scholarly journals Simulation study of 6–10 kV cable lines for transient processes calculation during earth faults

Vestnik IGEU ◽  
2021 ◽  
pp. 30-40
Author(s):  
V.A. Shuin ◽  
Yu.D. Kutumov ◽  
N.V. Kuzmina ◽  
T.Yu. Shadrikova
Keyword(s):  
Frequency Dependence ◽  
Single Phase ◽  
Transient Processes ◽  
Cable Line ◽  
Frequency Dependent ◽  
Cable Networks ◽  
Ground Fault ◽  
Three Phase ◽  
Frequency Independent ◽  
Cable Lines

As a rule, researchers do not consider the dependence of the inductance of cable lines on frequency in their scientific papers devoted to the calculation of transient processes during single phase-to-ground fault in 6–10 cable networks. In some cases, it can lead to significant errors in evaluation of current and voltage transient components parameters. Therefore, it is an urgent task to estimate defined errors and the scope of application of frequency-independent equivalent circuits and models of 6–10 kV cable lines during calculation and simulation of transient processes in case of single phase-to-ground fault. The authors applied PSCAD / EMTDC software to study the effect of the frequency dependence of the inductances of 6–10 kV cable lines on the calculation accuracy of transient processes during single phase-to-ground fault. It allows to simulate electric power systems models with the usage of both frequency-dependent and frequency-independent cable line models with round conductors only. To check the adequacy of the frequency-dependent three phase cable model developed in PSCAD software, the authors have used a frequency-dependent model of 6–10 kV three-phase cable with sector-shaped conductors designed in COMSOL Multiphysics software. The authors have developed an approach to develop of 610 kV cable lines models with frequency-dependent and frequency-independent parameters. The authors have obtained error estimation in transient current and voltage parameters during single phase-to-ground fault in cable networks models that do not consider the frequency dependence on inductance (for discharge components the error is 1520 %, for charging components the error is equal to 510 %). It is shown that models with cable line parameters defined according to spreading speed of electromagnetic wave, can be used for approximate calculation of transient current and voltage to solve most of tasks of investigation of transient processes during single phase-to-ground faults. Application of the developed recommendations to determine three phase medium voltage cable lines parameters will increase the calculation accuracy of transient processes during single phase-to-ground faults in 6–10 kV cable networks. Only application of frequency-dependent models of cable lines allows us to provide required accuracy to develop methods of distant earth fault localization in 6–10 kV networks.

scholarly journals Selection of parameters of overhead lines models when calculating transient processes during earth faults in 6–10 kV networks

Vestnik IGEU ◽  
2021 ◽  
pp. 5-17
Author(s):  
V.A. Shuin ◽  
Yu.D. Kutumov ◽  
N.V. Kuzmina ◽  
T.Yu. Shadrikova
Keyword(s):  
Single Phase ◽  
Transient Processes ◽  
Overhead Line ◽  
Transient Currents ◽  
Overhead Lines ◽  
Ground Fault ◽  
Three Phase ◽  
Frequency Independent ◽  
Protection Devices ◽  
Frequency Dependences

Single phase-to-ground faults are the most common type of faults in 6–10 kV overhead distribution networks. Arc intermittent single phase-to-ground fault (PSP) are the most dangerous for the network and the damaged element. They are followed by intense transient processes and, as a result, dangerous overvoltage rate and significant transient current surges at the point of insulation damage. PSP transients also have a significant effect on the selectivity and operation stability of protection devices against this type of damage. Therefore, the development of the methods and means to improve the operation efficiency of 6–10 kV overhead networks in case of PSP and technical improvement of protection devices in many cases is due to the need to calculate the transient processes that occur during insulation breakdowns of the network phase to earth. For the systems under consideration, the reliability of transient processes calculations in case of PSP is determined mainly by the accuracy of estimation of the parameters of 6–10 kV overhead lines, first of all, of inductance, which generally depends on the frequency of the transient current components. In the scientific papers devoted to the study of transient processes in case of PSP in medium voltage electrical networks, including 6–10 kV overhead networks, constant (frequency independent) values of inductance are used as a rule in the equivalent circuits and in the models of transmission lines. An urgent task is to estimate errors caused by the application of this approach to determine the parameters of 6–10 kV overhead lines during the calculations and modeling of transient processes during PSP, and cases of its application. Advanced methods of modeling of electric power systems and their elements have been applied with the use of COMSOL Multiphysics and PSCAD software to obtain the frequency dependences of the inductances of a 6–10 kV three-phase overhead line and study of their influence on the calculation accuracy of transient currents and voltages in case of PSP. The parameters of 6–10 kV overhead line models developed in the indicated software packages at a frequency of 50 Hz are set in accordance with the reference data. The authors obtain the errors estimation to determine the parameters of transient currents and voltages during PSP in 6–10 kV overhead networks when using transmission line models. The frequency dependences of inductance, which are up to 40–50 % in amplitude are not considered. The results show that application of frequency-independent models is permissible only in the cases when parameters of the calculated equivalent circuit of the network and position of PSP point remain practically constant, when solving problems that require high accuracy to determine the parameters of transient currents and voltages, for example, to determine remotely the location of a ground fault, it is necessary to use frequency-dependent models of 6–10 kV overhead lines. Introduction of the developed recommendations to determine 6–10 kV three-phase overhead lines parameters allow us to increase the reliability of calculations and to avoid raw errors when solving the problems which are related to the study of transient processes in case of earth faults in the networks of the given voltage class.

An investigation into the fundamental relationships between attenuation, phase dispersion, and frequency using seismic refraction profiles over sedimentary structures

Geophysics ◽  
1987 ◽  
Vol 52 (1) ◽  
pp. 72-87 ◽  
Author(s):  
R. S. Jacobson
Keyword(s):  
Frequency Dependence ◽  
Seismic Waves ◽  
Velocity Dispersion ◽  
Seismic Refraction ◽  
Systematic Investigation ◽  
Data Sets ◽  
Frequency Dependent ◽  
Frequency Independent ◽  
Apparent Attenuation ◽  
Seismic Refraction Data

Despite many attenuation measurements which indicate a linear functional frequency dependence of absorption or constant [Formula: see text] in sediments, several theories predict no such linear dependence. The primary justification for rejecting a first‐power frequency dependence of attenuation is that it implies that seismic waves cannot propagate causally. Seismic waves must also travel with some velocity dispersion to satisfy causality, yet there is a lack of velocity dispersion measurements in sediments. In‐situ attenuation is caused by two distinct mechanisms: anelastic heating, and scattering due to interbed multiples. Apparent, or scattering, attenuation can produce both frequency‐dependent and non‐frequency‐dependent effects. Accurate measurements of attenuation and velocity dispersion are difficult; it is not surprising that a systematic investigation into the frequency dependence of absorption and velocity has not been made. A reinvestigation into two seismic refraction data sets collected over thickly stratified deep‐sea fans indicates that [Formula: see text] should not be assumed to be independent of frequency. Further, significant frequency‐independent absorption is present, indicating a high degree of apparent attenuation. Phase, or velocity, dispersion was also measured, but the results are more ambiguous than those for attenuation, due to inherent limitations of digital signals. Nevertheless, the absorption and velocity dispersion results are largely compatible, suggesting that if apparent attenuation is observed, then the scattered waves propagate causally.

Frequency dependence of CO2 elimination and respiratory resistance in monkeys

1985 ◽  
Vol 58 (2) ◽  
pp. 653-657 ◽  
Author(s):  
J. W. Watson ◽  
A. C. Jackson
Keyword(s):  
Frequency Dependence ◽  
Nonlinear Frequency ◽  
Frequency Dependent ◽  
Dependent Behavior ◽  
Frequency Independent ◽  
Respiratory System Resistance ◽  
The Relationship ◽  
High Frequency Oscillatory ◽  
Large Frequency ◽  
Co2 Elimination

In dogs, respiratory system resistance (Rrs) is frequency independent, and during high-frequency oscillatory ventilation (HFO) the relationship between CO2 elimination (VCO2) and frequency is linear. In contrast, we found in rabbits a large frequency-dependent decrease in Rrs with increasing frequency along with a nonlinear relationship between frequency and VCO2 (J. Appl. Physiol. 57: 354–359, 1984). We proposed that frequency dependent mechanical properties of the lung account for inter-species differences in the frequency dependence of gas exchange during HFO. In the current study we tested this hypothesis further by measuring VCO2 and Rrs as a function of frequency in a species of monkey (Macaca radiata). In these monkeys, Rrs decreased minimally between 4 and 8 Hz and in general increased at higher frequencies, whereas VCO2 was linearly related to frequency. This is further evidence supporting the hypothesis that nonlinear frequency-VCO2 behavior during HFO is related to frequency-dependent behavior in Rrs.

The Mechanical Transient Process at Asynchronous Motor Oscillating Mode

2009 ◽  
Vol 25 (25) ◽  
pp. 23-26
Author(s):  
Uldis Antonovičs ◽  
Viesturs Bražis ◽  
Jānis Greivulis
Keyword(s):  
Transient Process ◽  
Single Phase ◽  
Asynchronous Motor ◽  
Half Period ◽  
Transient Processes ◽  
Negative Voltage ◽  
Stator Windings ◽  
Squirrel Cage ◽  
Three Phase ◽  
Oscillating Mode

The Mechanical Transient Process at Asynchronous Motor Oscillating ModeThe research object is squirrel-cage asynchronous motor connected to single-phase sinusoidal. There are shown, that by connecting to the stator windings a certain sequence of half-period positive and negative voltage, a motor rotor is rotated, but three times slower than in the three-phase mode. Changing the connecting sequence of positive and negative half-period voltage to stator windings, motor can work in various oscillating modes. It is tested experimentally. The mechanical transient processes had been researched in rotation and oscillating modes.

scholarly journals Analysis of Overvoltages Appearing in One-Sidedly Ungrounded MV Power Cable Screen

Energies ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1821 ◽  
Author(s):  
Aleksandra Schött-Szymczak ◽  
Krzysztof Walczak
Keyword(s):  
Single Phase ◽  
Field Studies ◽  
Power Cable ◽  
Cable Line ◽  
Medium Voltage ◽  
Ground Fault ◽  
Actual Outcome ◽  
Connection Type ◽  
Overvoltage Protection ◽  
Line Work

Changing the connection type of a medium voltage (MV) cable screen is linked to a decrease in power loss, although it may also lead to the generation of overvoltage in a metallic cable screen, which is hazardous for proper cable line work. In this paper, results of simulation and field researches are presented, showing the range of voltages that occurs in cable screens during single-phase ground fault. There are considered to be three scenarios according to the applied type of cable screen connection. Conducted researches allow the comparison of chosen methods of simulation with an actual outcome. Results obtained during simulation and field studies lead to the conclusion that the range of overvoltage occurred in a cable screen could in fact be dangerous for the cable line’s sheath insulation without proper overvoltage protection.

scholarly journals The impact of PV generation and load types on the impedance relays during both balanced and unbalanced faults

2021 ◽  
Author(s):  
Rashad M. Kamel ◽  
◽  
Heba M. Abdullah ◽  
Keyword(s):  
Power Generation ◽  
Dynamic Load ◽  
Distribution System ◽  
Single Phase ◽  
Dynamic Loads ◽  
Fault Resistance ◽  
Ground Fault ◽  
Three Phase ◽  
The State Of Kuwait ◽  
The Impact

Photovoltaic (PV) power generation and the types of connected loads both have an effect on protective impedance relays’ readings. This paper investigates this effect in a real distribution system installed in the State of Kuwait. It is found that, both the dynamic loads and the PV plants have considerable effects in the relay impedance value which vary according to the load type, PV connection and fault locationplace. Both single phase to ground fault (unsymmetrical fault) and three phase fault (symmetrical fault) are investigated. When single line to ground fault occurs at the PV bus (far from relay location), the dynamic loads increase the relay impedance while the PV plant decreases the relay impedance. When a single phase to ground fault occurs at the relay bus (load bus), the dynamic load decreases the relay impedance and the PV plant increases it. For a three-phase to ground fault at the relay bus, both dynamic load percentages and PV plant power generation have no effect on the protective relay impedance readings. At this condition, the relay impedance totally depends on the fault resistance. The main finding of this paper is that both the load type (especially dynamic load) and the PV plant have dominant effects on the protective impedance relay reading and setting. The distribution system planners and operators must consider the PV plant and types of load during designing, setting and adjusting the protective impedance relays. The most important point in this paper is considering real case study. This means that, the obtained results are more realistic than the assumed system in the other research. If the fault occurs at the location of the PV system’s bus when no PV power is generated, the dynamic load causes the relay impedance to increase, while connecting the PV decreases the relay impedance. The relay’s resistance and reactance increase from 0.3153Ω and 1.4950Ω, to 0.3456Ω and 1.6617Ω respectively when the dynamic load increases from 25% to 90% of the total load at constant high fault resistance. The relay resistance and reactance decrease from 0.2849Ω and 0.3443Ω (without PV plant), to 0.2195Ω and 0.3137Ω (with PV), respectively. When the dynamic load percentage increases from 25% to 90%, the resistance and reactance of the relay decrease from 1.0488Ω and 0.0051Ω, to 0.9526Ω and 0.0008Ω, respectively. This phenomenon is valid for all expected fault resistances. When considering constant dynamic load percentage and constant fault resistance, the relay resistance and reactance increase from 1.375Ω and 0.0022Ω (without PV) to 1.5745Ω and 0.0726 Ω (with PV), respectively. Based on those results, the impedance relay setting must be adjusted according to the percentage of the dynamic loads percentage, the PV penetration level, and the fault location.

Development of the Thermal Equivalent Circuit for Evaluating the Capacity of High Voltage Cables in Real Time

2014 ◽  
Vol 698 ◽  
pp. 586-591 ◽  
Author(s):  
Evgeny Zaytsev ◽  
Vladimir Lebedev
Keyword(s):  
Real Time ◽  
Equivalent Circuit ◽  
Cross Section ◽  
High Voltage ◽  
Thermal Processes ◽  
Power Capacity ◽  
Cable Line ◽  
Three Phase ◽  
Cable Lines ◽  
Transient Thermal

The authors of this paper justify the construction of the thermal equivalent circuit for a three-phase high voltage cable line that describes the transient thermal processes in the cross section of the line. According to the authors, the proposed scheme, if taken as a basis, allows to solve the task of evaluating the power capacity of high-voltage cable lines in real-time and predict heating of cables with the aim to prevent thermal degradation of the insulation.

scholarly journals Impact of Cable Configuration on the Voltage Induced in Cable Screen during Work with One-Sidedly Ungrounded Cable Screen

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4263
Author(s):  
Aleksandra Schött-Szymczak ◽  
Krzysztof Walczak
Keyword(s):  
Cross Section ◽  
Point Of View ◽  
Network Configuration ◽  
Cable Line ◽  
Network Characteristics ◽  
Ground Fault ◽  
Network Operation ◽  
Distribution Line ◽  
The One ◽  
Cable Lines

In the latest research, it has been proven that from the point of view of losses in a cable distribution line, the most advantageous operation is to work with two or one phase of metallic cable screen ungrounded. However, such an operation may cause changes in the network characteristics and thus the occurrence of undesirable phenomena. One of those characteristics is the overvoltages in those cable screens, which can lead to cable line damage. The simulation tests presented in this article are closely related to the unusual method of operation of the MV cable screens and their performance, and they address the question of whether in a given system ground fault overvoltages may be a significant threat to the operation of the cable. The research methods used to verify these risks are related to the simulation of the cable line operating states using the DIgSILENT PowerFactory program (DIgSILENT GmbH, Gomaringen, Germany). Overvoltage simulations were performed, taking into account changes in the network configuration, such as the method of cable screens grounding, the length of cable lines, the cross-section of the conductor and cable screen, or the method of operation of the neutral point. The results for the cable line modeled as a part of the MV network with the variables considered during the tests indicate the possible impact of the one-sidedly cable screen ungrounding on overvoltages in this cable screen. The obtained results at the level of a few kV in one-sidedly ungrounded cable screens show that the change of the configuration of the operation of these cable screens may affect the safety of the network operation.

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