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The control of very high switching frequency power electronic converter systems featuring latest generation wide bandgap devices requires current measurements with a very high bandwidth (BW) to achieve high closed-loop control dynamics. One example is an ultrahigh BW $\mathbf {4.8}$ MHz parallel-interleaved multilevel GaN inverter ac power source with a target large-signal output BW of $\mathbf {100}$ kHz. This work investigates the combination of commercially available low-frequency (LF) Hall-effect current sensors (BW $\mathbf {\approx 1}$ MHz) with suitable high-frequency (HF) sensors to extend the BW above $\mathbf {10}$ MHz, i.e., enough to measure the HF inductor current. Based on a conventional PCB-integrated Rogowski coil, for the HF sensor, three improved pickup coil (PUC) geometries based on proposals in the literature are investigated. The LF and HF sensor signals are combined with a precision fully differential combiner circuit. Design guidelines for the HF sensors as well as the combiner circuit are presented and thereby the influence of mismatches and tolerances is examined. The performance of the proposed HF sensors is experimentally verified and compared with previous solutions based on galvanically isolated inductor voltage sensing and a current transformer. The PUCs reach a BW $\mathbf {>50}$ MHz, which is an improvement by more than a factor of $\mathbf {50}$ compared to the fastest available Hall sensor. Furthermore, it is proven that all investigated sensors are capable to accurately measure the triangular inductor current ripple in a hardware prototype of the aforementioned ac power source. In a final step, the influence of common-mode (CM) disturbances originating from fast $\mathbf {{d}v/{d}t}$ switching transients on the sensor performance is analyzed. The presented current sensors achieve a CM rejection ratio of almost $\mathbf {100}$ dB. [ABSTRACT FROM AUTHOR]

Power systems can and have been impacted by harmonics generated during geomagnetic disturbances (GMD) events. These harmonics are generated from the part-cycle saturation of power transformers caused by the flow of geomagnetically-induced currents through grid-connected transformers. This article describes a system level harmonic analysis tool needed by the industry to perform an adequate assessment of GMD-related distortion impacts. When the results of a properly performed harmonic assessment are combined with the fundamental frequency analyses, a much more accurate evaluation of grid security during GMD can be obtained. The tool is publicly available for engineers, students, and researchers. It provides multiple examples, including a validation against published measurements from an experimental setup consisting of two back-to-back connected transformers in the Fingrid power network. Final of this article briefly discusses the results of that validation. [ABSTRACT FROM AUTHOR]

This article aims at developing a gradient boosting (GB) model with parameters optimized by the Bayesian optimization (BO) method for detecting various types of fault in an oil-immersed transformer and reactor. The developed model depicts higher accuracy in comparison with other machine learning (ML) techniques, such as XGBoost, AdaBoost, random forest, and support vector machine parameters being optimized by BO. A comparison of the skill score depicts the superiority of the developed Bayesian optimization-based gradient boosting (BO-GB) model with respect to Bayesian optimized other ML techniques. Further comparison of the model with conventional Duval pentagon verifies the accuracy of detecting the faults, which were missed by the former. Also, the software has been developed based on the proposed BO-GB method for the on-site detection of the fault. In addition, actual values of dissolved gases with respect to fault confirmed after the internal inspection of the transformer and reactor are tabulated and compared. The data so presented will help in utilizing the authentic dissolved gas data in addition to the already available IEC TC10 databases for future works. The study undertaken in this article will help utilities in diagnosing the incipient faults more accurately and precisely, thereby preventing hazardous operating conditions along with minimizing the downtime cost. [ABSTRACT FROM AUTHOR]

In this article, a new saturated amorphous alloy core-based inrush current limiter (ICL) has been designed and built to limit the inrush current of a power transformer. A toroidal core with a middle limb is developed using the Metglas amorphous alloy and the middle limb is excited with a dc current to saturate the amorphous alloy core. Only a very small dc excitation current is required using such a core when compared to that using a similar design with conventional materials. Under normal conditions, the saturated amorphous alloy ICL core steady-state impedance is low and has a negligible effect on the operation of the system. During the energization of a power transformer connected to the ICL, the large inrush current desaturates the amorphous alloy core, resulting in an increase in the ac winding impedance, which limits the peak amplitude of the transformer inrush current and harmonics. To validate the proposed saturated amorphous alloy core-based ICL, a prototype ICL has been built and tested in the laboratory. The experimental results show that the core power loss, core saturation, the fundamentals, and harmonics of the inrush current of the proposed saturated amorphous alloy core-based ICL are significantly better compared with those from the sheet steel core-based ICL. It is expected that the proposed saturated amorphous alloy core will be used in future inrush current limiters that can help to improve the performance of the power transmission and distribution system. [ABSTRACT FROM AUTHOR]

This article presents the implementation and performance testing of a bus-differential protection for buses, which interconnect battery storage systems (BSSs). The proposed bus-differential protection is based on employing the α β 0 components of the apparent powers flowing in all branches of the protected bus. The α β 0 components of the apparent powers are employed due to their ability to accommodate changes in the power flow direction in the branches connected to the protected bus. The apparent powers are determined using the measured voltage and currents in all branches connected to the protected bus. The proposed α β 0-based bus-differential protection is implemented and tested for internal and external faults, which are created during the charging and discharging of BSSs. Test results demonstrate the ability of the proposed α β 0-based bus-differential protection to initiate fast, accurate, and reliable responses to internal and external faults in the protected bus. Observed response features of the proposed protection are found to have minor sensitivity to the mode of operation of the BSS (charging and discharging), fault location (internal and external), and/or fault type. [ABSTRACT FROM AUTHOR]

Duplication of circuit breakers (CBs) in substations is not realistic due to economic and operational constraints. In the event of failure of a CB, adjacent breakers need to be called in to isolate the fault. Typically, a breaker-failure protection (BFP) function is integrated within commercial relays to monitor such situations. However, these functions are prone to maloperation because of subsidence in current transformers (CTs) resulting from faults with significant decaying dc component. To this end, a reliable reset algorithm for the BFP function is presented. After measuring the decaying dc component within a one-cycle moving window, the proposed algorithm accurately distinguishes between the alternating pattern of fault current and exponential decaying pattern in subsidence current. Its performance remains unaffected during change in fault current level, decaying dc component, CT saturation, level of subsidence, and random noise. Effectiveness of the proposed scheme in practical scenarios is demonstrated through a hardware setup validated through error analysis. Overall performance evaluation in terms of reliability indices testifies its superiority over available techniques. [ABSTRACT FROM AUTHOR]

This article presents and tests the performance of a digital differential protection for three-phase (3φ) converter transformers. The proposed digital differential protection is developed to comply with the ANSI 87T protection procedure. The presented protection is featured with fault detection based on the energy contents of the high-frequency subbands of the d−q axis components of differential currents. Desired energy contents are extracted using the phaselet transform (PHT), which can process signals without sensitivity to the variations in their phase shifts. Energy contents of the high-frequency subbands offer accurate, fast, and reliable detection, and identification of internal faults in any part of a 3φ converter transformer. The d−q PHT-based digital differential protection is implemented for performance evaluation using different 3φ converter transformers, when feeding controlled rectifier units. Performance results demonstrate accurate, fast, and reliable detection, and response to different types of fault, and nonfault events. Response features of the developed differential protection are complimented with simple implementation, reduced computations, and minor sensitivity to phase shifts, fault location, and loading levels. [ABSTRACT FROM AUTHOR]

In this article, a zero-voltage zero-current transition scheme suitable for a family of dual-phase interleaved converters is proposed. The transition network consists of an auxiliary transformer, a switch, and a clamp diode. This network uses a low component count structure, and yet achieves effective soft-transitions (zero-voltage turn-ON as well as zero-current turn-OFF) for the main switches. It facilitates zero-current turn-OFF of all the diodes along with zero-current turn-ON of the auxiliary switch. Additionally, the auxiliary transformer self-adjusts the current in the auxiliary network depending upon the loading conditions and thus the reactive energy during the soft-switching is low for the entire range of loads. A detailed theoretical analysis is presented by considering a high step-up dual-phase interleaved boost converter as an example. The feasibility of the proposed soft-switching scheme is implemented on the same and its effectiveness is demonstrated through experimental results which are obtained on a 400-W converter prototype. [ABSTRACT FROM AUTHOR]

An array of proportional-resonant regulators is often used in shunt active power filters to control the grid currents and reduce the harmonic distortion caused by a distorting load. The voltage that is necessary to compensate for the current harmonics must be consistent with the available dc-link voltage. In this article, three adaptive algorithms for the exploitation of the dc-link voltage are developed and compared. These algorithms adaptively change the voltage saturation of each regulator to preserve the control capability of the fundamental component of the current when the available voltage is not enough to control the filter current. Simultaneously, they try to improve the quality of the grid current because the dc-link voltage of the active power filter is allocated to the regulators to compensate only the most significant harmonics. Some experimental results are shown to demonstrate the feasibility of the three algorithms. [ABSTRACT FROM AUTHOR]

An unbalanced current protection relay (60C, 51NC) cannot operate fast enough to avoid catastrophic failure against high system fault currents within capacitor units because a traditional unbalanced current protection relay is not capable of classifying the transient fault current and switching inrush current. This article proposes a new algorithm for the detection and classification of these transient current signals. Simulations are performed using PSCAD/EMTDC programs. The outputs of the current signals are used as inputs for the discrete wavelet transform (DWT) process. The wavelet-based fault and inrush current detection and classification unit receive the captured transient current signals and use DWT to detect and analyze these signals. Actual inrush current signals from an experimental setup and shunt capacitor banks of 115 kV, 22 kV, and 6.6 kV are used to verify the proposed algorithm. The results show that the proposed algorithm provides good performance and accuracy in identifying faults and inrush currents. [ABSTRACT FROM AUTHOR]

Geomagnetically induced currents (GICs) in power grids are mainly caused by geomagnetic disturbances especially during solar storms. Such currents can potentially cause negative impacts on power grid equipment and even damage the power transformers resulting in a significant risk of blackouts. Therefore, monitoring GICs in power systems and developing solutions to mitigate their impacts before rising to a certain threatening level is urgently in need. Monitoring GICs is, however, quite a challenge and costly, as they usually appear in forms of dc components in the high voltage transmission lines, which are barely accessible through transformers. By examining the measured currents from the current transformers, this article proposes a framework to detect GICs in power transmission systems through a hybrid time-frequency analysis combined with machine learning technology. Simulated results verify that the proposed approach can promisingly estimate GICs in power systems during a variety of grid operating conditions. [ABSTRACT FROM AUTHOR]

This article proposes a new approach for reducing inrush currents in three-phase three-legged stacked-core power transformers. Although magnitudes of inrush currents may not be as high as short-circuit currents, they are extremely detrimental to normal operation of power transformers. In this article, a new controlled switching scheme that takes into consideration both core saturation and residual flux is proposed to reduce inrush currents. Also, a transient model based on the duality transformation between electric and magnetic circuits is proposed, where a nonlinear inductance is used to simulate core saturation. The proposed scheme is demonstrated on a real transformer by both laboratory experiments and performing simulations. The Alternative Transients Program is used to simulate a wide spectrum of possible operating conditions. The experimental and simulation results show that inrush currents are significantly reduced after utilizing the proposed scheme. Therefore, the proposed controlled switching scheme will result in relaxing inrush-current-related constraints in designing and manufacturing three-phase power transformers, which, in turn, will reduce their cost. [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]

A three-phase-isolated current-fed dc–dc converter with LCC-T resonant tank to achieve an efficient and compact design is proposed. Traditional dc–dc converters require an external parallel inductor to increase the transformer magnetizing current to realize soft switching under light-load conditions. The proposed LCC-T configuration eliminates this requirement and realizes light-load soft switching with reduced circulating current. In addition, the proposed topology maintains zero-voltage switching (ZVS) turn-ON of primary switches, ZVS turn-ON and zero-voltage-zero-current switching turn-OFF of secondary diodes for all load conditions. Steady-state operation, analysis, and design of the proposed converter are reported. Experimental results of 1-kW hardware prototype to verify the claims of the proposed analysis and design are presented. [ABSTRACT FROM AUTHOR]

The design of an innovative converter for ohmic heating of fluid foods is presented. Application-specific requirements are addressed with new solutions and verified on a commercial-size 60-kW prototype. A multioutput high-voltage (0.8 to 4 kV) transformer with automatic tap change enriches a basic H-bridge topology, enabling processing of a wide set of foods and allowing grounding one of the outputs. High power density is achieved by power switches Pareto optimization in the reliability-efficiency objectives and by pushing the switching frequency up to 30 kHz, solving the electrode corrosion problem, too. Reproducible and reliable operation is assured by three different control strategies: load variability is dealt with high-dynamics power control, repeatable output is guaranteed by input voltage compensation, and optimal working point is ensured by control of the transformer primary current dc component. This last control also allows removing the output capacitors, improving density metrics with respect to the state-of-the-art. Analytical models for all control strategies are given to support dynamic performance tuning while guaranteeing stability. [ABSTRACT FROM AUTHOR]

Power system protections are highly sensitive to decaying dc offset that could appear when a fault occurs. The consequences of this effect represent a challenge in the coordination of protection devices that have been widely studied. The elimination of the dc offset component of current transformers (CTs) measurements is the objective of this paper, including a new autonomous detector based on mathematical morphology. The idea enhances the digital signal processing to prepare the information before the protective device takes a decision. The detection and fast elimination of the decaying dc offset on current signals could improve the speed of protection, coordination, and selectivity. The paper presents the proposed algorithm and assesses the solution using alternative transient program. The model of the CT used for this validation is also presented. Results show the potential of the mathematical morphology for signal processing to delete the dc offset component. [ABSTRACT FROM AUTHOR]

Current differential principle is a well-known principle used for protection of transformers, motors, generators, buses, and any other type of power equipment with input and output current measurements. Further, the principle is used in developing percent differential protection, which can be programmed to the desired sensitivity for detecting in-zone faults and security during external faults. This protection dependability is usually achieved by modeling a differential-restraining characteristic with two regions, operating and nonoperating, and tracking the real differential restraint ratio during faults. Some external faults with high dc offset and high X/R system time constant would easily saturate the installed current transformers (CTs), which in return would cause high differential/restraint ratio above the preset characteristic into the operating region. In such cases, the differential protection would operate and cause unwanted transformer trip. This paper focuses on some enhancements applied to the differential principle of the main differential protection; it also defines guidance on how to setup the protection for better sensitivity and security. The paper is supported by fault cases, showing the improved security and dependability during internal/external faults with and without CT saturation. [ABSTRACT FROM PUBLISHER]

When generators or motors are started via variable frequency drive (VFD), initial frequency is very low, on the order of few hertz, and can be low for a considerable amount of time or even permanently. It is not well recognized in the industry about the consequences of low frequency on current transformers (CTs) performance and how this affects the protection performance as well. First, CTs are designed to operate at the nominal system frequency; however, when operating at low frequency, CTs could saturate at much lower currents; this can happen even at CT nominal current. Second, there are limits of the system frequency measurements in the protective relays, which will impact the correct current magnitude estimation, and therefore, the accuracy of the protection. And finally, protective relays need full power-cycle to measure current; power-cycle will be considerably longer at lower frequency, therefore affecting fault clearance time. This paper will educate engineers on how to consider CTs and protective relay's performance at lower frequencies to ensure adequate protection. It will also explore other solutions to address impact of low frequency on the CTs and protection. [ABSTRACT FROM PUBLISHER]

This paper provides a clear set of procedures and equations to follow in optimal current transformer selection for low-voltage motor control centers. Methods of using protective relay settings to minimize current transformer cost and size are also shared. The selection criteria are explained from the fundamental principles of operation of a current transformer and a protective relaying device. This paper shows how the current transformer ratio, voltage knee points, and relay protection elements can be selected together simultaneously to provide a low-cost high-performance system. This paper describes a case study in which the authors developed a simplified set of current transformer selection criteria for compact IEC low-voltage motor-control center drawers at a large oil and gas field in Central Asia. [ABSTRACT FROM PUBLISHER]

In industrial facilities with on-site generation, there are two major approaches to connect generators to the main distribution busbar. One is to connect generators through step-up delta-wye transformers with low-resistance grounded wye on the busbar side. The second common method is to connect generators directly to the main distribution busbar and use low-resistance grounding or hybrid grounding in the generator neutral. A grounding resistor in the step-up transformer’s wye side neutral or in the generator neutral will limit the ground fault in the main distribution system. When busbar differential protection is used on the main busbar, sensitivity for bus ground faults has to be evaluated to ensure detection of limited low-level ground faults. While step-up transformer grounding resistors can be selected to allow ground faults of higher magnitudes detectable by bus differential protection, the choice of grounding resistor is more complex when generators are connected directly to the main busbar. In such systems, a grounding resistor in the generator neutral limits the generator fault to protect the alternator core from excessive damage. At the same time, busbar differential protection needs to detect a limited low-magnitude ground fault on the bus. This paper discusses considerations to select the main distribution busbar differential protection type, CTs, and relaying scheme to enable detection of busbar ground faults limited by the generator low-resistance grounding resistor. [ABSTRACT FROM PUBLISHER]

This paper presents an experimental investigation of the performance of induction motors subjected to single phasing on the primary side of a distribution transformer that feeds the motors. While single phasing caused by, for example, loss of fuse or bad contact is permanent in nature, that caused by recloser operation is momentary and is the focus of this paper. Several motors and transformer connections were used to investigate the effects of the momentary interruptions of a phase on the performance of the induction motors. The conditions under which the motors are able to ride through the single phasing are presented and discussed. [ABSTRACT FROM PUBLISHER]

Traditional differential protection systems are applied on large power transformers using current transformers (CTs). However, because of high secondary currents (often exceeding 100 \kARMS), differential protection systems for electric arc furnace transformers have not been applied in the past due to the lack of commercially available CTs. This paper will present differential protection systems that have been in use for many years using Rogowski coil current sensors. These protection systems use high-precision printed circuit board Rogowski coil current sensors. This paper reviews the characteristics, designs, and application of these Rogowski coil sensors for advanced protection, control, and metering systems with new multifunction relays. This paper compares performance characteristics of new solutions based on Rogowski coil sensors with the conventional differential protection systems based on CTs, demonstrating that the new systems do not have the limitations of conventional technology. Operating experience from several site applications is included. [ABSTRACT FROM AUTHOR]

The primary function of protective devices is to remove faulted equipment from the electrical system. It is typically very advantageous for these devices to isolate as small of a section of the electrical system as possible. Overcurrent protection is the most common protection function used, as faulted equipment typically results in a large short circuit current. When overcurrent protection is employed, the overcurrent protection is typically coordinated with time so that the devices closest to the fault will operate and isolate only that section of equipment before devices farther from the fault operate and isolate larger pieces of the system. These time overcurrent devices must also be coordinated with damage curves for equipment such as buses and cables to clear the fault before the overcurrent can cause damage to the equipment. This concept of time coordination of overcurrent is well understood, and there are general guidelines applied to account for measurement error and other inaccuracies. The reduced signal levels provided to relays due to current transformer (CT) saturation are normally not considered during coordination studies. This reduced signal level will result in slower than desired operation of protective relays. Feeder relays could trip slower than upstream devices, isolating more of the power system than intended, or could allow primary equipment to be damaged before tripping. This paper will review the concept of coordinating time overcurrent relays and then discuss the concept of loss of coordination associated with CT saturation. This paper will model CT saturation from actual installations using the IEEE Power System Relaying Committee CT Saturation Calculator tool. This model data will be used to estimate the performance of protective relays. This paper will discuss methods to improve the coordination of overcurrent relays when faced with significant CT saturation. [ABSTRACT FROM AUTHOR]

A test program was completed to measure arc-flash incident energy from actual 480-V utility equipment to determine the most appropriate flame resistant clothing for utility workers. The equipment tested included self-contained and current transformer-rated meters, pad-mounted transformer secondary cubicles, power panels, and network protectors. Testing was performed to determine the sustainability of low-voltage arcs in actual utility equipment, to find the most appropriate calculation method to predict the measured incident energy, and to identify any key variables that would effect both duration and heat from this type of equipment. [ABSTRACT FROM AUTHOR]

Current transformers (CTs) are the basic interconnection between the power system and protective relays. One of the practical concerns for the protection engineer is the actual ability of a CT to replicate the primary current. This paper describes how CT replication error impacts protective relay performance by presenting three actual examples of relay performance. [ABSTRACT FROM AUTHOR]

High-resistance grounded (HRG) power systems have been used in many industries to minimize equipment damage, including but not limited to mining, petrochemicals, shore-to-ship power supplies, and many others. The system charging current value should be known for designing an HRG power system. One method of determining the system charging current is to perform engineering calculations involving the inherent capacitance to ground for each of the power system components. However, this method may not provide accurate data as the sneak capacitance to ground for power system components cannot be determined due to their installation configuration. Therefore, it is essential to have a reliable method of measuring the system charging current. Before describing the proposed method of measuring the system charging current, fundamental concepts of system charging current and its mathematical analysis are provided. In addition, power system arcing faults and the associated damage when a fault remains line–ground faulted, particularly in the case of a medium-voltage power system, are included. Finally, a novel and suitable method of measuring the inherent power system charging current is presented. [ABSTRACT FROM AUTHOR]

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]

This paper presents an extension of real-time tests of a wavelet-packet-transform-based technique for the differential protection of three-phase power transformers. The proposed technique is implemented using a DS1102 digital signal processor board and tested on two different three-phase power transformers with neutral resistance grounded. Different magnetizing inrush and internal fault currents are investigated with current transformer (CT) saturation for different loading conditions, including capacitive loads. The results show a complete independence from transformer parameters, load types, grounding method, or CT saturation. Furthermore, the proposed technique has high speed, good accuracy, small required memory, and reliable responses with reduced computational burden. In all cases of the investigated internal faults, the proposed algorithm is capable of identifying the fault and generating a trip signal in less than a quarter cycle based on a 60-Hz system. [ABSTRACT FROM AUTHOR]

Ensuring correct setting and installation of a transformer differential relay is critical. A transformer differential relay must detect internal faults, damaging overloads, and through-fault currents while remaining secure against misoperation. The ability to use wye-connected current transformers with microprocessor-based relays has simplified installations, and these relays provide better commissioning tools than those available with traditional relays. However, installations and commissioning remain complicated. Installation and settings errors continue to be widespread, implying a need for more rigorous commissioning tests. Even with greater commissioning effort, occasional wiring problems develop over time, and these can best be resolved through analysis of relay event-report data. In the interest of reducing transformer differential misoperations, we share in this technical paper practical lessons we have learned through experience with commissioning and relay event-report analysis. [ABSTRACT FROM AUTHOR]

Previously, ANSI/IEEE relay current transformer (CT) sizing criteria were based on traditional symmetrical calculations that are usually discussed by technical articles and manufacturers' guidelines. In 1996, IEEE Standard C37.110-1996 introduced (1 + X/R) offset multiplying, current asymmetry, and current distortion factors, officially changing the CT sizing guideline. A critical concern is the performance of fast protective schemes (instantaneous or differential elements) during severe saturation of low-ratio CTs. Will the instantaneous element operate before the upstream breaker relay trips? Will the differential element misoperate for out-of-zone faults? The use of electromagnetic and analog relay technology does not assure selectivity. Modern microprocessor relays introduce additional uncertainty into the design/verification process with different sampling techniques and proprietary sensing/recognition/trip algorithms. This paper discusses the application of standard CT accuracy classes with modern ANSI/IEEE CT calculation methodology. This paper is the first of a two-part series; Part II provides analytical waveform analysis discussions to illustrate the concepts conveyed in Part I. [ABSTRACT FROM AUTHOR]

This paper presents real-time implementation and testing of a wavelet-packet-transform-based algorithm for power transformer protection. The proposed algorithm is implemented using a DS1102 digital signal processor board and tested on two different three-phase power transformers. Different magnetizing inrush, normal (through-fault) and internal fault currents are investigated for different loading conditions. The results show a complete independence from both the transformer parameters and current transformer saturation. In addition, the proposed algorithm has reduced computational burden, high speed, high accuracy, small required memory, and high reliability. In all cases of the investigated internal faults, the proposed algorithm is capable of identifying the fault and generating a trip signal in less than a quarter cycle based on a 60-Hz system. [ABSTRACT FROM AUTHOR]

This paper describes current and voltage instrument transformer connections that are not physically conventionally connected as portrayed in ANSI Standards and Guides or relay manufacturers' literature. A three-line diagram of basic conventional current transformer connections for a two-winding-delta wye power transformer differential relaying is presented. The unconventional scenarios presented are: 1) one set of current transformers (CTs) being reversed or "rolled out"; 2) the other set reversed; and 3) both sets reversed from the conventional connection. Proper connection of these unconventional connected CTs is then explained. Also, the effect of reversed voltage transformer (VT) connections on directional overcurrent and directional power relay elements is presented. An example of how symmetrical component metering screens of a numeric relay were used to diagnose an incorrect VT connection is also presented. This paper is a primer on analyzing unconventional instrument transformer polarity connections and how to obtain the right connection to achieve the desired direction of operation or polarity as indicated in protective relay manufacturers' literature. [ABSTRACT FROM AUTHOR]

Presents a study that proposed an integrated scheme for protecting and controlling series injection voltage-source inverters used with electrical grid systems. Protection issues for series injection inverters; Elements of the integrated protection system; Protection system operation; Simulation and experimental results.

Presents information on a study which analyzed the characteristics of a coaxial current transformer (CCT). How it can be integrated into a test setup for both press-pack and module packages; Description of the test setup; Finite-element analysis; Experimental results.

Describes a method of accurately modeling three-phase transformer connections for power-flow and short-circuit studies using the underground wye-delta connection. Power-flow model development; Short-circuit model development; Summary.

Discusses the current transformer performance and the effect that the direct current (dc) component of an assymetrical fault current will have on current-operated protective relays. Effect of the dc tail on the fault-detector function of the relay; Different reaction of two specific breaker failure relays under the same input waveform.

Discusses the problems encountered with relay operation when high fault currents saturate low-ratio current transformers (CT's) and documented the possibility of misoperation of protective relays. Ground overcurrent relaying; Testing of ground sensor relays; Analysis of tests results; Conclusions.

Opinion. Presents the author's comments on the paper `Operation of Ground Sensor Relays Under Conditions of Partial CT Saturation.' Limitations of voltage applied to the relay; Observation on the current transformer saturation effect.