) and differential mode(DM) insertion loss with arbitrary input/output impedance is accomplished using a 4-ports S-parameters system for consideration of unbalanced factor. Using this method, when input/output used in specific system is known, CM/DM insertion loss of EMI filter inserted in the system can be calculated. Finally, we applied 4-ports modeling method to 'X/Y capacitor part' and suggested the algorithm for selecting suitable the value of Y-capacitor using mixed mode S-parameters and mixed mode chain S-parameters.

Study on the Output Performance of DFIG under Unbalanced Grid Voltage

This paper uses dynamic equivalent circuits to study the impact of the unbalanced grid voltage on a Doubly Fed Induction Generator (DFIG) and draws the curves between the voltage unbalance factor (VUF) and the output characteristics of DFIG. A mathematical model of the grid and rotor side converters (GSC and RSC, respectively) is given in the stationary αβ reference frame under unbalanced network voltage conditions, which could be used in the coordinated control of the GSC and RSC. Finally, simulation studies on a 1.5MW DFIG can verify the feasibility of the proposed coordinated control strategy which can be used to improve the performance and stability of the whole wind power generation system.