Voltage Harmonic Levels Research Articles

Comparative Analysis of Definitions for the Harmonic Emission Levels

To keep a high level of power quality, Distribution System Operators (DSOs) must keep harmonic voltage levels under limits specified in standards. These harmonic voltages are due to non-linear equipment connected inside installations, which inject harmonic currents into public networks. In order to apply emission limits per installation, DSOs need to have an accurate and reliable indicator to assess the harmonic emissions of an installation. In this paper, a comparative analysis of two definitions for assessing the harmonic emissions of installations is presented. Their respective advantages and drawbacks are pointed out.

Assessment of the Performance of Frequency Domain Models Based on Different Reference Points for Linearization

Power electronic-based loads are increasingly used in modern distribution systems. Such appliances inject harmonic currents into the power system and thus, they can have serious impacts on the power quality of the system. Therefore, it is necessary to find suitable frequency domain models of these loads to predict their contribution to the harmonic voltage levels. So far, various modeling approaches have been proposed in the relevant literature. Usually, they are parameterized based on laboratory measurements. In this paper, however, a circuit-based time domain model of a Compact Fluorescent Lamp (CFL) is implemented in MATLAB®/Simulink® and used for the parameter identification of three different frequency domain models. These models usually rely on a linearization of their emission characteristic and therefore, it is required to choose an appropriate reference voltage. As the supply voltage in real distribution systems is already distorted, the commonly made assumption of a sinusoidal reference voltage may increase the inaccuracy of models for strongly non-linear devices. Therefore, different reference points for the model parameterization are specified and their impact on the model performance under typical voltage distortions is studied.

Close accord on partial discharge diagnosis during voltage harmonics in electric motors fed by variable frequency drives

AbstractPartial discharge (PD) diagnostics test is a reliable solution for estimating insulation health conditions in power system components. During laboratory PD diagnostics, the effect of harmonic components in the voltage waveform generated by variable frequency drives (VFD) fed electric motors (EMs) is often overlooked. As VFD‐fed EMs operate at low speeds, the harmonic concentration in the voltage increases. It has been found that PD activity in VFD‐fed EM is significantly affected by the addition of harmonic components in the voltage, thus making it necessary to consider their impact when performing true PD diagnostics. This paper investigates the influence of voltage harmonic distortion produced in VFD‐fed EM on PD severity and the subsequent insulation degradation. Eight VFD‐fed EM are used to study the PD behaviour under different levels of harmonic pollution. The PD characteristics, such as inception voltage, pulse repetition rate, accumulated apparent charge, average discharge current, discharge power, and quadratic rate, are determined. Using probability distribution functions, PD activity and severity at various voltage harmonic levels are estimated. The proposed technique can be used to plan the maintenance activities that ensure the reliability for industrial applications dealing with the voltage harmonic distortion.

Harmonic Characteristics and Negative Sequence Analysis of Regenerative Braking for High-speed Railway

Background: The traction power supply system (TPSS) of railways mainly focuses on power quality analysis. In the study of harmonic and negative order currents, about 80% of the literature analysis are not specific enough， there is a lack of completeness in the simulation system. Objective: Analyze the influence of harmonic and negative current sequences of TPSS on the system circuit, and realize intelligent recognition for different working conditions. Methods: The converter is designed based on the transient direct current control technology and the harmonic model of grid-side regenerative braking is established. According to the parameters of CRH2 (CRH380AL) locomotive, the EMU model is built and run in the TPSS for joint simulation. The availability of the model is verified by combining the harmonic content and voltage level. Then, the distribution of negative sequence current under the no-load, traction and regenerative braking conditions of the system is analyzed in detail, and the negative sequence characteristic waveform under various conditions is obtained, so as to obtain the variation law of negative sequence current under different conditions. Results: Under the regenerative braking condition, the current harmonic distortion is much higher than that under the traction condition. From the analysis of voltage and current phase, the power factor of regenerative braking is also small. In the negative sequence analysis, the tip negative sequence current impact phenomenon occurs mostly during the traction operation of the train, while the current impact effect is weakened during regenerative braking, but the amplitude of the negative sequence fluctuation shows an increasing trend. Conclusion: The energy generated by regenerative braking will be utilized by the locomotive under traction, and these bad electric energy forms will have extremely adverse effects on the process of high-speed train receiving and changing current. These negative sequence analysis results can be used to identify and classify different working conditions and divide and conquer energy compensation actions to achieve energy saving and consumption reduction.

Synchronous Elastic Systems and Voltage Droop Optimization Using Stochastic Petri Net Model

Electric power systems play a significant role in modern society, serving billions of people. Therefore, there has been growing concern about the reliability and efficiency of the existing power systems; utilities are looking for technology to alleviate their concerns. One of the major concerns associated with voltage demand, is about system strength. System strength refers to the ability to withstand fault events, to maintain and control voltage waveform following these events. This paper aims to fill this gap by introducing synchronous elastic systems, using the SPN model, a connection strategy to improve frequency and voltage stability. In order to reach a more precise control effect, two working cases are considered for demonstrating the proposed control algorithm – droop control using SPN model. Droop control is realized by simulating the droop characteristics of generators and controlling the output voltage and frequency of the voltage source inverter (VSI) according to output power variation. Petri nets are classical tools for modelling and analyzing discrete event systems which are too complex to be described by automata or queuing models. The structural mechanism of the controller is based on the SPN model, which improves the problem of static error in the control of AC variables. The frequency domain characteristics are compared in detail and relevant parameters are designed. Controlling harmonic voltage levels within specified limits at the weakest point on the network ensures that other network locations will have better performance, hence, this study is highly appreciated.

Determination of the grid impedance in power consumption modes with harmonics

The paper investigates the harmonic impedance determination of the power supply system of a mining enterprise. This parameter is important when calculating modes with voltage distortions, since the determined parameters of harmonic currents and voltages significantly depend on its value, which allow the most accurate modeling of processes in the presence of distortions in voltage and current. The power supply system of subsurface mining is considered, which is characterized by a significant branching of the electrical network and the presence of powerful nonlinear loads leading to a decrease in the power quality at a production site. The modernization of the mining process, the integration of automated electrical drive systems, renewable energy sources, energy-saving technologies lead to an increase in the energy efficiency of production, but also to a decrease in the power quality, in particular, to an increase in the level of voltage harmonics. The problem of determining the grid harmonic impedance is solved in order to improve the quality of design and operation of power supply systems for mining enterprises, taking into account the peculiarities of their workload in the extraction of solid minerals by underground method. The paper considers the possibility of determining the grid impedance based on the measurement of non-characteristic harmonics generated by a special nonlinear load. A thyristor power controller based on phase regulation of the output voltage is considered as such a load. Simulation computer modeling and experimental studies on a laboratory test bench are used to confirm the proposed method. The recommendations for selecting load parameters and measuring device connection nodes have been developed.

Estimation of Harmonics in Partly Monitored Residential Distribution Networks With Unknown Parameters and Topology

The generalized adoption of power-electronic-based loads in residential networks is leading to increasing concern about harmonic distortion levels. At the same time, residential distribution systems are insufficiently monitored to provide a reliable analysis of harmonic limits compliance at the point of common coupling of customers. To address this problem, this paper proposes a practical method to estimate voltage harmonic levels in real time at all connection points of residential consumers. The proposed methodology assumes unknown network parameters and topology according to the limited data availability which is usual in low voltage residential networks. The proposed harmonic estimation method uses information gathered from conventional smart meters typically installed in the network (which register fundamental voltage and power) and from a reduced number of installed power quality monitors. A penetration of power quality meters below 10% has proved to provide accurate estimations of voltage harmonic levels at the whole network. The paper also proposes a methodology to optimally locate these power quality meters in the network. Validation of the methodology is performed in two different European distribution test networks with 55 buses and 471 obtaining satisfactory results. The method’s robustness and the parameters affecting accuracy are also analyzed in the article.

Transfer of Harmonics in Distribution Networks

This paper presents the role of the medium-voltage network and low-voltage loads in harmonic voltages with low-voltage customers and harmonic propagation. A general model as well as a detailed transfer function-based model are used. By applying them to an existing network, it is shown that remote low-voltage loads have a significant impact on the source and transfer impedance. The main impact occurs for a specific range of frequencies below the resonant frequency of the low-voltage network. The general model is able to estimate this frequency range with an acceptable level of accuracy. Furthermore, by utilizing the concept of overall transfer impedance, it is shown that voltage harmonic levels for harmonic orders around this frequency range are determined mainly by aggregated remote emission rather than local emission.

Contactless Voltage Distortion Measurement Using Electric Field Sensors

The measurement of harmonic voltage distortions in medium and high voltage systems is always regarded as a challenging task. For transmission systems, the widely used capacitor voltage transformers offer inadequate frequency responses for harmonic measurement. For distribution systems, voltage transformers are only available in limited locations. In order to provide a convenient and efficient solution for the situations above, this paper proposes a contactless method to measure voltage distortions. A small number of electric field sensors are used with partial knowledge of conductor geometry information of overhead lines. In addition, the method focuses on estimating the percentage harmonic voltage levels instead of the actual harmonic voltage values, which leads to a robust and simple measurement scheme. The proposed method has been validated by numerical simulations and experimental tests on a reduced scale model of an overhead transmission line.

Techno-economic Analysis of Non-linear DG Penetration in Radial Distribution Systems

Increasing penetration of Distributed Generation (DG) in recentyears has presented new challenges for planning and optimal operationof integrated distribution systems. In this scenario, harmonic distortionscaused by non-linear DG operation in the distribution networks havefurther added to the complexities of regulating such interconnectedsystems. In this article, a comprehensive analysis of unbalanced radialdistribution systems (RDS) integrated with non-linear DG has been at -tempted. The analytical assessment has been carried out by consideringvarious voltage harmonics in non-linear DG in the presence of shunt ca-pacitors in the radial distribution systems. Results are obtained for TotalHarmonic Distortion (THD) of voltage and current at various buses ofthe RDS, along with harmonic power profile. An economic assessmentof annual energy loss in the presence of non-linear DG has also been at-tempted. The proposed method is tested on two IEEE radial distributionfeeders interconnected with non-linear DG. Results show that the pres-ence of even acceptable level of voltage harmonics in non-linear DG cancause severe harmonic amplification in the entire network, consequentlyleading to increased energy losses for certain harmonic orders.

Techno-economic Analysis of Non-linear DG Penetration in Radial Distribution Systems

Increasing penetration of Distributed Generation (DG) in recent years has presented new challenges for planning and optimal operation of integrated distribution systems. In this scenario, harmonic distortions caused by non-linear DG operation in the distribution networks have further added to the complexities of regulating such interconnected systems. In this article, a comprehensive analysis of unbalanced radial distribution systems (RDS) integrated with non-linear DG has been attempted. The analytical assessment has been carried out by considering various voltage harmonics in non-linear DG in the presence of shunt capacitors in the radial distribution systems. Results are obtained for Total Harmonic Distortion (THD) of voltage and current at various buses of the RDS, along with harmonic power profile. An economic assessment of annual energy loss in the presence of non-linear DG has also been attempted. The proposed method is tested on two IEEE radial distribution feeders interconnected with non-linear DG. Results show that the presence of even acceptable level of voltage harmonics in non-linear DG can cause severe harmonic amplification in the entire network, consequently leading to increased energy losses for certain harmonic orders.

Light Wavelength and Power Quality Characteristics of CFL and LED Lamps under Different Voltage Harmonic Levels

Conventional light sources are less efficient as compared to the light emitting diode and compact fluorescent lamps. Conventional incandescent filament lamps are resistive and therefore do not depend on power quality parameters. In the electric power system, nonlinear loads are increasing rapidly and the high content of harmonic due to the nonlinear loads cannot be neglected. Harmonic generation from the light emitting diode and the compact fluorescent lamp is one of the main problems for power quality. In this study, the light efficiency and electrical characteristics of the light emitting diode lamps and compact fluorescent lamps are evaluated under various voltage harmonic levels. The results show that light emitting diode, produces more harmonics as compared to the compact fluorescent lamps, with the increase of the voltage harmonic distortion from 0.7% to 3.52% in the light emitting diode, current harmonic increased from 140% to 192%. The results also show that increase in voltage harmonic distortion just not only increase current harmonics distortion but also affect the light wavelength of the lamp.

Impact of Modern Electronic Equipment on the Assessment of Network Harmonic Impedance

Network harmonic impedance forms the link between harmonic currents emitted by individual devices and the harmonic voltage levels in the grid. It is essential for the definition of current emission limits in order to ensure electromagnetic compatibility between all equipment connected to the grid. Among all electrical equipment in future smart grid electronic devices, like PV inverters, EV chargers or lamps with electronic ballast, will have a dominating share. This is expected to have a considerable impact on the network harmonic impedance characteristic. This paper discusses the frequency-dependent input impedance of different types of modern electronic equipment and its potential impact on the network harmonic impedance. It is shown that the semiconductor switching results in a variation of the impedance within the fundamental cycle. This is not considered by the presently used assessment methods as they assume only passive network elements. Beside a method to measure these variations, several indices are introduced to quantify the level of its impact. This paper aims to provide some impulses for further discussions, particularly about the definition of network harmonic impedance in presence of electronic devices, the necessity to include these variations in realistic harmonic studies and if this has to be considered in the standardization.

Analysis of Windings in Variable Reluctance Resolver

In this paper, the relationship between the numbers of stator slots, winding polarities, and rotor poles for variable reluctance resolvers is derived and verified, which makes it possible for the same stator and winding to be shared by the rotors with different poles. Based on the established relationship, a simple factor is introduced to evaluate the level of voltage harmonics as an index for choosing appropriate stator slot and rotor pole combinations. With due account for easy manufacturing, alternate windings are proposed without apparent deterioration in voltage harmonics of a resolver. In particular, alternate windings with nonoverlapping uniform coils are proved to be possible for output windings in some stator slot and rotor pole combinations, which further simplify the manufacture process. Finite element method is adopted to verify the proposed design, together with experiments on the prototypes.

An Estimation Method to Determine Equivalent Circuit Parameters for Harmonic Analysis

SUMMARYThis paper proposes a new estimation method to determine arbitrary circuit parameters for the harmonic analysis of a distribution network. Harmonic analysis is important in maintaining electric power quality. An interesting phenomenon, a temporary cut‐down of the harmonic voltage level at dawn, even if demand is slightly increasing at this time, is often observed in actual power systems. This paper proposes to utilize observations of this phenomenon to estimate circuit parameters. In addition, it is claimed that a detailed equivalent circuit is preferable to a conventional simplified equivalent circuit for explaining the phenomenon. This paper also discusses the usefulness of the Harmonic Characteristics Curve, which is proposed in this paper as a new concept, at the secondary winding of the distribution transformer, and the correlation of PQ, the monitored values of the active and reactive power at the secondary winding of distribution transformer. This correlation should determine the equivalent fundamental frequency admittance of the shunt capacitors installed for distribution lines. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(1): 16–23, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22451

Considering Load Characteristics Harmonic Penetration in Zhengzhou Converter Station Nearly

This paper presents the rules of harmonic penetration in Zhengzhou harmonic voltage level. National standards limit the harmonic voltage distortion level in the buses, so study the UHV AC/DC hybrid system is significant to power grid. In order to find out the harmonic voltage level near Zhengzhou converter station, a method has been proposed in this paper, including the models of radiation power grid, load characteristics and converter station's AC filter. Finally, according to Zhengzhou converter station power frame sets up a detail model in the simulation software packages PSCAD/EMTDC to study the law of harmonic penetration.

DFIG 풍력발전기가 연계된 배전선로의 고조파 공진 특성에 관한 연구

There were telecommunication noise and malfunctions of the electronic devices occurred over a wide area due to the high harmonic voltage and/or current levels of the Back-to-back converter in the DFIG wind power system even though the magnitude of all harmonics is within the international standards. The triangular carrier signals of the PWM used in the power converter system is related to the telecommunication noise because they are in the range of audible frequencies and amplified by a variety of the standing waves that were excited by harmonic voltage sources in the weak grid system such as a long distance distribution transmission lines. This paper describes the characteristics of the harmonics in the wind turbine-generator, numerical analysis and simulation of the harmonics resonance phenomena in the distribution lines as well as measuring induced voltage of the telecommunication lines in parallel with power lines in order to verify the root cause of the telecommunication noise. These noise problems can occur in a wind turbine power system with a non-linear converter at any time, as well as photovoltaic power system. So, the preliminary review of suitable filter devices and switching frequencies of the PWM have to be required by considering the stability of the controller at the design stage but as part of the measures the effect of the telecommunication cable shields was analyzed by comparing the measured data between multi-conductor with/without shields so as to attenuate the sources of the harmonics voltage induced into the telecommunication lines and to apply the most cost-effective measures in the field.

Design Practices in Harmonic Analysis Studies Applied to Industrial Electrical Power Systems

Power system harmonics may cause several problems, such as malfunctions of electrical equipment, premature equipment failures and plant shutdowns. Accordingly, mitigation of these harmonics is considered an important target especially for industrial applications where any short downtime period may lead to great economic losses. Harmonic analysis studies are necessary to analyze the current and voltage harmonic levels and check if these levels comply with the contractual or international standard limits. If the studies reveal that the preset limits are exceeded, then a suitable harmonic mitigation technique should be installed. Harmonic analysis studies in the industrial electrical systems are discussed in many references. However, a comprehensive procedure for the steps required to perform a harmonic study is rarely found in the literature even though it is strongly needed for design engineers. This paper provides a comprehensive procedure for the steps required to perform a harmonic study in the form of a flowchart, based on industrial research and experience. Hence, this paper may be considered as a helpful guide for design engineers and consultants of the industrial sector.

Characteristics of power quality disturbances in Australia: Voltage harmonics

Management of harmonic voltage levels can impose significant economic impacts for both electricity suppliers and customers. For the case where harmonic voltage levels are high, economic costs include damage to equipment and associated loss of production due to high voltage harmonic levels as well as the costs associated with mitigation of harmonic currents, for example, harmonic filters. In the alternate scenario, ie. the case where harmonic voltage levels are acceptable, considerable expense may be incurred mitigating harmonic currents unnecessarily due to lack of knowledge of harmonic levels and/or network capabilities. As such, there is considerable potential for industry to make large economic gains if harmonic voltage levels can be better understood. Using data collected as part of an ongoing long-term power quality monitoring project, this paper details the characteristics of voltage harmonic behaviour on Australia electricity distribution networks.

Characteristics of Power Quality Disturbances in Australia: Voltage Harmonics

Management of harmonic voltage levels can impose significant economic impacts for both electricity suppliers and customers. For the case where harmonic voltage levels are high, economic costs include damage to equipment and associated loss of production due to high voltage harmonic levels as well as the costs associated with mitigation of harmonic currents, for example, harmonic filters. In the alternate scenario, ie. the case where harmonic voltage levels are acceptable, considerable expense may be incurred mitigating harmonic currents unnecessarily due to lack of knowledge of harmonic levels and/or network capabilities. As such, there is considerable potential for industry to make large economic gains if harmonic voltage levels can be better understood. Using data collected as part of an ongoing long-term power quality monitoring project, this paper details the characteristics of voltage harmonic behaviour on Australia electricity distribution networks.