Short-circuit Studies Research Articles

Maximal wind power penetration in radial MV networks

The increment of Distributed Generation (DG), especially wind power, in distribution networks has motivated the development of methodologies to evaluate their limits and effect in the power system. The distribution network is already characterized by variable parameters such as: loads, line parameters; the interconnection of renewable energy sources adds more uncertainties in planning studies. In this paper, a new approach is applied in Load Flow (LF) and Short-Circuit studies based on Monte-Carlo simulation (MCS) which takes into account network uncertainties to determine the maximal wind power penetration and its dispersion in the network.

A comparison study of on-chip short pulse generation circuits based on a coplanar waveguide

A few traditional pulse-forming circuits are implemented in a commercial 0.13 μm digital complementary-metal-oxide-semiconductor (CMOS) technology. These circuits, based on a coplanar waveguide, are analyzed and compared through Cadence™ Spectre simulations. The results show that these traditional pulse-forming-line (PFL) based circuits can be implemented in standard CMOS technology for short pulse generations. Further work is needed to explore the potential of the circuit techniques and to minimize parasitic effects.

Impact of Available Fault Current Variations on Arc-Flash Calculations

Prior to the arrival of the arc-flash hazard analysis and the incident energy calculations, it was common practice to perform short-circuit studies assuming an infinite source on the primary of the service transformer. With the main goal of a short-circuit study being to compare the maximum calculated short-circuit current to the short-circuit rating of protective devices, using an infinite source resulted in the most conservative short-circuit current. However, since the amount of energy available in an arc-flash incident is not only dependent on the available short-circuit current but also on the clearing time of the protective device, the assumption of an infinite source on the transformer primary will not guarantee the most conservative results for the incident energy calculations downstream of the transformer. This paper examines the effect of the utility available fault current on the incident energy calculations and proposes a new method to calculate the conservative arc-flash results in the event that the actual utility fault information is not available.

Rapid-Charge Electric-Vehicle Stations

Mass production of total electric vehicles capable of traveling longer distances results in a need for electric service stations that can satisfy the requirements for a significant amount of power provided in a time duration similar to that of filling a car with oil-based fuel. These vehicles would pull into the station, and need a large amount of power delivered over a short period of time for the rapid recharging of batteries which serve as their “fuel tank.” This paper investigates the effect of fast-charging electric vehicles on an existing utility company distribution system at several specified sites. This paper will cover power-flow, short-circuit, and protection studies at these sites using utility-grade software packages. In addition, the analysis of simulations of a recharging station where up to eight rapidly rechargeable vehicles come online at once will be presented.

Changes in brain G proteins and colonic sympathetic neural signaling in chronic-acute combined stress rat model of irritable bowel syndrome (IBS)

The role of the brain-gut axis interaction in the pathogenesis of irritable bowel syndrome (IBS) is not well understood. To examine this possibility, a novel rat model of IBS subjected to both chronic and acute stress (CAS) was established. G proteins play a crucial role in the pathophysiology of depression. The alpha 2A adrenoceptor (alpha(2A)-AR) and the norepinephrine reuptake transporter (NET) determine the sympathetic signal activity. It is conceivable that stress may induce brain G proteins, colonic alpha(2A)-ARs, and NET abnormal expression, which may be responsible for the abnormalities in IBS. Colonic motility, visceral sensation, and secretion were assessed by counting fecal pellets, abdominal muscle contractions in response to colorectal balloon distension (CRD), and short-circuit current study, respectively. Western blot analysis was used to investigate the expression of G proteins, alpha(2A)-ARs, and NET. Compared with control animals, the colonic epithelial secretion, fecal pellets, and numbers of abdominal muscle contraction induced by CRD were significantly higher in both acute stress only (AS) and CAS rats. However, the G proteins, alpha(2A)-AR, and NET expression changed differently in AS and CAS rats. We showed that exposure to either AS or CAS would cause the increase of secretion, motility, and sensation, but the change of protein expression in brain-gut axis was different. It may be responsible for the pathogenesis of IBS.

Modeling and Protection of Hexagonal Phase-Shifting Transformers—Part I: Short-Circuit Model

Owing to several advantages over traditional phase shifters, applications of hexagonal phase-shifting transformers (PSTs) keep expanding. These transformers are built with unique connections of their windings, neither delta nor wye. Short-circuit modeling and analysis methods are not yet fully established for hexagonal phase shifters. This work is divided into two parts. In this part, a digital model of a hexagonal PST is developed and validated. This original material is of assistance when performing short-circuit system studies, relay setting calculations, as well as when modeling internal faults and developing protection techniques for the transformer itself. This paper explains construction of hexagonal PSTs, deriving their sequence impedances under varying taps and compares the model with manufacturer test data and a physical made-to-scale model developed specifically for this study. The transient model introduced in this paper can easily be integrated into the commonly used Alternate Transients Program and real-time digital simulator modeling environments. Part II of this work presents original protection methods for hexagonal PSTs.

Distance protection coordination using search methods

In this paper, a methodology for calculating the setting impedance of zones 2 and 3 of distance relays is presented, The aim is to reduce protection coordination problems during fault occurrence and changes in the network configuration. The proposed method is based on the impedance seen by the distance relay when faults are simulated on adjacent nodes. The coordination and relay setting is obtained by means of computational algorithms developed to analyze the network topology, determine the pair of primary-backup relays and short circuit studies considering several types of faults in the power system. This process is carried out in an object oriented environment which allows a flexible approach to the user of the software. In the development of this tool search methods based on graph theory were used. The method was applied to an IEEE 14 nodes test system with satisfactory results.

Solução do problema de superação de disjuntores pela alocação ótima de dispositivos limitadores de corrente de curto-circuito utilizando algoritmos genéticos

Este artigo apresenta uma metodologia para auxiliar nos estudos de limitação de correntes de curto-circuito em sistemas elétricos com problemas de superação de disjuntores, através da alocação ótima de dispositivos limitadores. O problema de otimização é solucionado aplicando-se Algoritmos Genéticos e levando em consideração os requisitos de custo mínimo, alocação de um número mínimo de dispositivos e a máxima redução da corrente de curto-circuito. A detecção da superação do disjuntor é feita pela análise tanto da corrente de curto-circuito que o disjuntor deve interromper como também da relação X/R do sistema. O modelo computacional desenvolvido utiliza de modo integrado o programa ANAFAS do CEPEL, mantendo a compatibilidade com as bases de dados utilizadas em estudos de curto-circuito no setor elétrico brasileiro. Os resultados obtidos com o sistema IEEE14 e com um sistema real brasileiro de grande porte comprovam a robustez do modelo, apresentando soluções que satisfazem às restrições com custo de investimento reduzido para todos os cenários analisados.

誘導型風力発電機の短絡電流に及ぼす出力変動の影響

Effects of the fluctuation inherent in wind speed are studied by a probabilistic method. The random variation in wind speed is responsible for random behavior in output power and internal voltage of a wind power generator. In case of fault occurrence at the instant of high internal voltage, the resultant short-circuit current will be big, and vice versa. The DC component is also affected. According to the study, 2.4% and 1.3% increase of short-circuit current in AC and DC components are observed respectively in a large variation case. This implies that the wind speed variation should be considered for accurate short-circuit study. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(3): 27–36, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20721

Voltage-Sag Magnitude and Phase Jump due to Short Circuits in Distribution Systems with Variable Fault Resistance

Voltage sags mainly caused by line faults in transmission and distribution systems have become one of the most important power quality problems facing industrial and commercial customers, as well as utilities. Voltage sags are normally described by characteristics of both magnitude and duration. Phase-angle changes that greatly affect several electronic equipment should be taken into account in identifying and characterizing the sag phenomenon. In this article, voltage sags due to line faults, such as three phase-to-ground, single line-to-ground, and line-to-line faults, for fault impedance (resistance) variation are firstly characterized by using symmetrical component analysis. Different line fault types, fault resistance magnitudes, and their effect on voltage sag magnitude variations together with phase-angle jumps are examined. In order to verify the analyzed results, simulations based on power circuit models are presented. The described methodology is useful in short-circuit studies by giving a quick qualitative assessment of the voltage sag magnitude and phase jump when fault resistance is changed between its extreme values.

Locating faults in the transmission network using sparse field measurements, simulation data and genetic algorithm

The paper presents a modeling and simulation approach to locate a fault in a transmission network. The basic concept is to match phasors recorded during fault with the corresponding phasors obtained by simulating the same fault. For the simulation, it is necessary to assume a fault location in a power system model, and then carry out short circuit study. The matching degree can be calculated by a pre-set criterion. The operation is repeated till the best match is found. The process of finding the best match is an optimization problem, therefore, the genetic algorithm (GA) is introduced to find the optimal solution. The proposed approach is suitable for situations where only sparsely recorded field data is available. Under such circumstances, the proposed approach can offer more accurate results than other known techniques.

Locating faults in the transmission network using sparse field measurements, simulation data and genetic algorithm

The paper presents a modeling and simulation approach to locate a fault in a transmission network. The basic concept is to match phasors recorded during fault with the corresponding phasors obtained by simulating the same fault. For the simulation, it is necessary to assume a fault location in a power system model, and then carry out short circuit study. The matching degree can be calculated by a pre-set criterion. The operation is repeated till the best match is found. The process of finding the best match is an optimization problem, therefore, the genetic algorithm (GA) is introduced to find the optimal solution. The proposed approach is suitable for situations where only sparsely recorded field data is available. Under such circumstances, the proposed approach can offer more accurate results than other known techniques.

A new approach to bus impedance matrix building

Modern power systems are probably the largest real physical systems in existence today. Digital computers used to solve power system planning and operational problems require network matrices either in impedance form or admittance form. Initially the use of bus impedance matrix ( Z Bus) was not encouraged due to time, memory and computational requirements. Later it was realized that the bus impedance matrix could be efficiently used for short circuit and stability studies. In this paper a new approach for bus impedance matrix building is proposed and the results are compared with that of Brown's algorithm [Trans. AIEE 79 (part III) (1960) 1277].

Auto-check circuit breaker interrupting capabilities

Circuit breakers in a utility network are designed to quickly isolate short-circuited equipment from the rest of the system. The short-circuit current changes with switching operations and with the addition and removal of generating sources. Hence, electric utilities must check their breakers periodically using computer simulation to ensure that the breakers are capable of interrupting the short-circuit currents. The recent proliferation of independent power producers (IPP) has made breaker-rating studies a much more routine procedure for utility engineers. The aim of these studies is to see if the existing circuit breakers are adequate when the proposed generators are put in service. The need for efficient and accurate breaker-rating software is greater now than ever. The benefit of computerized breaker-rating studies has been recognized for many years. Most utilities have breaker-rating software of some kind. What is not well known about breaker rating is the inherent difficulty in rating breakers using the sequence-network model that is commonly used for short-circuit studies. The breaker-rating program was improved by making the description of the breaker more flexible, universal, and easy to apply. This is the breaker connection model.Once breaker data is entered into a database, a breaker-rating program greatly reduces the time and effort required to ensure that breakers will work property in the event of a fault.

A Short-Circuit Current Study for the Power Supply System of Taiwan Railway

The western Taiwan railway transportation system consists mainly on a mountain route and ocean route. Taiwan Railway Administration (TRA) has conducted a series of experiments on the ocean route in recent years to identify the possible causes of unknown events that cause the trolley contact wires to melt down frequently. The conducted tests include the short-circuit fault test within the power supply zone of the Ho Long Substation (Zhu Nan to Tong Xiao) that had the highest probability for the melt down events. Those test results, based on the actual measured maximum short-circuit current, provide a valuable reference for TRA when comparing against the said events. The Le Blanc transformer is the main transformer of the Taiwan railway electrification system. The Le Blanc transformer mainly transforms the Taiwan Power Company (TPC) generated three-phase alternating power supply system (69kV, 60Hz) into two single-phase alternating power distribution systems (M phase and T phase) (26kV, 60Hz) needed for the trolley traction. As a unique winding connection transformer, the conventional software for fault analysis will not be able to simulate its internal current and phase difference between each phase current. Therefore, besides extracts of the short-circuit test results, this work presents an EMTP model based on the Taiwan Railway Substation equivalent circuit model with a Le Blanc transformer. The proposed circuit model can simulate the same short-circuit test to verify the actual fault current and accuracy of the equivalent circuit model.

Short-circuit, coordination, and harmonic studies

The most common system studies done on power systems include: load flow, short-circuit, stability, motor starting, harmonic analysis, switching transient, reliability, cable-ampacity, ground mat and protection coordination studies. The three studies addressed in this article are short-circuit, coordination, and harmonic studies.

Using short-circuit currents to perform a protective device coordination study

The article provides a brief background on the fundamentals of short-circuit analysis. Following that background is a discussion of how various types of phase overcurrent protective devices respond to the short-circuit current waveform. Based on this discussion, the short-circuit currents which are necessary to perform a protective device coordination study are specified. A comparison of the two types of short-circuit studies follows, based on the complex impedance network representation of the power system. The results of the comparison are then used to present recommendations for how the results of a computer-aided study to compute short-circuit current duties can be applied to determine the short-circuit currents necessary to select the settings of phase overcurrent protective devices. Finally, a sample industrial power system is provided to clarify the recommendations.

Modeling and Experimental Study of 3-Phase Short-Circuits of a Double-Cage Induction Machine

Three-phase short-circuits of the induction machine yields to high levels of stress in an induction traction drive. To study these operations, the authors propose to model the machine by a multiple cage equivalent circuit. This enables us to take into account the deep bar effect with accuracy. The identification of the equivalent circuit and its validation are carried out experimentally for a 30-kW double-cage induction motor.

A new approach to modeling three-phase transformer connections

The modeling of three-phase transformer connections for power-flow and short-circuit studies can take on many forms, depending upon the assumptions made. Too many times, simplifying assumptions lead to answers that are totally wrong. Exact models of the various connections must be used if correct results are to be achieved. The exact models must satisfy Kirchhoff's voltage and current laws, and the ideal relationship between the voltages and currents on the two sides of the transformer windings and the models must represent any phase shift that is a result of the particular connection. New models for all common three-phase transformer connections have been developed that satisfy all of the requirements stated above. This paper limits the discussion to the ungrounded wye-delta connection and the model developed for use in power-flow and short-circuit studies.

Study methods of induction traction motor three phase short circuits

The authors propose study methods of three phase short circuits of an induction traction motor. Methods are based on finite element model or equivalent circuits of the machine and take into account, more or less accurately, saturation and deep bar effects. Depending on the modeling level, they can be used to study short circuit torque or current maxima, waveforms or local constraints. The proposed methods are applied to a 1.5 MW - 4 pole traction motor short circuit study.