Three-phase Currents Research Articles

Voltage Unbalance Compensation in Distribution Feeders Using Soft Open Points

Soft open points (SOPs) are power electronic devices that may replace conventional normally-open points in distribution networks. They can be used for active power flow control, reactive power compensation, fault isolation, and service restoration through network reconfiguration with enhanced operation flexibility and grid resiliency. Due to unbalanced loading conditions, the voltage unbalance issue, as a common problem in distribution networks, has negative impacts on distribution network operation. In this paper, a control strategy of voltage unbalance compensation for feeders using SOPs is proposed. With the power flow control, three-phase current is regulated simultaneously to mitigate the unbalanced voltage between neighboring feeders where SOPs are installed. Feeder voltage unbalance and current unbalance among three phases are compensated with the injection of negative-sequence and zero-sequence current from SOPs. Especially in response to power outages, three-phase voltage of isolated loads is regulated to be balanced by the control of SOPs connected to the feeders under faults, even if the loads are unbalanced. A MATLAB/Simulink model of the IEEE 13-bus test feeder with an SOP across feeder ends is implemented, and experimental tests on a hardware-in-the-loop platform are implemented to validate the effectiveness of the proposed control strategy.

Analysis of the symmetry of 3D silicon melts flow generated by a bitter traveling magnetic field in a cylindrical crucible

Full 3D numerical simulation and experimental characterization of the topology and sensitivity of a magnetohydrodynamic flow pattern driven by a travelling magnetic field generated by a specifically designed cylindrical Bitter coil have been carried out. This Bitter coil has six windings composed of multiple circular copper plates and insulator separators disposed in a specific way for an optimum round circulation of electric currents, which are three-phase currents at a network frequency. For experimental characterization, experimental measurement data of radial components of the induced magnetic field (Br) at different z-positions were used without any liquid metal for different applied electric currents, and ultrasound Doppler velocimetry was employed to acquire the vertical velocity component along the beam axis in the centre and at different azimuthal positions for a fixed radial coordinate in the liquid GaInSn alloy. On the other hand, for numerical characterization, a numerical model has been developed using the Comsol MultiphysicsTM software to resolve the set of magnetohydrodynamic equations, fundamentally based on low frequency and low magnetic induction, and on an averaged expression of the Lorentz force. The results clearly show that the choice of 3D modelling and the Bitter coil design, which generates instabilities, can change significantly the usually expected axisymmetric torus-type magnetohydrodynamic flow topology and result in a distinct 3D flow configuration. Figs 8, Refs 16.

«Drehstrom» – вращающийся ток (к 160-летию со дня рождения М.О. Доливо-Добровольского)

The article is devoted to the beginning of the activity of Mikhail Osipovich Dolivo-Dobrovolsky. The end of the 1880s is characterized by the rapid development of alternating current technologies. The works of G. Ferraris, C.S. Bradley, N. Tesla, J. Venstrom, F.A. Heselvander and other electrical engineers significantly advanced the theory and practical use of alternating current. Nevertheless, the level of development of new electrical devices was still low, which hindered their widespread use. Within a relatively short period of time from 1888 to1891, Dolivo-Dobrovolsky developed a practically suitable electrical system based on three-phase currents. Mikhail Osipovich developed a simple, reliable three-phase induction motor with excellent electromechanical characteristics and together with it the entire chain of three-phase devices for generating, transporting and distributing electricity: three-phase transformers, generators, and power lines. Dolivo-Dobrovolsky's ideas were brilliantly embodied in the 170-km long Laufen–Frankfurt power transmission, which became a vivid example for electrical engineers around the world and an impetus for further widespread use of three-phase current.

Compound Fault Diagnosis Method of Modular Multilevel Converter Based on Improved Capsule Network

When submodule (SM) compound fault occurs in the Modular multilevel converter (MMC), the time-domain waveform characteristics of output current and internal circuiting current of MMC are not obvious, especially on the condition of high-level MMC. To address this issue, A compound fault diagnosis method based on an improved capsule network (CapsNet) is proposed in this paper. Firstly, The front end of the network adopts the feature extraction structure of One-dimensional Convolutional Neural Network (1DCNN) combined with Long and short-term memory network (LSTM). Then, the original data of MMC three-phase output currents and three-phase circulating currents are used as fault detection signal. The back-end employs a main capsule layer and a digital capsule layer structure, and realizes the transfer of feature vectors through a dynamic routing algorithm. This feature extraction structure combines the light weight of 1DCNN and the sequential sensitivity of LSTM. While ensuring that the information is fully extracted, the computational cost of the model is greatly reduced. Furthermore, the overlapping sampling method is used to construct and expand the sample sets. Compared with the other three common deep learning methods, their fault diagnosis performance under the condition of different levels and levels changing are analyzed respectively. The experimental results demonstrate that the proposed method has excellent cross-domain learning ability and high fault recognition accuracy.

Predictive Direct Torque Control Application-Specific Integrated Circuit With a Fuzzy Proportional–Integral–Derivative Controller and a New Round-Off Algorithm

This study developed a predictive direct torque control (PDTC) application-specific integrated circuit (ASIC) with a fuzzy proportional.integral.derivative (PID) controller and a new round-off calculation circuit for improving the ripple response of a hysteresis controller when sampling and calculating delay times in an induction motor drive. The proposed PDTC ASIC not only calculates the stator’s magnetic flux and torque by detecting three-phase currents, three-phase voltages, and rotor speed but also eliminates large ripples in the torque and flux by using the fuzzy PID controller. Furthermore, the proposed round-off algorithm reduces the calculation error of the composite flux. A fuzzy voltage vector switching table is proposed not only to speed up the calculating speed but also to resolve the instability generated by its large torque and flux ripples. The Verilog hardware description language was used to implement the hardware architecture, and the aforementioned ASIC was fabricated using the 0.18-μm 1P6M CMOS process of the TSMC by employing the cell-based design method. The predictive calculations, fuzzy PID controller, fuzzy voltage vector switching table, and round-off calculation algorithm improved not only the ripple issue faced in traditional direct torque control but also the control stability and robustness. The measurement results indicate that the proposed PDTC ASIC has an operating frequency, a sampling rate, and a dead time of 50 MHz, 100 kS/s, and 100 ns, respectively, at a supply voltage of 1.8 V. The power consumption and chip area of this ASIC are 1.0027 mW and 1.169 × 1.168 mm2, respectively. The main advantages of the proposed PDTC ASIC are its low power consumption, small chip area, robustness, and convenience.

Pengembangan Nominal Aturan Fuzzy pada Metode Fuzzy Mamdani untuk Menyeimbangkan Beban Tiga Phasa pada Saluran Distribusi Tegangan Menengah

The use of electrical equipment on the customer side with low voltage absorbs unbalanced power. The load unbalances in each phase will result in an unbalanced current, resulting in a phase voltage shift in the secondary coil of the 20 kV/380 V medium voltage transformer. Shifting the voltage in the distribution transformer phase, then causes the flow of current in the transformer neutral wire causing losses. This paper proposes a fuzzy logic method with the Mamdani fuzzy inference system (FIS) to balance three-phase load currents at seven feeders of 20 kV medium voltage distribution at PLN Rayon Taman Jawa-Timur. The feeders are Ngelom, Tawang Sari, Geluran, Bringin, Masangan Kulon, Palm Residence, and Pasar Sepanjang. There are three input variables used, namely the load current in phase R, phase S, and phase T respectively. There are three output variables in one FIS block, namely changes in load current in phase R, phase S, and phase T respectively. With the number of fuzzy rules as many as 509 rules, the proposed method is able to produce the lowest load current unbalance value of 1.6% at Palm Residence Feeders. The development of a nominal (number) of fuzzy rules in the Fuzzy Logic Method with FIS Mamdani is able to reduce the value of unbalance load current at the 20 kV medium voltage distribution feeder better than the method proposed by previous researchers.

Quaternion Fourier Transform spectral analysis of electrical currents for bearing faults detection and diagnosis

This paper suggests a new method for detecting and diagnosing bearing faults in three-phase asynchronous devices using the periodogram estimation of the Power Spectral Density of the three-phase electrical current space vector. Rather than a single single-phase spectral analysis or a space vector component spectral analysis using the classic Fourier Transform, The Quaternion Fourier Transform was used to do a full spectral analysis of the three-phase currents scheme. Spectral indicators are given from the Quaternion Power Spectral Density and their use suggested for accurate detection and diagnosis of bearing faults via the quaternion's formalism. To validate this approach, the proposed indicators were compared to fault indicators derived from a single-phase or inferred from the real and imaginary parts of the currents space vector. The results reveal that two of the new metrics outperform the classic ones derived from either single-phase spectral analysis or the three-phase space vector components spectral analysis (classification rates of 94.2 percent and 93.8 percent, respectively). These findings support the preference for three-phase approaches over single-phase approaches, as well as the ability to extend classical research methods developed for single-phase systems to three-phase systems using the Quaternion Fourier transform.

Verification Methodology for Simulation Models of the Synchronous Generator on Transients Analysis

During transients that occur in an electric network, large currents can flow and large electromagnetic torques can be developed in electric generators. Accurate calculation of currents and magnetic fields during transients is an important element in the optimal design of generators and network parts, as well as mechanical parts of machines and other torque transmission parts. This paper describes the modeling of a sudden three-phase short-circuit on a synchronous generator using the finite element method (FEM) and the dynamic model. The model for simulations that use the FEM was built in the MagNet software package, and the dynamic model is embedded in the MATLAB/Simulink software package. The dynamic simulation model of a part of a network with two identical generators, represented by equivalent parameters, was developed. The results obtained after the simulation of a sudden three-phase fault in the generators by both methods are presented, including three-phase voltages, three-phase currents, machine speeds, excitation voltages, and mechanical power. In particular, the short-circuit current in the phase with the highest peak value was analyzed to determine the accuracy of the equivalent parameters used in the dynamic model. Finally, the results of these two calculation methods are compared, and recommendations are presented for the application of different modeling methods.

A novel traveling wave arrival time detection method in power system

This paper proposes a high-speed and accurate method for extracting the arrival times (ATs) of traveling waves (TWs) in the power system that can be used for fault location applications and transmission line protection. The proposed method is based on the expression of the traveling wave as the exponentially damped component superimposed on the sinusoidal wave in a small time window. Also the sine component is removed by using approximation and consecutive differences of the input signal samples (the modal components of three-phase voltages or currents) from the resulting wave. Due to the fact that the estimation of traveling wave arrival times (TWATs) is done applying basic mathematical operations in the time domain, the proposed method, in addition to the simplicity of implementation, has the appropriate accuracy and speed for applications such as online fault location and protection purposes. In order to evaluate the performance of the proposed approach in fault locating, a 230 kV transmission line is modelled in EMTP/ATP. Then, the fault location under various conditions of faults such as changes in location and type of fault, fault conditions as well as variations in the measurement noise level and sampling frequency are studied using MATLAB.

Reactive power control of grid-connected photovoltaic micro-inverter based on third-harmonic injection

<span lang="EN-US">This paper presents four interleaved flyback DC-DC converters. Each flyback converter contains a separate maximum power point tracker (MPPT). The MPP tracker is used to collect the maximum power value from photovoltaic panel by using (P&O) algorithm with an output of reference current. In latest years, the active third-harmonic injection circuit have received much interest, this technique contributed to getting a better quality of injection current into the utility grid and control the reactive power. For converting direct current to three-phase sinusoidal currents, a line-commutated current source inverter type (CSI) with filter is used. The developed micro-inverter of (1000 W) offers an expanded range of reactive power control with balanced three-phase output power and good efficiency 95.07%. The effectiveness of the suggested system is clarified through the MATLAB program simulation. The system proposed in this paper has proven its effectiveness in obtaining reactive power control, nearly sinusoidal three-phase output currents and it is compared with the traditional PV micro-inverter system. The comparison shows that the PV micro-inverter is best in more specification than the traditional PV system such as efficiency and total harmonic distortion (THD) and the system losses.</span>

A New Modulated Finite Control Set-Model Predictive Control of Quasi-Z-Source Inverter for PMSM Drives

In this paper, a new modulated finite control set-model predictive control (FCS-MPC) methodology is proposed for a quasi-Z-source inverter (qZSI). The application of the qZSI in this paper is to drive the permanent magnet synchronous machine (PMSM). The proposed methodology calculates the optimal duration time (ODT) for the candidate vector from the switching patterns of the inverter after it is selected from the FCS-MPC algorithm. The control objective of the FCS-MPC are the three-phase currents of PMSM, when the motor speed is below or equal to the base speed. While at a speed beyond the based speed, the inductor current and capacitor voltage of the qZS network are added as control objectives. For each candidate optimal vector, the optimal time, which is a part of the sampling interval, is determined based on minimizing the ripples of the control objectives using a quadratic cost function. Then, the optimal vector is applied only to the inverter switches during the calculated ODT at the start of the sampling interval, while the zero vector is applied during the remaining part of the sampling interval. To reduce the calculation burden, the zero-state is excluded from the possible states of the inverter, and the sub-cost function definition is used for the inductor current regulation. The proposed modulated FCS-MPC is compared with the unmodulated FCS-MPC at the same parameters to handle a fair comparison. The simulation results based on the MATLAB/Simulink© software shows the superiority of the proposed algorithm compared to the unmodulated FCS-MPC in terms of a lower ripple in the inductor current and capacitor voltage, and a lower THD for the PMSM currents.

Fault Line Selection Method Based on Transfer Learning Depthwise Separable Convolutional Neural Network

With the continuous development of artificial intelligence technology, the value of massive power data has been widely considered. Aiming at the problem of single-phase-to-ground fault line selection in resonant grounding system, a fault line selection method based on transfer learning depthwise separable convolutional neural network (DSCNN) is proposed. The proposed method uses two pixel-level image fusions to transform the three-phase current of each feeder into the RGB color image, which is used as the input of DSCNN. After DSCNN self-feature extraction, the fault line selection is completed. With the consideration that not all of power distribution systems can obtain a large amount of data in practical applications, the transfer learning strategy is adopted to transplant the trained line selection model. The smaller number of DSCNN parameters increases the portability of the model. The test results show that not only does the proposed method extracts obvious features, but also the line selection accuracy can reach 99.76%. It also has good adaptability under different sampling frequencies, different noise environments, and different distribution network topologies; the line selection accuracy can reach more than 97.43%.

Fault Detection System for 500 kV AC Fault Current Limiter Based on High-Coupled Split Reactor

Aiming at the problem of limiting high short-circuit current in 500 kV AC power grid, we develop an economical-type fault current limiter (FCL) based on high-coupled split reactor (HCSR), namely, HCSR-FCL. This paper addresses designing the early fault detection system of HCSR-FCL. Firstly, it introduces the working principles of HCSR-FCL and gives the system design of HCSR-FCL control system. Subsequently, it discusses the real-time requirement of the HCSR-FCL control system, and apply an early short-circuit fault detection algorithm based on the ratio of the summation of squared three-phase currents (SSC). Then, it gives implementation of the applied algorithm, and also designs the hardware of fault detection unit. Finally, simulation verification on RTDS (real-time digital simulation system) platform is given. Experimental results show that the designed system can detect short-circuit fault rapidly and robustly. When short-circuit occurs, the control system designed can output control signals, which enables the FCL into operation quickly.

Cascaded Multilevel Rectifier with Common High Voltage Direct Current (HVDC) Bus and Its Control Method

In order to realize the voltage equalization and minimize the total harmonic distortion rate of current of cascaded multilevel rectifier with common high voltage Direct Current (HVDC) bus, the cascaded multilevel rectifier with common high voltage DC bus and its control method are studied. The output side DC voltage of the cascade multilevel rectifier with common high voltage DC bus is sampled, and the output DC current signal amplitude is obtained according to the calculated output side DC voltage signal. On this basis, the AC side voltage corresponding to the applied switching state and the switching state corresponding to the rectifier in the sampling period are solved. The driving signal of the switch device is generated and sent to the corresponding switch device to realize the active power factor correction and sinusoidal input current, so as to realize the balanced control of output DC capacitor voltage of cascaded multilevel rectifier with common High-Voltage Direct Current (HVDC) bus. The test results show that this method can effectively control the three-phase output current of the rectifier and ensure the maximum output of the current. The lowest total harmonic distortion rate of the output phase voltage is about 40%, which can effectively ensure the stability of the output phase voltage after control.

Penentuan Kapasitas PMT SF6 Pada Bus 70 KV Menggunakan Simulasi Program ETAP

The electric power system consists of several components, namely generation, distribution, transmission and load. Along with the rapid development of technology in the field of electricity today, a protection system is installed at substations, one of which is a powerbreaker (PMT) at each substation. In the event of a disturbance, the protection relay will detect and instruct the breaker to open or disconnect the circuit from the disturbance, then a circuit breaker will receive a signal from the relay and in the end will decide the circuit according toits current rating. Based on the type of PMT isolation media, PMT is divided into 4 types, one of which is the SF6 gas isolation media type. This type of PMT can be used to cut currents up to 40 KA and in circuits with a voltage of 765 KV. It must be noted that if the current is very large at the time of short circuit, then the thing that must be considered is the capacity of thebreaker itself. To determine the breaker capacity, it is sought from the largest short-circuit current, namely a three-phase short circuit. In finding a three-phase short circuit current can be simulated using the ETAP (Electric Transient Analysis Program) program. ETAP can simulatepower flow and short circuit current. The results of the calculation of the PMT capacity on the 70 KV bus are 0.324 KA and from the results of the calculation and analysis of the PMT it is included in the rating of 12.5 KA where the PMT with the rating value can decide the fault current from 0.9 KA -7.74 KA

Classification and direction discrimination of faults in transmission lines using 1D convolutional neural networks

<span lang="EN-US">This paper presents a fast and accurate fault detection, classification and direction discrimination algorithm of transmission lines using one-dimensional convolutional neural networks (1D-CNNs) that have ingrained adaptive model to avoid the feature extraction difficulties and fault classification into one learning algorithm. A proposed algorithm is directly usable with raw data and this deletes the need of a discrete feature extraction method resulting in more effective protective system. The proposed approach based on the three-phase voltages and currents signals of one end at the relay location in the transmission line system are taken as input to the proposed 1D-CNN algorithm. A 132kV power transmission line is simulated by Matlab simulink to prepare the training and testing data for the proposed 1D- CNN algorithm. The testing accuracy of the proposed algorithm is compared with other two conventional methods which are neural network and fuzzy neural network. The results of test explain that the new proposed detection system is efficient and fast for classifying and direction discrimination of fault in transmission line with high accuracy as compared with other conventional methods under various conditions of faults.</span>

UNJUK KERJA SISTEM PENTANAHAN TRANSFORMATOR PADA GARDU INDUK 150 KV PT. AMMAN MINERAL NUSA TENGGARA

Short-circuit faults is a faults that must be overcome by protective equipments. One of the protective equipment is a grounding system that serves to reduce the fault current to the ground. The grounding system that will be analyzed in this research is grounding system of the transformer at 150 kV substations PT. Amman Mineral Nusa Tenggara (AMNT) which is then compared to other type of grounding which is gorunding with resistance and reactors in relation to reducing the short circuit current. This research was conducted with a simulation with secondary data from PT. Amman Mineral Nusa Tenggara. The method used is the Newton-Raphson method to obtain power flow in the normal state of the system. Short-circuit fault analysis is carried out in a simulation using ETAP 12.6 Software. The results showed thatthat solid-grounding of the transformer at 150 kV substations PT. AMNT conducts a large fault current. For single line-to-ground faults the magnitude is 2.658 kA at 0% fault distance or at the beginning of the transmission line and this value decreases with the fault distance away from the power plant system. Resistance grounding, whether with low resistance (12 and 40 Ohm) or high resistances (500 Ohm) do not fulfill its grounding requirements. For grounding using a 108 Ohm reactor, the magnitude of single line-to-ground faults is 1,001 kA at 0% fault distance or at the beginning of the transmission line and this value decreases with the faults distance away from the power plant system. This value still fulfill its grounding requirements which is the available ground-fault current should be at least 25% and preferably 60% of the three-phase fault current.

A Three-Phase Current Tacholess Envelope Order Analysis Method for Feature Extraction of Planetary Gearbox under Variable Speed Conditions.

Planetary gearboxes are the key components of large equipment, such as wind turbines, shield machines, etc. The operating state of the planetary gearbox is related to the safety of the equipment as a whole, and its feature extraction technology is essential. In assessing the problem of the non-stationarity of the current signal under variable speed conditions and the difficulty of evaluating the operating state of the planetary gearbox under a tacholess condition, a three-phase current, variable-speed tacholess envelope order analysis method is proposed. Firstly, a tacholess rotation speed estimation is completed by extracting the trend term of the instantaneous frequency of the asynchronous motor’s three-phase currents. The motor slip rate is assumed to be constant. Then, the envelope order analysis signal is obtained by re-sampling in the angular domain. Finally, the features of the envelope order signal are extracted, and a linear discriminant analysis (LDA) algorithm is used to fuse multiple indexes to generate a comprehensive feature reflecting the operating status of the planetary gearbox. The results of the simulation analysis and experimental verification show that the proposed method is effective in evaluating the operating state of the planetary gearbox under variable speed conditions. Compared with the traditional time–frequency ridge extraction method, the tacholess speed estimation method can improve the instantaneous speed estimation accuracy. The comprehensive index of envelope order completes the planetary gearbox state identification process, and a 95% classification accuracy rate is achieved.

Strategies to Increase the Transient Active Power of Photovoltaic Units during Low Voltage Ride Through

Due to a limitation in the magnitude of the three-phase output inverter currents, the output active power of the photovoltaic (PV) unit has been de-rated during low voltage ride through, which brings great instability risk to the power system. With the increase in the penetration rate of new energy, the impact of the power shortage on the system transient stability increases. It is of great significance to analyze the impact of this transient power shortage on system stability. This article explores methods to improve the active power output capability of photovoltaic units during low-breakthrough periods. A transient simulation model of a grid-connected PV generator with low-voltage ride-through (LVRT) capability is presented, under the condition of meeting the overcurrent capacity of the PV inverter and the requirement of dynamic reactive power support supplied by the PV generator specified in the China grid codes (GB/T 19964-2012) during grid fault. An example system with high PV penetration is built. The change principle and influencing factors of PV transient active power output are analyzed. The simulation model is designed in PowerFactory/DIgSILENT, and several types of three-phase voltage sags are performed in simulation to assess the impact of the active current reference calculation method and the maximum inverter output current (Imax) limit value on the PV active power output. According to the three indexes, namely the maximum active power of PV unit during the fault, the power improvement gradient and the power surge after the fault is cleared. Simulation results showed that using the orthogonal decomposition method to calculate the active current reference can make full use of the current capacity of the converter. Setting Imax to 1.1 rated current of photovoltaic inverter (IN) can reduce the cost-effectiveness ratio of the transient active power output of the PV unit. Therefore, we aim to improve the unit’s transient active power output capacity and realize the optimal effect of improving the transient active power shortage of the system.

High-Efficient Brushless Wound Rotor Synchronous Machine Topology Based on Sub-Harmonic Field-Excitation Technique

This paper presents a new high-efficient three-phase brushless wound rotor synchronous machine (BL-WRSM) based on a sub-harmonic field excitation technique. In the proposed machine topology, the stator is equipped with two different three-phase windings: (1) main armature winding, and (2) additional armature winding. The main armature winding is based on a 4-pole winding configuration, whereas the additional armature winding is based on a 2-pole winding configuration. Both windings are supplied current from two different inverters, i.e., inverter-1, inverter-2, and simultaneously. Inverter-1 provides the regular input current to the main armature winding, whereas inverter-2 provides a three-phase current of low magnitude to the 2-pole additional armature winding. This generates an additional sub-harmonic component of MMF in the airgap beside the fundamental MMF. On the other side, the rotor is equipped with (1) harmonic, and (2) field windings. These windings are electrically coupled via a rectifier. The fundamental component of MMF produces the main rotating magnetic field, whereas the sub-harmonic MMF gets induced in the harmonic winding to produce harmonic current. This current is rectified to give DC to the rotor field winding to attain brushless operation. To authenticate the operation and analyze its performance, the proposed BL-WRSM topology is supported using 2-D finite element analysis (FEA) in JMAG-Designer. Later on, the performance of the proposed brushless topology is compared with the customary BL-WRSM topology to verify its high efficiency, high output torque, low torque ripple, and low unbalanced radial force on the rotor.