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This article presents a performance comparison of the solid, low impedance, high impedance, frequency-selective, and isolated grounding systems. A grounding system (for any power system component) is designed as an impedance ($\bar{Z}_{G}$) that connects the neutral point to the ground. The impedance $\bar{Z}_{G}$ is constructed using a combination of $R$ , $L$ , and $C$ elements. The values and combination type (series or parallel) of $R$ , $L$ , and $C$ determine the possible influence of $\bar{Z}_{G}$ on ground currents and potentials. Each grounding system is related to a system voltages level, a specific combination of $R$ , $L$ , and $C$ , and a range of $R$ , $L$ , and $C$ values. The solid, low impedance, high impedance, frequency-selective, and isolated grounding systems are designed for a $3\phi$ transformer and a $3\phi$ synchronous generator in order to compare their influences on ground currents and potentials during ground faults. The transformer and generator are tested for line-to-ground and double line-to-ground faults with all designed grounding systems. Test results show that some grounding systems can reduce ground currents only, while others can reduce ground potentials only. Such capabilities can be used to fulfill certain system and operation requirements (e.g., service continuity, ground capacity, etc.). [ABSTRACT FROM AUTHOR]

In this article, experimental performance assessment and comparison are presented for solid, low impedance, high impedance, frequency-selective, and isolated grounding (IG) systems. The typical design of a grounding system (for low and medium voltage generation, transmission, and distribution systems) is based on selecting an impedance ($\bar{Z}_{G}$), which is used to connect the neutral point and the ground. The impedance $\bar{Z}_{G}$ is typically composed from a combination of $R$ , $L$ , and $C$ elements. The combination type (series or parallel), along with the values of $R$ , $L$ , $C$ elements, allow estimating the possible effects of $\bar{Z}_{G}$ on ground currents and potentials during ground faults. In this article, solid, low impedance, high impedance, frequency-selective, and IG systems are designed for a 35-kVA $3\phi$ transformer and a 5-kVA $3\phi$ synchronous generator, for purposes of assessing and comparing their effects on ground currents and potentials during ground faults. The laboratory transformer and generator are tested for line-to-ground and double line-to-ground faults with all designed grounding systems under different loading levels. Experimental results show that some grounding systems can effectively reduce ground currents, and other grounding systems can effectively reduce ground potentials. These capabilities and features can be used to achieve certain system and operation mandates, including ground capacity, maximum allowed overvoltage, and service continuity. [ABSTRACT FROM AUTHOR]

This article investigates factors affecting the contributions of battery units to fault currents in grid-connected battery storage systems (BSSs). The work in this article is intended to examine the effects of the state-of-charge (SOC) on battery currents that are drawn due to faults. This article also examines the impacts of charger controller actions on the currents drawn from battery units to faults in grid-connected BSSs. The impacts of the SOC and charger controller on battery currents due to faults are examined for the lead-acid, lithium-ion, and nickel–cadmium battery units. Examination results show that the battery currents due to faults are directly dependent on the SOC. Moreover, these results show that actions of charger controller can support the battery terminal voltage, thus preventing the fast reduction of the SOC. The support of the battery terminal voltage helps in limiting the currents drawn from battery units during faults. The effects of the SOC and charger controller are verified using a 1-MW, $3\phi$ grid-connected BSS, which has lead-acid battery units. Several faults have been created during charging and discharging operations, and at different values of SOC. Test results confirm the direct dependence of battery currents (due to faults) on the SOC. In addition, obtained results demonstrate the ability of charger controller to limit the currents drawn from battery units due to faults in different parts of a grid-connected BSS. [ABSTRACT FROM AUTHOR]

This article presents a method to include fault currents in the reliability analysis of motor drives. The presented method is based on formulating a fault current matrix (FCM), the elements of which are values of the currents flowing in all parts of a motor drive. The FCM is processed using the principal component analysis (PCA) to determine the pattern of variations in all currents due to any failure event. The output of the PCA is used to determine the failure rates for all parts of a motor drive. Determined failure rates can provide a tool to set an adequate action (mitigation, maintenance, or shutdown) to ensure a reliable and safe operation during and post any failure events experienced by the motor drive. The validity and accuracy of the PCA-FCM method are verified by employing it in the reliability analysis of different motor drives with different ratings. Results demonstrate the advantages of including fault currents in setting adequate actions in response to possible failure events. [ABSTRACT FROM AUTHOR]

Three-phase ($3\phi$) power transformers can have their windings configured to create local neutral points, which can be connected to ground. The grounding of a $3\phi$ power transformer is intended to limit ground currents (including fault currents) and limit ground potentials. These objectives can be translated into the resistive grounding that is usually designed based on system ratings and transformer parameters. The resistive grounding, however, can impact the flow of the harmonic components present in the exciting currents of a $3\phi$ power transformer. As a result, undesired harmonic components are induced in primary and secondary voltages. This article presents the design and performance of a frequency-selective grounding that can achieve the objectives of grounding a $3\phi$ power transformer. The developed grounding is designed to provide a resistive path for low-frequency currents (faults), and to create a low impedance path for high-frequency currents (harmonics). The frequency-selective grounding is experimentally tested for a $3\phi$ power transformer with different primary and secondary winding configurations, different fault types, and source grounding. Test results show that the developed grounding can reduce the ground potential, harmonic distortion in primary and secondary voltages, and ground fault currents with a minimum interference with ground fault protective devices. [ABSTRACT FROM AUTHOR]

This paper reviews approaches used to detect and identify arcing currents, including arcing current faults. The reviewed approaches are categorized as the time-domain, frequency-domain, and time–frequency approaches. The time-domain approach extracts shoulders (zero values of the current around zero crossing points), spikes and jumps, abnormal magnitudes (lower or higher than normal), and high rate of change of the current. The frequency-domain approach extracts the high-frequency components, harmonic components, sub-harmonic components, and cross-correlation indicator. The time–frequency approach extracts high-frequency sub-bands that contain non-stationary frequency components, which may have non-stationary phases. The three approaches are implemented to test their accuracy, computational requirements, and sensitivity to system parameters. These tests are performed by processing of currents that are collected for normal and dynamic conditions, conventional faults, and currents with high or low arcing components. Test results provide a performance comparison for the tested approaches. [ABSTRACT FROM AUTHOR]

This paper presents the development and performance evaluation of a digital protection for interconnected distributed generation units (DGUs). The developed protection detects and responds to transient disturbances (fault and nonfault conditions) based on the magnitudes and phases of the high-frequency sub-band contents, which are extracted from the $d$–$q$-axis components of the currents flowing through the point-of-common-coupling (PCC). These magnitudes and phases are extracted by six phaselet frames that are realized by a modulated filter bank that is composed of six digital high-pass filters (HPFs). The coefficients of HPFs are determined by biorthogonal phaselet basis functions. Extracted magnitudes and phases of the high-frequency sub-band contents of PCC $d$–$q$-axis current components provide signature information for accurate detection and identification of faults. The performance of phaselet frames-based digital protection is experimentally tested for two wind energy conversion systems (WECSs) and a photovoltaic (PV) system under different fault and nonfault conditions. Test results demonstrate reliable and timely responses, along with negligible sensitivity to the type and control of DGUs, type and location of faults, and loading levels. [ABSTRACT FROM PUBLISHER]

This paper presents an innovative implementation of the wavelet packet transform (WPT) using Butterworth passive (BP) filters for differential protection of power transformers. The proposed implementation is based on designing cascaded stages of high-pass third-order Butterworth filters with cutoff frequencies identical to the cutoff frequencies of WPT-associated digital quadrature mirror filters. These high-pass filters (HPFs) are designed to extract the second-level high-frequency components present in three-phase differential currents. Extraction of these frequency components is required in order to detect and classify transients in three-phase power transformers. The output of the designed Butterworth HPFs is utilized to initiate a trip signal in case of internal-fault currents. The third-order Butterworth HPFs are designed to simplify their practical implementation as well as their integration with the differential protective relay for the tested power transformer. Different magnetizing inrush, through-fault, and internal-fault currents are investigated for different loading conditions. Performances of the proposed BP-filter-based differential relay are compared with those of the digital WPT-based relay. Comparison results show that the Butterworth filter WPT-based differential relay is able to provide a low-cost, good diagnosis, and fast responses to internal-fault currents. [ABSTRACT FROM PUBLISHER]