Earth Fault Conditions Research Articles

Including Shield Wires in the Analysis of Transient Processes Occurring in HVAC Transmission Lines

The article presents an analysis of electromagnetic transient processes in long ultra-high voltage transmission lines, taking into account shield wires. It was shown that EMTP and Matlab/Simulink software are currently widely used in the study of transient processes in power lines. The EMTP software package uses the finite element method when integrating the equation that mathematically models the distributed parameter transmission line. The Matlab/Simulink software uses the d’Alembert method. In both cases, it is not known how the boundary conditions for the partial differential equation that mathematically models the transmission line are determined. The power line is analyzed as a distributed parameter system, described by a second-order partial differential equation. The advantage of the proposed method of calculating the boundary conditions for the abovementioned equation is the use of boundary conditions of the second and third types of Neumann and Poincaré, which allowed us to take into account the mutual influence of shield wires and phase conductors of the line in one power system. On this basis, the methodology for obtaining time domain graphs, spatial distributions, and traveling wave distributions of voltages and currents for phase conductors and line shielding wires is presented. The results of a computer simulation of transient processes when switching on the power line, taking into account controlled phase commutation and under single-phase earth fault conditions, are presented. All calculation results of transient processes presented in the article were obtained exclusively using numerical methods.

Proposed Approach to Investigate the Current and Voltage Distributions of Isolated and Grounded Systems During Earth Fault Conditions

Proposed Approach to Investigate the Current and Voltage Distributions of Isolated and Grounded Systems During Earth Fault Conditions

Monitoring, Detection and Locating of Transient Earth Fault Using Zero-Sequence Current and Cable Screen Earthing Current in Medium Voltage Cable and Mixed Feeders

This paper presents the final development of an expert system utilizing a measurement of cable screen earthing transient current. The developed system allows for identification and location of earth fault in underground cable and mixed lines (underground cable and overhead line) and monitoring of an earthing system and cable screen connections. The unique feature of the developed earth fault locating system is the possibility of identification of line type and branch of the MV underground cable or mixed feeder under earth fault conditions. As a result, the time to remove failure can be greatly reduced and the number of earth fault indicators installed in the distribution network can also be reduced. Unfortunately, in order to operate properly, the previously developed system requires a fundamental—50 Hz component of the measured zero-sequence cable core current and cable screen earthing current; therefore, short transient earth faults without steady-state earth fault currents cannot be localized and categorized even though the transient earth faults have a negative impact on the power system. According to measurements performed by the authors, transient earth faults are relatively frequent, which causes stress to insulation. The number of transient earth faults may be reduced by ensuring proper maintenance of the distribution system. Unfortunately, because of the very large area of the distribution feeder, often in the range of tens of kilometers or even around a hundred kilometers, and many potential causes of earth faults, it is very difficult to localize the transient earth fault and determine the cause of the earth fault. Herein, we present the possible causes of transient earth faults and methods developed for the analysis of transient earth faults. Moreover, the novel algorithm for transient earth fault detection and location is proposed. The proposed algorithm has a self-learning capability and can identify branches of the distribution feeder under transient earth fault conditions. The effectiveness of the proposed algorithm is confirmed thanks to the performed network experiment.

A Novel High-Frequency Voltage Standing-Wave Ratio-Based Grounding Electrode Line Fault Supervision in Ultra-High Voltage DC Transmission Systems

In order to improve the fault monitoring performance of grounding electrode lines in ultra-high voltage DC (UHVDC) transmission systems, a novel fault monitoring approach based on the high-frequency voltage standing-wave ratio (VSWR) is proposed in this paper. The VSWR is defined considering a lossless transmission line, and the characteristics of the VSWR under different conditions are analyzed. It is shown that the VSWR equals 1 when the terminal resistance completely matches the characteristic impedance of the line, and when a short circuit fault occurs on the grounding electrode line, the VSWR will be greater than 1. The VSWR will approach positive infinity under metallic earth fault conditions, whereas the VSWR in non-metallic earth faults will be smaller. Based on these analytical results, a fault supervision criterion is formulated. The effectiveness of the proposed VSWR-based fault supervision technique is verified with a typical UHVDC project established in Power Systems Computer Aided Design/Electromagnetic Transients including DC(PSCAD/EMTDC). Simulation results indicate that the proposed strategy can reliably identify the grounding electrode line fault and has strong anti-fault resistance capability.

저압직류 접지시스템의 지락경로 흐름 분석에 따른 감전 보호기법

This paper presents protection techniques against electric shock in low voltage DC(direct current) grounding systems depending on the analysis of earth fault current paths. Firstly, the comparison between alternating current and direct current on human was conducted, and current threshold values for each current path and for long duration were analyzed. Secondly, the analyses of the earth fault current flows were performed depending on the grounding types and earth fault conditions. Lastly, based on these analyses, adequate protection measures of electric shock depending on low voltage DC grounding types were provided.

Instantaneous Value and Equal Transfer Processes-Based Current Differential Protection for Long Transmission Lines

According to the theory of equal transfer process of transmission lines (ETPTL), the voltages along the line and the current through the line transformed by the same linear transferring link still satisfy the original distributed parameter-based transmission-line model. It is proved that the voltage signals near power frequency along the line follow the law of linear distribution. On the basis of the aforementioned analytical results, an ETPTL-based new current differential protection scheme for long transmission lines by using restructured instantaneous value was presented. The primary voltage and current experience equal transfer processes and are transformed to be virtual instantaneous values before they are used by differential protection. According to the instantaneous voltage value of the transmission line, the instantaneous values of the capacitive current can be calculated. After removing this current, the instantaneous value-based differential criterion can be implemented. The results of Alternate Transients Program simulation test results show that the proposed technique has highly reliability, fast speed, excellent performance under high-resistance earth-fault conditions, and phase selection ability.

Automatic disconnection under AS/NZS 3000 and the impact on supply utilities

While electricity distributor works are exempt from compliance with AS/NZS 3000 under most circumstances, all of the electrical installations connected to the network do have to comply.AS/NZS 3000 requires automatic disconnection under both overcurrent and earth fault conditions. Compliance with automatic disconnection under earth fault conditions is often measured by earth fault loop impedance, but this is only part of the picture.In any fault current analysis there needs to be some confidence in the impedance of the upstream network. The designers, contractors and inspectors are using assumptions to assess their compliance in a self regulated industry, and some of these assumptions may not be valid.This paper discusses the confidence limits and the impact on contractors and installers complying with AS/NZS 3000.

Stand alone intelligent digital distance relay

Remote end infeed causes problems in distance relay especially under high resistance earth fault conditions. Although a distance relay set to an ideal operating region can cover the fault resistance at one particular load condition, the operating region is affected by changes in load condition. Hence a distance relay may overreach or underreach when load changes. From the main factors which affect the ideal digital distance relay operating region, a stand alone intelligent digital distance relay which can adapt to these changes is presented. This approach does not need communication links from the remote end of the line or the system control center. Numerous computer simulations have been carried out on realistic system configurations and the results show that there is a high potential for developing an intelligent digital distance relay.

Ideal operating region of digital distance relay under high resistance earth fault

Remote end infeed has caused a lot of problems to distance relay measurement especially under high resistance earth fault conditions. The measured impedance may be larger or smaller than the actual value. This paper describes the main factors which affect the ideal distance relay operating region and how it is related to the active and reactive power flow in the line. This would help to solve the problems in the development of an intelligent adaptive digital distance relay which does not need communication links from the remote end of the line or the system control centre.

Recursive Constrained Algorithms for Short Circuit and Earth Fault Protection of Generator-Transformer Unit

Recursive constrained algorithms for short circuit and earth fault protection of generator/transformer unit Recursive constrained protective relaying algorithms are developed for extracting 50 Hz and 150 Hz components of voltage and current signals of the generator-transformer unit. These frequency components are used for detecting internal short circuit and earth fault conditions of the combined unit. The proposed algorithms were satisfactorily tested for various simulated conditions of the system.

New approach to distance protection for resistive double-phase to earth faults using adaptive techniques

Distance protection is prone to mal-operation under resistive double-phase to earth fault conditions. This is caused by the relay measuring the incorrect impedance to the fault due to the influence of infeed from the remote end of the line. The paper describes two adaptation techniques, one for use with the earth elements, and one for use with the phase elements, which enable the correct impedance to be measured, and hence improve distance protection performance under such fault conditions.

New distance protective relay with improved coverage for high-resistance earth faults

Distance-type protective equipment often has, for a variety of practical reasons, rather limited tolerance to high-resistance earth-fault conditions. In this paper, a new distance relay, which has increased resistive coverage, is described, and it is shown to possess a characteristic which varies so as to accommodate more closely the impedance measured for various prefault loading conditions. Complicated setting procedures are avoided, and the results of dynamic tests show that the accuracy of the measurement can be maintained. A high degree of immunity to balanced phenomena such as power swings and operation during faults not involving a particular phase is inherent to the new relays. The paper concludes with a presentation of results relating to an application involving a 220 kV line of unearthed construction.

Distance-protection performance under conditions of single-circuit working in double-circuit transmission lines

When double-circuit transmission lines are operated with one of the circuits isolated and earthed at both ends, relaying conditions can arise that influence the choice of the forward-reach settings of distance protection. Earth-fault conditions during single-circuit working in this way give rise to apparent-impedance values presented to the protection that are generally less, and to errors in impedance measurements that are correspondingly greater, than for the same fault conditions during normal operation, when both circuits are in service together. The paper reports computer studies which seek to compare the discriminative performance of distance protection under earth-fault conditions during double-circuit and single-circuit operation and which, in particular, provide an account of the relaying conditions likely to be encountered in single-circuit operation. Apparent impedance values and associated relaying errors are summarised in tabular form for fault and prefault conditions relevant to a typical 400 kV interconnection, on the basis of which an assessment of the discriminative performance of distance protection in single-circuit working is made.

Measuring accuracy of distance protection with particular reference to earth-fault conditions on 400kv looped-circuit interconnections

The paper provides a detailed evaluation of the errors arising in the measurement of impedance by distance protection, when applied to 400kV double-circuit lines formed in the widely used looped interconnection. An accurate separation of the errors arising from primary-circuit interphase and intercircuit mutual coupling, nontransposition of phase conductors, and fault resistance, is developed; and the fault and prefault operating conditions for which the errors have their greatest individual and combined effects are formulated. Extensive computer evaluations of errors under single-phase-to-earth fault conditions are tabulated, on the basis of which their consequences in relation to the fault operating performance of distance protection are assessed.

Some factors affecting the accuracy of distance-type protective equipment under earth-fault conditions

Some factors affecting the accuracy of distance-type protective equipment under earth-fault conditions

Some factors affecting the accuracy of distance-type protective equipment under earth-fault conditions

Distance-type protective schemes are widely used in conjunction with e.h.v. overhead lines. Because of imperfections in the measuring elements, transformer errors, etc., it is necessary to allow a factor of safety when applying such schemes, and therefore instantaneous operation is only provided for faults in part of the line length. Improvements in relay performance have tended to reduce the normally adopted safety margin. It was felt that the magnitudes of certain errors which can arise were not sufficiently appreciated and that they should be investigated, to indicate the possible risks incurred when reducing the safety margin. The first part of the paper is concerned with the errors introduced when schemes based on transposed-line performance are applied to an untransposed single-circuit line, this practice being invariably adopted. It is shown that, when earth faults occur, schemes may overreach appreciably (10% or more) under these conditions and that false tripping could occur if first-stage settings much in excess of 80% of the line length were used. While this source of error could be eliminated by using correctly set sound-phase compensation, it is unavoidable if residual compensation is employed. The second part deals with errors caused by the mutual effects between adjacent circuits of a double-circuit set of lines. It is shown that schemes used to compensate for the mutual effects can lead to incorrect operation of an equipment when earth faults occur on the adjacent line. Such schemes are therefore unsatisfactory. If the practice of neglecting the mutual effects is adopted, there are measuring errors, but these do not tend to lead to maloperation whatever first-stage settings are used, and thus this method appears to be preferable.

Limitations of distance-type protective equipment when applied to long extremely-high-voltage power lines

On power lines the currents which flow solely in the phase conductors travel near the velocity of light whereas those which return through the ground and overhead earth wires travel more slowly, the speed depending on the line spacings, conductor sizes and nature of the ground. The full steady-state equations for a 3-phase line are developed and a particular line is examined to show the magnitude of this effect. The effect of transposing a line is also indicated. The steady-state performance of basic distance protection fitted with compensating equipment to allow for the effects of the currents in the sound phases during earth faults is studied, using the line equations. It is shown that large errors of measurement occur under earth-fault conditions on long lines fed from small sources. The performance for faults which do not involve earth is satisfactory. It is shown that non-transposition of a line makes the apparent impedance of a fault on a line depend on the source impedance. This causes further errors in the assessment of the positions of faults of all types. The high transient time-constants on long lines increase the chance of maloperation during the transient period. It is concluded that distance protection may not be satisfactory on very long lines and that a study must be made of the complete power system before a decision can be made about its suitability for any particular application.