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Fuses are commonly used to provide medium voltage (MV) protection to distribution transformers. Unfortunately, there are certain deficiencies introduced when primary-side fuses are used. In paper mill power systems, given the unique organization of the paper mill loads around individual feeders to facilitate load shedding, it may be advantageous to provide transformer differential relay protection from the primary of the transformer to the load side of the main secondary breaker instead of primary fuse protection. This protection can then trip either a primary-side grounding switch (with fuses) or a primary-side feeder circuit breaker using a fiber or a WiMAX (Worldwide Interoperability for Microwave Access) connection. Protection against overload is provided by a secondary main circuit breaker and by design. [ABSTRACT FROM AUTHOR]

This paper provides the electrical equivalent circuits of high-resistance grounded (HRG) power systems other than the delta–wye-connected utility power supply transformer included in Part I of this paper. This paper also provides the HRG of a medium-voltage generator for connection to an industrial power system and to a utility power system, and this paper discusses a line–ground fault with fault resistance. Three-line diagrams of ungrounded power systems are also included to illustrate the HRG application and its effect on the ground fault current during the line–ground fault. The damage at the fault location is based on the assumption that the fault remains a line–ground fault until it is cleared by appropriate ground fault protection relays. The fault resistance and the fault current that have an effect on the damage at the fault location are included. This paper provides guidance to update the current edition of the IEEE STD. 142, with respect to HRG systems. [ABSTRACT FROM AUTHOR]

After a transformer failed following a double-phase fault, there was an interest in understanding how the fault mechanism led to the failure. This paper investigates this fault condition in detail and demonstrates the underlying challenges in correcting the failure. The electrical and thermal system models were developed and simulated to analyze the transformer response under double-phase fault conditions. Experimental measurements validated the simulation results on a real three-phase distribution transformer. This paper presents the results from simulated and experimental analysis from double-phase fault on a Yg–Yg distribution transformer. [ABSTRACT FROM AUTHOR]

Significant changes have occurred in the protection and grounding of generators in the past 15 years that impact generators at petroleum refineries and chemical plants. This paper updates the author's earlier paper on the subject of generator protection upgrades and highlights areas of protection that are still not addressed by some generator owners, as well as new protection areas not previously addressed. New generator protection changes are reflected in recent IEEE guides such as C37.102-2006. This paper discusses these changes as they apply to industrial generators and the risks of ignoring them. This paper outlines the risks in several functional areas where old generator electromechanical relay protection is inadequate. In addition, this paper discusses hybrid grounding of the generator stator windings, which substantially reduces stator ground fault damage—avoiding lengthy generator outages to repair. This type of grounding is a relatively new concept in generator grounding introduced in a series of IEEE Industry Applications Society (IAS) Working Group papers publicized in 2002. This grounding scheme has been installed on a number of generators but must be coupled with proper relaying and transient overvoltage protection. This paper also highlights the major new protection requirements for gas turbine starting with a load commutating inverter and protection advances made possible by the use of digital technology, which have fostered new methods not possible with older technologies. [ABSTRACT FROM AUTHOR]

This paper provides a follow-up to the paper The Effects of System Grounding, Bus Insulation and Probability on Arc Flash Hazard Reduction—The Missing Links. In that paper, system grounding and bus insulation were considered a means of reducing the probability of an arc flash incident by approximately two orders of magnitude. In September 2013, additional testing was conducted on a low-voltage motor control center (LVMCC) with the expectation that engineering enhancements such as insulated vertical bus, high resistance grounding, and other techniques could be implemented to further reduce the probability of an arc flash incident. The testing performed was with faults initiated in locations typically found in operating petrochemical facilities, in LVMCCs, with the starter unit door open. This paper discusses the findings of testing on real-world electrical equipment in an effort to further understand and minimize the probability of an arc flash incident. This paper reviews the physics of the arcing fault and how ignition wire, geometry, and the number of anode/cathode pairs all contribute to arcing fault energy and personnel exposure. [ABSTRACT FROM PUBLISHER]

The use of electronic equipment and other dc-compatible appliances in homes and offices is increasing at a very fast rate, as well as the distributed generation of energy. These two statements will most likely trigger, in a near future, the adoption of district-scale dc grids, connecting dc microgeneration plants and consumers, in an effort to cut the number of conversion steps required to deliver power to dc appliances. DC–DC converters will be fundamental in these systems, allowing the establishment of several voltage levels. The reliability of these converters plays a critical role, ensuring service continuity of the loads connected to them. With the increment of reliability in mind, this paper proposes a simple yet effective open-circuit fault diagnostic method suitable for interleaved dc–dc boost converters, but equally functional for other dc–dc converter topologies. The improvements introduced in this paper greatly simplify the diagnostic action, while making the correct diagnostic of faults independent of the switching duty cycle. Moreover, an alternative reconfiguration scheme is proposed to mitigate the adverse impacts of such faults. To prove the effectiveness of these strategies, a three-phase interleaved boost converter prototype was used in the experiments. [ABSTRACT FROM AUTHOR]

This paper describes the International Electrotechnical Commission (IEC) type A (ac only) ground-fault detection circuit and its limitations in accurately detecting electrical ground-fault currents in today's modern electrical installations. Discussed are the effects of waveform modifying power sources and the effect of the dc component on the efficacy of type A safety devices. Limitations of the UL1053 standard for ground-fault sensing and relaying equipment are discussed. The paper will lead to recommending and applying IEC type B (ac/dc) detection technology for solving these shortcomings. [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]

This paper discusses the protection requirements to interconnect a typical refinery to the utility system. However, the information provided is applicable to other industrial facilities that have generation. It covers applications involving service to a refinery that normally requires a transformation between the utility's supply voltage and the refinery's utilization voltage. This paper specifically addresses refineries with generation that are connected to utility transmission circuits. The protection discussed must protect the refinery from the effects of utility system faults, but must also protect the utility from the effects of refinery faults. Coordination between these two systems is essential to minimize the effects of fault-induced outages. This paper specifically addresses typical refinery–utility interconnections system one-line designs, determining utility supply performance expectations, impact of generation on interconnection protection, relay functional requirements for typical interconnections protection, relay communication requirements, and grounding of the interconnection transformer(s) and its impact on protection. In addition, this paper will discuss the North American Electric Reliability Corporation requirements and their effect on refinery interconnection protection. [ABSTRACT FROM AUTHOR]

High resistance grounding (HRG) is a well-proven technology for improving electric reliability for many industrial and utility facilities such as used in petrochemical, automotive, and generating plants. Many such facilities require the increased reliability for production and operational reasons. This paper will discuss the improved personnel safety aspects of using HRG on low-voltage systems. In particular, this paper will discuss the following: 1) the probability of the three common faults occurring within an industrial plant, namely, three-phase, phase-to-phase, and ground faults; 2) how the probability of a ground fault can be used to improve electrical safety with HRG; 3) the impact of a ground fault on a system and the speed at which the ground fault on a solidly grounded system may propagate into a multiphase fault; 4) the risk reduction of a ground fault on an HRG system propagating into a multiphase fault; 5) the potential reduction in serious and fatal arc blast injuries through the use of an HRG system; and 6) potential single-pole breaker clearing issues when a second ground fault occurs on a second phase. This paper will include comments from recent testing, which was conducted at the KEMA Laboratories and presented in a recent IEEE Industry Applications Society Petroleum and Chemical Industry Committee paper in September 2014. [ABSTRACT FROM AUTHOR]

This paper deals with a hybrid energy source consisting of a proton exchange membrane fuel cell, two storage devices, and a load. Generally, this type of source constitutes of nonisolated dc–dc converters. In order to have galvanic isolation for safety reasons and a high voltage ratio, we introduce another system based on the use of three-port isolated dc–dc converters. The storage device can be either a battery or a supercapacitor. This paper presents a control strategy for the hybrid source and includes a global efficiency analysis of power sharing between modules. The proposed system is validated through different simulation results. Additionally, some experimental results are given for the single module operation. [ABSTRACT FROM AUTHOR]

Emerging environmental awareness, government subsidies, and deferred utility investments have created an environment that favors the proliferation of distributed energy resources (DERs) in distribution systems. While beneficial, these DERs create operational challenges to the power utility, ranging from additional safety risks to unstable system operation. Among those, traditional feeder overcurrent protection can become desensitized due to the additional fault contribution output by DERs. In some cases, it may not be possible to protect the entire distribution line. This effect is introduced in this paper as the Apparent Effect, which accounts for the reduction in fault contribution from the substation. Its extent varies depending on the DER technology, i.e., synchronous, induction, doubly-fed induction generators, or inverter-based DERs. Substantial investment may be required to overcome this effect and maintain feeder protection dependability. This paper characterizes this issue analytically and suggests the application of system reconfigurations that can result in mitigating the problem. [ABSTRACT FROM AUTHOR]

The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Standard 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs (IBDGs) are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for IBDGs on industrial and commercial power system protection schemes are investigated. It is shown that the inverter control mode has a direct impact on its fault current levels and duration. A simplified distribution network model with IBDG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of IBDGs with various types of controllers. [ABSTRACT FROM AUTHOR]

This paper presents a combinational-logic-based approach for identifying faults that could occur in the drivetrain of an electric vehicle (EV). A real-time simulation model of an EV is used to study the behavior of available sensor signals and control commands, with specific measured quantities, during vehicle operation. Those quantities could be, but are not limited to, mean values of the phase currents, DC bus current, traction motor speed (if available), in addition to control command quantities. Focus is given to these quantities which are abundant in vehicle inverters and controllers for no added sensing costs. Those quantities carry information of offsets and disturbances that could occur under faulty operating conditions compared to nominal operation, and are thus observed and studied under these conditions. Using such information, a method is developed using simple combinational logic and thresholds to diagnose a fault occurring at any time during a vehicle drive cycle. By combining features of measured quantities that behave similarly irrespective of when the fault occurs during a driving cycle, the proposed method is fault-time-insensitive. The proposed method is presented and validated by real-time simulations to capture over 20 different faults injected at different drive cycle times and in different drivetrain components—electric machine, inverter, transmission, and sensors. Results show that the proposed method is able to robustly and successfully diagnose different faults irrespective of when would they occur. [ABSTRACT FROM AUTHOR]

This paper discusses some of the main issues that are generally found in protection systems of low-voltage electrical installations and presents a methodology that can be used to analyze and upgrade the existing power system protective devices in these low-voltage distribution systems. The upgrades of existing operating systems, especially low-voltage systems, always face an economic challenge where the monetary value spent on upgrades has to be justifiable against the benefit derived. If understood clearly, the benefit of upgrades to existing protective systems is larger than just making these systems safer. A gated approach for the upgrade and proper management of such systems can help in planning for future expansions, provide reliability of equipment, and decrease the overall risk for the operation of any facility. [ABSTRACT FROM AUTHOR]

This paper continues investigations of the concept of maximum low-voltage circuit breaker ratings that facilitate fast tripping for arcing faults with a selectively coordinated system. Motor loads are the focal point of this work. Guidelines are provided for maximum motor horsepower ratings that should be used depending on the kilovoltampere rating of the supply-side transformer. Using the guidelines should prevent a situation from occurring where the coordinated main circuit breaker short time and instantaneous settings are not sensitive enough to detect main bus arcing currents, and dangerous levels of arc incident energy are possible. [ABSTRACT FROM AUTHOR]

Many applications that use high-energy plasma are realized using microwave tubes (MWT) that operate at peak power in the range of hundreds of MW and frequency in GHz. One failure mode of the MWT is due to the excess energy in the tube during internal arcing events. Crowbar is used to protect the MWT by diverting the energy during fault. To compute the energy released into the MWT, the dc fault current model and the MWT model are essential. An equivalent fuse wire model is utilized for the MWT for the crowbar applications. The paper proposes a model for the dc fault current, the analysis for which is based on Joules Integral energy concept. The model provides flexibility to choose a range of practically observed reactance to resistance ratio ($X{/}R$) of transformer and also allows the use of a range of dc current-limiting resistances that are utilized in the high-voltage (HV) power supply circuits in microwave applications. The nonlinearity of the system due to the multipulse diode rectifier is also considered by introducing a correction factor in the model. This paper shows that the same correction factor can be applied for both dc side parallel- and series-connected rectifier circuits. Both dc fault current and MWT models are verified experimentally. Using the model, a 10 kV, 1 kA crowbar is built to limit the energy in MWT below 10 J. [ABSTRACT FROM AUTHOR]

There are many methods to ground generators. This paper will discuss the advantages and disadvantages of each. This paper will progress from low-resistance grounding of a single source to complex systems with multiple sources. Although this paper is focused on medium-voltage bus-connected generators, there is no reason the techniques could not be utilized in low-voltage multiple-source systems. [ABSTRACT FROM AUTHOR]

To minimize ground fault during a line-to-ground fault condition, it has been a common practice to use high-resistance grounded (HRG) power systems, both at low voltage and at medium voltage (MV). The criteria for designing HRG systems are very well known to the industry; however, the opinion of industry experts has been divided on limiting the use of HRG systems for MV systems to voltages of less than 4.16 kV and phase-ground fault currents of less than 10 A without clarifying that it applies to systems that require continuous operation upon first detecting line-to-ground fault, as it is now in the Recommended Practice for Grounding of Industrial and Commercial Power Systems. This paper will review the background history of HRG power systems and their application to MV systems for specific industries and will make the case that voltages need not be limited to less than 4.16 kV and the phase-ground fault current to less than 10 A, so long as the faulted power system is isolated within ten cycles and that there are no directly connected motors. This paper will discuss the potential damage and protection requirements of HRG systems for MV applications to ensure that a line-to-ground fault is cleared before it involves other phases to make a multiphase arcing ground fault. [ABSTRACT FROM AUTHOR]

Large induction motors used in variable speed industrial applications (digging, traction, etc.) undergo dynamic stresses at high power levels. Their lifetime is reduced as compared with constant speed motors and downtime costs are very high. To monitor the condition of such motors, advanced sensor instrumentation is considered, including installation of Hall effect flux sensors inside the motor airgap. Such an advanced instrumentation enables continuous measurement of the airgap flux in both time and space domains simultaneously. This allows for advanced fault detection algorithms. This paper presents a method for early diagnosis of stator turn-to-turn faults and static eccentricity, and differentiation between these two conditions. The paper demonstrates that the proposed method detects, localizes, and quantifies both faults with high accuracy and sensitivity. Furthermore, each fault can be detected at an incipient stage and its development can be predicted. The results of the presented study have been supported by both simulation and experimental results obtained on a laboratory scale induction motor. Based on the results presented in the paper, a real-time condition monitoring system has been developed. [ABSTRACT FROM AUTHOR]

Doubly fed induction machine (DFIM) is increasingly being preferred in large rated variable speed pumped storage power plants (PSPP), because it provides better energy efficiency due to optimization of pump/turbine efficiency. Increased efficiency results from the flexibility of operating speed at different hydraulic heads. In doubly fed configuration, partial rated power converters feed the rotor circuit. Parallel-connected back-to-back voltage-source converter on rotor side is responsible for starting, braking (dynamic/regenerative), and speed (real power) control of the unit. This paper presents smooth starting and regenerative braking, and assesses performance under power converter and sensor faults of a 250-MW DFIM pump turbine unit to be commissioned in Tehri PSPP, India. Survivability of the unit during faults is analyzed based on current, speed, and dc-link voltage. Further, this paper investigates fault-tolerant operation of 250-MW DFIM unit at open-circuit fault in converters. A 2.2-kW DFIM is tested in the laboratory to corroborate the simulation. [ABSTRACT FROM AUTHOR]

An industrial medium voltage (MV) system usually consists of multiple power sources such as utility tie transformers and generators. These are normally low-resistance grounding as shown in Fig. 1 . When a ground fault occurs at the generator stator, ground currents from its own neutral circuit and external power sources will flow into the fault and cause damages to the stator winding. The IEEE Generator Grounding Working Group issued a guideline for generator grounding practices, which recommends using a hybrid grounding system to minimize the ground fault damage induced by its own neutral grounding source. This paper will evaluate the total ground fault damages based on the arcing power energy to derive a maximum MV system ground current that would limit the ground damage to 1800 kW-cycle or 30 kJ as the minimum arcing power energy damage as suggested by Conrad and Dalasta [10]. [ABSTRACT FROM PUBLISHER]

A common practice is to install a service disconnect or a main disconnect for a feeder system in the same enclosure compartment as the downstream overcurrent protective devices. This can result in potential safety risks of shock and arc flash. This paper will address the advantages and disadvantages of isolating a service disconnect for electrical service for industrial and commercial installations from the perspective of prevention through design. This paper will compare shock and arc-flash hazard for both cases when the service disconnect or a main breaker is isolated and when it is in the same enclosure. [ABSTRACT FROM AUTHOR]

This paper proposes a diagnosis technique algorithm for a brushless dc motors under a stator inter-turn fault (ITF) condition using input impedance. The algorithm has early detection and various speed-range detection advantages. To early and accurately detect the ITF, the rotating speed, input current, voltage, resistance, and inductance must be analyzed. Therefore, we choose the input impedance as the detection factor because it includes all these factors. In this paper, the fault-detection system works without requiring a fast Fourier transform and the calculation of the negative-sequence impedance from the comparison of the measured impedance with the database impedance. The proposed technique was verified by the simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper describes a procedure for calculating generator circuit breaker duty. Currently, commercially available software products help in determining the duty for a general-purpose circuit breaker. However, further calculations are needed to determine the duty for a special-purpose generator circuit breaker. IEEE Std C37.010-1999 provides the calculation procedure for general-purpose circuit breakers. In order to evaluate a special-purpose generator circuit breaker, this paper will expand the steps and methodology used in IEEE C37.010-1999 by presenting a procedure and detailed calculations for finding a duty multiplication factor based on the test $X/R$ ratio of generator circuit breakers given in IEEE C37.013-1997 (Standard for AC High-Voltage Generator Circuit Breakers Rated on a Symmetrical Current Basis). This way, engineers can still make a generator circuit breaker assessment although generator circuit breaker evaluation module is not included in many commercial short-circuit programs. [ABSTRACT FROM AUTHOR]

This paper expands on the work of a previous paper that presented the possibility of a significant reduction of incident energy on the secondary of medium-voltage to low-voltage (MV–LV) transformers with the combination of a high-speed grounding switch (HSGS) and traditional MV current limiting E-rated fuses. It was shown that when the HSGS is applied at a location between the E-rated fuse load terminals and the transformer's primary connection and controlled by relays on the LV side, incident energy can be reduced to less than 1.0 cal/cm2. The first paper focused on the results from a high-power test lab, whereas this paper discusses the issues related with its application on typical power systems and lessons learned from installations at several locations. Application considerations include a review of relay requirements, coordination of E-rated fuses, requirements for resistance grounded systems, modeling in analysis software, and field installation considerations. [ABSTRACT FROM PUBLISHER]

This paper presents an overview and techno-economic feasibility study of solid-state fault current limiters (SSFCL) for low-voltage residential and commercial applications. An SSFCL is proposed to be installed upstream inside a conventional panelboard or load center. The simulation results demonstrate the effectiveness of utilizing SSFCL for residential houses and commercial buildings and the advantages of fast fault current limiting and great reduction of fault energy. Some physical design considerations are made for installing an SSFCL including their fault-current-limiting inductors inside a panelboard or load center. The proposed SSFCL solution potentially has best overall benefits compared to the conventional mechanical solution and other solid-state-based solutions. [ABSTRACT FROM AUTHOR]

In the safe-critical applications such as electric/hybrid electric vehicles, the reliability of the machine drive system is vital. Among the various machine fault types, the uncontrolled generator fault (UCGF) at high speed is one of the most serious faults that could damage the machine drive system. In this paper, the fault protection capability of a novel hybrid-excited doubly salient synchronous machine (HEDSSM) is examined to illustrate its great capability to prevent the dangerous overvoltage issue from the UCGF. Permanent magnet flux of the novel HEDSSM is inherently short-circuited when the field excitation current is not fed into the excitation windings. Therefore, when the UCGF is detected in the high-speed region, the dc-link overvoltage issue can be effectively reduced by forcing the field excitation current to zero. Since only the field excitation current is utilized to protect the machine and power inverter from the UCGF, it is easy to implement and the concept of proposed control strategy can also be applied to other hybrid-excited machines. Finally, the proposed control strategy is verified by both simulation and experimental results on the HEDSSM. [ABSTRACT FROM AUTHOR]

The huge untapped energy from ocean waves is one of the ideal solutions for world energy crisis. This paper proposes a linear-generator-based direct power conversion plant model to generate the electrical energy from ocean waves. The linear generator output is of variable magnitude and variable frequency in nature. In this paper, this variable output is converted to fixed dc voltage by using a diode bridge rectifier and a dc-link capacitor. The linear generator along with a diode bridge and a capacitor forms a wave power unit. These wave power units can be connected in series and parallel to meet the power ratings. A reliable multilevel inverter is fed from the wave power units to ensure uninterrupted tapping of power from this abundant renewable energy source. The reliable inverter operation is analyzed under open- and short-circuit faults in switches by reconfiguring the carrier waves of sine pulsewidth modulation during fault conditions. A fault detection algorithm using a single sensor at the output is also proposed to detect the faults in the switches of the proposed reliable inverter. The proposed plant model with a linear generator and a reliable inverter is simulated using ANSYS MAXWELL and MATLAB/Simulink. The plant model is tested using a programmable ac source for emulating the linear generator and the developed prototype of the diode bridge rectifier and the reliable multilevel inverter. [ABSTRACT FROM AUTHOR]

In this paper, a fault-tolerant control scheme for a low-speed squirrel cage six-phase induction generator (SC6PIG) connected to a full-scale back-to-back converter structure is proposed and tested on an experimental 24-kW wind turbine test bed that represents a 1/100 of the electrical power of a grid-connected real wind turbine multiphase generator (2.5 MW). The aim of this paper is to define a suitable control algorithm that allows the electrical generation despite the loss of one to three phases on the generator or converter sides. Furthermore, the pole number of the generator is increased to simplify or eliminate the gearbox in such a way as to reduce mechanical sensitivity. Indeed, by multiplying the phase and pole numbers, the robustness against mechanical and electrical faults is improved compared to that of a classic three-phase generator associated with a gearbox. Simulation and experimental tests carried out on a 24kW-230V-24-pole SC6PIG in healthy and faulty mode (one phase missing) assess the feasibility and capacity of the proposed strategy. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) has been a promising candidate in high voltage direct current (HVdc) transmission systems. Due to the features of simple structure, low cost, and low power losses, half-bridge (HB) is usually adopted as the submodule circuit in the traditional MMC. However, an HB submodule circuit-based MMC does not have the capability of blocking dc short-circuit fault, which obstructs the development of low-cost HVdc systems with overhead lines. In order to solve this problem, an MMC with active clamped T-type submodule (ACTSM) to own dc fault blocking capability is proposed in this paper. Compared with other submodule circuits, the proposed ACTSM has many features, such as symmetrical blocking capability, low power losses, low voltage stress, and low amount of independent drive signals. The topology, operation principle, dc fault blocking capability, and distribution of power losses of the ACTSM are presented in this paper. The effectiveness of the ACTSM-based MMC is validated by both simulations and experiments. [ABSTRACT FROM AUTHOR]

Stand-alone operation of distributed generations (DGs) under an islanded mode is achieved by appropriate switching of controllers from grid-parallel to stand-alone mode. Conversely, during grid restoration, reverse switching operation is employed. These operations cause voltage quality issues; among these issues, voltage dips and swells are two crucial events that are encountered during and subsequent to islanding. This paper characterizes the voltage dips and/or swells caused by the islanding of DG and its subsequent pre- and post-islanding events. Pre-islanding events encompass the fault-initiated islanding scenarios, whereas postislanding events are associated with transitional state, island stabilization, and grid-reconnection states. Considering pre- and post-islanding scenarios, this paper classifies and characterizes the voltage dips and swells using an algorithm incorporating three-phase voltage ellipse and three-dimensional (3-D) polarization ellipse parameters. Three-phase voltage ellipse parameters, namely, major axis, minor axis, and inclination angle of an ellipse, are exploited for characterization and classification of voltage dips/swells based on their affected phases, whereas 3-D polarization ellipse parameters are employed for classifying seven dip types, namely, A, B, D, F, E, C, and G. Islanding and its subsequent scenarios are simulated using a test distribution network of Australia embedded with DG, and the voltage dips and swells are characterized using the proposed algorithm. [ABSTRACT FROM AUTHOR]

High-resistance grounding (HRG) is preferred in many industrial applications where continual operation during ground fault conditions is critical. However, there are some drawbacks for the traditional HRG detection methods to locate a ground fault in adjustable speed drive systems. The existing methods cannot detect or identify which phase faulted once the drive has HRG fault. A leakage flux linkage detection-based method for HRG fault identification is proposed in this paper. It will be used to identify the faulted phase of the drive. [ABSTRACT FROM AUTHOR]

A breaker-less shipboard medium-voltage dc (MVDC) system is gaining more attention recently due to its advantage in dealing with a dc fault by using switched-mode power modules and disconnectors. The specific power module investigated in this paper is the power conversion module (PCM) that transforms power from a MVDC to a low-voltage dc (LVDC) bus. The PCM plays an important role in a system-level fault management. The recently emerging isolated modular multilevel dc/dc converter and the widely used dual active bridge converter are promising solutions for PCM applications. The control algorithms including fault protection strategy for both topologies have been developed and presented in this paper. The MVDC side fault and LVDC side fault of each topology has been analyzed and evaluated. The simulation and experimental results are provided to demonstrate the fault protection features of two topologies in a breaker-less dc system. [ABSTRACT FROM AUTHOR]

This paper demonstrates the impacts of an electronically triggered fault current limiter (ET-FCL) on typical single-ended and main–tie–main (MTM) medium-voltage switchgear arrangements. The fast acting (less than 1 ms) ET-FCL described in this paper effectively opens the normally closed tie connection between two mains, thereby disconnecting one of the sources to the fault. An ultrafast opening of the tie connection simplifies protection coordination by not having to coordinate the main breaker relay with the tie breaker relay at maximum fault levels. System benefits include the following: significantly lower arc flash energy for downstream faults, faster backup clearing times for a feeder relay/breaker failure, reduction of motor starter dropouts due to fault-produced voltage dips, improved system stability, improvement in utility's CAIDI reliability index, reduced stress on switchgear breakers, and overall lower capital costs on new construction (switchgear, cables, etc.). This paper demonstrates relay setting changes on typical single-ended and MTM arrangement with and without applying the ET-FCL. Impacts on incident energy reduction, backup clearing times, dynamic system stability, and voltage dips will be discussed. [ABSTRACT FROM PUBLISHER]

Ground faults are among the major causes of disrupting the safe, secure, stable, and profitable operation of doubly fed induction generator (DFIG) based wind energy conversion systems (WECSs). On one hand, minimizing the possible damage in a DFIG-based WESC, caused by ground faults, requires accurate detection and fast response of ground protective devices. On the other hand, the responses of ground protective devices are highly dependent on ground currents and potentials, especially during high-impedance ground faults. This paper investigates the influences of grounding configurations on the responses of ground protective devices used in DFIG-based WECSs during high-impedance ground faults. Investigated influences are observed through the ability of ground protective devices, used in DFIG-based WECSs, to quickly and accurately respond to high-impedance ground faults for different grounding configurations. In this paper, the solid, low-resistance, high-resistance, and open grounding configurations are tested for DFIG-based WECS in order to establish comprehensive investigations. The results of the investigations show that the responses of ground protective devices vary depending on ground fault currents, which can have different levels due to the grounding configuration. Moreover, the results of the investigations reveal that the frequency-selective grounding configuration can offer a minimum impact on the responses of ground protective devices used in DFIG-based WECSs. [ABSTRACT FROM AUTHOR]

Where transformers are used to step down from medium voltage to low voltage, a widely used low-cost solution for primary protection is a fused load break switch. While this device provides good short-circuit protection, it provides limited protection for arcing faults on the transformer secondary and the incoming terminals of the downstream equipment connected to it. Consequently, the arc flash (AF) energy levels in this region can be very high ( > 40\ \mboxcal/cm^2) when compared with the rest of the electrical distribution system and may result in dangerous operating conditions. This paper examines a range of options for primary and secondary protection, identifying those that may result in higher levels of AF energy, and presents guidelines for the selection and application of solutions that have been implemented in existing and new installations, achieving a significant reduction in incident energy levels ( < 8\ \mboxcal/cm^2), while addressing concerns for reliability and selective coordination. Piecewise, linear modeling of transformer energization transient response is presented and compared with conventional engineering practice for selecting primary protection. Common assumptions made in modeling instantaneous overcurrent elements will be analyzed, modified, and exploited to achieve reliable application of blocking signals between devices in a protective scheme. Finally, the physical layout of electrical equipment will be discussed as a criteria for optimizing protection schemes to achieve safety by design. [ABSTRACT FROM AUTHOR]

The proper implementation of high-resistance grounding of mine power systems reduces personnel hazards by limiting ground fault current and permits selective detection and clearing of faults. As described in IEEE Std. 142, high-resistance grounding employs a neutral resistor of high ohmic value, with the value of the resistor selected to limit the neutral ground resistor current to a magnitude equal to, or slightly greater than, the total capacitance charging current. Research has shown that the zero-sequence resistance of high-voltage mine distribution systems can be considerably larger than the magnitude of the system capacitive reactance, thereby violating the definition of high-resistance grounding. This paper outlines procedures for the proper sizing of the neutral grounding resistor (NGR) considering system capacitance. This paper begins with a discussion of problems associated with distributed capacitance in high-voltage high-resistance-grounded mine power systems. Subsequently, procedures for determining system capacitance, sizing the NGR, and establishing relay pickup settings are given. These procedures are straightforward to apply and require no computer modeling for implementation. Numerical examples applied to a high-voltage longwall utilization system and an underground mine distribution system are provided. [ABSTRACT FROM AUTHOR]

The open-neutral fault occurring on the low-voltage feeder may result in overvoltage. This fault is very difficult to detect at the supply side of the feeder. To solve this problem, an idea that employs the sudden change of the third harmonic current in the feeder as the index to identify the open-neutral fault was proposed in the previous literature. This method can be accomplished by installing the embedded chip into the circuit breaker or other fault protective devices at the supply side of the feeder and therefore enhance their protection ability. The aim of this paper is to thoroughly investigate and validate the details of this method from the selectivity and sensitivity perspectives. In this paper, the procedure for the determination of the proper criteria to meet the selectivity requirement is introduced, and the detective rate to quantify the sensitivity of the detection method is proposed. The measurement based simulations and experiments were conducted as well to verify this method. The results are also presented. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the behavior of electromagnetic forces during the occurrence of faults inside transformers as result of transients in the electrical systems. The methodology is based on the modeling of a single-phase 50-MVA transformer subjected to inrush currents through finite-element method. In this perspective, the values of inrush currents, obtained by the alternative transient program software, are used to estimate the magnetic field density dispersion in the transformer, and to find the values of forces in axial and radial directions. These forces components are distributed along the energized windings for observing the loads behavior in high-voltage windings. This paper will thus present investigations of electromagnetic forces, structural deformation, stresses, and safety factor on transformer's winding when subjected to inrush current. [ABSTRACT FROM PUBLISHER]

In a microgrid, the overcurrent relays see significant variation in the short-circuit currents during transition between grid-connected and islanded modes of operation. Further, with the disconnection of one or more distributed generators (DGs), the changes in the short-circuit currents are observed by the relays. As a consequence, the existing protection scheme may either delay the relay operation or fail to operate. This paper proposes an optimal and single protection scheme suitable for all operating modes of microgrid along with every type of phase faults in the system, i.e., three-phase symmetrical (3\text-\phi ), line-to-line, and double line-to-ground faults. The optimal setting of the directional overcurrent relays is obtained using a metaheuristic-based optimization algorithm. Moreover, the proposed scheme is validated using GE Multilin, model-750/760, overcurrent relay in ETAP (industrial simulation software) on the modified IEEE 9-bus 4-DG microgrid. [ABSTRACT FROM PUBLISHER]

This paper presents a fault identification and tolerant method for switched reluctance motor (SRM) drives. The reliability of a power transistor in a power converter is the source of most problems in several industrial applications. It is critical to correctly diagnosis the faults occurring in a drive system to avoid harmful accidents and to ensure continuity of operation. In this paper, two types of faults, namely, short- and open-circuit faults, are analyzed on the basis of the current patterns of the power transistors of SRM drives. A fault is detected when the measured amplitude of the current differs from that of the normal-state current. A fault-tolerant scheme is applied according to the type of fault. Simulations and experiments are performed on a 1.0-kW SRM drive. The results are presented to verify the validity of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper presents protection strategies for a medium-voltage dc (MVDC) microgrid at a remote area mine site. The microgrid is operated to provide high power quality and reliability to sensitive loads and to improve the energy efficiency of the mining equipment. In the MVDC microgrid, various local distributed energy resources have been used, including photovoltaic arrays, wind turbines, a fuel-cell stack, an energy storage system, and mobile diesel generators. For the protection of transmission lines, a communication-based differential protection scheme with solid-state electronic relays is employed to isolate the faulted part of the MVDC microgrid. This is further reinforced by dc overcurrent protection as a backup. Earlier research work had neglected the backup protection for dc systems. In addition, communication-based dc directional overcurrent protective relays are used for both source protection and load protection to support a bidirectional power flow. MATLAB/Simulink modeling and simulation results are presented and discussed to illustrate the proposed system's dependability and security. [ABSTRACT FROM PUBLISHER]

This paper intends to show some special topics on ground-fault protection. Single-line-to-ground faults are the most common fault type, the protection engineer has to understand how often these occur, the nature, and also the effects of a single-phase arcing fault. System grounding also affects the magnitude of fault current, protective devices selection, and settings. This paper discusses line-to-ground (LG) and associated issues, such as transformer energization and line-charging current. Such considerations shall be addressed when setting grounding relays and to adopt the best LG protection practices. [ABSTRACT FROM PUBLISHER]

The growing interest in clean and sustainable electric energy pushes toward increasing the interconnection of wind energy conversion systems (WECSs) to utility grids. The designs of the majority of WECSs employ power electronic converters (PECs), which generally have nonlinear and switched characteristics. The characteristics, operation, and control of PECs in WECSs can result in nonconventional voltage–current behaviors during faults. This paper investigates the voltage–current behaviors during faults that occur in grid-connected WECSs. Two types of WECSs are considered in this paper, which are the doubly fed induction generators and permanent magnet generator based WECSs. The voltage–current behaviors are investigated in experimentations for different faults occurring in different parts of the test grid-connected WECSs. [ABSTRACT FROM PUBLISHER]

One of the requirements for safe, stable, sustainable, and profitable operation of doubly fed induction generators (DFIGs)-based wind energy conversion systems (WECSs) is the accurate and reliable protection against electrical faults, in particular, ground faults. The performance of protective devices employed to achieve this requirement is highly dependent on the grounding configuration of the DFIG-based WECS. This paper investigates impacts of the grounding configuration on the performance of protective devices used to protect DFIGs-based WECSs from electrical ground faults. Investigated grounding configurations include solid grounding, low-resistance grounding, high-resistance grounding, and no grounding. This paper also investigates the use of a capacitor in parallel with a low resistance, as a grounding configuration, to limit ground potentials, reduce ground currents, and minimize impacts on responses of ground protective relays. The impacts of the grounding configurations on protective devices are observed through their ability to identify faults, as well as their speed to respond to identified faults. Simulation and experimental results reveal that adequately designed low-resistance grounding offers the minimum impacts on protective devices used for ground protection of DFIG-based WECSs. [ABSTRACT FROM PUBLISHER]

Aeronautical ground lighting (AGL) systems have been developed to deliver warnings and status indications to pilots and maneuvering area vehicle drivers on runways. Their role in preventing the hazard of runway incursions, present in the aviation industry, is therefore crucial. AGL systems basically consist of a primary series lighting circuit, which is supplied at constant current and high voltage (e.g., 5 kV), and AGL transformers supplying ground lights at their secondary sides. Protection of persons against electric shock in AGL systems cannot be conveyed by disconnection of supply as ground faults would cause the out-of-service of the lighting system, thereby compromising the safety of aerodromes; alternative protective measures are therefore employed. In this paper, the authors examine the electrical safety issues present during maintenance of AGL systems, often performed live in order to guarantee the continuity of the service. Experimental measurements on AGL isolating transformers have been also reported in this paper, and possible solutions to improve the electrical safety of operators are proposed. [ABSTRACT FROM AUTHOR]

High-resistance ground (HRG) systems have gained popularity in process applications due to their ability to continue operation after a single line-to-ground fault and to limit the escalation of a single line-to-ground fault to a multiphase event. Part I of the companion paper has set the guidelines for designing safe and reliable HRG systems on industrial power systems used with linear loads and the effect of increased line–ground voltage stress on motor loads during fault conditions. However, literature on characteristics and pitfalls of HRG systems when used with nonlinear power converter systems is limited. Part II investigates anomalies of HRG systems used with nonlinear power converters such as neutral voltage shifting, increased line–ground transient fault voltages for both motor and ac source terminals and their voltage compatibility issues, increased neutral grounding resistor power dissipation, susceptibility of ground fault sensing equipment to nuisance tripping, and dc-bus voltage resonance on faults. Part II also investigates HRG zero-sequence fault current characteristics and paths observed under various fault locations in a common ac or a common dc-bus pulsewidth-modulated adjustable speed drive (ASD) system. Part II concludes with a summary of application guidelines when using ASD HRG systems. [ABSTRACT FROM PUBLISHER]

This paper provides a discussion on the theory behind reducing the risk and severity of an arc flash incident. In particular, the variables associated with the calculations of energy from an arcing fault are presented in an effort to show the futility of present methods for determining incident energy levels in the electrical industry. A number of commonly ignored design concepts that significantly reduce the risk of electrical hazards will be discussed, two of which include: 1) system grounding; and 2) solid insulation. This paper will discuss risk and the management of risk as a means of reducing the probability of an incident. It will then show how risk reduction should be used in the design, construction, operation, and maintenance of electrical equipment as means for the safeguarding of employees in the workplace. [ABSTRACT FROM PUBLISHER]

Protection systems are one of the most critical components in the transmission system and are becoming more digital with ongoing automation. These digital systems are prone to vulnerabilities/attacks, and exploitation of these vulnerabilities may cause major impacts on the electric grid performance. Multiple alarms reported in the control center could be a result of the faults (expected operations) or failures in the protection system (anomalies/ unexpected operation). Situational awareness gained through sensors such as a phasor measurement unit (PMU) and data acquired through the cyber system provide an opportunity to develop continuous cyber-physical monitoring of the system. Note that relay data are not reported in the control center continuously. This paper presents a cyber-physical data analytics based technique to monitor transmission protection system and detect malicious activity. Initially, continuous monitoring of PMU data is utilized for data anomaly detection, which includes bad or missing data using long short-term memory (LSTM). Then, PMU data of interest are utilized for failure diagnosis, using a semisupervised deep autoencoder model. In this research, cyber anomalies are modeled by manipulating the setting/logic design of protective devices, and a ridge regression based classifier with a feature engineering pipeline is used to detect cyber anomalies. The results from the deep autoencoder model and ridge regression based classifier are then utilized for detailed investigation to find the root causes of the observed events assisted by the cyber log data from the protection devices. The algorithm is validated using a real-time simulation of the IEEE test system with industrial hardware relays and PMUs in the loop. Data analytics algorithm running on server utilizes these real-time data continuously for anomaly detection and classification for the developed use cases. [ABSTRACT FROM AUTHOR]