Analysis Of Overvoltages Research Articles

Modeling Induction Motor for Prediction of High frequency problems

In this paper a novel high-frequency model of Induction motor is presented for investigating induction motor behavior in a wide electromagnetic interference (EMI)-frequency range from 100 Hz to 30 MHz. This model is suitable for prediction of common mode current, EMI problems and terminal over-voltage analysis. The model parameters are estimated by asymptotical method using novel differential and common-mode impedance measurements. The values of parameters are limited in a specified range and then optimized using genetic algorithm (GA). A least mean square method is used with GA optimization to solve the identification problem. The proposed model can also be used to predict the high-frequency problems and design EMI filters to improve electromagnetic compatibility limitation in cable fed motor-drive system. In order to validate the proposed high-frequency motor model, novel common-mode and differential-mode measuring tests have been carried out on the 9.3 kW industrial induction motor using a network analyzer in a wide frequency range as described. Very good agreement was seen between the experimental and simulation results of the proposed model in both magnitude and phase.

The model of a vacuum circuit breaker in MATLAB software for the analysis of overvoltages and overcurrents in capacitive electrical circuits

The paper presents the method of modelling a vacuum circuit breaker in MATLAB/SIMULINK software and also the results of verification of its operation and practical usefulness for conducting analysis of overvoltages and overcurrents occurring in commutated capacitive electrical circuits. Examples of digital simulations of overvoltages and overcurrents in selected electrical circuits are also provided and the optimal conditions for the switching off of capacitor banks are determined. (Model lącznika prozniowego w programie MATLAB oraz analiza przepiec i przetezen w obwodzie pojemnościowym).

Transformer Switching With Vacuum Circuit Breaker: Case Study of PV Inverter LC Filters Impact on Transient Overvoltages

This paper presents the analysis of possible transient overvoltages that can be generated during vacuum circuit-breaker (VCB) operation at the connection point of a photovoltaic power-plant. A typical switching event that is related to the VCB concerns energization and de-energization of the unloaded transformer. However, at the typical photovoltaic powerplant, the transformer is fed by an inverter equipped with LC (or LCL) filters that are necessary for limitation of harmonics and ripple in voltage and current. From the point of view of switching operations, the inductance and capacitance of the low-voltage (LV)-side connected filter affect the natural frequency of the transformer, which is reflected by different transient system response during VCB operation. In this paper, laboratory measurement of overvoltages generated during distribution transformer switching by means of VCBs is analyzed. The impact of the LC filter connected at the LV side on the overvoltages suppression was studied. Electromagnetic Transients Program-Alternative Transients Program simulations were conducted in order to verify the possibility of transients elimination by means of the additional series-connected RL choke at the transformer medium-voltage side.

C/H 철탑 종단접속함 보호용 피뢰기 리드선 길이에 따른 뇌과전압 분석

This paper describes the lightning arrester transients in cable head termination. The installation references of cable head tower and lightning arresters are firstly reviewed, then the performance of lightning arrester operation is also evaluated based on lightning overvoltage analysis by the change of grounding lead cable length. This paper finally proposes the optimal length of grounding lead cable at the cable head termination. The limited lightning current is also proposed according to the change of grounding lead cable length. The results will contribute to protecting insulation breakdown failure against lightning surge at the terminations and joints.

Measurements of the quantitative lateral analytical resolution at sputtered gold-layers with the FEG-EPMA JEOL JXA-8530F

In this paper we present measurements of the quantitative lateral analytical resolution of the field emission (FEG) electron microprobe JEOL JXA-8530F. In particular, the minimum thicknesses of gold layers that are suitable for an accurate quantitative analysis are determined for several measurement parameters. Both, low voltage analyses at acceleration voltages from 15 kV to 5 kV and low overvoltage analyses at 13 and 15 kV are regarded. For both methods a minimum analytical resolution well below 170 nm is obtained while the X-ray signal is 5 times lower for the low overvoltage method. Special care is taken for the preparation of the test specimen. A Ag-layer reduces fluorescence effects and the cleaved surfaces are polished by a gentle focussed ion beam. The porosity of the gold layers is regarded by a separate measurement of the density (17.6 g/cm3). The results coincide well with Monte Carlo simulations of the source volume of generated X-rays if the reduced density of the gold layers and experimental determined values of the beam diameter are used. Additionally the results are used to investigate methods to estimate the width of the source volume of emitted X-rays by the superposition of the beam diameter and theoretical predictions of the width of the electron interaction volume. The linear sum of both gives a quite good agreement.

Overvoltage Analysis Considering Transmission Tower Models Based on Impedances and Inductances

It is clear that lightning strokes produce overvoltages on Transmission Lines (TLs), which can be higher that the Basic Insulator Level (BIL), generating a fault or short circuit. Thus, in order to adequately analyze when a lightning hits on a TL, it is necessary to simulate different elements corresponding to Electric Power Systems (EPSs) as real as possible. In this context, transmission towers are considered crucial parameters in lightning studies, which must be correctly selected and simulated in order to consider reflected voltage waveforms from cross arms. Based on the above said, this paper presents a comparative study corresponding to the transmission tower simulation using two models. The first uses inductances, and the second uses distributed parameters impedances characterized by their impedance and travel time. This paper presents voltage variations that exist in each phase, using different lightning features. Alternative Transients Program (ATP) is used to simulate the TL model considering different lightning currents and the two tower models. Results show that the impedance model analyze reflected waveforms, while that the inductance model does not analyze this issue.

Modeling and Insulation Performance Analysis of Composite Transmission Line Tower Under Lightning Overvoltage

In this paper, a new non-uniform multiconductor transmission line model combining with lumped circuit elements for a composite transmission line (TL) tower under lightning strokes is established. The metal ground-wire cross arms, the metal tower main body and its bracings are modeled as equivalent horizontal and vertical TLs, respectively. The two grounding ladders are regarded as two parallel-vertical TLs considering their mutual coupling. These distributed TL parameters are calculated by analytic equations. The composite arms are equivalent as lumped capacitances determined by employing 3-D finite-element method. The lightning overvoltage analysis for a 330-kV composite tower is performed by applying the hybrid model. The incident and reflected voltages are calculated. The insulation performance evaluation for the composite tower is discussed in detail.

NIF-Based Frequency-Domain Modeling Method of Three-Wire Shielded Energy Cables for EMC Simulation

This paper focuses on the modeling method of energy cables used in power conversion systems, in the aim of EMC simulation and overvoltage analysis. Based on the node-to-node functions method, a simple frequency-domain model with a reduced number of equivalent impedances is considered and applied to three-wire shielded cables, along with a fast identification method based on a cascaded-cell model. Even though the model eventually includes nonphysical virtual impedances, simulation in frequency domain provides accurate results when compared to equivalent experimental measurements, for various cable lengths and in short simulation times. Time-domain waveforms are then extracted from frequency-domain simulation and confirm the effectiveness of the proposed method in a wide frequency range up to 50 MHz. Finally, a good match has been found between experimental and simulation results of voltage overshoots on a buck power converter system.

Analysis of Temporary Overvoltages During Open-Phase Faults in Distribution Networks With Resonant Grounding

This paper analyzes the temporary overvoltages (TOVs) that may appear in open-phase states in distribution networks with resonant grounding. The high overvoltages recorded during the open-phase states exceed the overvoltages corresponding to the existing theory. The detailed analytical study of the temporary overvoltages is performed. The closed-form expression of the neutral voltage is derived. The conditions for maximum phase-to-earth overvoltages are obtained. The case study for open-phase faults in the 33-kV resonantly grounded distribution network is described. The dependence of the TOVs on the number of distribution feeders, on the feeder loading, on detuning factor, on the additional damping factor, as well as on the saturation of the voltage transformers are analyzed. Remedies for the reduction of TOVs are considered. Detuning of the Petersen coil is compared with the permanent connection of the wattmetric resistance in parallel to the Petersen coil.

An Analysis of Transient Overvoltages during the Energization of Electric Ship Propulsion Systems.

This paper addresses the resonance phenomena that can occur in an isolated distribution system during transient events such as repeated energizations or power converter switching. In particular, the aim of this study is to analyze the energization of an onboard radial distribution system installed on an electric ship and to determine how the various leakage parameters that can cause resonance problems such as high peak overvoltages when the circuit breaker is closed are relevant. The paper presents a detailed model of whole distribution system, which is validated using infield measurements that refer to a real case in which these events damaged the ships transformers, causing it to be removed from duty.

Modeling of wind turbine transformers for the analysis of resonant overvoltages

Switching transients and earth fault in a wind farm collection grid are two transient phenomena which can lead to resonant overvoltages at the LV terminal of the wind turbine transformers as well as inside HV and LV windings. The aim of this paper is to analyze the potential of the resonant overvoltage for various winding designs; disc, layer and pancake. In this way, the least vulnerable winding design can be recommended. For this aim, a 500kVA transformer test object with the three aforementioned winding types has been designed and manufactured. Similar geometrical characteristics are used for all the three windings. By measuring the frequency response, the resonant frequencies can be found and the amplitude of the transferred voltage at these frequencies can be compared. The windings are also modeled in this paper in detail based on analytical functions. This RLC ladder model is verified by the measurements.The measurements and modeling results show that all winding designs have a resonant frequency around 800kHz for the transferred voltage to LV terminal. Disc winding shows the lowest amplitude of the transferred overvoltages (6p.u.). The layer winding, also has a resonance at 1.6MHz with an even higher transferred overvoltage (80p.u.). The frequency response of the pancake winding has characteristics of both disc and layer windings. In spite of having the lowest transferred overvoltage peak, the disc winding has many additional resonant frequencies in the range of 100kHz–1MHz. This could excite resonances in other parts of the winding. Consequently, pancake winding designs might be the most promising to minimize resonance situations.

Analysis of switching transient overvoltages in the power system of floating production storage and offloading vessel

Large transient overvoltages can be caused by the switching operation of vacuum circuit breakers (VCBs) during disconnection of induction motors. In this paper VCBs, cables, generators, busbars, induction motors and surge arresters are modeled by making use of ATP-EMTP. Switching transient overvoltages of four typical induction motors under the starting, the full load and the light load working conditions in the power system of the selected floating production storage and offloading (FPSO) vessel are analyzed. A suitable protection against the switching transient overvoltage is proposed and the results are presented accordingly.

Lightning Impulse Corona Characteristic of 1000-kV UHV Transmission Lines and Its Influences on Lightning Overvoltage Analysis Results

The lightning overvoltage is one of key issues in designing the insulation of transmission line and power apparatus. Usually the influence of the impulse corona is ignored in numerical analysis of electromagnetic transients in power systems due to the lack of experimental data. But the relationship between the overvoltage and the insulation size of 1000-kV ac ultra-high voltage (UHV) power systems enters the nonlinear region, and a small decrease in overvoltage will lead to a high reduction in insulation size and bring huge economical benefits. So fully understanding the corona characteristics of the 1000-kV UHV transmission line is helpful to understand the actual wave process and realize a suitable insulation design of the 1000-kV UHV system. Experiments on the lightning impulse corona characteristic of bundle conductors for 1000-kV transmission lines are carried out in the China UHV ac test base and the impulse corona Q-V curves of different bundle conductors are obtained. The results show that the impulse corona leads the increment of the capacitance of the conductor. Analysis on the Q-V curves shows that the occurrence of the positive impulse corona has a time delay after the lightning impulse voltage exceeds the corona inception voltage and the delay time is a tenth of a microsecond. At the end of this paper, a simulation model for corona based on the empirical formulas of Q-V curves fitted from the test results is proposed, and is applied to the overvoltage analysis of 1000- kV transmission line and substation. The analysis results show the lightning impulse corona has a large influence on the lightning overvoltage of the transmission line and substation.

직류배전시스템에서 피뢰기 및 가공지선 접지간격 변경에 따른 뇌과전압 해석

It is anticipated that AC distribution system can be replaced by DC distribution system in the near future because of the operation of various distributed source or microgrid system. However DC distribution system replacing 22.9kV AC distribution line is not sufficiently studied still. This paper describes lightning overvoltage analysis among many research fields should be studied to realize DC overhead distribution systems. DC distribution system is modeled using EMTP and overvoltage is analyzed according to interval of arrestor location, earth interval of overhead grounding wire and grounding resistance. It is evaluated that analysis results can be effectively used to design of future DC distribution system.

Relevant Factors to a Statistical Analysis of Overvoltages - Application to Three-Phase Reclosing of Compensated Transmission Lines

This paper describes the statistical study of important factors that influences transient over voltages resulting from three-phase reclosing of shunt compensated transmission lines. These factors include the model used for transmission line representation and the influence of line transposition. Additionally, the over voltages reduction to proper levels depending on the type of control technique are illustrated and analyzed in statistical terms. The evaluation covers three shunt compensation degrees. The digital simulations were performed using the PSCAD/EMTDC software.

Derivation of Theoretical Formulas of the Frequency Component Contained in the Overvoltage Related to Long EHV Cables

Recent studies of long extremely high-voltage (EHV) cables show the importance of performing temporary overvoltage analyses. As the switching of EHV cables can trigger temporary overvoltages, it is important to find the dominant frequency component contained in the switching overvoltages of these cables. Since there are no theoretical formulas to find the dominant frequency, it is generally found by means of time domain simulations or frequency scans. The derivation of theoretical formulas has been desired as the formulas would be useful in verifying the results of time-domain simulations or frequency scans. In addition, the formulas could eliminate the necessity of building simulation models of some network components. In order to address this need, this paper derives theoretical formulas to find the dominant frequency in long cable energization overvoltages. The accuracy and practical usefulness of the formulas are confirmed by comparing them with the results of time-domain simulations.

Hydrogen-fed PEMFC: Overvoltage analysis during an activation procedure

The present study aims at obtaining a better understanding on the changes that the membrane electrode assembly (MEA) of a H2-fed fuel cell experiences along an activation procedure. An activation protocol was set-up considering six loading cycles performed at 25°C. After each loading cycle, the electrochemical characterization was performed using polarization curves, Linear Sweep Voltammetry (LSV), Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). Polarization curves showed an effective increase of the MEA performance along the activation procedure, with the maximum power density increasing from 116.1mWcm−2 to 229.9mWcm−2 and the overall efficiency increasing from 9.3% to 19.7%. Simultaneously, it was observed a decrease on the Tafel slope and an increase on the exchange current density, indicating improved catalyst characteristics. From the LSV experiments it was concluded that hydrogen crossover at open circuit increases along the activation procedure, however the open circuit voltage (OCV) also increases, mainly due to an overvoltage decrease caused by mixed potential. CV experiments showed that the available catalyst area also increases. From the impedance experiments it was observed that the proton exchange membrane (PEM) and the anode and cathode charge transfer resistances decrease along the activation cycles. The opposite trend was verified for the anode and cathode double layer capacitances.

Analysis of Transient Overvoltage in 220 kV Saturated Core HTS FCL

Saturated Core High Temperature Superconducting (HTS) Fault Current Limiter (FCL) is one kind of limiters that can work effectively on short-circuit current limitation. In this paper, an equivalent circuit model depending on ac coil of HTS FCL is built for voltage distribution analysis under transient overvoltage. The equivalent circuit components, such as the capacitances and inductances, are calculated by using finite element method. The voltage distribution and oscillation analysis of ac coil may benefit to the insulation design of HTS FCL.

Multivariate Analysis of Transformer Resonant Overvoltages in Power Stations

In this paper, cable-transformer resonant overvoltages are studied on the low-voltage (LV) side of a 410-MVA generator step-up (main) transformer, due to ground fault and energization. The transformer is placed in a network configuration often found in Norwegian hydropower stations. The overvoltages are calculated when systematically varying the length of the high-voltage (HV) side cable and that of the cable between the main transformer LV side and the station transformer. This multivariate analysis is performed efficiently, using frequency-domain calculations and the inverse Numerical Laplace Transform. Time-domain simulations are used for analyzing the critical cases in detail. Both types of calculations make use of a blackbox, wideband model of the transformer, and novel procedures are introduced for initializing computations from correct 50-Hz initial conditions. Among the findings are that extreme overvoltages can occur on the station transformer if current-limiting reactors are placed in series with the cable between the main transformer LV side and the station transformer.

Mixed Over-Voltage Decomposition Using Atomic Decompositions Based on a Damped Sinusoids Atom Dictionary

The main purpose of this paper is to establish a signal decomposition system aiming at mixed over-voltages in power systems. In an electric power system, over-voltage presents a great threat for the system safety. Analysis and identification of over-voltages is helpful to improve the stability and safety of power systems. Through statistical analysis of a collection of field over-voltage records, it was found that a kind of complicated signals created by mixing of multiple different over-voltages is difficult to identify correctly with current classification algorithms. In order to improve the classification and identification accuracy of over-voltages, a mixed over-voltage decomposition system based on the atomic decomposition and a damped sinusoid atom dictionary has been established. This decomposition system is optimized by using particle swarm optimization and the fast Fourier transform. Aiming at possible fault decomposition results during decomposition of the over-voltage signal, a double-atom decomposition algorithm is proposed in this paper. By taking three typical mixed over-voltages as examples, the validity of the algorithm is demonstrated.