Overvoltages and Harmonics on EHV Systems

The objective of this paper is to present an approach for isolating the harmonic contents in both voltage and current waveforms of the montage feeder of Gharb Talkha substation (60/11 KV). A novel technique using Discrete Wavelet transform (DWT) for the analysis of the waveforms harmonics content At the beginning the substation is simulated using Simulink toolbox in Matlab program with and without the presence of capacitor bunk. The obtained voltage and current waveforms are compared to the actual data. The proposed model is used to study the effect of replacing the capacitor bank with single tuned parallel passive filter. The resulting current and voltage waveforms are analyzed using the proposed DWT technique. The analysis showed that the Total Harmonic Distortion (THD) of both voltage and current waveforms is improved as well as the power factor.

Electromagnetic transients are the tidal waves of electric power systems. These momentary voltage surges generally lasting only fractions of a second can be powerful enough to disrupt normal operations and even cause serious damage to major pieces of equipment, such as transformers. Created by lightning, line faults, substation switching functions, and other sudden events along a utility network, transients must be taken into account both in choosing equipment ratings for a power system and in setting its operating parameters. Like the builders of a seawall that must withstand the highest expected waves from the ocean, engineers trying to guard against damage from transients face an extraordinary design task. Most of the huge computer simulation codes related to power systems either model steady-state conditions or deal with system stability problems. The analysis of electromagnetic transients, on the other hand, requires a much more detailed examination of how some critical portion of a power system will react to conditions that can change greatly in microseconds. For many years, simulation of transient effects was performed by special-purpose analog computers called transient network analyzers (TNAs). These machines, which are still in use, recreate a portion of the power system in miniature, complete with voltage sources representing generators and various kinds of capacitive or inductive loads. TNAs are generally adequate but relatively inflexible, tedious to set up, and cumbersome to use. Once a system configuration is modeled, many simulations can be performed. Given the need to manually reconfigure TNA circuits to represent changes in a system, however, the analyzers can also be quite expensive to use. During the late 1960s, Herman Dommel of the Bonneville

This work presents the development and implementation of four control configurations for photovoltaic inverter. These configurations are: Proportional Integral plus Resonant controller, Proportional Integral plus Repetitive controller, Proportional Integral-Proportional plus Resonant Controller and Two Degrees of Freedom plus Repetitive control with the aim of reducing the Total Harmonic Distortion in Voltage. These techniques are useful in island mode operation of an inverter when it is working as a voltage source in microgrid. In this operation mode, these control techniques are successfully applied when the inverter feeds linear and nonlinear loads. The purpose is to keep the output voltage waveform, frequency and amplitude according to the standard IEEE 519. It is use is justified because currently most of the loads have nonlinear characteristics which increase considerably the Total Harmonic Distortion in voltage. A comparative analysis derived from inverter simulations with nonlinear loads has been performed in order to validate those control techniques, considering that its application to feed line loads proves to be effective.

This paper presents a Genetic Algorithm-based approach for optimal placement and sizing of passive power filters to mitigate harmonics in radial distribution systems with linear and nonlinear loads. The problem is formulated as a nonlinear multi-objective optimisation problem with equality and inequality constraints. For solving this problem, the Genetic Algorithm’s performances are analysed and evaluated using the standard IEEE 18- and 33-bus test systems. The optimal solutions are obtained based on the following four optimisation criteria: (1) minimisation of the maximum level of the total harmonic distortion in voltage, (2) minimisation of the initial investment costs of the filters, (3) minimisation of total active power losses in distribution lines and (4) a simultaneous minimisation of the maximum total harmonic distortion in voltage, initial investment costs of filters and total active power losses. The system harmonic levels are estimated using the Decoupled Harmonic Power Flow algorithm. Simulation results, obtained using the proposed Genetic Algorithm-based approach, are compared with those obtained using other optimisation algorithms and verified using the Harmonic Analysis module of the Electrical Transient Analysis Program. It is shown that the Genetic Algorithm-based approach provides effective, robust and high-quality solutions.

Transient study of two 500 kV coupled lines in a transient network analyzer

Experiences on using a workstation cluster to implement a real-time digital transient network analyzer

The authors report results confirming the practicability of a real-time digital simulator for the bulk power transmission network using a commercially available component called a transputer. The use of the method of characteristics to model transmission lines combined with the architecture of the transputer allows a parallel processor connection topology identical to that of the network, where one or more transputers are assigned per bus. There is no theoretical limit on the size of the network. Present technology allows an integration step size in real time of about 150 mu s for a full three-phase model. >

Harmonics are one of the key power quality issues on the front burner in the power system. Advancements in solid-state technology in recent times have resulted in the proliferation of non-linear loads which are the main sources of harmonics. Harmonics penetration in power system networks is detrimental to effective system operation and can result in frequent failures and damage to electrical equipment. This, therefore, creates the need for harmonic mitigation in power system networks for power quality enhancement. This work examined the impact of a shunt passive filter (SPF) in minimizing harmonic distortion on an electrical distribution network considering the power network layout of 7-Up Industry Plc as a case study. The indices for quantifying the level of harmonic distortion and shunt passive filter design for harmonic mitigation in power networks were respectively analysed and presented. The considered 7-Up Industry Plc power network was modelled and simulated with and without SPF in MATLAB/Simulink software environment R2020a. The voltage and current total harmonic distortion, VTHD and ITHD, from the two system states, were evaluated. The observed voltage and current waveforms from the simulation of the test network without any filter applied were distorted, signifying the harmonics’ presence. The estimated VTHD and ITHD values with no filter used were 6.084 and 19.79 % respectively. SPF application on the test network mitigated the VTHD and ITHD to 0.7802 and 2.448 %, giving an improvement of 5.304 and 17.342 % respectively in the minimization of voltage and current total harmonic distortion compared to the no filter case. This study established that a shunt passive filter is suitable for power quality enhancement in an electrical distribution network. Keywords: Electrical distribution network, harmonics, non-linear load, power quality, shunt passive filter, total harmonic distortion

Pantograph arcing with AC supply generates transients, cause asymmetries and distortion in supply voltage and current waveforms and can damage the pantograph and the overhead contact line. The asymmetry generates a net dc component and harmonics, which propagate within the traction power and signalling system and causes electromagnetic interference. Unlike DC-fed systems (Part I), the arcing in ac supply is complex because of the zero crossing of currents and voltages. In this paper, we discuss the mechanisms of sliding contact and arcing between pantograph-contact wire using the experimental setup described in Part I. Influences of various parameters and test conditions on arcing phenomenon and their signature patterns on the supply voltage and current waveforms are presented. It is shown how the arcing mechanism and corresponding asymmetry in the voltage and current waveforms are governed by line speed, current, supply voltage, inductive load, and pantograph material. The asymmetry in the current waveform is mainly due to the difference in the duration of successive zero-current regions and uneven distortion of the waveshapes. This, in turn, creates the asymmetry in the voltage waveform. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the electromagnetic interference due to pantograph arcing in AC traction systems.

The results of Transient Network Analyzer (TNA) studies evaluating the feasibility of low-side switching long transformer terminated lines is reported. It is shown that overvoltages following line dropping and fault clearing can severely stress surge arresters and circuit brtakers exceeding capabilities specified in ANSI standards. These overvoltages are often not carefully considered in design studies, since the available literature on low-side switching of EHV transmission lines primarily deals with energizing the line and transformer.1,2,3,4

Multi-level inverter used in applications that require high power. The important factor in multi-level inverter is Total Harmonic Distortion (THD). This study discuss nine level cascaded H-bridge multilevel inverter. Also, proposed the effects of using filter on waveform and Total Harmonic Distortion (THD) of output voltage and current. Discussed LC low pass filter and sinusoidal pulse width modulation as control technique of switches. Comparison THD of nine level cascaded H-bridge multilevel inverter with and without filter. The proposed level and filter are design and simulate by MATLAB 2010 Version 7.11.0. The simulation results show the effects of using filter on THD and waveform of output voltage and current. Different methods for choosing filter value are used to illustrate the filter effect.

A carrier-based synchronous type single phasephase synchronous inverter (S-PSI) is proposed to develop the inverter output phase and voltage waveform. The major problem of the microgrid connected inverter is unbalanced DC supply, high switching loss, power quality and phase error. Therefore, to overcome those issues, a phase synchronous technique can perception not only conventional DC to AC inverter but also low-frequency inverter source ripple current reduction with lower switches of the inverter. However, a carrier-based synchronous PWM control technique is proposed for capable of regulating both side of the inverter input and output performance. The working performance of the S-PSI is analyzed, including steady-state behavior, efficiency, and circuit parameters. As well, the equivalence of the switching control technique and the similarity of inverter evaluate circuit parameters are exposed between this S-PSI and a traditional two-level inverter. In addition, lowpass LCL filters are utilized to convert squire wave to sine wave with same frequency and to reduce the higher harmonic distortion of the microgrid voltage. Balanced resistive load of = 11 $\Omega$ for star configuration and input DC voltage, ± 340V have assume to design the inverter. From the simulated results, the carrier-based S-PSI systems are developed the phase error of 55%, reduced 11% of THD and the conversion efficiency of 97.02%. Finally, it highly appreciated that the proposed design will improve the microgrid system.

Multilevel inverters with a large number of steps can generate high quality voltage waveforms, good enough to be considered as suitable voltage source generators. An advanced multilevel inverter topology is proposed to optimize number of bidirectional switches. In this work the an five-level cascade H-bridge Inverter, which uses multicarrier based control structure and two capacitor with 10 switching MOSFETs topology is being presented. Analysis is done for RL and pure resistive load. The PWM strategy reduces the THD and this strategy enhances the fundamental output voltage. The experimental and simulated results show that total harmonic distortion of output voltage and current waveform shapes are 5.16 % and 5.77% respectively for RL load which are within the acceptable limits.

Asymmetric Cascaded H-bridge (ACHB) level inverters can output more voltage waveforms with fewer cascaded units while ensuring the quality of output voltage waveforms, so they have attracted more and more attention. Taking the topology of Type-III asymmetric CHB multilevel inverters as the research object, a Modified Hybrid Frequency Pulse Width Modulation (MHF-PWM) strategy is proposed in this paper. This modulation strategy overcomes the local overshoot of low-voltage unit in the presence of traditional Hybrid Frequency Pulse Width Modulation (HF-PWM), thus completely eliminating the low frequency harmonics in the output voltage waveform of Type-III ACHB nine-level inverters, and the Total Harmonic Distortion (THD) of output line voltage of the modulation strategy is lower than that of PS-PWM strategy in the whole modulation degree, which effectively improves the quality waveform of the output line voltage. At the same time, the strategy can also improve the problems of current backflow and energy feedback caused by the high-voltage unit pouring current to the low-voltage unit, thereby reducing the imbalance of the output power of the high-voltage and low-voltage units. Finally, the Matlab/Simulink simulation model and experimental platform are established to verify the validity and practicality of the modulation strategy.

In the past decade, wind power capacity has experienced tremendous surge for a growing electrical energy demand. With generation of wind power, wind power can be made in usable form with the help of prominent technology named permanent magnet synchronous generator (PMSG) which is directly driven by back to back converters. However, grid integration with wind brings the problems of harmonic distortion and fluctuations present in voltage. This paper aims to reduce the total harmonic distortion (THD) which are present in current and voltage waveforms. For reducing THD, artificial technology (AI) such as artificial neural network (ANN) and (FLC) fuzzy logic control-based techniques have been modeled, simulated and analyzed. The AI-based harmonic filter is placed between the network and wind system which enhances the power quality during disturbances. The AI-based filter with wind turbine, model of PMSG and model power electronic converters are implemented in MATLAB/Simulink environment.