Low Resistance Faults Research Articles

Fault Identification of UHVDC Transmission Based on DF-AD and Ensemble Learning

High-resistance ground faults are difficult to detect with existing ultrahigh voltage direct current (UHVDC) transmission fault detection systems because of their low sensitivity. To address this challenge, a straightforward mathematical method has been proposed for fault detection in UHVDC system based on the downsampling factor (DF) and approximation derivatives (AD). The signals at multiple sampling frequencies were analysed using the DF, and the AD approach was used to generate various levels of detail and approximation coefficients. Initially, the signals were processed with different DF values. The first, second, and third order derivatives of the generated signals were calculated by the AD method. Next, the entropy features of these signals were computed, and the Random Forest-Recursive feature elimination with cross-validation (RF-RFECV) algorithm was used to select a high-quality feature subset. Finally, an ensemble classifier consisting of Light Gradient Boosting Machine (LightGBM), K Nearest Neighbor (KNN), and Naive Bayes (NB) classifiers was utilized to identify UHVDC faults. The MATLAB/Simulink simulation software was used to develop a ±800 kV UHVDC transmission line model and perform simulation experiments with various fault locations and types. Based on the experiments, it has been established that the suggested approach is highly precise in detecting several faults on UHVDC transmission lines. The method is capable of accurately identifying low or high resistance faults, irrespective of their incidence, and is remarkably resistant to transitional resistance. Furthermore, it exhibits excellent performance in identifying faults using a small sample size and is highly reliable.

A novel fault monitoring method based on impedance estimation of power line communication equipment

Due to the close relationship between power grid fault and impedance, there is a significant defect in the use of power line communication (PLC) equipment to monitor and locate power grid faults, which is the lack of real-time impedance information. Therefore, this study proposes a new fault monitoring method based on impedance estimation of power line communication equipment. The channel frequency response (CFR) obtained from the PLC receiver is used to estimate the high-frequency input impedance to monitor and locate the ground fault of the power grid in real time. Firstly, based on the multi-conductor transmission line theory, bottom-up channel modeling method and impedance estimation technology, the basic principles of fault monitoring and location methods are clarified. Then, modeling and analysis of cables in different situations are carried out, and the characteristics of the factors affecting the impedance in CFR are extracted by variational modal decomposition (VMD), and the estimation results of impedance are obtained by inversion analysis. Based on this, the impedance change and machine learning algorithm are used to track and identify the abnormal state of the power line to achieve high-sensitivity positioning of the cable fault. The simulation results show that the method has a good identification effect on high and low impedance cable fault, and has a better effect on low resistance fault monitoring. The fault location error is less than 2.13%, and has a good positioning accuracy.

A nonunit two-stage protection scheme for DC transmission lines in high-voltage DC grids

Nonunit protection is suitable for the primary protection of DC lines in high-voltage DC (HVDC) grids because of its rapidity. However, most existing nonunit protections are not sensitive enough for remote-end high-resistance faults. To solve this problem, a novel nonunit two-stage protection capable of tolerating high-resistance faults is proposed in this paper. First, the propagation process of a traveling wave (TW) generated by the fault is presented, revealing the insufficiency of fault TW-based protections to tolerate remote-end high-resistance faults. Then, the TW generated by the DC circuit breaker (DCCB) located on the opposite end is analyzed, and its characteristic difference between the internal and external faults is discussed. Moreover, the nonunit two-stage protection scheme that contains stage-I and stage-II protections is proposed. Stage-I protection rapidly identifies the closed-end and remote-end low-resistance faults using the fault TW. Stage-II protection identifies the remote-end high-resistance fault using the TW generated by the DCCB, and the fault clearing time is reduced by combining the DCCB operation. The protection criteria, setting principle and operation process of the proposed protection scheme are presented in detail. Finally, a large number of PSCAD/EMTDC simulations validate the excellent performance of the proposed scheme, including a high fault resistance tolerance, quick fault clearing time, and no requirements of excessive sampling frequency and complex mathematical operations.

Simplified protection algorithm for fault detection and localization in DC microgrid

In a microgrid, conventional overcurrent and current direction based protection techniques have limitations during high resistance faults. Besides, ring configuration microgrids offer bidirectional power flow rather than unidirectional power flow. Moreover, DC microgrids own low line resistance and high DC link capacitance; it results in an immense increase in current. During fault conditions, it may cause an undesirable disconnection of resources and make the system unreliable. An accurate and fast operating protection strategy is needed to explore and achieve the above mentioned challenges. To start, with the difference in consecutive current sample data, the current difference index has been evaluated. The non-zero index is granting the estimation of frequency using natural characteristics of fault current, which correctly discriminates an incipient fault and sudden switching loads. Thereafter, by adopting local voltage and current samples during the fault, estimated inductance has been exploited, which possesses polarity and magnitude to isolate the fault and identify the fault position, respectively. The proposed method genuineness for numerous cases like low and high resistance faults at various locations, including close-in faults, bidirectional power flow, different load conditions, and other configurations is validated in MATLAB/Simulink environment. This method precisely estimates fault location under the aforementioned cases. A comparative study of the proposed scheme with existing protection methods has been carried out, proving that this method is more accurate and enhances the relay dependability.

Research on Low-Resistance Grounding Fault Line Selection Based on VMD with PE and K-Means Clustering Algorithm

Aiming at the fault line selection problem in the single-phase grounding system of the distribution network, a new fault line selection method based on VMD and permutation entropy feature extraction combined with K-means clustering algorithm is proposed. This method is a hybrid algorithm that can effectively identify fault line selection. Firstly, a simulation model is built and its zero sequence current is collected. The variational modal decomposition method is used to decompose the collected zero-sequence current into multiple intrinsic modal functions, which can not only effectively reduce the influence of harmonic components and noise in the characteristic signal but also facilitate the calculation. The extracted intrinsic mode function is calculated by permutation entropy (PE), and the calculated entropy value is constructed into a matrix to highlight the fault characteristics of the line; then, the matrix is subjected to K-means cluster analysis through the preprocessing algorithm and the faulty line is correctly distinguished. Then, regression verification is performed. Finally, it is verified by the recorded wave data of the real test site and then analyzed and compared with other algorithms. The proposed method shows that when a single-phase ground fault occurs, the ground fault line selection can be effectively identified under different transition resistances, grounding resistances, and fault distances. Therefore, this method can accurately identify the fault line selection, and the accuracy rate is 100%, which has a certain use value.

Differential DC Component-Based Relaying Scheme for Transmission Lines

ABSTRACT Protection engineers and academicians are continuously working towards better relaying for modern transmission structures. This has become a requirement because transmission structure, nowadays, is being updated with new technologies, e.g. flexible AC transmission system devices. In this paper, it has been observed that the differential DC plays an important role in distinguishing the internal and external faults. A criterion is then developed based on this unique feature of the differential DC for the identification of faults in modern transmission lines. The performance of the proposed criterion has been tested with the help of simulation study carried out using EMTDC/PSCAD software for a variety of fault types with variations in fault location, fault resistance, fault inception angle, and compensation level. Furthermore, the performance of the proposed algorithm is also investigated for several rare conditions such as evolving faults, cross-country faults, noise in measurement, and measurement error. The results prove that the scheme is selective, accurate, and robust for uncompensated and series-compensated lines while it is accurate for low resistance faults in the case of a shunt-compensated line.

A novel current amplitude differential protection for active distribution network considering the source-effect of IM-type unmeasurable load branches

The current amplitude differential protection is one of the effective means to overcome the deficiencies of the conventional over-current protection in the active distribution network. However, the existing criterions are rarely immune to the unmeasurable load branches especially the IM-type unmeasurable load branches. Therefore, this paper derives the positive-sequence equivalent model of the IM during fault occurrence. Then, the general variation law of the current amplitude difference between both terminals is revealed. For the passive unmeasurable load branch, the current amplitude difference is greater than its original value under internal faults while smaller under external faults. But for the IM-type unmeasurable load branch, such difference can exceed its original value temporarily under external low-resistance faults. To cover the maximum possible current amplitude difference during external fault occurrence, the adaptive operation characteristic curve is established. Accordingly, a novel protection scheme based on the pre-fault and post-fault current amplitude differences is proposed. The simulation results show that the proposed protection can avoid the risk of mal-operation in various external fault scenarios and identify internal faults sensitively.

Optimized bandpass admittance criteria for earth fault protection of MV distribution networks

This paper is concerned with the new method of earth fault detecting in MV distribution networks. The goal of investigations was to enhance protection sensitivity to low resistance faults resulting in small increase of voltage and residual currents in protected feeders. The earth fault detection criteria for three earthing methods and details of the criteria optimization algorithm are presented. The multi-option protection criteria optimization was based on relaying signals obtained from MV distribution network modelling in EMTP. The reliability of the protection algorithm for sustained and intermittent arcing earth faults is discussed.

Novel Fault Detection and Localization Algorithm for Low-Voltage DC Microgrid

Accurate estimation of fault location is highly crucial for swift maintenance and early power restoration. Since faults in dc networks are time critical, this article proposes a new fault detection and localization scheme for a low-voltage direct current (LVdc) microgrid network. Low-resistance faults are detected by observing voltage across the inductor whereas high-resistance ground faults are identified by measuring ground current at the relay location. Thereafter, based on iterative method, fault location is estimated by comparing analytically derived fault current with the measured value of fault current. Genuineness of the suggested technique has been assessed by simulating various internal, external, and simultaneous faults on a typical LVdc microgrid network modeled in power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) environment. The proposed method is capable of detecting and locating both low- and high-resistance dc faults without utilizing remote-end quantities. Subsequently, initial guess has minimal impact on the convergence and accuracy of the proposed algorithm. Comparative evaluation of the proposed technique with other techniques clearly proves its superiority in terms of better discrimination against external faults, rapid detection during internal faults, independency on the network topology, and higher accuracy for fault distance estimation against all types of internal faults.

Electrical and Thermal Effects of Fault Currents in Aircraft Electrical Power Systems With Composite Aerostructures

The upward trend for the use of electrical power on state-of-the-art aircraft is resulting in significant change to the design of power system architectures and protection systems for these platforms. There is a pull from the aerospace industry to integrate the electrical power system with the aircraft’s structural materials to form an embedded system, reducing the need for bulky cable harnesses. This directly impacts the fault response for ground faults and ultimately the development of appropriate protection systems. Such structural materials include composites such as carbon fiber reinforced polymer (CFRP). This paper presents the experimental capture and analysis of the response of CFRP to electrical fault current, which indicates the need for two distinct sets of electrical ground fault detection criteria for low and high resistance faults and identifies the threshold resistance for this distinction. By extrapolating these results to develop models of CFRP for use in transient simulation studies, the key electrical fault detection thresholds for speed, selectivity, and sensitivity for a dc system rail to ground fault through CFRP are identified. This provides the first set of key factors for electrical fault detection through CFRP, providing a platform for the design of fully integrated structural and electrical power systems, with appropriate electrical protection systems.

Zero-Sequence Voltage-based Method for Determination and Classification of Unloaded Overhead Line Operating Conditions at the Moment of Energization

Overhead line energization can be performed under normal or faulty conditions. The latter indicates an occurrence of a fault along the line that exists at the moment of energization. This can lead to significant over-voltages that could endanger proper line operation. The issue gets more complex to protective devices when it comes to high-resistance faults, which impair the ability of relays to react promptly and accurately. Consequently, installation of additional detection devices becomes necessary. This paper proposes a novel method that properly detects and classifies line operating conditions at the moment of energization. The method is designed to be useful for utilities and it can be considered as a low-cost, fast, and accurate detection and classification approach, suitable for dealing with both low-resistance and high-resistance faults. Through comprehensive mathematical modeling it was found that both normal and faulty conditions during line energization are accompanied by the zero-sequence voltages of specific characteristics. The differences between zero voltage sequences are reflected in harmonic content, magnitudes of dominant frequencies, and their phase angles in regard to supply voltage. These findings are taken as the method's detection and classification criteria. The validity of the proposed model is verified by simulations and by field measurements.

Hybrid Passive-Overcurrent Relay for Detection of Faults in Low-Voltage DC Grids

Detection of high-resistance faults on meshed low-voltage dc grids poses a challenge, as such faults have very low fault current magnitudes. This paper proposes a hybrid passive-overcurrent relay to overcome this problem. The proposed relay consists of one current and one voltage transducer, as well as two passive elements: 1) an inductor; and 2) a capacitor. For bolted and relatively low-resistance faults, the relay uses a simple overcurrent function to detect the resultant high fault current magnitudes within 2 ms. On the other hand, for relatively high-resistance faults, a real-time discrete wavelet transform is used to detect the voltage transients generated by the relay passive elements in less than 5 ms. Furthermore, the proposed relay is inherently capable of identifying the type of fault. The proposed approach relies on local-bus measurements to detect and classify various types of faults with resistance up to 200 ohms. Analytical modeling proves that the proposed approach is system independent. Testing the hybrid passive-overcurrent relay on a ±750 V meshed TN-S dc grid reveals that the proposed relay is fast, sensitive, and selective under various conditions.

Analysis and Application of the Neutral Voltage in Resonant Grounding Grid

There are often some problems during operation of the resonant grounding grid, such as tracking failure, excessive tuning, and oversize residual current caused by compensation not matching grounding fault. A new idea is proposed to solve the problems about using of the neutral voltage detection, analysis and calculation. Firstly, neutral voltage characteristics are analyzed. Secondly, neutral voltage is applied to the calculation of tracking sensitivity, and the problems of tracking failure and excessive tuning are effectively solved. Thirdly, change of operation mode and grid disturbance are distinguished by using characteristics of neutral voltage variation. Lastly, the formulas of neutral voltage ranges are derived, which can distinguish high-resistance grounding fault from low-resistance grounding fault and achieve a smart compensation. This solves the problem of excessive residual current. Simulations verified the above conclusions and the results are satisfied.

Fault location and diagnosis in a medium voltage EPR power cable

This paper presents a case study on fault location, characterization and diagnosis in a length of shielded 11 kV medium voltage ethylene-propylene rubber (EPR) power cable. The defect was identified on-site as a low resistance fault occurring between the sheath and the core. A 43 m section was removed for further analysis. The fault resistance was characterized and the location of the defect pinpointed to within a few cm using a combination of time-difference-of-arrival location and infra-red imaging. A combination of X-ray computed tomography, scanning electron microscopy and energy dispersive X-ray spectroscopy were then applied to characterize any abnormalities in the dielectric surrounding the breakdown region. A significant number of high density contaminants were found to be embedded in the dielectric layer, having an average diameter of the order of 100 μm, a maximum diameter of 310 μm and an average density of 1 particle per 2.28 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to determine the geometry and elemental composition of some initial contaminant samples. It was concluded that contamination of the EPR layer, combined with an observed eccentricity of the cable¿s core and sheath resulting in a reduced insulation gap, may have led to an electric field concentration in the region of the defect sufficient to initiate breakdown. Preventative strategies are discussed for similar families of cables, including more stringent dielectric testing requirements at the manufacturing stage and PD monitoring to detect incipient failure.

An Adaptive Decision Logic to Enhance Distance Protection of Transmission Lines

This paper introduces adaptive decision-making logic to improve the performance of distance protection of transmission lines. The proposed approach incorporates the trajectory of the measured impedance into the relay final decision-making logic through a weighting procedure. Two criteria are used to weigh the impedance plane appropriately, where higher weights are assigned to the faults occurring at the interior areas of the relay protective zone and low resistance faults. The weights assigned to impedance samples are added together considering the amount of smoothness of the measured impedance trajectory. An adaptive neurofuzzy inference system (ANFIS) is used to implement the proposed decision logic. Meanwhile, the fault current amplitude is considered as the other input of the ANFIS network to accelerate the relay operation for close-in faults and to incorporate an index for the source-to-line impedance ratio into the final decision-making logic. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach provides a very reliable technique to make the distance protective scheme faster and smarter. It helps to achieve the optimal compromise between the protective relay operation time and security.

Analytical prediction of abnormal temporary overvoltages due to ground faults in MV networks

The paper deals with the temporary overvoltages that build up in radial MV distribution networks following the inception of a 1-phase-to-ground fault. It will be demonstrated that, for extended cable/overhead MV distribution networks with ungrounded neutral, in case of low resistance faults at critical locations along overhead lines, the neutral voltage can reach very large values, significantly higher than 1 p.u. (up to 2.5 p.u.). The attendant temporary overvoltages on healthy phases can be very large, much higher than √3 p.u. (up to 3.5 p.u.). Fault currents are also affected, reaching twice the value calculated with simplified methods, i.e. neglecting series impedances. Quick yet accurate analytical formulas for the prediction of maximum overvoltages, fault currents and critical fault distances are presented, together with their validation by detailed ATP-EMTP simulations. The results of a study on an existing Italian 15 kV–50 Hz extended mixed cable/overhead distribution network are finally presented and discussed.

Development of a fault locator for a branch line

Formerly, only pulse radar and the Murray loop bridge could be utilized in a cable fault location method that is applicable to branch lines. Those methods need a terminal connection at the far end. Therefore, it is difficult in fault location involving branch lines. Pulse radar is applicable only for high-resistance ground faults and the Murray loop bridge is applicable only for low-resistance ground faults. We have developed current-detection pulse radar and tested it. In high-resistance ground fault location, the measured result includes discharge delay error. Therefore, we have proposed an error correction method and confirmed it. In addition, we have designed a new cable fault location method of pulse radar and tested it. © 2000 Scripta Technica, Electr Eng Jpn, 134(2): 19–28, 2001

Adaptive travelling wave protection algorithm using two correlation functions

In this paper, the performance of the correlation function-based travelling wave protection algorithm for high resistance faults is investigated. The reason for its inaccuracies is revealed by the lattice diagram. To eliminate its limitation, an auxiliary cross-correlation function (CCF) is proposed to act as its complement, which takes advantage of the signal that causes the inaccuracies of the standard CCF. For high resistance faults, both the template and the desired signal of the auxiliary CCF have the same prominent feature, which makes them easy to be identified, and the fault location can be acquired from them correctly. An adaptive strategy is designed to select the correct result from the two CCFs so that it can deal with both low resistance and high resistance faults. Simulation results show that the reliability and accuracy of the travelling wave protection have improved significantly.

Co-ordination of overvoltage and short-circuit protection for aircraft A-C systems

The purpose of a circuit protector (CP) is to clear faults and thus permit the remainder of the system to continue normal operation. The function of overvoltage protection is to prevent damage to utilization equipment by de-energizing the generator when system overvoltage exists. Proper co-ordination is necessary to prevent nuisance tripping of the overvoltage relay (OVR) during low-resistance faults.