Voltage Components Research Articles

Techno-Economical Effects of Adopting Small Capacity Transformers on Ado-Ekiti 11/0.415 kV Power Distribution Networks

The major portion power loss in power system occurs in the components of low voltage (LV) networks. Low voltage distribution system (LVDS) configuration has been observed to contribute significantly to power loss and unacceptable voltage drop in the system due to its structure and higher current flow in the network. The adoption of small capacity transformers as high voltage distribution system (HVDS) configuration is increasingly applied to the network for power loss reduction and the improvement of voltage profile. This study aims to evaluate the technical and economic implication of the use of HVDS configuration on Ado-Ekiti 11/0.415 kV power distribution networks and provide necessary recommendations. The network data was obtained and modeled on NEPLAN software for simulation and technical evaluation of the networks. The existing LV lines were upgraded to high voltage (HV) and remodeled with small capacity transformers and comparative analysis of the technical and economic effects of the networks were carried out. The results obtained showed that there could be feeder capacity increase of 92.03 kW and power loss reduction of 347.17 kW and 459.72 kVar following reconfiguration from LVDS to HVDS. The losses in the transformers and lines were significantly reduced by 37.8% for HVDS configuration when compared with the LVDS configuration. The voltage profile was significantly improved with voltage deviations in the range of ± 0.01 to ± 0.03 of bus voltage for the HVDS network when compared to the existing network. The cost of implementation of the HVDS network substation was calculated to be ₦807,238,715.50 and with the combination of annual savings and an increment in tariff of ₦5/kWh in the billing charge of unit energy consumption resulted in a payback period of 2 to 3 years for the estimated capital investment. This study showed that technical performance of HVDS implementation on the Ado-Ekiti network feeder was better than that of the existing network.

Fast Harmonic Rejecting Control Design to Enable Active Support of Charging Stations to Micro-Grids Under Distortion

This paper proposes a fast harmonic rejecting control design to enable active support of electric vehicle (EV) charging stations to micro-grids under distortion. The proposed harmonic rejecting strategy is applied to control bidirectional converters and storage elements in charging stations to improve performance of charging stations under various distorted conditions. In this approach, power quality of both ac- and dc-grids is improved by actively rejecting unwanted harmonic components in voltages, currents, and powers. A fast dynamic control design can actively reject harmonic components where harmonic filters are used to eliminate unwanted components in signals. The paper shows that the proposed harmonic rejecting method can result in a simple control design in stationary frames without any phase-lock-loop ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PLL</i> ) blocks. A two-stage optimization method is introduced under the predictive control fashion, i.e., optimizing vector angle for control performance and then modulating vector magnitude by coordinating one active- and one zero-switching state. The comparative results prove that not only control performance is resilient under distorted conditions but also the power quality on both ac- and dc-grids is actively improved. Both MATLAB/Simulink and real-time experimental platforms are used to verify the efficacy of the proposed approach in terms of compensating the reactive power, rejecting the imbalance harmonic distortions, and smoothing the dc-voltage.

Performance Analysis of Matrix Pencil Method Applied to High-Resolution Measurement of Supraharmonics

Supraharmonics emitted by power electronic equipment will cause electromagnetic interference. However, there is no uniform standard for the measurement of supraharmonics. Unlike non-parametric methods, such as Fourier transform, the matrix pencil method has attracted the attention of researchers in many fields because of its super-resolution characteristics. In this paper, an attempt is made to apply the matrix pencil method to the high-resolution measurement of supraharmonics. Noting that parametric methods offer a promising alternative strategy for high time-resolution analysis of supraharmonics, the matrix pencil method is introduced for high-resolution measurements and estimating the supraharmonic components in grid voltage and current signals. By deriving and analyzing the Cramér–Rao bound of the method, two excellent properties of the matrix pencil method are found: robustness to time-varying signals in supraharmonics measurements and accuracy in frequency localization of components with large amplitudes. Meanwhile, the effectiveness of the matrix pencil method when applied to the high-resolution estimation and measurement of supraharmonics in grid signals is demonstrated by measuring, estimating, and analyzing grid voltage and current signals containing different typical supraharmonics characteristics. This parametric approach opens up a new avenue that allows more signal information to be obtained while maintaining high accuracy, thus enabling the analysis of supraharmonics with higher time resolution.

Pilot protection method of half-wavelength AC transmission lines based on random matrix theory

The fault characteristics of ultra-high voltage (UHV) half-wavelength (HWL) transmission lines exhibit significant differences from those of conventional transmission lines, which renders the conventional relay protection method unsuitable for ensuring the protection of HWL. To solve this problem, a pilot protection method of HWTL based on random matrix theory was proposed. Voltage and current fault components obtained at the protection installation on both sides of the line were used as the input of the random matrix to form the singular value equivalent matrix, and the eigenvalues of the random matrix at both ends were calculated. The faults inside and outside the area were determined according to the distribution of the eigenvalues in the circular plane area. The protection scheme avoids the data synchronization problem at both ends of the line. Real time digital simulation system (RTDS) simulation revealed that the proposed protection method can protect the full length of the line, is suitable for various fault types and fault conditions, and exhibits excellent resistance to transition resistance.

Active power filter module function to improve power quality conditions using GWO and PSO techniques for solar photovoltaic arrays and battery energy storage systems

This study aims to unbalanced power quality (PQ) conditions analysis of solar photovoltaic arrays and battery energy storage system (PV-BESS) integrated active power filter module (APFM). Here, the APFM's role is to mitigate the PQ issues that existed by the nonlinear loads. The standalone PV-APFM design is negligibly reliable approximated to a hybrid PV-BESS system because of its fluctuation and high environmental reliance. Further, here the research challenge is to optimise the APFM controller gain coefficients by the grey wolf optimization (GWO) algorithm and apply this technique to current and voltage harmonic loops (CHL-VHL) to achieve the best answer to enhance the unbalanced PQ conditions. The multi-objective functions (MOFs) to crack the problem include the total harmonic distortion (THD) of current and voltage components. The particle swarm optimization (PSO) approach will be considered a complementary method for validation and comparison with the outcomes obtained from the GWO procedure. Four case studies in imbalance conditions have been considered to confirm the proposed method in MATLAB-Simulink software.

Short-Circuit Fault Detection and Quantitative Analysis Based on Mean-Difference Model With Variational Modal Decomposition

Abstract Short-circuit failure is one of the triggers for thermal runaway of lithium-ion batteries, which can lead to serious safety issues. This paper attempts to estimate the short-circuit resistance of the cell using the mean difference model and relies on the estimated results to make a quantitative analysis of short-circuit fault. To achieve this goal, a combination of forgetting factor recursive least squares and extended Kalman filter is used to estimate the average open-circuit voltage within the battery pack. Subsequently, since both the open-circuit voltage (OCV) and intrinsic mode function (IMF0) components reflect the low-frequency characteristics of the battery voltage, we propose a new method based on the variational modal decomposition to extract the differential open-circuit voltage of the battery and finally make an estimate of the short-circuit resistance after obtaining OCV of the battery using the idea of the mean difference model (MDM). In addition, the effectiveness of the proposed method is verified under different degrees of short-circuit faults by connecting different resistors to the series battery pack.

Modified Extended Complex Kalman Filter for DC Offset and Distortion Rejection in Grid-Tie Transformerless Converters

Proper operation of the grid-tie transformerless converters under unbalanced and distorted conditions entails a precise detection of the frequency and fundamental component of the grid voltage. One of the main problems that could arise during the estimation of grid parameters is the existence of a DC offset generated from measurement and A/D conversion. This undesirable induced DC offset could appear as a part of the reference sinusoidal current of grid-tie converters. Although literature has proposed the use of an extended complex Kalman filter (ECKF) for the estimation of positive and negative sequence voltage components as a promising competitor to phase locked loops, mitigating the effect of possible DC offsets when a Kalman filter is employed remains scarce. This paper proposes a new extended complex Kalman filter to improve the filter stability for estimating the frequency and the fundamental positive and negative symmetrical components of the grid voltages, where DC offset, scaling error, and noise can successfully be rejected. The theoretical findings are experimentally validated.

Principles for Implementation of Digital Power Direction Control in Microprocessor Current Protections

In the existing microprocessor-based directional current protection lines from phase-to-phase short circuits, digital power direction elements are used, which, as a rule, are switched on at full currents and voltage according to the so-called 90-degree pattern. With this switching scheme, a “dead” zone appears only in case of three-phase short circuits close to the protection installation site, which make up a small fraction of all possible types of such damage. Nevertheless, its presence is a significant drawback of the power direction organs. The principles of organ execution based on digital operations with orthogonal components of input voltages and currents have been considered. The result of the functioning of the power direction body is reduced to the development of an information sign equal to: one – with the direct direction of power; minus one – when it is in the opposite direction. To eliminate the “dead” zone, the work of the organ is organized using the voltage “memory”. In order to obtain the required duration of the “memory”, frequency compensation is implemented. The study of the effectiveness of the decisions made, as well as the behavior of the power direction control in normal and emergency modes, has been carried out by the method of a computational experiment. In the MATLAB-Simulink-SimPowerSystems dynamic simulation system, models of the electrical system and a digital power direction control have been developed. The results of the research have shown that the joint use of the existing and proposed principles for the implementation of a digital power direction control ensures an increase in its technical perfection and eliminates the “dead” zone while maintaining its stable operation for an arbitrarily long period of time.

Analysis of the DC/DC Zeta topology converter ripples by applying its limiting continuous mathematical model

Objectives. A DC/DC Zeta topology converter represents a unipolar electronic device for converting an input positive voltage into a stabilized output voltage of the same polarity, which can be set at voltages both below and above the input voltage. The aim of this work is to analyze Zeta converter circuitry, which requires the following tasks to be solved: using Kirchhoff’s Circuit Laws, obtain systems of equations describing converter operation in the phase of energy accumulation and in the phase of energy transfer; using a method proposed by A.I. Korshunov, combine the resulting systems of equations into a marginal continuous mathematical model; using expressions describing constant components of currents and voltages in Zeta converter, analyze their ripples and obtain equations for their calculation; compare the current and voltage values obtained from the continuous limiting mathematical model with the Zeta simulation results.Methods. The tasks are solved using Kirchhoff’s rules and the method for obtaining the limiting continuous mathematical model proposed by A.I. Korshunov. The results are analyzed using a circuit modelling in NI Multisim.Results. It is shown that the phase coordinates of the mathematical model tend to real values of converter currents and voltages at a switching frequency of the power switch of more than 200 kHz. A strong correspondence was established between the calculated ripple values and their values obtained in the simulation (when changing the duty factor).Conclusions. Mathematical models comprise the basis of unified calculation methods for any radio electronic circuit. The developed limiting continuous mathematical model allows a range of changes in current flowing through the choke windings and voltages on capacitor plates to be evaluated, including their maximum and minimum values for various converter parameters, such as power switch switching frequency, duty factor, element ratings, etc. Obtaining this information in turn enables the rational selection of the electronic component base of the converter.

Open-Circuit Fault Diagnosis for Permanent Magnet Synchronous Motor Drives Based on Voltage Residual Analysis

With the widespread application of permanent magnet synchronous motor (PMSM) drives, the demand for safety and reliability has increased. Inverter open-circuit fault is a frequent and severe failure that requires reliable detection and remedial measures. This paper proposes an open-circuit fault diagnosis technique based on voltage residual analysis that does not require additional voltage sensors. The proposed technique analyzes the characteristics of the reference voltage and the actual output voltage under both healthy and fault conditions. To achieve fast and reliable fault detection, it uses the DC component and second harmonic component in the residual voltage between estimated voltage and controller reference voltage. Once an open-circuit fault is detected, the polarity of the DC component is capable of identifying the fault location. The effectiveness and robustness of the proposed technique are verified through simulations and testing on a triple redundant PMSM under various load and speed conditions.

DEVELOPMENT OF A COMPREHENSIVE APPROACH TO DIAGNOSING THE OVERHEAD LINE FAULTS LOCATION IN SINGLE-PHASE GROUND FAULTS BASED ON A DIGITAL SUBSTATION DATA PROCESSING ALGORITHM

Link for citation: Sushkov V.V., Sukhachev I.S., Sidorov S.V. Development of a comprehensive approach to diagnosing the overhead line faults location in single-phase ground faults based on a digital substation data processing algorithm. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр. 66-77. In Rus. Relevance. Emergency of electric complex of outgoing transmission lines is associated with the occurrence of damage to the line isolation and the resulting transients, marked by the presence of higher harmonic components of currents and voltage, which reduce the reliability and energy efficiency of electrical equipment of oil and gas companies: degrade the mechanical characteristics and efficiency of electric motors, accelerate aging of their isolation, disrupt the operation of control systems and emergency automatics, fault diagnostics systems. One of the reasons of high-level emergency situations, outages and emergency repairs in electric complexes of outgoing transmission lines of oil and gas companies is appearance of phase-to-ground faults. A large number of changing factors are known to influence the reliability of phase-to-ground fault location methods: parameters of transmission line operating mode, its structural and electrical parameters, fault type, transient resistance value, ground resistance and others. Inclusion in the transmission line fault location algorithms of averaged values of a number of the factors listed above independent of changes of humidity of soil and air, its temperature and other factors causes an error of methods of fault location up to 30 %. Accordingly, the research to develop a fault location method for overhead transmission lines with isolated neutral points during phase-to-ground faults based on a digital substation data processing algorithm, accounting for tower parameters and natural-climatic factors, is relevant. Objective: improving the reliability of power grids and providing consumers with power of the required standard by applying a digital fault location system to the outgoing transmission lines electrical complex. Methods: mathematical analysis of a power transmission line, taking into account its design features and natural-climatic factors on the basis of the method of mirror images; mathematical analysis of steady-state and transient modes of transmission line operation considering self and mutual parameters terms of wires; transmission line currents and voltages Fourier analysis; validation of developed method of phase-to-ground fault location in power grid of Tyumen region energy company. Results. The authors have developed the phase-to-ground faults location method for transmission lines in power grids with isolated neutral points, which differs in the following – first the faulty overhead line feeder branch is identified by correspondences between the negative sequence voltage values of the phase voltages at the transformer substation inputs, and then the distance to the location of the single-phase ground fault is determined along the branch line based on the resonant frequencies of the line taking into account its design features and natural and climatic factors.

Power Quality Analysis for Light-Duty Electric Vehicles: A Case Study in Malta

This paper presents a power quality analysis for multiple electric vehicle charging stations of the AC-Level 2 type in a real-life case study. The data was collected with a power quality analyzer that measured the main distribution system feeding nine 7 kW charging stations in a commercial site with light-duty vehicles in Malta, Europe. The relevance of this study to the specific case of Malta is accentuated by the topological challenges of the country; high density of road vehicles, with 18,000 vehicles for each square kilometer; and ambitious targets of reaching carbon neutrality by 2050. Data were collected over six days on an actual charging system with real-life charging patterns. Various results are presented in this paper, including three-phase system voltages and currents, individual harmonic voltage and current components, total harmonic distortion and total current demand distortion. These measurements were compared with standardized thresholds for low-voltage equipment used in public spaces, mainly as stated in IEEE 519-2014.

Passive Island Detection Method Based on Positive Sequence Components for Grid-Connected Solar–Wind Hybrid Distributed Generation System

This paper presents the development and practical implementation of a new passive island detection method for grid-connected hybrid distributed generating systems. The method employs positive sequence voltage and current components at the point of common coupling. The product of the difference in positive sequence voltage and the difference in positive sequence current is used to produce the Islanding Detection Index (IDI). Islanding is identified when the IDI magnitude surpasses a predefined threshold over a predefined delay time. Even in the case of a zero power mismatch condition, the proposed method can identify the islanding condition in under 70 msec. Its effectiveness is validated under various operating circumstances. It provides excellent stability against various non-islanding situations, avoiding unwanted tripping. The suggested method also has the advantages of being simple and inexpensive to implement, having no adverse effects on output power quality, not requiring a classifier, not being system-dependent, and working regardless of the quantity and type of distributed generation connected to the utility grid. The obtained detection timings were compared to those previously reported in the literature, confirming the proposed approach’s superiority. The suggested work utilizes the OPAL-RT real-time hardware-in-loop environment and MATLAB/Simulink.

A modified mutual impedance based backup protection for series-compensated transmission lines

This paper proposes a modified mutual impedance based backup protection for series-compensated transmission line. In case of failure of current-differential scheme, distance relaying scheme provides protection by calculating and comparing positive-sequence impedance up to fault point. However, non-linear operation of metal-oxide varistor (MOV) result in continuously varying equivalent impedance across series-capacitor during fault which affects the reach and directional discrimination feature. Inter-phase mutual impedance of line up to fault point is proportional to the distance of fault from relaying point and therefore can be exploited as a reliable relaying parameter for backup protection purpose. The reason is that the equivalent impedance across MOV protected series-capacitor does not alter inter-phase mutual impedance up to fault point. This mutual impedance can be computed utilizing sequence components of voltage and current phasors measured by phasor measurement unit (PMU) at line ends. Existing mutual impedance based scheme is highly influenced by fault resistance and synchronization error. The proposed modified algorithm is developed to overcome the effects of fault resistance and synchronization error as compared to previously developed scheme. The performance is assessed for different single line-to-ground (SLG) and double line-to-ground (LLG) fault cases with variations in fault resistance, fault distance (FD) and compensation level. Simulation results affirm the advantages of proposed scheme as an extra layer of protection over conventional schemes and prove superiority in performance over existing mutual impedance based scheme. Experimental results also demonstrate the feasibility of deployment for practical applications.

Space vector-based model predictive current controller for grid-connected converter under unbalanced and distorted grid without a phase-locked loop

This paper presents an improved current control strategy for a three-phase voltage source converter connected to distorted grid. The proposed controller can successfully compensate the induced harmonic currents, while suppressing possible active power ripple. To manage various objectives and deal with tough restrictions, model predictive control can offer a promising solution. However, a modified extended complex Kalman filter is introduced to estimate the positive and negative fundamental components of the grid voltages which are used with the real and reactive power references to generate pure sinusoidal reference currents without the need for a phase-locked loop (PLL), avoiding its challenges under abnormal grid conditions. An improved space vector-based model predictive control (SVM-MPC) is proposed to regulate the real and reactive power components. The main target of this controller is to maintain harmonic free grid currents, even in unbalanced and distorted grid conditions, with enhanced performance in terms of fast dynamic response and good steady-state behavior. The proposed SVM MPC uses Pythagoras theorem to determine duty factors, avoiding trigonometric functions, which improves the computational burden and implementation complexity. In addition, fixed switching frequency can be ensured. Simulation and experimental results are carried out to validate the effectiveness and the practical feasibility of the proposed controller under distorted grid conditions.

LTP Modeling and Analysis of Frequency Coupling in PLL-Synchronized Converters for Harmonic Power Flow Studies

As known, nonlinear loads in power systems originate harmonic distortion and power quality issues. Converter-interfaced loads exhibit a nonlinear behaviour as well and may largely contribute to increase the harmonic pollution. The nonlinearities introduced by the PLL-synchronization and power control originate, indeed, a coupling mechanism between fundamental and harmonic frequencies. These harmonic coupling effects are not captured by traditional Norton/Thevenin equivalent converter models, leading to inaccurate harmonic power flow analyses. This paper proposes a Linear Time Periodic model of a PLL-synchronized converter to be used in Harmonic Power Flow analyses. A realistic 18-bus distribution grid hosting substantial amount of power-electronic interfaced resources is used as a case study. It is revealed that, in high grid loadability condition and with distorted grid supply voltage, the harmonics are significantly amplified by the converters and the fundamental components of the buses voltages are reduced, representing a risk for the voltage stability. This phenomenon is also influenced by the tuning of the current control loop and the PLL. The accuracy of the presented analyses is validated by comparing the harmonic power flow results with time-domain simulations.

Development and testing midpoint voltage balance algorithms of three-level inverters

Nowadays, the use of inverters is increasing in more and more applications. Environmental awareness is becoming a trend, so more and more people install solar energy systems on their houses, which also require the use of inverters. Higher power levels have led to the emergence of three-level inverters which has opened up new challenges, such as the issue of midpoint voltage balancing. This paper discusses voltage balancing and voltage ripple reduction techniques for three-level inverters with Neutral-Point Clamped (NPC) topology. The balancing is based on injecting zero-sequence voltage component in carrierbased modulation. The viability of the modulation techniques are verified by computer simulation and then tested on hardware.

ЕФЕКТИВНІСТЬ ЗАСТОСУВАННЯ МАКСИМАЛЬНОГО СТРУМОВОГО ЗАХИСТУ В ПІДЗЕМНИХ МЕРЕЖАХ

The article considers the use of maximum current protection in underground mine electrical networks, which disables short-circuit currents with an absolute value greater than the starting currents of powerful electric motors. It was determined that these protections have a number of disadvantages. The article reveals that the protection with the current-time characteristic is more perfect than the maximum current protection, but in the case of arcing short circuits, the values of which can be less than the starting ones in absolute value, the protection activation time significantly exceeds the permissible value. Protection with filters of symmetrical components of currents and voltages reduces the sensitivity to two-phase short circuits with a connected load, protection at the level of the third harmonic in the event of a short circuit has a limited range of action and requires duplication. It was investigated that with the use of valve converters and thyristor schemes for controlling the drives of lifting installations and conveyor transport in underground networks, the level of higher harmonic currents increased. In the practice of work of domestic and foreign enterprises, it has been proven that capacitor banks, which are installed to compensate for reactive power, have protection against overcurrents and shortcircuit currents, but with non-sinusoidal voltage, in a number of cases, they quickly fail because they are overloaded with higher harmonics. The article shows that with the increase in the power of the engines of the underground district networks and the manifestation of the asymmetry of the air gap, the higher harmonics given exceed the permissible values. Therefore, the article presents the most promising directions for the construction of systems for the protection of mine distribution underground networks and electrical installations

ДОСЛІДЖЕННЯ ВПЛИВУ ІМПУЛЬСНИХ ПРОЦЕСІВ В ОБМОТКАХ ТРАНСФОРМАТОРА

The article examines the existence of uneven voltage distribution under the action of transient voltage, which is the main cause of insulation breakdown of power transformers. In fact, the winding of the power transformer has no tap and cannot be directly used to measure the impulse voltage. The study of pulse voltage distribution measurement is important and practical in engineering. The voltage distribution for the isolated neutral, when the current does not flow through the winding ipr = 0, occurs according to the exponential dependence, and the amount of overvoltage is equal to the initial voltage on the winding of the transformer, which decreases. When the induced voltage is varied along the winding of a transformer with an isolated neutral in steady state, the entire winding takes the same potential with respect to ground and the steady voltage is a straight line. It follows that in the case of an insulated neutral, the end of the winding must have the same insulation as the beginning. The change in maximum voltage is presented when U0 changes in the range from 550 kV to 850 kV. In the work, the change of U0 from values (550-850 kV) to 0 V was studied, with the length of the coil wire x=l= 100 m. Thus, in both cases, it is not difficult to determine the sum of the amplitudes of individual harmonics at any point of the winding. During the development of self-oscillations, the voltage exceeds the set value, and tends to decrease the frequency of self-oscillations. On the basis of the conducted research, transient overvoltage distributions in the transformer windings were calculated. These results will be useful for designers to evaluate the resistance of transformer insulation to transient voltages and further optimize the graded longitudinal insulation. Transient overvoltage distributions in transformer windings are modeled. It was concluded that the impulse voltage distributions in the transformer windings are mainly related to the high-frequency components of the winding voltage.

Analysis of equilibrium points and optimal grid support of grid-forming modular multilevel converter for balanced and unbalanced faults

This short-communication presents a steady-state analysis of a grid-forming Modular Multilevel Converter (MMC) providing optimal voltage support to the AC network under normal and constrained conditions. The analysis is performed based on a multi-objective function (OF) optimization problem which prioritizes to maximize the positive-sequence and to minimize the negative- and zero-sequence voltage components at the point of common coupling (PCC) while it also considers the minimization of the arm impedance losses, respectively. If the voltage condition at the PCC is satisfied, the optimization attempts to reduce the arm impedance losses; otherwise, the algorithm prioritizes the PCC’s voltage components in order to minimize the error. Different network voltage and internal fault scenarios are evaluated, where it is shown that the suggested problem formulation can be used to obtain the optimal MMC’s quantities, providing voltage support during the faults.