Method Of Symmetrical Components Research Articles

Modified symmetrical component method for characterization of unbalanced voltage sags

This paper suggests a modification in symmetrical component (SC) method, used for characterization and classification of voltage sags, by incorporating an angle, ɸ, in it. The ɸ is considered as an angle between drop in positive-sequence voltage components, associated with single line-to-ground and line-to-line faults. The modified formula is tested on two data sets of real power systems and compared with the SC method. The results suggest that this modification offers advantages of giving accurate comprehensive information on the nature of (i) voltage sag, (ii) associated fault, and (iii) faulted buses, simultaneously. This study aims to establish a precise characterization method for voltage sags due to faults in low-voltage resistance-grounded distribution systems (LVRGDS), as their more frequent occurrence and vulnerability of economic impacts to industrial customers than the shallow voltage sags due to faults in high-voltage solidly grounded transmission systems (HVSGTS). For this, the variations in φ, for different fault locations in LVRGDS and HVSGTS, are evaluated, resulting in large values of φ in LVRGDS. These larger values of φ establish better characterization capability, for voltage sags in distribution systems, with the proposed method than the SC method. Also, the capability of φ to identify the behavior of un-faulted phase voltages has been revealed. Copyright © 2015 John Wiley & Sons, Ltd.

Impedance characteristics study of three-phase aircraft power wires

This paper proposes an accurate measurement circuit for three phase aircraft power wires. The impedance characteristics of the three-phase aircraft power wires are related with the following three factors: frequency, wire laying forms, and the distance from the wire to aircraft skin. Three-phase power wires were modeled in this paper using Ansoft’s large finite element analysis software Maxwell. While the circuit to measure the positive sequence impedance and zero sequence impedance were separately built with Ansoft Simplorer. Then the voltage and current data of the three-phase wires under test can be obtained by co-simulating with Maxwell and Simplorer. Sequence impedance can be calculated according to symmetrical component method. The impacts of frequency changing, wire laying forms, as well as the distance between the wire and aircraft skin on phase sequence impedance were thoroughly analyzed. Finally, the simulation results were verified by experimental study. The results can be used as reference for future design and implementation of aircraft cables.

Analysis and Calculation of DC-Link Current and Voltage Ripples for Three-Phase Inverter With Unbalanced Load

In this paper, an analysis and calculation of the dc-link current and voltage ripples are presented for a three-phase inverter with unbalanced load. A comparison of the dc-link average and root-mean-square (rms) currents between considering and ignoring high frequency harmonics of the output current is drawn. It is shown that high frequency harmonic currents have little effect on the dc-link current, and therefore, they can be ignored. Based on the symmetrical components method, the dc-link average and harmonic rms currents are derived, and the dc-link voltage ripple is compared between the balanced and unbalanced loads. It can be found that the dc-link current and voltage ripples consist of not only high frequency harmonics but also the double fundamental frequency harmonic, and the voltage ripple is independent of the positive-sequence component and determined by the negative-sequence component, under the unbalanced load. Experimental results are shown to verify the accuracy of the theoretical analysis.

English

The ideas presented in this paper are intended to be representative the more straightforward application of the fuzzy mathematics techniques in power systems. When the 3-phases system is not symmetrical due to line to line current fault as a result of unbalanced load and unbalanced faults, the analysis is down by Symmetrical Component method after transform the fuzzy magnitudes into crisps quantities using the defuzzification technique. A computational problem with fuzzy impedance fault is presented.

Rapid Tracking of Grid Variables Using Prefiltered Synchronous Reference Frame PLL

For synchronization applications, synchronous reference frame (SRF) phase-locked loop (PLL) is widely deployed. Its performance is excellent when the input voltage consists of only fundamental positive sequence (FPS) component. If the grid voltage is unbalanced or polluted with harmonics and dc offset, its performance degrades. Many modifications were proposed to address this issue. However, the removal of dc offset and fundamental negative sequence (FNS) component without compromising the dynamic performance still remains a challenging task. To this end, this paper presents a rapid Type-1 SRF PLL scheme with preloop filtering stage for tracking the attributes of grid voltage FPS component. Fixed sampling period sliding discrete Fourier transform (SDFT) and instantaneous symmetrical components method are employed in the preloop stage. With this modification, the dc offset, harmonics and the FNS component are rejected and only the FPS component enters the PLL. As a result, transients vanish quickly. However, when the grid frequency drifts, SDFT causes amplitude and phase errors, and Type-1 PLL introduces a steady-state tracking error in phase. These errors are compensated with the help of an error correction criteria. Robustness and the improved transient response of the proposed scheme are demonstrated with an experimental study involving real-time controller board (dSPACE DS1104) and three-phase programmable power source.

Voltage sag mitigation in an Indian distribution system using dynamic voltage restorer

Now a day’s most power quality problems in distribution systems are related to voltage sags. Hence, diverse solutions have been tried to compensate these voltage sags to circumvent financial losses due to voltage sag at industries. Dynamic voltage restorers (DVRs) are now becoming more recognized in industries to diminish the impact of voltage sags to sensitive loads. The DVR, which is placed in series with a sensitive load, must be able to react speedily to a voltage sag if end users of sensitive equipment are to experience no voltage sags. This paper discusses the use of series reactive injection as a voltage regulator. The proposed approach is to develop analytical aspects and to illustrate these by an example of a real Indian distribution system. Voltage sag can be eliminated by continuously injecting very small voltage profile to the system. The scheme combines the method of instantaneous symmetrical components and complex Fourier transform relations. The proposed technique, based on half-cycle averaging, can mitigate voltage sag at desired locations in distribution systems. The proposed methodology is applied in a 4 bus system and a real Indian distribution system. 2015 Published by Elsevier Ltd.

Research on the Steady-State Performances of a Novel Energy-Efficient Single-Phase Induction Motor

In this paper, a novel energy-efficient single-phase induction motor with three parallel-connected stator windings and two external capacitors has been proposed. By selecting the appropriate capacitors, the currents in the three windings will be approximately symmetric at rated load, thus high rated efficiency can be obtained. Based on the symmetrical component method, the condition for balanced operation is analyzed and the method for determining the requested capacitances is also obtained. The approach for calculating the steady-state performance is proposed.

A Novel SPLL and Voltage Sag Detection Based on LES Filters and Improved Instantaneous Symmetrical Components Method

The software phase-locked loop and the voltage sag detection algorithm are the two key factors to evaluate the performance of a dynamic voltage restorer, whose dynamic response is usually impacted by phase jump, voltage unbalance, and harmonics of the grid voltage. This paper proposes a novel algorithm based on the combination of least error squares filters and an improved instantaneous symmetrical components method. Hence, a detailed theoretical procedure is first presented. Then, the simulation model is built in MATLAB/SINMULINK. To verify its effectiveness, a series of comparison and analysis have been carried out. Also, a 10-kV/2-MVA prototype is developed with a voltage sag generator platform. Finally, experiments have been done and the results show that the novel algorithm has an improved dynamic response compared with the traditional methods.

Effect of TCVR Controlled Voltage on Short-Circuit Calculations in Case of Ground Fault in the Algerian Network

Flexible AC Transmission Systems (FACTS) technology has been developed to control voltage and reactive power in power systems by incorporating high speed power electronic devices. The FACTS device presented in this research work is Thyristor Controlled Voltage Regulator (TCVR) which is a novel FACTS device that aims to control system voltage and hence improves voltage regulation. This paper studies the effect of voltages injected by TCVR, whether positive or negative, on short-circuit calculations. The type of fault considered is a ground fault that occurs at the end of a high voltage line compensated at its mid point by TCVR while maintaining a fixed fault resistance. A case study is selected for a high voltage power line in the Algerian transmission network. In this research work, the illustrated simulation results show perfect agreement with the presented theoretical analysis which is based on the method of symmetrical components.

АВТОМАТИЗОВАНИЙ СИНТЕЗ НЕСИМЕТРИЧНИХ ТРИФАЗНИХ ОБМОТОК

The article presents the results of the software of the automated synthesis of two-and three-phase windings with a reduced level of asymmetry. The necessity of using such a weakly asymmetric windings periodically arises on the enterprises specializing in the repair of electrical machines, so the task of such symmetrize windings design is relevant. Algorithm of synthesis of these multi-phase windings is based on balancing - achieving of practical symmetry on harmonics symmetry that ensures the correct application of the method of symmetrical components to perform a detailed harmonic analysis of the winding MDS. Implementation of this algorithm in manual mode requires multiple graphic design of vector diagrams and performing of repetitive routine calculations, therefore characterized by higher labor input. The proposed software is characterized by a user-friendly interface. Both automated and manual input of initial data, as well as their operational adjustment are provided. Visualization module of vector diagrams eliminates the need of manual graphic design, on the order reduces the time required in the process of balancing using the method of successive approximations and provides almost complete symmetry by working harmonica. On the second stage the compliance of detailed harmonic analysis and printing of the obtained results or saving in files are provided so you can use them for subsequent determination of operational properties of electric machines, in which such winding are used. Effectiveness of the developed software is illustrated by the example of symmetrize three-phase winding synthesis with demonstration of performance technology of each stage of design and comparing of its electromagnetic properties before and after balancing.

지중 송전선로 대칭분 임피던스 해석을 위한 EMTP 전후처리기 개발과 활용

Power system fault analysis has been based on symmetrical component method, which describes power system elements by positive, negative and zero sequence impedance. Obtaining accurate line impedances as possible are very important for estimating fault current magnitude and setting distance relay accurately. Especially, accurate calculation of zero sequence impedance is important because most of transmission line faults are line-to-ground faults, not balanced three-phase fault. Since KEPCO has started measuring of transmission line imepdance at 2005, it has been revealed that the measured and calculated line impedances are well agreed within reasonable accuracy. In case of underground transmission lines, however, large discrepancies in zero sequence impedance were observed occasionally. Since zero sequence impedance is an important input data for distance relay to locate faulted point correctly, it is urgently required to analyze, detect and consider countermeasures to the source of these discrepancies. In this paper, development of pre/post processor to ATP (Alternative Transient Program) version of EMTP (Electro-Magnetic Transient Program) for sequence impedance calculation was described. With the developed processor ATP-cable, effects of ground resistance and ECC (Earth Continuity Conductor) on sequence impedance were analyzed.

Real-Time Load Balancing and Power Factor Correction of Three-Phase, Four-Wire Unbalanced Systems with Dstatcom

This paper presents the design and implementation of a distribution- level static synchronous compensator (DSTATCOM) used for the real-time load compensation of three-phase, fourwire power distribution systems with unbalanced loads. First, use of the symmetrical components method derives a feedforward compensation scheme for the DSTATCOM. The system block diagram of the DSTATCOM is then built. A computer simulation is performed for preliminary verification. Finally, a hardware prototype is built using a TMS320C6711-based controller. Experimental results verify the functionality of the DSTATCOM.

지중송전선로의 대칭분 임피던스 모델링에 관한 연구

Power system fault analysis is commonly based on well-known symmetrical component method, which describes power system elements by positive, negative and zero sequence impedance. The majority of fault in transmission lines is unbalanced fault, such as line-to-ground faults, so that both positive and zero sequence impedance is required for fault analysis. When unbalanced fault occurs, zero sequence current flows through earth and groundwires in overhead transmission systems and through cable sheaths and earth in underground transmission systems. Since zero sequence current distribution between cable sheath and earth is dependent on both sheath bondings and grounding configurations, care must be taken to calculate zero sequence impedance of underground cable transmission lines. In this paper, EMTP-based sequence impedance calculation method was described and applied to 345㎸ cable transmission systems. Calculation results showed that detailed circuit analysis is desirable to avoid possible errors of sequence impedance calculation resulted from various configuration of cable sheath bonding and grounding in underground cable transmission systems.

The effect of fast changes in voltage unbalance on vibration characteristics of asynchronous motors

The effect of voltage unbalance in electrical networks that supply electrified traction loads on the operating regimes of large asynchronous motors (AMs) is considered. Based on the method of symmetrical components and analysis of hodographs of magnetic fields of AMs with a short squirrel-cage rotor, the influence of various types of voltage unbalance (continuous and intermittent) on its vibration characteristics is studied. It is shown that an increase in magnetic induction in the air gap of an AM causes an increase in radial vibration generating forces in the case of voltage unbalance. The obtained results indicate that alternating voltage unbalance can be riskier for AM operation than is constant voltage unbalance, in addition to having increased levels of AM vibrations. It is concluded that the use of new parameters of electric-energy quality allowing determination of instantaneous values of unbalance amplitude and the angle between symmetrical components of voltage of positive and negative phase-sequence is reasonable. The relevance of this research is confirmed by typical cases of AM shutoff at an oil-pumping station due to tripping of vibration-protection sensors.

Dual-Current Loops Control Strategy of PWM Rectifier under Unbalanced Grid Voltage Conditions

The unbalanced grid voltage causes the current harmonics, the fluctuation of the active power in AC side and the fluctuation of the DC voltage. The dual-current loops control strategy can slove those problems. The positive and negative sequence components of grid voltages and currents were calculated based on the symmetrical component method and were used to calculate the instantaneous power in double dq rotate coordinate, which ratate at positive and negative synchronous angular velocity respectively. The dual-current loops control strategy was finally verified in simulation by comparing with the conventional synchronous PI current control. The simulation results show the dual-current loops control strategy is effective on eliminating the fluctuation of the active power in AC side and the fluctuation of the DC voltage.

Analysis of Two-Phase Operation Mechanism of Three-Phase Motor Based on Capacitor Phase Shift Method

In the absence of a three-phase power source, single-phase operation of three-phase induction motor used single-phase power source had a certain practical significance. In this paper, utilized symmetrical component method analysed the asymmetric circuit system of motor, will be voltage and current of the three-phase stator windings decomposed into positive, negative and zero sequence three groups symmetrical components. The theory is analyzed and the formula is deduced of capacitor phase shift method, solved the problem of starting torque, proposed to add starting capacitors and deduced the optimal value of starting capacitor. Finally, the single-phase operation of three-phase induction motor is simulated and verified by simulation software.

The Economic Operation of Common Coupling Groups of Distribution Transformer

Based on the method of symmetrical components of D, 11 and Y, o distribution transformer coupling two different effects of different magnetic circuit coupled to the three-phase system with a system-generated analysis and comparison. Analysis of the difference between the two groups of different connections on the transformer structure. Described in the single-phase short circuit fault clearing, 3n harmonic current suppression and affordability aspects of single-phase unbalanced load, D, ll coupling transformers are significantly better than Y,0 coupling transformer. This has necessarily important for the study of energy loss reduction.

Effects of Unbalanced Voltage on the Steady State of the Induction Motors

This paper examines the proper application of three phase induction motors when supplied by unbalanced voltage. To analyze the effects of unbalanced voltage on torque of the induction motors, it has defined 32 unbalanced points, with 8 different types of voltage unbalance, and four levels of Voltage Unbalanced Factor, measured with Symmetrical Components method. In each unbalanced point the Torque Ripple Factor are calculated to show the effects of unbalanced voltage. 

Coupling induction motors to improve the energy conversion process during balanced and unbalanced operation

This paper assesses the steady-state performance of cascaded IMs (induction motors) operating under voltage unbalance. Small sizes induction motors are connected in cascade instead of one big size induction motor to improve the electromagnetic system and to make the energy conversion process more efficient during both balanced and unbalanced operation. The two mechanically coupled induction motors could have the same ratings or different ratings. The paper analyzes the coupled machines system using the method of symmetrical components and MATLAB/Simulink software. The definition of the voltage unbalance using CVUF (complex voltage unbalance factor) is used. Coupling of induction motors with DC (direct current) motors is examined to investigate the effect of cascading on the electromagnetic torque of the entire set. A comparison of the effect of the unbalanced voltage on single and cascaded machines is illustrated. The purpose of such comparison is to determine which one has the best performance during the balanced and unbalanced operations. Furthermore, this paper assesses the impact of connecting induction motors in cascade on the energy conversion process.

Performance Simulation and Analysis of a Novel Single-Phase Permanent Magnetic Synchronous Motor

This paper presents a novel energy-efficient single-phase permanent magnet synchronous motor with three-phase stator windings which are connected to two external capacitors in series connection, supplied by the single-phase AC power. The positive sequence impedance and negative sequence impedance of the novel single-phase permanent magnet synchronous motor are presented based on the symmetrical component method, the condition for balanced operation is analyzed and the method for determining the requested capacitances is also obtained. The simulation model of the motor is constructed in d-q stationary reference frame. The transient performance of the proposed motor is simulated and the simulation results proved the validity of the proposed motor.