Characteristics Of Voltage Waveform Research Articles

Enhancing the Performance of Eskom’s Cahora Bassa HVDC Scheme and Harmonic Distortion Minimization of LCC-HVDC Scheme Using the VSC-HVDC Link

Cahora Bassa, a thyristor-based High Voltage Direct (HVDC) link, transmits 1920 MW of power from a hydro-power plant in Zambezi River, north of Mozambique, to Apollo Substation in Johannesburg, South Africa. The high degree of harmonics distortion that is transferred into the AC side of the transmission network and the continuous increase in the rate at which commutation failure occurs during systems disturbance are both flaws in the utilization of this HVDC converter technology. AC and DC filters with rugged controllers are often used to minimize this effect but are limited in scope. Modern converter technology, such as the Voltage Source Converter (VSC), was proposed in this study to reduce harmonics content level, increase power transfer capabilities, enhance network stability, and reduce the rate of commutation failure occurrence. This paper, therefore, evaluates the performance analysis of the Cahora Bassa HVDC link and its level of harmonic distortion in the line commutated converters. A proposed method of utilizing VSC HVDC is provided as a suitable solution using three modular-level voltage source converter technology. Current and voltage waveform characteristics during a three-phase short circuits fault were analyzed, and the latest developments in the area of VSC HVDC were discussed. The results show a lower total harmonics distortion with the usage of VSC HVDC converter technology at the inverter station. The continuous occurrence of commutation failure was minimized by implementing a new converter architecture. The network simulation and analysis were carried out using the DIgSILENT PowerFactory engineering software tool.

A statistical-based criterion for incipient fault detection in underground power cables established on voltage waveform characteristics

The incipient faults which mainly occur due to the electric arc occurrence in the power cables with insulation defects are hardly detectable by the conventional protective relays, and over time can develop into a permanent fault in the system. Employing Kalman filter, this paper puts forward a method to detect the incipient faults and to discriminate them from other similar incidents in the power system. The proposed method is established on the comparison between the waveform of the measured voltage and fundamental component of the measured voltage, estimated by Kalman filter algorithm in the sending end of the cable during the fault. Employing the difference between the measured and estimated waveforms, the incipient fault detection and discrimination are carried out within two stages. In the first stage, event detection is relegalized by comparing the standard deviation of the obtained error with a certain threshold. The second stage is conducted to find the incipient fault based on the non-attenuating characteristic and quasi-periodic nature of the incipient fault. The feasibility of the proposed method is verified through computer simulation using four different electric arc models and also the acquired experimental data from real incipient faults.

Validity of Three-Fluid Plasma Modeling for Alternating-Current Dielectric-Barrier-Discharge Plasma Actuator

The validity of numerical modeling of discharge plasma in dielectric barrier discharge plasma actuator is evaluated by comparing the simulation and experimental results under the same conditions. Discharge plasma behavior is numerically simulated based on a three-fluid plasma model. Regarding the induced jet structure, although the simulation tends to underestimate the jet thickness and overestimate the maximum velocity, the discrepancies are small considering the quite simple modeling. In addition, the values of thrust force in the simulation are consistent with those in the experiment only within 10–20%. On the other hand, the simulation underestimates the power consumption by 40–50% mainly due to the assumption of two-dimensionality. Furthermore, the thrust force and power consumption are investigated from the viewpoint of characteristics for voltage amplitude, voltage waveform, and dielectric material. As a result, the discharge mode in the simulation, which strongly affects the electrohydrodynamic force generation characteristics, needs to be consistent with that in the experiment to reproduce the voltage waveform characteristics of thrust force. In addition, to reproduce the dielectric material characteristics of thrust force, not only permittivity but also secondary electron emission coefficient needs to be set to appropriate values for each material.

An Incipient Fault Location Method Based on Impedance Calculation

Incipient faults are precursors to permanent faults. The location of incipient faults can effectively prevent permanent faults and reduce the losses caused by faults. In this paper, the Mary fault model is used to simulate the incipient faults by using the arc gap theory to study the incipient fault current and voltage waveform characteristics. An incipient fault location algorithm is proposed on the fault voltage and current waveform characteristics. The line reactance and fault location are obtained by least squares method. Optimizing the algorithm reduces the amount of computation and preprocessing the results to reduce the interference of the error. Finally, a 10kV single-core cable model was built by PSCAD/EMTDC to verify the reliability of the algorithm.

The Influence of Natural Contamination on Pollution Flashover Voltage Waveform of Porcelain Insulators in Heavily Polluted Area

It is significant to reveal the characteristics of voltage waveform of porcelain insulator with heavy industry pollution in flashover test. In this study, the contamination of insulator samples came from heavy industry pollution areas was measured. The voltage and leakage current signals in the pollution flashover test were recorded completely. A parameter, Uw, was formed by summing the variation slope of the peaks of voltage on insulator of each power frequency cycle. It quantified the fluctuant accumulation of voltage signal waveform. Another parameter, Kfv, was formed by calculating the drop slope of voltage at flashover. It was analyzed that the effects of the pollution severity and contaminant content of insulator on fluctuant accumulation of voltage signal and the drop slope of voltage at flashover. It is found there is a positive correlation between the ratio of non-soluble to soluble deposit on insulator, RNE, and the pre-flashover voltage fluctuant accumulation, Uwb. Moreover, the very heavily polluted insulators have ultra-high value of Uwb, the medium and light polluted insulators have the outstanding value of Kfv.

Control of the Jet Induced by the Plasma Actuators (Effect of the Applied Voltage Characteristics on the Jet Direction)

The effects of voltage waveform characteristics on the flow induced by using a dielectric barrier discharge plasma actuator (DBD-PA) have been investigated in this study. It is known that the flow is induced in the direction from the upper electrode to the bottom electrode, then tangential one-way flow can be generated by using DBD-PA with asymmetric electrodes. We found, however, that it is possible to control the flow in certain conditions when offset voltages with a square wave are varied. Setting the negative offset, the flow is reversed from the bottom electrode to the upper electrode by applying square wave. It should be noted that it is not reversed by sine waves even with same amplitudes and frequencies. Our experimental results indicate that the voltage surge velocity is important to realize reversed flow induced by DBD-PA.

Mode Transition of an Atmospheric Pressure Arc Plasma Jet Sustained by Pulsed DC Power

An atmospheric pressure arc plasma jet sustained using pulsed DC power is studied by examining its appearance using a high-speed camera and measuring current and voltage waveforms at the powered electrode using current and high-voltage probes. Given the seemingly uniform in time visual appearance, the high-speed camera images show that the plasma jet undergoes some transition within each power cycle. Current and voltage waveform characteristics suggest that such a transition is most likely due to a glow-to-arc mode transition. The occurrence of this transition is controlled by the plasma physics rather than by the duty cycle of the pulsed power.

Study of wire breaking process and monitoring of WEDM

Wire rupture in the Wire Electrical Discharge Machining (WEDM) process is a serious problem to manufacturers. A new computer-aided pulse discrimination system based on the characteristics of voltage waveform during machining was developed in this paper. With the use of this system, a large amount of sparking frequency data during wire rupture process and under normal working conditions were collected and analyzed. Two symptoms of wire rupture were identified: the excess of arc sparks, and a sudden rise of the total sparking frequency. The governing mechanisms of these two types of wire rupture were found from the SEM and EDAX analyses of the ruptured wire electrode. Furthermore, an index to monitor wire breaking was identified, and its relationships with the metal removal rate and machining parameters were found. Based on the results obtained in the paper, a control strategy to prevent wire from rupturing while at the same time improving the machining speed is proposed.

Sampling and real-time methods in electro-optic probing system [LSI testing

Sampling and real-time methods in electro-optic (EO) probing systems using a laser diode (LD) for measuring the voltage waveform at internal nodes of the high-speed LSI are described, comparing performance to other electric instruments. The voltage sensitivity was improved by using an external ZnTe E-O probe and a low-noise LD. A sampling system using a pulsed LD has a frequency bandwidth of 10 GHz and a minimum detectable voltage of 430 /spl mu/V//spl radic/Hz. The corresponding values for a real-time system using a CW LD and a high-speed photodetector are 480 MHz and 23 mV with 700 accumulations. Each system is based on a mechanical prober and a microscope. The advantages of a high temporal resolution, noncontact and noninvasive method are demonstrated during various measurements in several different areas: standing waves on a stripline, ring resonator and voltage waveform characteristics in a high-speed MMIC by the sampling method, long logic pattern signal, voltage waveforms at internal nodes in an ECL IC and those of a transport electrode in CCD by the real-time method. >

Effects of nonlinear loads on optimal capacitor placement in radial feeders

The nonlinear portion of electrical loads has increased significantly in recent years. Harmonic currents injected by these loads into the distribution system should be considered when solving the capacitor placement problem in order to assure that the optimal solution does not result in excessive harmonic distortion. A voltage-dependent current injection load model is presented to determine voltage waveform characteristics and additional losses at harmonic frequencies. Computer simulations show that the optimal capacitor sizes and locations depend heavily on the load model used at fundamental frequency and on harmonic signals, especially when limits are imposed on voltage waveforms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>